Alternatives for Efficient and Sustainable Production of Surimi: A Review

Authors

  • A.M. Martín-Sánchez,

    1. Authors Martín-Sánchez, Navarro, and Pérez-Álvarez are with Industrialización de Productos de Origen Animal (IPOA), Grupo 1 UMH, Grupo REVIV, Generalitat Valenciana, Dept. de Tecnología Agroalimentaria, Escuela Politécnica Superior de Orihuela, Univ. Miguel Hernández, Carretera de Beniel, km 3,2, Orihuela, 03312, Alicante, Spain. Authors Martín-Sánchez and Kuri are with Food and Nutrition, School of Biological Sciences, Univ. of Plymouth, Drake Circus, Plymouth, PL4 8AA, U.K. Direct inquiries to author Kuri (E-mail: v.kuri@plymouth.ac.uk).
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  • C. Navarro,

    1. Authors Martín-Sánchez, Navarro, and Pérez-Álvarez are with Industrialización de Productos de Origen Animal (IPOA), Grupo 1 UMH, Grupo REVIV, Generalitat Valenciana, Dept. de Tecnología Agroalimentaria, Escuela Politécnica Superior de Orihuela, Univ. Miguel Hernández, Carretera de Beniel, km 3,2, Orihuela, 03312, Alicante, Spain. Authors Martín-Sánchez and Kuri are with Food and Nutrition, School of Biological Sciences, Univ. of Plymouth, Drake Circus, Plymouth, PL4 8AA, U.K. Direct inquiries to author Kuri (E-mail: v.kuri@plymouth.ac.uk).
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  • J.A. Pérez-Álvarez,

    1. Authors Martín-Sánchez, Navarro, and Pérez-Álvarez are with Industrialización de Productos de Origen Animal (IPOA), Grupo 1 UMH, Grupo REVIV, Generalitat Valenciana, Dept. de Tecnología Agroalimentaria, Escuela Politécnica Superior de Orihuela, Univ. Miguel Hernández, Carretera de Beniel, km 3,2, Orihuela, 03312, Alicante, Spain. Authors Martín-Sánchez and Kuri are with Food and Nutrition, School of Biological Sciences, Univ. of Plymouth, Drake Circus, Plymouth, PL4 8AA, U.K. Direct inquiries to author Kuri (E-mail: v.kuri@plymouth.ac.uk).
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  • V. Kuri

    1. Authors Martín-Sánchez, Navarro, and Pérez-Álvarez are with Industrialización de Productos de Origen Animal (IPOA), Grupo 1 UMH, Grupo REVIV, Generalitat Valenciana, Dept. de Tecnología Agroalimentaria, Escuela Politécnica Superior de Orihuela, Univ. Miguel Hernández, Carretera de Beniel, km 3,2, Orihuela, 03312, Alicante, Spain. Authors Martín-Sánchez and Kuri are with Food and Nutrition, School of Biological Sciences, Univ. of Plymouth, Drake Circus, Plymouth, PL4 8AA, U.K. Direct inquiries to author Kuri (E-mail: v.kuri@plymouth.ac.uk).
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Abstract

ABSTRACT:  The links between fish processing and negative environmental impact need to be minimized. The overexploitation of white fish stocks has compromised supply, the use of energy contributes to a high-carbon footprint, and the water resources required are also high. An option is to resort to the use of alternative species and fisheries by-catch, together with the maximum utilization of fish. In addition, edible proteins from a range of sources could be converted into added-value products using surimi-like processes. The surimi industry requires large amounts of freshwater and discharges wastewater with a high organic load. By exploring available options on processing technologies and management of the environmental impact, this review discusses the potential role of surimi and opportunities for sustainable fish processing.

Introduction

Surimi is a Japanese term for deboned, minced, and washed fish flesh, which is then used for the manufacture of seafood imitation products such as crab legs. These are perceived to have wholesome and nutritious attributes (Guenneugues and Morrissey 2005), which, together with an affordable price, have contributed to the increasing worldwide consumption of surimi-based products. However, whereas the demand for fish is increasing, it is clear that its availability is decreasing, particularly for some fisheries.

The commercial demand for the white-fleshed fish is higher than for others, and therefore the industry mainly depends on them (Venugopal 1997; Venugopal and Shahidi 1998). The surimi industry also demands white fish mainly because of the importance of the whiteness and textural properties of the resulting products (Navarro 2007). At the same time, numerous species are underutilized because they are linked to some technological problems. Even conventional processing methods such as canning, salting, drying, and smoking incur limitations (Pérez-Álvarez and others 2007) with some of the so-called “less valuated fish,” which include pelagic fish species, for example, when they are too small (Karayannakidis and others 2008a). However, according to FAO (2007) the catch of these small species is increasing, whereas some of the most valuable species such as Alaska pollock (Theragra chalcogramma) are declining. Hence, the manufacture of surimi can be an alternative to revalue and make use of these fish that are unwanted or unsuitable for other processes (Karayannakidis and others 2008a).

Surimi is made from minced meat, providing opportunities to use different sources of protein in its production, such as underutilized species with little or no commercial value, including nonfish species. The surimi process, parts of it or modified versions, could be a way of exploiting resources that otherwise would be neglected by the food industry and consumers. Fortunately, the use of novel species for the production of surimi is increasing. Besides fish, the potential for other resources, such as cephalopods (Sánchez-Alonso and others 2007a; Cortés-Ruiz and others 2008) and crabs (Baxter and Skonberg 2006), is being studied for surimi production with the incorporation of new methods and technologies. Even surimi-like products from deboned chicken meat, beef, pork, and others have been reported in different studies (Min and Lee 2004; Navarro 2005, 2006; Hah and others 2007; Jin and others 2007a, 2007b; 2008; 2009; Stangierski and others 2008). These products are especially useful for making profitable some residual parts and underutilized animals such as spent lying hens (Navarro 2005; Jin and others 2009).

Another area of opportunity is the increase in the yield from the fish employed in surimi production. Moreover, the repeated washes during surimi processing entail elevated requirements of freshwater and high contamination of the wastewater (Guenneugues and Morrissey 2005; Park and Lin 2005). Energy use and the reduction of food travel is seen as important, however, the “food miles” traveled are not necessarily related to carbon emissions. To address sustainability issues in this sector, the following points should be considered: the highest exploitation of the raw materials, utilization of fisheries by-catch and underutilized species, evaluation of the stock, preservation of the environment and natural resources, minimization of pollution, and reduction of water consumption. Therefore, surimi processors will benefit from eco-efficiency initiatives to achieve a more sustainable process, and to reduce its ecological impact, but also to improve the economics of the process (Guenneugues and Morrissey 2005; Park and Lin 2005) and to address the growing concerns for the sector's carbon footprint and demand for social and environmental accountability.

Therefore, the purpose of this study is to highlight the importance of a production based on sustainable strategies with the environment and the raw material resources, and also, to discuss the opportunities that surimi offers to maximize the use of protein resources. In addition, for a more eco-efficient production of surimi it is necessary to address water consumption, wastewater, and the pollution potential of the processing.

Surimi Processing

Surimi is one of the major fish meat transformations. Basically, surimi is a wet concentrate of high-quality myofibrillar proteins from raw minced fish flesh. The proteins are salt-solubilized and then heated to form a surimi hydrogel (Numakura and others 1990; Navarro 2007; Chen and Huang 2008). It is used as an intermediate product in the manufacture of a variety of foodstuffs (CAC 2005a, 2005b), such as the traditional Japanese kamaboko or shellfish imitation products which include crabsticks, crab legs, crab meat, young eel, scallops, and others (Benjakul and others 2003a; Carvajal and others 2005; Blanco and others 2006). The greatest demand for surimi is in wealthier countries: United States and Japan, and European countries. Most surimi is produced in the United States and Japan, but increasingly other Asian countries are investing in their processing capabilities. Europe produces significantly less, with yearly imports of raw material of about 40 to 50000 tons over the last few years, but imports of finished products were over 70000 tons per year. Surimi is mainly consumed at the Mediterranean countries and the United Kingdom, and produced in locations over the Mediterranean and the Baltic region (Catarci 2007; Vidal-Giraud and Chateau 2007). Thus surimi processing and marketing involves a significant international movement of materials, mostly bulk-frozen.

Raw materials

Surimi is obtained from mechanically deboned fresh fish flesh, usually from white-muscle fish as it is shown in Table 1. Alaska pollock is the most valuable species because it has good gelation properties, desirable odor, white color, and good cooking tolerance. Thus, it is used for the higher-quality surimi. Pacific whiting (Merluccius productus) is also one of the main species for surimi production (Velázquez and others 2008).

Table 1—.  Potential and current use of most representative marine and freshwater species as raw material for surimi production, including the fat content (LF, MF, HF)A and source climate.B
Marine or freshwater speciesSource climateFat contentPotential/useCCommentsReferences (use/comments)
  1. ALF = low fat content (0.5% to 2%), MF = moderate-fat content (2% to 5%), HF = high-fat content (>5%), based on sources below.D

  2. BBased on average season values; CW = cold water, TW = temperate water, SW = subtropical water, TrW = tropical water, TT = temperature tolerant.

  3. C(+++) = choice material/ widely used/ most desirable, (++) = A good option/ use could be developed / some potential, (+) = challenges for application, low quality.

  4. D Data sources =aAnonymous (2009); bFAO (2009b); cFAO (2002); dOliveira and Bechtel (2006); eSidhu and others (1970); fJu and Harvey (2004); gHolland and others (1993); hWada and others (1976); iBenjakul and others (2002a); jCorser and others (1999); kAckman (1995); lIriarte-Rota and Romero-González (2006); mSirot and others (2008); nKrzynowek and Murphy (1987); oKucukgulmez and others (2008); pYoshie-Stark and others (2009); qBenjakul and others (2005b).

Alaska pollock (Theragra chalcogramma)CWaLFd+++The most preferred fish specieGuenneugues and Morrissey (2005)
Antartic krill (Euphausia superba)CWbMF/HFe, f+Low recovery yield, highly hydrolytic enzymesChen and Jaczynski (2007a)
Arrowtooth flounder (Atheresthes stomias)CWaMFd++High protease content. Problems with cutting machinery due to flatfish shapeGuenneugues and Morrissey (2005)
Atka mackerel (Pleurogrammus azounus) and Japanese jack mackerel (Trachurus japonicus)TWa/TrWaHFg+Dark muscle, high lipid content, myoglobin. Potential for low-priced surimi productsGuenneugues and Morrissey (2005)
Barracuda (Sphyraena spp.)STW/TrWaMFh++Low gel-forming ability.
Used sometimes, when in season.
Guenneugues and Morrissey (2005)
Bigeye snapper (Priacanthus spp.)TrWaLF1+++Available and suitableGuenneugues and Morrissey (2005)
Blue tilapia (Oreochromis aureus) and Nile tilapia (Oreochromis niloticus)TT/TrWaMFj++Abundant. High content of pigments and fishy odourRawdkuen and others (2009)
Common carp (Cyprinus carpio); Grass carp (Ctenopharyngodon idellus); Silver carp (Hypophthalmichthys molitrix)TTaMFk++High postharvest lossesJafarpour and Gorczyca (2008); Luo and others (2001); Yuan and others (2005)
Croaker (Sciaenidae)STWaMFj+++Produce a high-quality surimiGuenneugues and Morrissey (2005)
Hairtal (Trichiurus lepturus)STWaMFl++Low gel-forming ability, but a good tasteGuenneugues and Morrissey (2005)
Hoki (Macruronus novaezelandiae)STWaLFm++Produce a high-quality gel, but is used for other product forms.Guenneugues and Morrissey (2005)
Jonah crab (Cancer borealis)CWcLFn+ Baxter and Skonberg (2008)
Lizardfish (Saurida spp.)STW/TrWaLFo++Low quality surimi, freshness decrease quicklyBenjakul and others (2008)
Northern blue whiting (Micromesistius poutassou) and Southern blue whiting (Micromesistius australis)TWaLFp+++Lower quality than Alaska pollock surimiGuenneugues and Morrissey (2005); Trondsen (1998)
Pacific herring (Clupea pallasii)TWaHFo++Dark colorReppond and others (1995)
Pacific whiting (Merluccius productus)TWaLFn+++One of the most used. Presence of protease from MyxosporidiaGuenneugues and Morrissey (2005)
Pike-conger eel (Muraenesocidae)TrWaHFm++Preferred for fishballsGuenneugues and Morrissey (2005)
Pink salmon (Oncorhynchus gorbuscha)STWaMFm++Coloured meatPark and Morrisey (2000)
Sardine (Sardina pilchardus)STWaHFm+Dark muscle, high lipid content, myoglobin, and so on.Bentis and others (2005)
Striped mullet (Mugil cephalus)STWaHFn++Dark fleshed fishRamírez and others (2000)
Threadfin bream (Nemipterus spp.)STW/TrWaMFq+++Produce a high quality surimi when it is freshGuenneugues and Morrissey (2005)
Trout (Cynoscion nothus) and Rainbow trout (Oncorhynchus mykiss)STWaMFn++ Díaz-Vela and others (2008)

It is paramount for surimi producers to find profitable uses of by-catch fish species or abundant fish that would otherwise not be suitable to sell in other presentations, and thereby to supply their needs (Holmes and others 1992). Table 1 summarizes widely used and the most studied freshwater and marine species for surimi production. The most common light muscle fish, such as Alaska pollock and Pacific whiting are included. Also, underutilized fish species, such as some fatty dark-fleshed fish species, are listed with notes on technological problems such as soft muscle, small size, very high content in fat, or the presence of many bones (Bentis and others 2005).

Some of the species in the table are freshwater fish. Catches from freshwater fisheries have increased quickly due to the development of aquaculture, accounting for 36% of total production in 2006 (FAO 2009a). However, the commercial value of these species is low, and therefore they could be used for surimi production (Luo and others 2001). The classification according to the species water temperature is proposed because the differences during muscle protein gelation are linked to the environment temperature.

Raw Materials Preparation

The raw fish is filleted, including heading, gutting, and removal of the backbone to eliminate viscera and impurities. This step influences the quality and yield, because endogenous and microbial proteases from guts and skins, which could be carried into the flesh and contaminate the mince, will affect the gel-forming ability of the surimi if they are present in high quantities. Researchers in Thailand (Benjakul and others 2002b, 2003c) have shown that the use of headed and gutted fish as raw material for surimi slows down proteolytic deterioration, and that even whiteness of the resulting surimi may be higher than that of surimi from whole fish. The use of air pressurization (4 to 5.4 atm) to remove adhering residues could reduce the fresh water needs and maximize the yield, when this process has been properly adjusted (Toyoda and others 1992).

After that, belt-drum type meat separators are used to eliminate bones, fins, or skin. To increase the yield of this operation the holes should be as large as possible according to the process conditions (Toyoda and others 1992).

Once the raw fish flesh has been obtained, it is washed several times with fresh water to remove sarcoplasmic proteins such as enzymes and heme proteins, other nitrogenous compounds, fat, blood, pigments, odorous compounds, and other impurities that would reduce surimi quality; but washing also improves the quality of the myofibrils (Vilhelmsson 1997; Carvajal and others 2005; CAC 2005b; Hultin and others 2005). Thus, the number of washes depends on the fish species, fish conditions, type of wash, and the desirable quality of the surimi (Carvajal and others 2005). As a result, a better texture, color, and odor are obtained in the final product (Park and Lin 2005). After each wash, a dewatering step takes place. This involves screening, the use of dehydrators, or the use of centrifuges, which is more efficient to recover the fine particles lost from the screens (Toyoda and others 1992; Park and Lin 2005). However, all these washing steps require large quantities of freshwater and produce the corresponding volume of wastewater rich in organic matter, besides high protein losses. (Park and Lin 1996). Lin and Park (1997) evaluated the effect of water reduction during leaching in Pacific whiting (Merluccius productus) and found that using a reduced water/meat ratio, and increasing the wash cycles to 4 and the wash time to 10 min, also removed sarcoplasmic proteins, although the moisture content increased. Alternative washing techniques that have been studied to improve the removal of the undesirable compounds include:

  • 1Air-flotation washing (AFW) to achieve a deeper removal by air infused into the cold water where bubbles facilitate stirring, and bring the mince to the surface (Chen 2002).
  • 2The improvement of color and texture by means of alkaline washing is also possible, since it increases the solubility of the sarcoplasmic proteins and the muscle pH, which in turn reduces the rate of denaturation. Also, salt can be added to improve the removal of heme pigments in a salt–alkaline washing (SAW) (Hultin and others 2005; Balange and Benjakul 2009b). The yield resulting from the SAW is lower than that from AFW (Chen 2002), and the SAW surimi showed a gel forming ability only slightly higher than that of the surimi prepared with AFW. Because AFW can be completed in a shorter time (10 to 15 min) in comparison with the 60 min required by SAW to achieve some discoloration and gel-forming properties, it would be the preferred method, but the real advantage is that only around 50% of the water is required, in comparison with alkaline washing (Chen 2002).
  • 3Washing with ozone produces decoloration due to its strong oxidant ability, because the structure of the heme pigment is attacked (Buckley and others 1975). Nonetheless, washing with other oxidizing agents, such as hydrogen peroxide and sodium hypochlorite have shown to improve texture in bigeye snapper (Priacanthus tayenus) by the formation of disulfide bonds, since they oxidate the sulfhydryl groups (Phatcharat and others 2006).

The fish meat is then refined to remove the last impurities and pressed in a screw-press to eliminate the moisture excess, thus concentrating myofibrillar proteins, and improving gelation as the surimi paste is formed (Mendes and Nunes 1992; Toyoda and others 1992). Frequently a 0.1% to 0.3% mixture of NaCl and CaCl2 is used in the final wash water to increase the removal of water (Park and Lin 2005). This highly labile product is normally frozen with cryoprotectants (sucrose, polyalcohols, and polyphosphates among others) to preserve the capacity to form a gel after thawing (Reynolds and others 2002; CAC 2005a, 2005b).

Mechanism of gelation

A gel is configured by a continuous matrix of interconnected proteins holding water and low-molecular-weight particles (Aguilera 1992). During the surimi gelation process, the myofibrillar proteins (myosin and actin mainly) are solubilized by the added salt and actomyosin is formed. Thereby, heating the previously obtained fish mince paste, the network is formed when sufficient intermolecular bonds occur and it is stabilized by ionic linkages, hydrophobic interactions, covalent bonds (disulfide bonds and covalent cross-linking), and hydrogen bonds (Aguilera and Rademacher 2004; Lanier and others 2005).

Generally, a thermal gel is formed in a 2-step heating process to improve gelling characteristics (Lee 1984). The 1st step, known as setting or “suwari,” enhances the protein network and strengthens the texture of the gel at low temperature as it changes from sol to gel (Montejano and others 1984; Kamath and others 1992). In this step the gel is thawed if it has been previously frozen, chopped, and mixed with water and salt to solubilize the myofibrillar proteins, prior to incubation below 40 °C. Suwari can take place within a short period (2 to 4 h) near 40 °C (high-temperature setting) or a longer period (12 to 24 h) at lower temperatures, 0 to 40 °C (low-temperature setting) (Wu and others 1985). After setting, the suwari gel is cooked at 80 to 90 °C in a 2nd step, becoming a rigid and irreversible gel (Montejano and others 1984; Kimura and others 1991).

Once the surimi paste is prepared, seafood analogous products can be made with different forms, textures, and flavors, reproducing attributes of natural equivalents, such as crabmeat or lobster tails (Park 2005a). Among those attributes a paramount quality factor is texture; that is why the gel strength, as it is used to grade surimi, will directly influence quality and price (Hu and others 2007).

Factors affecting the gel quality

Freshness of the raw material is the most important prerequisite in surimi processing; and to obtain a high quality product it is required to minimize postmortem deterioration (Wasson 1992; Seymour and others 1994; Choi and others 2005). The loss of freshness depends on factors such as denaturation of the myofribrillar proteins, the level of proteolysis, and the muscle pH (Hamann and MacDonald 1992). Freshness will determine the gelation properties of the surimi and the water holding ability (Hall and Ahmad 1997; Carvajal and others 2005). Moreover, fresher fish will need less amount of water during leaching. Therefore, processing fish within 12 h after harvesting would be ideal. For extended periods, fish should be kept at 5 °C, but gel strength will drop quickly in just a few days (Toyoda and others 1992).

The environmental temperature, particularly in tropical fish species, will also have an effect on the rate of denaturation. Higher water temperatures increase the thermostability of myofibrillar proteins, varying even in the same specie during the different seasons (Yuan and others 2005). Therefore, optimal conditions for setting vary according to the species; cold-water fish species show a lower thermostability and consequently the setting temperature is lower for these fish than for those from warm waters (Ramírez and others 2000). Also, seasonal changes such as those observed during the spawning season, can affect the proteolytic activity in the muscle (Hamann and MacDonald 1992).

Surimi gels made from frozen fish undergo a loss of cohesiveness during storage time, because the myofibrillar proteins experience denaturation and aggregation. If formaldehyde is formed from trimethylamine oxide, which is accumulated in most marine species, although it variable between species, the gels become rigid, since formaldehyde can form cross-links between myofibrillar proteins. Thus, lower storage temperatures would slow down the rate of these reactions (Hamann and MacDonald 1992). Also, oxidation of myofibrillar proteins during frozen storage causes the formation of some covalent bonds, which consequently alters protein networks even after grinding. This, together with a decrease in Ca2+-ATPase and other changes, affects the gel-forming ability of fish muscle (Benjakul and others 2005a, 2005b, Moreno and others 2008, 2009a). Borderias team at Inst. del Frío (Moreno and others 2009b) have studied the changes of surimi gels during frozen storage (Moreno and others 2009a) and measured the detrimental effect of freezing–thawing cycles on the quality of hake surimi gels, and established the usefulness of caseinate addition, particularly when the muscle was not homogenized to obtain small particle sizes. To improve the gel quality of surimi from frozen fish, ingredients such as reducing agents have been studied by Benjakul and others (2005a), who found that cysteine was suitable to increase the gel-forming ability.

Role of endogenous enzymes

Some species, such as several tropical fishes, and of particular importance, Pacific whiting, have endogenous proteases or contain exogenous proteases from parasites. High protease activity reduces yield and quality in surimi production (Morrissey and Sylvia 2004; Rawdkuen and Benjakul 2008). Even in some areas, this fish has become an underutilized resource because it is prone to be parasitized (Mazorra-Manzano and others 2008). When the gel is heated at 50 to 60 °C for long periods, in a process referred to as “modori,” an irreversible proteolytic degradation of myofibrillar proteins occurs, resulting in the disintegration of the gel structure (An and others 1996; Benjakul and others 2001; Hultin and others 2005). Modori is mainly due to the autolysis by these sarcoplasmic enzymes when activated at postmortem pH, which include heat-stable proteases such as cathepsins, alkaline proteases, and calpains. Therefore, the quality, gel strength, and myofibrillar protein functionality are compromised, limiting its use by the industry (An and others 1996). Another cause of quality loss is the incidence of parasites because they also contain protease enzymes (Seymour and others 1994; Moran and others 1999; CAC 2005b).

Although sarcoplasmic proteins are water-soluble, some of them may remain after washing. However, some techniques can reduce their proteolytic activity, including the addition of food-grade protease inhibitors (Morrissey and others 1993), high hydrostatic pressure (HHP) (Ashie and others 1996), or rapid heating (Carvajal and others 2005).

Food-grade protease inhibitors, which are capable of limiting the modori phenomenon and enhance gelling properties, have made possible the use of Pacific whiting among other species for surimi production (Benjakul and others 2004c; Guenneugues and Morrissey 2005). The most frequently used inhibitors are egg white and whey protein concentrates, while beef plasma protein is the most effective protease inhibitor, although it was forbidden after the occurrence of bovine spongiform encephalopathy (Choi and others 2005). Other protein additives have been proposed (Kang and Lanier 1999; Benjakul and others 2004c; Park 2005b), but in all cases some disadvantages arise. Recently, Li and others (2008) found that the addition of rainbow trout plasma protein improved whiteness, gel texture, and even water-holding capacity of Alaska pollock surimi, which would allow one to reutilize fish blood, a waste product with high disposal costs. Piyadhammaviboon and Yongsawatdigul (2009) have also investigated the ability of threadfin bream sarcoplasmic proteins from surimi wash-water to enhance gelation of the lizardfish surimi; they suggested that these proteins protect the myosin heavy chains from proteolysis. Nevertheless, formulation and the process involving the addition of these compounds during surimi gelation and the development of new food-grade inhibitors need to be optimized (Rawdkuen and others 2004; Rawdkuen and Benjakul 2008).

New heating technologies could overcome the proteolytic degradation of myofibrillar proteins. Considering that from 50 to 70 °C these proteases are activated, a rapid heating through this temperature range would minimize their activity (Choi and others 2005). These temperature profiles cannot be achieved with conventional methods, but microwave heating (Greene and Babbitt 1990) and ohmic heating (Yongsawatdigul and others 1995) are rapid heating methods that show good potential for commercial application (Choi and others 2005).

Also, HHP is very promising in surimi industry, not only to attack proteases but also for the gelation process. It consists of the application of HHP for a specified time. It causes chemical changes without heating, what affects myofibrillar proteins, because it is solubilized more easily (Cheftel 1995; Cheftel and Culioli 1997; Jiménez-Colmenero 2002). In addition, the transmission of the pressure is uniform and almost immediate resulting in processing times, which are less dependent on sample size and geometry (Jiménez-Colmenero 2002). Another advantage of new technologies such as HHP and ohmic heating, considering that consumer attitudes are a key factor in the successful application of new technologies, is that they do not generate negative reactions among health professionals who must appraise nutritional benefits and product safety (Delgado-Gutiérrez and Bruhn 2008).

Not all the sarcoplasmic enzymes have negative effects on surimi gelation. Calcium-dependent endogenous transglutaminase (TGase) is responsible for enhancing the textural properties of surimi during suwari (Carvajal and others 2005). Covalent ɛ-(γ-glutamyl) lysine cross-linking between myosin heavy chains is catalyzed by TGase at low temperatures (Kimura and others 1991; Choi and others 2005). For that reason, setting at low temperatures improves the gel strength of surimi products (Moreno and others 2008), and a 2nd quick-heating process at high-temperature aims to inactivate heat-stable proteases to avoid modori and to shorten setting time (Benjakul and others 2004a).

Because differences in the optimal temperature of TGase according to the environmental temperature of the fish, it is necessary to take into account that setting temperature may vary among species. For example, Benjakul and others (2003a, 2004a) studied the setting temperature, medium (25 °C) and high (40 °C) of several tropical fish species. Good quality gels were obtained, but longer times were required to increase the gel quality in the medium-temperature setting by endogenous TGase, whereas at high-temperature setting an extended setting would decrease surimi gel strength.

Use of additives to improve quality of surimi

The gel strength of surimi can be enhanced by the addition of several ingredients. Protease inhibitors are commonly used to avoid the modori phenomenon, such as plasma proteins, egg white, potato extract, and whey protein concentrate; although color and flavor may be altered (An and others 1996; Benjakul and others 2004b). Other additives are added to increase the water-holding capacity (phosphates) (Park 2005b), to act as fillers, thickeners or gelling agents (hydrocolloids and polysaccharides) (Montero and others 2000; Pérez-Mateos and Montero 2000), while others such as calcium compounds (Lee and Park 1998), chitosan (Benjakul and others 2003b), and oxidizing agents (Phatcharat and others 2006) seem to act by forming stronger protein gel networks.

Likewise, cross-linking enzymes such as a non-calcium-dependent microbial TGase (MTGase) can be added to improve the mechanical properties. Furthermore, this MTGase is more stable, catalyzes the reaction at higher temperatures than the endogenous TGase (Lee and others 1997; Gómez-Guillén and others 2005), and shows a greater activity than fish TGase (Hemung and others 2008). Furthermore, MTGase has demostrated to enhance the gel quality of lizardfish surimi even after 10 d of storage in ice (Benjakul and others 2008), and was also effective in dark and fatty fish, such as sardines (Sardina pilchardus) (Karayannakidis and others 2008b), in white shrimp (Tammatinna and others 2007), and in other muscle products, such as beef gels (Castro-Briones and others 2009).

Improvements of Surimi Yield

The availability of new technologies allows higher extraction of fish proteins and the exploitation of novel fish species. The most significant developments include:

  • 1Application of new equipment, such as deboning machines to obtain a fish paste by mechanical separation (Ramírez and others 2007a), and new cutting machines may increase the recovery of fish meat (Guenneugues and Morrissey 2005). Conventional filleting machines are not designed to handle small fish, giving a low yield and fillets of inferior quality, with impurities from viscera, such as proteases. Smaller fish filleting machines are available, at a higher cost, however, more suitable equipment for eviscerating fish of varying size to obtain a higher yield has been patented by Nicklason (2000). Also, a variation of the surimi fabrication process suggests a mince–crushing step before washing and/or crushing the refiner waste mince to increase surface area (Kanda and others 1993). Thereby, fresh water requirements are reduced, and the quality and yield of surimi are improved.
  • 2Maximization of whole fish utilization by means of meat recovered from materials such as frames and collar cuts which can be used in low-quality surimi (Guenneugues and Morrissey 2005; Velázquez and others 2008). Equipment for a greater extraction of meat, and also for extraction from waste body parts, has been patented (Kragh 2002).
  • 3Decanters are available to improve the yield, and some are also suitable to deal with problematic species, and to operate producing a constant residual water content in the solids, with reduced power consumption and power loss, thus allowing a more optimized process regardless of the raw materials. Therefore, the use of decanters to replace the screw presses reduce several process stages and increase the yield of the surimi processing, from 55% to approximately 70% of the mince, according to equipment suppliers (Alfa Laval 2003, 2008; Flottweg AG 2009; Westfalia Separator Industry 2009).
  • 4A significant proportion of fish proteins are lost in the washing steps and in the screw presses, but the recovery of small meat particles from the wash water using new decanter technology is possible (Hultin and others 2005). Water is mixed with minced meat from fish frames in a washing module, then refined and dewatered in a decanter centrifuge. These proteins can be mixed with the main dewatered surimi, in the fabrication of a secondary grade surimi line, such as for crabstick manufacturing, increasing the yield up to 20%, and obtaining a better-quality surimi, when compared to the exclusive use of pelagic fish (Guenneugues and Morrissey 2005; Alfa Laval 2008). With the use of decanters for both steps, the overall yield may increase up to 50% (Alfa Laval 2008).
  • 5Analysis, assessment, and optimization of the factors that influence process yield, such as temperatures, times, and washing ratios (Guenneugues and Morrissey 2005).
  • 6Use of novel extraction techniques that increase protein yield. Hultin and Kelleher (1999, 2000) developed a process for surimi production (Figure 1) involving a high or low pH-mediated solubilization of the proteins as a 1st step, since myofibrillar proteins are highly soluble at pH below 3.5 or above 10.5. After the solubilization follows a decanting step where the lipids are skimmed and those impurities that are denser than water, such as skins and bones, are removed by sedimentation, centrifugation, or filtration. A subsequent step is an isoelectric precipitation of the muscle proteins by adjusting the pH to their isoelectric point (5.2 to 5.5). Thus, most of the proteins become insoluble, allowing their recovery by centrifugation or filtration. Although this protein isolate also contains sarcoplasmic proteins and impurities, these are removed with further washes during the surimi process (Hultin and others 2005).
Figure 1—.

The acid and alkaline solubilization processes for protein isolates carried out in the laboratory. Adapted from Hultin and others (2005).

Consequently, this pH-shift process achieves the highest yields and the gelation properties are also improved (Carvajal and others 2005). An additional advantage is the removal of more lipids than during conventional surimi processing. Also the alkaline pH-shift method is effective for stabilizing residual heme groups, reducing its prooxidative character (Kristinsson and Hultin 2004; Hultin and others 2005). Thereby, processing of raw materials that tend to undergo lipid oxidation may be improved through the use of the alkaline method. Moreover, this method maintains a better protein gel-forming capacity because it is carried out under cold conditions, it is faster than the standard process, contaminates less, uses less water, and allows the incorporation of low-value source of proteins, such as dark-fleshed fish, into value-added human foods. The protein recovered has a lower lipid content, which minimizes lipid oxidation and makes the product more stable. Furthermore, the fish can be used with skin and bones, allowing both the utilization of by-products (heads, collarbones, backbones, and so forth) and whole underutilized species (Nolsoe and Undeland 2009).

Hence, this new method could become an essential element in the surimi industry (Hultin and others 2005). A further advantage of the pH-shift process is its suitability to process unstable materials and those where the separation of the meat is difficult. The acid method presents usually the advantages of higher protein yields, higher solubility, and lower levels of sediments. However, the conventional surimi and alkali-produced protein isolates generally result in stronger and whiter gels than the acid-produced proteins. Also, because the alkaline process removes more lipids, the protein isolates are more stable toward lipid oxidation than the acid ones. Therefore, the purpose of the processing, the uses of the isolates, and the raw material will determine the choice of method. Nevertheless, initial trials are recommended to optimize the process, considering the variations of raw materials (Nolsoe and Undeland 2009).

Surimi from Underutilized Species

Surimi from small fatty dark-fleshed fish

Several whitefish species have been mentioned as preferred species for surimi manufacturing (Benjakul and others 1997, 2003a; Guenneugues and Morrissey 2005). However, it is necessary to take advantage of the availability of alternative resources for surimi production, such as small fatty pelagic fish. Considering that about 40% of the total fish catch in the world is dark-muscle fish, and a large quantity of this fish catch is underutilized pelagic species, such as sardine (Sardina pilchardus) or horse mackerel (Trachurus trachurus), there is great interest in the development of methods to make use of them for human consumption (Hultin and others 2005). They are harvested as by-catch of other species, but to a degree remain unused because only low-quality surimi is obtained from them, or they are utilized for low-priced products. Problems with the rapid deterioration of fish quality, color, small size, fishy odor, and flavor, low muscle pH, high fat content, and high concentration of sarcoplasmic protein occur, and therefore the gelation process could be affected to a degree that would limit their utilization in surimi production (Shimizu and others 1992; Hultin and others 2005; Lin and others 2005).

The composition of dark muscle is the major problem when incorporated into surimi, mainly because besides its higher lipid content and susceptibility to oxidize, dark meat has greater proteolytic activity, more trimethylamine oxide and higher concentrations of sarcoplasmic proteins (Shimizu and others 1992; Sánchez-Zapata and others 2008; Eymard and others 2009); therefore, it shows higher susceptibility to modori. Myoglobin and hemoglobin are responsible for the red color of dark muscle but they also promote lipid oxidation (Sánchez-Zapata and Pérez-Álvarez 2007). Nevertheless, the role of sarcoplasmic proteins such as myoglobin is controversial; some researchers state that they hamper myosin cross-linking during the gelation process, others consider that these proteins do not interfere with the myofibrillar proteins (Park and Park 2007). Also, dark-fleshed fish mince experiences a sharp pH drop after slaughter, often below 6, in comparison with 7, approximately, for Alaska pollock. This pH around the isoelectric point of the proteins increases their denaturation rate, affecting the gelling ability of pelagic species flesh kept in chilled storage for a day or 2. Additionaly, surimi from pelagic fish presents a higher and stronger proteolytic activity than surimi from light-fleshed species (Hamann and MacDonald 1992; Shimizu and others 1992; Hultin and others 2005). Thus, the process for obtaining high-quality surimi from fish mince with increasing contents of dark muscle could be more difficult, mainly due to the problems discussed previously.

The industrial use of these species undergoes complex issues, nonetheless, the use of decanter technologies, alternative washing methods, and novel extraction systems are allowing processing of flesh from these fish species into surimi, with increasing process yields (Morrissey and others 2005). Washing is a crucial process because it removes many of the components that cause low quality and poor stability (Hultin and others 2005; Karayannakidis and others 2007). By increasing the washing cycles (Kim and others 1996), or the washing time and the water quantity (Chen and others 1997), the color of surimi can be improved. However, long washes weaken the gel-forming ability (Bentis and others 2005), they consume large amounts of water, and cause contamination problems (Hultin and others 2005). The addition of NaHCO3 in the first washing solution and the use of a decanter to remove the extra oil have been recommended. Additional suggestions are to remove heme proteins by the addition of sodium pyrophosphate and the use of reduced pressure during washing (Hultin and others 2005). A preventive antioxidative method would be washing the minced fish tissue under conditions that prevent rupture of the red blood cells as it would reduce the pro-oxidant effect of the hemoglobin released during mincing (Richards and Hultin 2002, 2003; Hultin and others 2005). New decanters, which use centrifugal force, can be used to fatty or dark-fleshed fish, just a 2nd washing step may be required before decanting (Alfa Laval 2008). Other washing techniques have been studied:

  • 1A great increment in the gel-forming ability of fatty fishes is achieved by a first alkaline saline leaching (0.15% NaCl in 0.2% NaHCO3) during 15 to 20 min, followed by washes in water of salt–water if needed. Thus, the pH increases, and thereby the rate of denaturation and the concentration of heme pigments are reduced (Shimizu and others 1992). Chaijan and others (2004) analyzed mince from sardine (Sardinella gibbosa) and mackerel (Rastrelliger kanagurta) washed with different concentrations of NaCl solutions. This resulted in a higher removal of myoglobin, increased gel-breaking force, and a superior gelling ability and whiteness when compared with the conventional method.
  • 2Chen and others (1997) and Jiang and others (1998) evaluated the use of ozonation in mackerel (Trachurus japonicus) during 10 to 20 min and during 30 min, respectively, to improve color. While these short treatments had a whitening effect, adversely, the ozone reduced the gel-forming ability, and the fish oil suffered oxidation. To overcome the oxidant effect of the ozone Wu and others (2000) added NADPH-sulfite reductase from Escherichia coli and other chemical reducing agents (bisulfite, sodium nitrite, and sodium thiosulfate) to mackerel (Scomber japonicus) surimi, and managed to improve the gel-forming properties.
  • 3The use of hydrogen peroxide to bleach the mince is also effective, but methionine, cysteine and unsaturated fatty acids are affected, and proteins are precipitated (Meacock and others 1997).

In regards to the addition of ingredients, recent research (Balange and Benjakul 2009a) has shown that the addition of oxidized phenolic compounds can improve surimi gel strength through the formation of cross-links after reacting with proteins. These compounds tend to decrease whiteness, but they may not have a negative effect on the color of surimi made from dark flesh meat. Another option is to remove as much of the dark muscle from the fish as possible. Suzuki and Watabe (1986) reported that surimi prepared from very fresh sardine light muscle has the same quality as high-grade Alaska pollock surimi, although it is darker than that from white-fleshed fish. However, a meat separator has been unsuccessfully used for removal of high levels of the dark muscle, resulting in low yield, with loss of some light muscle and high product costs (Ochiai and others 2001; Hultin and others 2005).

Several considerations for production of surimi from dark-fleshed muscle fish would be also beneficial:

  • 1A proper last dewatering after washing is an essential stage to ensure good quality (Eymard and others 2005).
  • 2To face the seasonal variations that fatty fish show in lipid content, it is better to aim to catch them when their content is lower (Hultin and others 2005).
  • 3If the fish is not very fresh, due to its rapid deterioration, it is impossible to make surimi from small pelagic species (Suzuki and Watabe 1986). For that reason has been made trials with surimi from frozen pelagic fish, such as Sardina pilchardus (Karayannakidis and others 2008a). Nonetheless, a gel with good quality was obtained just from sardines frozen stored up to 20 d.
  • 4The whiteness of surimi from these species could be affected. Hence, the addition of whitening agents such as titanium dioxide, calcium carbonate, and soybean oil has been proposed, although gel-forming ability might be delayed, mainly when an excessive amount of whitening agent is used (Meacock and others 1997; Benjakul and others 2004b). Also, Schnee (2006) proposed and patented the addition of alkaline earth phosphates to improve the whiteness of surimi without affecting the structure and the taste.
  • 5Another alternative to make use of dark-fleshed species and low-quality fish meat is the production of deep-fried kamaboko, which is popular in Japan. After frying, the color in the surface is dark, but in this case, whiteness is not a decisive quality attribute (Konno 2005).

Overall, an ideal method, both efficient and economical, to obtain the flesh without contamination from dark muscle has not been found (Hultin and others 2005). But fortunately, the development of new techniques facilitates the production of dark-meat fish surimi, resulting in better-quality surimi.

Surimi from freshwater fish species

The growing volume and diversity of inland fish farming, is turning increasing interest on some species as raw material for surimi for a more efficient alternative to add value, as occurs with silver carp (Hypophthalmichthys molitrix) (Liu and others 2008b). This carp is appreciated for its white color and attractive taste, but the high amount of fish-bone in the edible portion makes difficult the production of fillets, resulting in higher rates of unused meat.

Properties of freshwater fish muscle show differences with regard to other marine species. Although these species show only moderate gel forming ability and the frozen storage affects the protein properties, it can be utilized adapting the parameters of the gelation process (Ganesh and others 2006). According to Luo and others (2001) they would need a longer time and higher temperature, since the myofibrillar protein of freshwater fishes are more stable to heat.

To improve the properties of freshwater fish species surimi some variations in the process have been studied:

  • 1This surimi is considerably affected by proteases, such as cathepsins (Liu and others 2008a); therefore, it requires the control of the modori state. Luo and others (2008) found that 10% of soy protein isolate could decrease the development of modori in silver carp surimi, but more research would be necessary to optimize the process.
  • 2Chitosan in catfish (Pangasius sutchi) enhanced the gel strength (Kungsuwan and others 2002). Mao and Wu (2007) also added chitosan in grass carp (Ctenopharyngodon idellus) and concluded that chitosan improves gel color, texture, and prevents lipid oxidation.
  • 3Different methods for processing of common carp (Cyprinus carpio) were studied by Jafarpour and Gorczyca (2008) who reported that the best texture and color was obtained with the conventional method of surimi processing, but using a centrifuge instead of a decanter and filtering to remove the sarcoplasmic proteins, together with effective dewatering.
  • 4Rawdkuen and others (2009) have investigated the properties of surimi obtained from tilapia (Oreochromis ssp.) by the acid–alkaline process to increases protein yields and reduce lipids and pigments; finding that other aspects, such as gel strength needed improvement. Effective removal of scales, bones, and skin particles from rainbow trout (Oncorhynchus mykiss) processing by-products has been achieved by isoelectric solubilization/precipitation, but gels from the recovered myofibrillar protein still showed proteolysis with added beef plasma proteins, and further use of potato starch, transglutaminase, and phosphate to reduce proteolysis were required to achieve a desirable functionality (Chen and Jaczynski 2007a, 2007b; Chen and others 2007). Another study on the application of the acid–alkaline process for the recovery of the proteins left after cutting the catfish fillets managed to produce an increase in the yield of the fish for human consumption (Kristinsson and others 2005).
  • 5Due to the pink color that common carp confers to surimi, hydrogen peroxide has been added to improve color, but the structure of the gel was affected (Jafarpour and others 2008).
  • 6The addition of protease inhibitors, such as soy protein isolate (Luo and others 2008) and food-grade serine inhibitors in tropical tilapia (Tilapia niloticus) surimi (Yongsawatdigul and others 2000), and MTGase to improve the poor gel-forming ability (Ni and others 1999; Ni and others 2001) have given positive results.
  • 7Different gelling ingredients have been also considered; among others, xanthan combined with locust bean (Ramírez and others 2002) and pectins (Barrera and others 2002) in silver carp (Hypophthalmichthys molitrix).

Surimi from cephalopods

Besides the use of fish muscle, it is possible to manufacture gelling products from Cephalopoda. They have some advantages including its color, low fat content, mild flavor, and they represent an abundance of underutilized species. Despite the fact that acceptable collagen-based edible gels can be obtained as reported by De La Fuente-Betancourt and others (2009), the traditional method to make surimi cannot be applied to cephalopod muscle. Its myofibrillar protein is much more water-soluble than fish muscle, with some odorous compounds, and its high protease activity cause decreased functionality of the obtained product (Izquierdo-Jiménez and others 2003; Careche and Borderías 2004; Sánchez-Alonso and others 2007a; De La Fuente-Betancourt and others 2009).

Surimi from cephalopods such as the giant squid (Dosidicus gigas) is a new product from the concentrate of muscle protein of its main myofibrillar proteins. According to Careche and Borderías (2004), this concentrate could be produced by neutral pH solubilization and further isoelectric precipitation, while a recent study (Cortés-Ruiz and others 2008) states that manufacture is also possible under acidic conditions. There is an improvement in the gel-forming ability of the concentrate when it is mixed with sodium chloride or potassium chloride and/or other additives and ingredients, prior to heating or high-pressure treatment, which modifies its texture. Thus, a heat-stable gel is obtained for the production of substitutes or other products that are surimi-like (Careche and Borderías 2004).

This kind of surimi differs from conventional fish surimi in a number of characteristics. For example, its structure is particularly fine and with acid pH and, as a result, the volume of released water after thawing is higher and the product yield is lower. Therefore, ingredients such as wheat fiber have been tested to bind this free water (Sánchez-Alonso and others 2007b). The gelation properties of cephalopod muscle also can be improved by means of (HHP) before heating (Nagashima and others 1993).

Surimi from crab

The important amount of Jonah crab (Cancer borealis) harvested as by-catch of the lobster industry, together with the increase in consumer demand for Jonah crab claws, have generated interest in the use of the crab meat. Its mild flavor and relatively low cost make crab a potential resource of protein for surimi production (Baxter and Skonberg 2006, 2008). One concern is that while the claws are the most popular part, after their removal the crabmeat left behind is wasted. Therefore, a low-value crab mince can be obtained from the neglected meat using mechanical deboning equipment. However, the profitability and utilization of this resource could increase with new uses, such as the formation of surimi-like gels (Baxter and Skonberg 2008).

A drawback results from the common practice of cooking the whole product before becoming available for surimi processing, with the subsequent denaturation of proteins, causing a significant loss of functionality. But Baxter and Skonberg (2006) demonstrated that washed crab mince obtained from previously cooked Jonah crab meat is suitable to produce gels with acceptable characteristics, which can be used as the main ingredient in protein gel-based products.

Surimi from other marine species

Other species have potential to be alternative resources for surimi production. For instance, fatty-fish escolar (Lepidocybium flavobrunneum) is a by-catch of tuna, which remains underutilized. However, it is discarded because more than 90% of its lipid content (18% to 22%) is wax ester, a material that causes diarrhea after ingestion. Therefore, the use of escolar meat for surimi production would only be enabled after reducing its lipid and wax contents. As Pattaravivat and others (2008) suggest, the use of a palmitic sucrose ester solution seems to be a method of lipid removal after the first washing. In addition, the quality of the obtained gel was better than surimi of medium gel strength (SA grade), confirming that escolar meat could become a suitable material for surimi production.

The potential for adding krill, squid, or octopus at low proportions into acidified fish muscle mixtures with the aim to produce a ready-to-eat prototype has been successfully demonstrated, but firmness and an adequate moisture level was only achieved when a critical ratio of fish mince was included in the formulations, as explored by De Juan-Segovia and Kuri (2007, 2008).

Antarctic krill (Euphausia superba), probably one of the most abundant marine species, has not been used for surimi production due to the high quantities of resulting by-product, and low yield of recovered proteins. The application of the isoelectric solubilization/precipitation method has allowed the higher yield recovery of functional muscle proteins from whole krill in a continuous mode. This allows one to produce krill protein concentrates and surimi gels, with the potential of recovering fat fractions and maintaining high levels of omega-3 polyunsaturated fatty acids (Chen and Jaczynski 2007a; Gigliotti and others 2008). Nevertheless, more research is needed to optimize this process. Applications for surimi processing from shrimp has been developed at the Bureau of Fisheries and Aquatic Resources (BFAR) at the Philippines, and summarized by Abella and others (1995).

The manufacture of surimi from Elasmobranchs (sharks, rays, and skates) has been also studied, since they were considered underutilized due to their shape, meat odor, and taste (Venugopal and others 2002). However, these species are now threatened by over-explotation in high seas fisheries, especially sharks by the high value of their fins, but also they are harvested as by-catch in considerable amounts in some places (Turan and others 2007; Dulvy and others 2008). Reports about surimi from sharks and rays are scarce, but Turan and Sonmez (2007) found that thornback ray (Raja clavata) was a suitable resource for surimi production, and Kailasapathy and Salampessy (1999) made surimi from angel shark (Squatina spp.) with the addition of urease to remove the urea from shark mince without affecting the myofibrillar proteins.

Surimi-like materials

In the last few years, interest has increased towards the utilization of nonmarine organisms for the production of surimi-like gels. Specifically, some low-value meats, or animal by-products that would not be used as foods unless processed, can sometimes be suitable for turning low-value materials into useful surimi ingredients. For example, surimi from mechanically deboned chicken meat has been studied as a solution to use residual parts such as necks, backs, breast frames, and the meat adhering to the carcasses (Smyth and O’Neill 1997; Antonomanolaki and others 1999; Navarro 2005, 2006; Jin and others 2009). Spent layers provide material with high potential for surimi-like products since they are underutilized (Nowsad and others 2000; Jin and others 2007a). Carcasses from these old hens have tough and dry muscles, properties that could be modified by processing, mainly during the thermal gelation (Yang and Froning 1992; Kijowski and Richardson 1996). Beef, pork, and sheep muscles also, and even beef or pig hearts, have been used to produce surimi-like materials (Wan and others 1993; Zepeda and others 1993; Wang and Xiong 1998; Jin and others 2007b; Kang and others 2007).

The differences between functionality of red muscles, such as leg and neck, and white muscles, such as breast, have been studied (Amato and others 1989; Lan and others 1995; Navarro 2005; Navarro and others 2007) and the consensus is that red muscle produces a stronger gel. However, red meat has a high fat content, more heme pigments, and high levels of collagen, causing problems when it is used in the production of surimi-like materials (Park and others 1996). Consequently, repeated washing of minced meat with water or low ionic strength aqueous solutions (that is, sodium chloride or lactic acid) to remove fat, pigments, sarcoplasmic proteins, and other materials are necessary to obtain higher myofibrillar protein concentrations (Varnam and Sutherland 1995; Sayas Barberá and others 2001). Only then will the resulting filamentous structure (fibrous network) of the gel be of acceptable textural properties (Yang and Froning 1992; Antonomanolaki and others 1999).

High collagen content could be inconvenient. Collagen is very insoluble in water or saline solution, and, along with the myofibrillar proteins, it is retained during surimi processing. Heating can change collagen to gelatin, which seems to interfere with the gelation of the myofibrillar proteins. While fish muscle has a small proportion of collagen, and it does not seem to affect its gelling ability, mammalian and avian muscle tissue has high concentrations of it. Therefore, it is necessary to reduce the connective tissue content when preparing surimi by conventional washing methods to obtain improved properties (Carvajal and others 2005). Some approaches have been studied, including the method for separating proteins from connective tissue based on the lower strength of muscle protein than that of connective tissue, which was developed by Hultin and Riley (2007); however, more research is needed to improve the qualities of these surimi-like products.

Recuperation of Solids from Surimi Processing

The wastewater produced after washing and refining the mince contains insoluble components such as myosin fractions, scales, fat, and other tissue fibers; and also soluble components such as enzymes, polypeptides, blood components, and inorganic minerals. There is an increasing interest within the food industries in using fish body parts for different foods and functional ingredients, together with the processing of by-products into value-added components (Morrissey and others 2005; Nolsoe and Undeland 2009). For example, bioactive compounds of interest such as proteases (Mireles and Morrissey 2002) or other sarcoplasmic proteins (Piyadhammaviboon and Yongsawatdigul 2009) can be obtained by ultrafiltration of the surimi wash-water (SWW), which contains TGase, and therefore can be used as gel enhancer in surimi production (Piyadhammaviboon and Yongsawatdigul 2009); emulsifiers from fractions extracted from cod after the pH-shift method have been recovered (Nolsoe and Undeland 2009), and also the acid-soluble collagen from the refiner discharge, which may be used as a functional ingredient (Park and others 2007); even antioxidants have been found in SWW (Morrissey and others 2005).

On the one hand, washing removes small flesh particles, including myofibrillar proteins (Park and Lin 1996, 2005) and factors, such as changes in pH and ionic strength, proteolysis, and mechanical forces may diminish the recovery of myofibrillar proteins. Around 40% to 50% of the myofibrillar proteins is lost in soluble or insoluble forms during mincing, washing, screening, and screw-pressing. The water from washing and dewatering operations carries approximately 15% of the myofibrillar proteins. Thus, depending on how the washing is done, the concentration of solids in the SWW can range from 0.5% to 2% (Morrissey and others 2005). However, normally this SWW is discarded as waste (Krasaechol and others 2008).

On the other hand, methods for the efficient recovery of proteins from SWW are emerging. Soluble proteins can be separated by ultrafiltration, which removes a high percentage of them; although a large membrane area would be necessary. The resulting concentrated protein has a dark color and strong odors, but it could be used in animal feed. However, an advantage of ultrafiltration is the possibility of recycling processing water (Marti and others 1994; Lin and others 1995; Montero and Gómez-Guillén 1998; Park and Lin 2005). One method could be flocculation of the soluble proteins by ferric chloride or chitosan–alginate; this would allow their recovery and the reduction of organic matter before discharging, but ferric chloride has a high toxicity (Marti and others 1994; Velázquez and others 2007). Methods based on the addition of chemical compounds to modify the properties of the water have been recently studied by Bourtoom and others (2009). They concluded that the precipitation of proteins can be achieved with ethanol (60g ethanol/100g SWW), since this organic solvent reduces the dielectric constant of the water; but also by shifting pH, with a larger yield at pH 3.5, close to the isoelectrical point. But a study for the characterization of the recovered proteins is needed to know their functionability. Another method could be heating the thermo-sensitive proteins to induce coagulation and precipitation. This could be done by steam or hot water in direct contact, although the water consumption would be increased (Huang and others 1997), and also by ohmic heating (Benjakul and others 1997; Huang and others 1997). In fact, current work on the coagulation of protein in SWW under continuous ohmic heating following a separation to reduce the biological oxygen demand of wastewater, as well as protein recovery, has been reported to be of high energy efficiency (Kanjanapongkul and others 2009). The electric energy directly heats the fluid quickly and uniformly, with an additional advantage of applying a clean technology without the need for any chemical additives. This continuous process is considered to have potential commercial applications.

Insoluble solids can be recovered from SWW by centrifugation without affecting the functional properties of proteins (Ramírez and others 2007b); however, according to Lin and others (1995), the use of microfiltration is a more economical alternative for insoluble components. Decanter centrifuges are normally used for the recovery of fine particles lost through the dewatering screens and screw presses (Park and Lin 2005). Moreover, if the pH-shift method is used, the extraction of by-products will be facilitated and, as reported for sardine processing (Nolsoe and Undeland 2009), will allow to take advantage of recovering the proteins in the soft jelly, which otherwise would be discarded after the first centrifugation. Taskaya and Jaczynski (2009), also found a very efficient recovery of proteins from the isoelectric solubilization/precipitation of process water by the application of anionic flocculants of high molecular weight.

Park and Lin (2005) suggest that a certain quantity of these recovered meats may be recycled into high-quality surimi paste, but also that it can be marketed as low-grade surimi. Lin and others (1995) reported that proteins from the SWW microfiltration had high functional properties and, when compared to conventional surimi, their composition was similar. When the authors substituted 10% surimi with the recovered insoluble proteins, they found that the quality of the gel was the same as the quality of surimi without these proteins. Ramírez and others (2007b) stated that adding 1% of insoluble solids from SWW actually improved the mechanical properties of Pacific whiting surimi, obtaining also an acceptable color without the need to add higher quantities. Velázquez and others (2008) obtained similar results using Alaska pollock. However, when the proteins added to high-quality surimi were soluble, the mechanical properties of the gels improved, but increased in redness (Velázquez and others 2007). The mechanical properties seem to be due to a higher absorption of water by the particles, allowing a higher number of protein-protein interactions. But an excessive proportion will negatively affect the protein network (Velázquez and others 2008).

Therefore, the recovery of solids from surimi processing has important advantages: it maximizes the utilization of seafood resources and the productivity, it reduces waste, it generates treated water that may be reused in the seafood processing operations, and even the mechanical properties of surimi are enhanced in some cases (Velázquez and others 2007, 2008). Moreover, the use of pH-shift isolation of proteins shows a considerable potential for using underutilized muscle proteins, including complex raw materials (Nolsoe and Undeland 2009). Fish proteins derived from surimi processing can find a number of uses, depending on the setting of particular processing facilities and the cost-benefit of processing materials, which can include direct incorporation into the surimi mince, or other uses such as those compiled by Keller (1990), which include uses as pet food ingredients, protein hydrolysates, particularly if there is a high bone content, fishmeal, protein concentrates, protein preparations for animal feeds, recuperation of pigments in some instances, extraction of chitin, preparation of flavorings, fish silage, and composting by a range of techniques.

Management of the Enviromental Impact of Surimi Processing

In general, the major problems for the seafood industry concern utilization of natural resources. They include large requirements of freshwater, the negative impact on the environment as a consequence of discharging processing water that has not been adequately treated, and the poor utilization of fish resources (Morrissey and others 2005).

Surimi processing, as is shown in Figure 2 can be divided into 2 main stages. The 1st phase (heading, gutting, deboning, and mincing) prepares the fish mince for the 2nd one (washing and refining of mince), and all stages consume water. Surimi processing from white-flesh fish requires a large amount of chilled water because of the extensive washing. The mean consumption for washing is about 27m3 per ton of surimi (Afonso and Bórquez 2002). The minimum might be less than 10 to 15 L of water for shore-side operations and less than 5 to 7 L for at-sea operations to produce 1 kg of surimi (Park and Lin 2005); and water is often discharged carrying proteins, oils, and other organic materials (Huang and others 1997; Afonso and Bórquez 2002). Considering that 2 to 3 million metric tons of fish per year (2% to 3% of the world fisheries supply) are used for surimi production (Vidal-Giraud and Chateau 2007), the worldwide consumption of water, and the contamination and loss of valuable components are notable. In addition, the use of water is becoming more expensive; therefore, the industry is interested in the reduction of water usage and the improvement of washing efficiency. In fact, during the last 20 y the better ratios of water/meat and the washing cycles have been linked to a more effective washing process. Excessive washing increases the water requirements and also the wastewater, and it results in the loss of myofribrillar proteins. Therefore, increasing the washing time and the number of washing cycles with a lower water/meat ratio would be attainable with the same washing effect with less water (Park and Lin 2005).

Figure 2—.

Wastewater during surimi processing and a water recycling washing system. Adapted from Lee (1990) and Morrissey and others (2005).

However, wastewater is the biggest problem for the surimi industry and, therefore, it is the aim of companies to develop efficient methods for wastewater treatment and protein recovery. Several of the methods to recover solids from the SWW have been mentioned before. They bring about the reduction of the polluting load and the possibility of added solids incorporation into the surimi paste. Additionally, the cost for the disposal of the wastewater is reduced; also, higher productivity is achieved when the recovered proteins from SWW are incorporated into primary products or some bioactive compounds are extracted (Morrissey and others 2005). The relevance of this line of work on the recovery of by-products from seafood processing flows is becoming more important. Funding and work are sometimes directed to animal feed applications, such as pellets, and lately energy production from by-catch waste, while only a few groups carry out research directed towards human food (Torres and others 2007; J.W. Park, unpublished data).

Another alternative to reduce the cost of pollution control is the application of the pH-shift method in surimi production, because the SWW has low protein content, and thus a lower biological oxygen demand. This makes possible multiple reuses of the water; also, no components that would contribute to pollution are added during the process (Hultin and others 2005). The development of an unwashed surimi seems viable, and it additionally has the advantage of including more bioactive compounds as an inhibitor of angiotensin I converting enzyme (enzyme for increasing blood pressure); and there is a reduction in water usage and pollutants during the process (Yoshie-Stark and others 2009).

For the recycling of wastewater, Lee (1990) suggested the principle of counter-current washing, which consists, basically, in using cleaner water in the later washes. For example, in a 3-step washing process, the water from the 2nd dewatering can be reused in the 1st wash, whereas the water from the 3rd wash is re-circulated to the 2nd wash. Therefore, the water from the 1st step would be discharged with high levels of undesirable impurities, and the last wash is with freshwater. In this case, recycling the SWW in 2 of the 3 steps could reduce water usage by two-thirds; it would also save waste management costs and energy costs due to the refrigeration of the water. All this needs to be tested on a large scale before its implementation on a commercial production scale, but producers seem to reject this possibility (Park and Lin 2005). Nevertheless, Clark (2008) reports that in a clam processing operation, by recycling the water by this method, important savings were achieved by reducing freshwater usage.

Another point that should be considered at some stages in the processing is the real requirement of freshwater. For instance, during heading, gutting, and deboning, water is injected in the machines to remove fish fluid and the pieces adhered to the machines. After that, large amounts of water are usually used for transporting skins, viscera, and backbones from filleting and deboning machines to the scrap delivery system. These steps do not need to use freshwater; they can utilize recycled water (Morrissey and others 2005).

Regarding surimi from pelagic fish, such as sardines, contamination is even higher. Solid by-products represent 30% to 60% of the whole fish, in addition to the wastewater. However, the application of ultrafiltration has been assessed by Dumay and others (2008), and it seems to be a suitable technology for the recovery of proteins and lipids from the SWW from pelagic fish process water, while in effluents with high charges of compounds it has been possible to work with centrifugation, controlled hydrolysis, and membrane technology to recover lipids and proteins. Therefore, the use of efficient membrane and filtration systems and emerging separation technologies will enable better use of resources for surimi production.

Solid waste is also produced during surimi processing from the heads, viscera, skin, frames, and bones. It can be used as fishmeal after drying, but expensive equipment is required and the wastewater may have a difficult treatment. Likewise, this solid waste can be used for composting to elaborate fertilizers (Morrissey and others 2005). A more economical process is the manufacture of fish protein hydrolysates (Benjakul and Morrissey 1997), and has been used even as cryoprotectant in lizardfish surimi (Arvanitoyannis and Kassaveti 2008). Furthermore, due to the elevated concentration of proteases in the by-products, fish sauce can be made by fermentation (Morrissey and others 2005). A further opportunity to add value to fish by-products, and particularly the skins, is to obtain gelatine that can be used by food processors as a gelling agent and to produce edible films (Norziah and others 2009).

Fish oil is another important waste; nevertheless, the high content of omega-3 fatty acids, such as eicosapentanoic acid and docosahexaenoic acid, makes this by-product be considered as nutraceutical and a food ingredient, since they claim to prevent heart diseases. However, the oil is removed during the washing steps and is not recoverable for this purpose, being used frequently for heating, mixed with other fuel oils. Considering the larger use of pelagic species with higher amount of oil, the recovery of this oil as a high commercial value could be another area of research (Morrissey and others 2005).

However, it is necessary to establish the most suitable process and the one with the lowest energy consumption to make by-product recovery profitable (Morrissey and others 2005). More studies are needed to overcome some of the difficulties with regards to the extraction methods, recovery methods, but also to design and adapt affordable equipment for the industry, which may result in more profitable processes. The introduction of new technologies will reduce the producers’ burden of solid waste and wastewater, which may tip the balance and be a factor for the potential widespread application of these operations.

Conclusions

The sustainability credentials of surimi processing are debatable. On the one hand, the process is an effective way to take advantage of underutilized fish species and nonfish species, making the use of such resources more sustainable and profitable. But on the other hand, surimi is associated with the use of declining fish stocks, large volumes of freshwater, high levels of contaminated wastewater, and poor use of whole fish for human foods. The introduction of novel species in the industry could enable processors to maintain a profitable level of business and minimize some environmental impacts, particularly if they are able to process a range of raw materials with variable qualities. Additional aspects which producers need to consider are mainly those related to water use and waste, minimizing input, reusing where possible, and recovering material from flows. This may require an advanced understanding of all material properties and behavior which would benefit from both conventional and emerging separation technologies. More sustainable and ethical processing would result in long-lasting enterprises that manage the bottom line wisely and respond to their stakeholder needs.

The extraction yield of proteins from fish is another challenge, but successful trials with innovative technologies such as the pH-shift method are steps into the right direction, particularly because these technologies also make possible the reduction of water requirements. The introduction of the countercurrent washing principle could save a major quantity of water. Finally, the attainment of lower pollution loads by means of the recovery of useful compounds, such as proteins or functional fats from the washwater, would turn waste into profit.

In addition to legislation and enforcement pressure, the effort from the fish industry to increase efficiency and to improve its operations footprints is likely to result in more sustainable practices. With the possibility of the use of more advanced technologies, including HHP, ohmic and microwave heating, advanced decanting and filtration, among others, improvement of current practices and the development of value-added products, mainly using mince from low-cost fishery resources, the surimi industry will have a good future.

Acknowledgments

The work of A.M.M.S. was supported by a grant from Caja de Ahorros del Mediterráneo (CAM); V.K. is a fellow (on sustainability in the food chain) at the UP Centre for Sustainable Futures (CETL), funded by The Higher Education Funding Council for England. Thanks to Alfa Laval, Spain, for information provided.

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