Quality evaluation of surimi and fish nuggets from Queen fish (Scomberoides commersonnianus)

Abstract The purpose of this study was formulation and evaluation of physicochemical properties of fish and surimi nuggets prepared from Queen fish (Scomberiodes commersonnianus) during 90 days of storage. Chemical analysis showed that surimi nuggets contained less protein, fat, and ash due to washing steps during surimi preparation. The titratable acidity, peroxide, and TBA values for fish nuggets were significantly higher than surimi nuggets during frozen storage (p < .05). Moreover, the textural properties of the products exhibited more firmness of surimi nuggets before cooking compared with fish nuggets (p < .05) and more firmness of fish nuggets after cooking compared with surimi one (p < .05). Furthermore, surimi nuggets were lighter and had lower total bacterial counts rather than fish nuggets during frozen storage (p < .05). SDS‐PAGE of the samples during storage exhibited more intensity of the bands related to α‐actinin, actin, and β‐tropomyosin in surimi nuggets compared with that for fish nuggets. Moreover, the sensory evaluation showed that acceptability of surimi nuggets was more than that for fish nuggets after frozen storage. These results showed that surimi nuggets had higher quality indicators rather than fish nuggets.


| INTRODUC TI ON
Surimi is the odorless and white stabilized myofibrillar protein paste prepared from deboned fish flesh during the several washing process to remove the lipids and undesirable substances (Priyadarshini, Xavier, Nayak, Dhanapal, & Balange, 2017). Surimi has good gelforming ability which is used for manufacture of high-quality and value-added seafood products (Moreno, Herranz, Pérez-Mateos, Sánchez-Alonso, & Borderías, 2016). Type and condition of washing process during the surimi production plays an important role on quality of surimi-based products because of an effective removal of the proteolytic enzymes and lipids (Priyadarshini et al., 2017).
However, other parameters such as fish species, protein content, pH, and temperature have an influence on rheological properties of surimi (Panpipat, Chaijan, & Benjakul, 2010).
In addition, as its unique functional characteristics, several studies have been conducted to production of surimi from different fish species and treatments (Moon, Yoon, & Park, 2017;Panpipat et al., 2010;Priyadarshini et al., 2017;Yin & Park, 2015). Although, due to the increasing consumer nutritional requirements, the food industry is trying to manufacture the varieties of products from by-product or less valuable fishes while still maintaining their desirable sensorial characteristics (Ali, Mansour, E-lBedawey, & Osheba, 2017).
Further, there is a growing interest to find ways to innovative and nutritive foods. Thus, during the last years, many researches have been subjected to prepare and evaluation of textural and

| Surimi preparation from S. commersonnianus
Surimi was prepared using the method of Moosavi-Nasab, Alli, Ismail, and Ngadi (2005) with some modifications. Frozen minced S. commersonnianus was obtained from local market (Shiraz, Iran). A quantity of frozen fish was thawed overnight at 4°C and washed (10 min) with chilled water using a 1:4 (w/v) ratio of minced to water. The washed mince was subjected to dewatering by covering with cheesecloth. The washing procedure was repeated three times. Appropriate quantities of sodium chloride (0.2% NaCl) were incorporated by blending with the mince.

| Nugget preparation from fish minced meat
Fish nuggets were produced as above described with fish minced meat instead of surimi. About 1 Kg fillets were minced and mixed with ingredients according to Table 1, then stored overnight (−20°C).
Flour was used as the dust and stored at −3°C.

| Proximate compositions
Determination of nuggets composition (moisture, lipid, protein, and ash) was carried out according to the AOAC (1995). Moisture content was determined using an oven. Kjeldahl and Soxhlet-Henkel methods were used for the determination of total protein (crud protein, N = 6.25) and fat content respectively. Also, ash content was measured by mineralization at 550°C.

| pH and titratable acidity measurement
The pH was measured for the homogeneous mixtures of nugget and distilled water (1:4, w:v) at the first and end of the storage using pH meter (PHT-110, LABTRON, Iran). Titratable acidity was measured as by titration to neutrality with 0.1 N NaOH and calculated as ml of 0.1 N NaOH/g sample (Capita, Llorente-Marigomez, Prieto, & Alonso-Calleja, 2006).

| Peroxide value (PV)
PV of nuggets was calculated with the method of AOCS (1997). The sample (3 g) was heated in a water bath (60°C for 3 min), then thoroughly agitated for 3 min with 30 ml of acetic acid-chloroform solution (3:2 v/v), followed by the addition of saturated potassium iodide solution (1 ml). The reaction mixture was allowed to stand in the dark for 5 min and then was titrated with standard solution of sodium thiosulfate (25 g/L). The PV was calculated as meq/kg sample using the following equation: where S is the volume of titration (ml), N the normality of sodium thiosulfate solution (N = 0.01), and W the sample weight (kg).

| Thiobarbituric acid (TBA) value
Thiobarbituric acid value of surimi and fish nuggets was performed as described by Sallam, Ishioroshi, and Samejima (2004)

| Nugget texture analysis
Texture profile analysis (TPA) of nuggets was measured before and after cooking by the method described by C. Cardoso, Mendes, and Nunes (2008) using a Texture Analyser (Texture Pro CT V1.3 Buil 15). Chilled and fried samples were tempered to bring to the room temperature (25°C). The nuggets were cut into uniformsized pieces (6 × 3.5 × 1 cm) and placed on the sample holder.
Then, puncture test was carried out by penetrating the sample to breaking point with metal probe equipped with 6-mm-diameter spherical head using the speed of 6 mm/s. Finally, breaking force (N) and breaking deformation (mm) were evaluated. Three measurements were taken from each sample and averaged for statistical analysis.

| Color analysis
Color measurements of nuggets were obtained using a colorimeter chamber. Color parameters (L*, a* and b*) were gained from different spots on surface of each sample using Photoshop software (CS3; Nguyen & Hwang, 2016).

| Sensory assessment
Sensory evaluation of nuggets was conducted using twelve assessors who trained prior to the experiment, using a 5-point hedonic scale (5 = like extremely, 1 = dislike extremely) following the method by Carpenter, O'grady, O'callaghan, O'brien, and Kerry (2007).
Sensory assessment for various quality attributes of each fried nuggets such as taste, aroma, texture, color, and overall acceptability was recorded. Nuggets were fried, and the assessors were then served with slice of nugget presented in individual booths under clear white fluorescent light together with cold water to clean the palate between samples. The Descriptors were rated on a scale from "1" representing the lowest score and "5" the highest one. The assessors were demanded to appraise the nuggets quality by scoring for the parameters.

| Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)
The freeze-dried nuggets were analyzed for protein composition and molecular weight using SDS-PAGE, as described by Laemmli (1970).
The samples (20 μg) were mixed (1:1) with a sample buffer containing dithiothreitol, heated for 5 min in a boiling water bath, then loaded into a 1.5-mm acrylamide gel slab (10% T) assembled in a vertical electrophoresis unit. After electrophoresis, the gels were stained for 2 hr with a solution containing 0.5% Coomassie Brilliant Blue R-250, 40% methanol, and 7% acetic acid. The excess stain was removed with a solution containing 40% methanol and 7% acetic. The molecular weights of samples were estimated by reference to the relative mobilities of standard proteins.

| Microbiological analysis
To determine the total plate count (TPC) for each sample, applied the spread plate method using Plate Count Agar. The average number of colonies for each sample was expressed as log 10 cfu/g sample (AOAC, 1995).

| Statistical analysis
Data were analyzed by SPSS 19 with ANOVA and Duncan's multiple range test for mean comparison. All analyses were carried out in triplicate at least. Significance of differences was defined as the 5% level (p < .05). Table 2 indicates the chemical composition of nuggets at the first day.

| Proximate composition
According to the results, surimi nuggets had the lower moisture, protein, and lipid content rather than fish nuggets significantly (p < .05).
The lower protein content of surimi nuggets was probably due to the loss of protein during the washing process of surimi production.

| pH and titratable acidity
The results of pH and titratable acidity of nuggets are shown in Table 3. As can be seen, fish nuggets had higher titratable acidity rather than surimi nuggets (p < .05). In addition, the acidity of two nugget formulations also increased throughout the whole storage period (p < .05). Generally, the nuggets prepared with surimi had lower acidity significantly at the end of storage period (p < .05), whereas, higher titratable acidity was observed in fish nuggets. In addition, there were no significant differences between pH of both nugget samples. The initial pH in surimi and fish nuggets was 7.40 and 7.35, respectively. However, storage had a significant effect on pH value and a reduction was observed in pH of samples throughout the storage (p < .05). During the whole storage period, the pH reached to 6.85 in surimi nuggets, while it was 6.75 in fish nugget.
The reduction in pH might be related to the fermentation of some ingredient or due to the addition of spices (Vanitha et al., 2015).
Additionally, the reduction in oxygen and enhancement of CO 2 content because of aerobic microflora growth might cause pH decline after three months . The pH value around 6.8-7 is acceptance limit of fish meet and higher than 7 is considered to be spoiled. Although, pH value is not reliable indicator of quality control (Mahmoudzadeh, Motallebi, Hosseini, Haratian, et al., 2010). However, our results were in agreement with Haq et al. (2013) who obtained the pH of fish burger from grass carp about 6.60 and claimed the burger produced from mince with around neutral pH had appropriate quality attributes. In addition, Ejaz et al. (2013) obtained similar observation in the pH (6.6 ± 0.05) of pangus catfish burger.

| TBA value
Lipid oxidation is an important factor for spoilage in frozen fish and fishery products and can negatively affect protein functionality, also causes discoloration, off-odor, and off-flavor in products  Table 4. The lower TBA value was observed in the product consisted of surimi (0.02 mg malondialdehyde/kg) compared with fish nuggets (p < .05).
In addition, the enhancing of TBA values with the prolongation of storage period was observed (p < .05). At the beginning of the storage, TBA values were determined as 0.02 ± 0.00 (mg malondialdehyde/kg) and 0.03 ± 0.00 (mg malondialdehyde/kg) for surimi and fish nuggets, respectively. TBA value for both nugget formulas increased to 0.04 ± 0.00 (mg malondialdehyde/kg) and 0.05 ± 0.00 (mg malondialdehyde/kg), respectively, as the storage time increased (p < .05). TBA in an important indicator for fish and fish product quality. It seem the washing process of surimi production decreased the TBA value due to removing the considerable amount of lipid (G. R. Shaviklo, Thorkelsson, Arason, Kristinsson, & Sveinsdottir, 2010).
The same result was found in Tokur et al. (2006) Table 5 shows the TPA results of nuggets before and after cooking.

| TPA
As can be seen, the hardness exhibited a significant difference between surimi and fish nuggets before cooking (p < .05) and the high-

| Color analysis
Colors expressed as L* value (lightness), a* value (redness), and b* value (yellowness) were analyzed during storage and are presented in as two major pigments from the muscle during the washing which was strongly influenced by the pH and NaCl concentration (Chaijan et al., 2004;Rawdkuen et al., 2009). Leaching process has a beneficial effect on color by increasing lightness and reducing redness (A. R. Shaviklo & Rafipour, 2013). Moreover, the reduction in redness might be related to oxymyoglobin formation as a result of protein oxidation (Chaijan et al., 2004). As expected fish nugget had higher a* value because of its higher lipid content and oxidation susceptibility. However, Al-Bulushi, Kasapis, Al-Oufi, and Al-Mamari (2005) found that the lightness of fish burger prepared from arabian sea

| Sensory evaluation
Sensory attributes of samples were evaluated on the first and last day of storage time ( Figure 1). In general, the sensory scores given by the panel of judges to taste, aroma, texture, color, and overall acceptability varied significantly between the surimi and fish nuggets (p < .05). It seems, surimi nuggets had higher score rather than fish nuggets in all attributes on the first day. However, no significance difference was observed between aroma of surimi and fish nuggets at the end of storage (p > .05). Furthermore, no significant changes occurred in taste, aroma, texture, and color of surimi nuggets during Means with different capital letters in each row and small letters in each column are significantly different (p < .05). Each value is expressed as Mean ± SD, and test was conducted in triplicate.
storage while it is evident from Figure 1 that the sensory score of fish nugget given by the assessors decreased as the storage interval increased. Moreover, the texture of fish nugget got stiff and get lower score in aroma, color, and overall acceptability at the end of storage (p < .05). One of the main factors of effects on texture properties is water holding capacity (WHC). It can be seen, nuggets formulated with surimi had better texture score rather than fish nugget. This can be attributed to the better WHC of surimi gel network (Filomena-Ambrosio et al., 2016). This phenomenon is related to washing with NaCl because chloride ions penetrate into the myofibrillar proteins and increase the electrostatic repulsion between filaments, thus increase the protein's affinity for water and enhance the entrapped water (Wang, Zhang, Bhandari, & Yang, 2018). Moreover, water attracted to negative charges of the myofibrillar proteins such as helical structure of myosin and increased the WHC. In addition, some additives such as phosphate resulting in the dissociation of the actomyosin into the actin and myosin. Thus phosphate played a prominent role in the properties of seafood by increasing the water retention in products (Filomena-Ambrosio et al., 2016). The results also showed that nuggets made from surimi were favored by assessors because surimi nuggets scored higher for all attributes at the end of storage whereas the other one scored lower. It seems that the washing process of surimi production has crucial impact on myoglobin removal, color improvement, and gel strengthening of surimi (Jin et al., 2007); thus, surimi nuggets had better color and texture properties rather than fish nugget. This result is in agreement with the results of Vanitha et al. (2013) who obtained the high score for sensory properties of fish cutlet and fish burger after 90 days of storage. F I G U R E 1 Sensorial evaluation of surimi and fish nuggets during storage F I G U R E 2 SDS-PAGE patterns of proteins in nuggets at 0 and 90th day of storage at −20°C. Column 1: marker, columns 2 and 3: surimi nuggets, and columns 4 and 5: fish nuggets at 0 and after 90 days of storage, respectively

| Microbiological analysis
The changes in the TPC of products during frozen storage were enumerated, and the results are presented in Table 8. A steady decrease in TPC from the initial value of 4.55 log 10 cfu/g to 3.59 log 10 cfu/g was observed in surimi nuggets stored at −20°C over a period of 90 days while the bacterial count of fish nugget was initially 4.59 log 10 cfu/g which reached to 3.63 log 10 cfu/g at the end of storage period (p < .05). In addition, a significant difference was observed in TPC of surimi and fish nuggets (p < .05). The hygiene condition of fish handling and surimi preparation had an important role on the initial microbial count of samples (A. R. Shaviklo & Rafipour, 2013).
In addition, the reduction in microbial count of products could be attributed to the effect of freezing on preservation of growth and activity of microorganisms or powerful antimicrobial properties of spices used in products (Jamshidi & Shabanpour, 2013;Vanitha et al., 2013). For instance, the garlic's potential to destroy microorgan-

| CON CLUS ION
In summary, in an effort for innovative utilization of surimi, we have successfully prepared surimi nuggets from S. commersonnianus.
The monitoring of proximate composition of nuggets revealed that surimi nuggets contained less protein, fat, and ash due to washing steps during surimi preparation. The chemical parameters (titratable acidity, PV, and TBA) and TPA values of both samples increased with the storage period; however, surimi nugget showed better results. Although the increase in hardness of both nuggets was observed after cooking, but surimi had appropriate texture property.
Moreover, the color attributes were decreased during the storage; however, the sensorial evaluation of samples exhibited that the surimi nugget had higher hedonic scores rather than fish nugget (p < .05). In addition, the SDS-PAGE confirmed the similar bands in both nugget formulations. Further, the successful production of surimi nuggets had lower microbial count rather than fish nuggets.
This study suggested that applying surimi with appropriate amount of ingredients formulation could develop an alternative ready-to-eat product from fish.

ACK N OWLED G M ENT
The authors hereby acknowledge support of this research by the Center of Innovation and Entrepreneurship of Shiraz University.
We would like to thank Ala health-based food processing and biotechnology company for their participation in microbial analysis of nuggets.

CO N FLI C T O F I NTE R E S T
We declare that we have no conflict of interest.

E TH I C A L S TATEM ENTS
This study does not involve any human or animal testing.