An overview of factors affecting the quality of beef meatballs: Processing and preservation

Abstract Beef meatball (BM) is a traditional delicious snack with rich nutrition and unique flavor, making it a preferred choice for most consumers. However, the quality of BM is easily affected by many factors, such as the processing, storage, and preservation, which limit the competitive positioning with respect to its market. Therefore, it is essential to pay attention to each step during the processing of BMs. Based on previous studies, this systematic review focuses on the effect of key processing factors (including raw materials and ingredients, beating, cooking methods, storage, and preservation) on the quality of BMs. Additionally, this study assessed the effect of each process factor on the physicochemical, sensory, nutritional, and safety attributes of BMs. Finally, the existing review will be beneficial in examining/describing the factors impacting the quality of BMs during processing, which would provide theoretical reference and scientific basis for the standardization and industrialization of BMs.

few reports on the factors influencing the quality in the processing of BMs exist. In this review, therefore, the research progress in the factors affecting the quality of BMs in three areas, including ingredients, processing process, storage, and preservation, is discussed. Figure 1 shows the schematic diagram of the review.
The purpose is to provide theoretical and technological guidance for the production of high-quality BMs, and the implementation of reasonable quality control procedures for BM production.

| PRO CE SS ING PRO CEDURE S OF B EEF ME ATBALL S
The production process of BMs mainly includes mincing meat, beating, cooking, and preservation. These procedures are as follows: First, the beef and back fat were separately passed through a grinder, fitted with a 3-mm diameter plate. Then, the minced meat was placed in a beating machine or a chopper. The seasonings containing salt, sugar, sodium tripolyphosphate, starch, ice water, back fat, and so on were put into the beating machine or the chopper and fully mixed. Additionally, the order of adding materials should be considered. In general, the raw meat is chopped and mixed first, and the ingredients such as salt and water are added. The purpose of this procedure is to maximize the extraction of salt-soluble proteins, thereby forming emulsion and good texture of BMs. Third, the meat batters prepared are shaped into meatballs with diameters of 30 mm and cooked by different cooking methods. Finally, the appropriate preservatives, and packaging materials are utilized to effectively develop color stability and delay or restrain the oxidation process of BMs. Figure 2 shows the technological processes involved in BMs' production. Table 1 shows the purpose of each ingredient and process.

| Effect of distinct parts of beef on the quality of beef meatballs
The quality of beef is influenced by the postmortem aging time, varieties, and carcass parts. Besides, the part of beef is the main factor influencing beef quality. It is different from the content of components and nutrients in various parts, resulting in significant variations in the taste and flavor quality of meat products after processing (Zwolana et al., 2020). Also, there are differences in the water retention of muscle due to the differences in the beef parts.
The gel properties (representing three-dimensional (3D) network structures formed by the cross-linking of protein molecules) of the muscle fiber proteins are affected by the muscle types. This property had been demonstrated to contribute to the water and fat retention capacity and the flavor adsorption efficacy of BMs.
The main reason for the changes in gel attributes of various parts of meat is due to the different types of muscle fibers and the vitality of related endogenous enzymes. The gel retention and gel network structure of beef meatballs are positively correlated with the content of myofibrillar protein (MP). In recent years, some researchers have studied the suitability of processed meat products from different beef parts. Rhee et al. reported that different beef parts had various effects on the quality characteristics and suitable processing methods. The authors also noticed that the biceps femoris was more suitable for roasting than the adductor, supraspinatus, and semitendinosus. Besides, the biceps femoris had the lowest cooking loss rate and the best tenderness after processing, potentially caused by the shorter biceps femoris sarcomere and increasing protein degradation (Rhee et al., 2004). Existing studies have demonstrated that the sensory attributes (e.g., color, taste, odor, texture, and overall acceptance) of beef are significantly affected by the different parts of beef under the same processing conditions (Lawrence et al., 2001;Maria et al., 2012). In addition, the different parts of beef remarkably affected the flavors of beef, which could be explained by the fact that different parts of the meat had various volatile organic compounds (Legako et al., 2015;Xu et al., 2020). The mentioned research outcomes as well showed that the distinct parts of beef could significantly affect the quality of meat products. Conclusively, it is necessary to select the appropriate parts (round steak) of beef to prepare BMs with good quality. Also, attention should be paid to the combination of sensory and instrumental analysis (gas chromatograph-time-of-flight mass spectrometer (GC-ToF-MS), electronic nose (E-nose)), so as to provide the fundamental and supporting data for the industrialization and standardization of BM production.

| Starch types
The BMs' formula mainly includes lean meat, fat, water, starch, salt, spices, garlic, black pepper, sugar, monosodium glutamate, and so on. Many scholars have studied the effects of salt/fat substitutes, dietary fiber, and functional additives on flavor attributes, functionality, and yield of BMs (Kehlet et al., 2017;Liu et al., 2015;Petersson et al., 2014). Starch is one of the most widely used ingredients in meat-based products, especially in BMs. The addition of starch can improve the firmness of meatballs, acting as a filler, while also enhancing the water-holding capacity (WHC) and the gel strength. The starch with a high content of amylopectins, such as cassava, waxy corn, and potato starch, is generally selected and added to meatballs, due to its ability to improve the yield, stability, and water retention of meatballs. Furthermore, when meat products are heated, protein denaturation reduces the water-binding capacity, while starch could absorb this part of water and produce gelatinization. On the other hand, water retention increased with increasing amylopectin content. Wu used potato, corn, cassava, and rice starch in myofibrillar protein-starch composite gels. Low-field nuclear magnetic resonance (NMR) demonstrated that adding starch changed the relaxation area, but increased the relaxation time; indicating that the addition of starch could improve the water-holding capacity (WHC) of the myofibrillar protein-starch composite gel, among which cassava starch was the best (Wu et al., 2020). Similarly, Serdaroglu et al. indicated that the incorporation of 2% or 4% corn starch (corn flour (CF)) resulted F I G U R E 1 Schematic diagram of the review F I G U R E 2 The technological process for beef meatballs' preparation TA B L E 1 The purpose of each ingredient and process in beef meatballs

Ingredient and processing procedures
Purpose Reference

Starch
Starch added to meat minced could improve the firmness of products, acting as a filler, while also improving gel strength Wu et al. (2020) Transglutaminase Transglutaminase could reduce the amount of salt and phosphate usage, reduce or completely eliminate cooking losses, and create a gel structure in the foods in which it is present Pietrasik andChan (2002) Erdem et al. (2020) Hydrocolloids Hydrocolloids had been used in the meat products for film-forming, fat-replacing purposes, and stabilizing Jimenez et al. (2013) Nonmeat proteins Nonmeat proteins were attributed to form the gel network structure of myofibrillar protein Nishinari et al. (2014) Salt The role of NaCl in the solubilization of myofibrillar proteins is one of the main factors that make its addition mandatory in meat products. NaCl also reduces water activity, thus contributing to the preservation of the product Choia et al. (2014) Water Water is attributed to the dissolution of ingredients Nuray and Oz (2019) Fat substitute The fat substitute in meatballs improves the overall flavor based on the sensory evaluation Ran et al. (2020) Beating Beating enlarges the contact surface between water and protein in muscle tissue, thereby increasing the retention ability of minced beef  Cooking Cooking improves the heat-induced gelation ability of beef myofibrillar protein Behannis et al. (2020) Storage and preservation Delay or restrain the oxidation process, effectively expending the shelf-life of beef meatballs Desvita et al. (2020) in an increment in protein content of cooked meatballs and had no detrimental effect on sensory properties, except appearance (Serdaroğlu & Değırmencioğlu, 2004). Wu et al. indicated that rice starch had a negative effect on the gel system, because the particles of rice starch were smaller and their distribution was not uniform, which could not support the entire protein network system as a filler (Wu et al., 2020). Compared with native starch, the functional properties of modified starch were significantly improved (Ryszard et al., 2021). Khalil noticed that patties formulated with the right amount of modified corn starch had higher cooking yield and moisture content (Khalil, 2000). It can be seen that different starch types have various effects on the quality of BMs. At present, there are almost no data on the application of modified starch in studying the gel properties of MP and the quality of BMs.
Thus, the modified starch and other ingredients can be used in a particular proportion to study the effect of BMs.

| Transglutaminase
The use of enzymes is an imperative method for improving the quality of meat products during processing. Protease is a useful additive of meat product, to modify the protein structure of food, tenderize the meat, and endow meat products with various excellent properties. Protease is divided into five categories.
Transglutaminase (TGase) has the characteristics of water retention and strong gel ability. The enzyme can not only shorten the relaxation time of free water and enhance the binding capacity of meat emulsion on water molecules; but is also helpful to gel crosslinking of minced meat and enhance cross-linking between protein molecules, which may be linked to the formation of ε-(-glutamyl)lysine bond catalyzed by the TGase (Ahhmed et al., 2007). Erdem et al. indicated that the addition of TGase could significantly improve the springiness and chewiness of BMs (Erdem et al., 2020).
Moreover, Tseng et al. observed that the yield of meatballs increased after supplementing TGase without any apparent effect on color. Texture, juiciness, and overall acceptability as analyzed by sensory evaluation were not statistically affected until the level of TGase reached 1.0% (Tseng et al., 2000). Notably, scanning electron microscopy (SEM) indicated firmer and more regular gel structures of meatballs with increasing TGase concentration, which is possibly due to the interaction between transglutaminase and myosin (Ahhmed et al., 2007;Erdem et al., 2020;Tseng et al., 2000). Therefore, the addition of TGase seems to be a beneficial method to enhance the quality and yield of BMs. Still the effect of enzymes on BMs depends on various conditions, such as enzyme reaction temperature, reaction time, and so on.

| Hydrophilic colloid
Hydrophilic colloids are a promising class of natural agents that can be used to improve water retention and reduce protein loss in meat. Hydrophilic colloids are widely employed in meatballs under certain conditions, due to their functional properties such as thickening, gelling, and emulsifying abilities. For instance, scientific reports indicated that hydrophilic colloids such as flaxseed gum, carrageenan, sodium alginate, and gelatin have commonly been applied in meat products (Feng et al., 2018;Kang et al., 2020).
As reported in the previous work of Ulu, the addition of carrageenan to low-fat meatballs was more effective than guar gum for the textural properties after cooking (Ulu, 2006).

| Nonmeat proteins
Nonmeat proteins, such as soybean separation protein, egg white protein, and whey protein, are incorporated into the processing of BMs. This is probably attributed to the nonmeat proteins that are effective on forming the gel network structure to bind water and fat, making BMs have high springiness and viscosity. The protein content in isolated soybean protein accounts for more than 90%.
It effectively impacts on improving the water-holding capacity (WHC), water/oil retention, yield, and gel strength of BMs (Nishinari et al., 2014). Odiase et al. showed that the addition of soy protein reduced cooking loss and enhanced water retention of BMs. Those authors also observed that meatballs with soy flour inclusions at 10% and 15% were most acceptable (Odiase et al., 2013). In addition, existing studies have suggested that the addition of soy protein and carrageenan can greatly enhance the gel strength and the water retention of beef minced (Gao et al., 2019;Hao et al., 2016).
However, as a potential allergen, soybean protein may risk the health of the consumers. Moreover, the addition of a large amount of soybean protein can easily soften the textural characteristics and produce odor of the product. Furthermore, Serdaroğlu found that the addition of whey powder (WP) did not affect the sensory properties of meatballs. The addition of 2% or 4% WP significantly increased cooking yield and water-holding capacity, regardless of the fat level (Serdaroğlu, 2006). The above studies also showed that the independent addition of different nonmeat proteins was beneficial to improve the quality of meat products. However, due to the differences in the structure and function of various nonmeat proteins, the effect of single use is often not ideal. The independent use of a single nonmeat protein may be detrimental to the quality of meatballs. This is mainly due to the differences and deficiencies in the structure and functional properties of various nonmeat protein types. Therefore, different types of nonmeat proteins to BMs were made up for the functional deficiency of each component. Besides, the directional changes in protein structure can be done through physical modification (e.g., microwave, pulsed electric field, ultrasonication) and chemical modification (such as macromolecular binding modification, chemical modification of protein side chain groups, and limited hydrolysis modification of peptide chain), which are beneficial to produce the satisfactory and acceptable BMs for the consumers.

| Water addition
The addition of water in BMs is conducive to the dissolution of various raw materials so that they are easily mixed. In addition, starch can fully absorb the water and exert maximum gelatinization ability,

| Fat substitute
The fat in meatballs improves the taste, texture, and flavor and enhances its acceptability (Hu & Yu, 2015).  Table 2 shows the advantages and disadvantages of common fat substitutes in BMs.

| EFFEC T OF B E ATING ON THE QUALIT Y OF B EEF ME ATBALL S
Chopping and beating are two important treatment methods in the emulsification process, which are an important stage in manufacturing finely comminuted meat products. Beating machine simulates beating and blending meat with a stick, the traditional way the meatballs were produced in Asian communities. Other studies have also shown that gel strength had the minimum value at 80°C, which may be due to prolonged heating time that negatively impacts the texture of MP gel (Huang et al., 2021).
During the process of chopping, salt-soluble protein is used as a continuous phase to fully wrap the dispersed phase, which promotes the springiness and chewiness of BMs. The mechanism of springiness and chewiness can be further explored in the followup study, from the chopping and beating, and other factors. Only by grasping the key points of chopping and beating in practice can one produce high-quality BMs. Table 3 shows the principles, advantages, and disadvantages of different beating methods.

Formulations of beef meatballs Advantages Disadvantages Reference
Adzuki beans flour (ABF) The total combined percentage of fat and corn flour from the meatball formulation was replaced with 50% (w/w) ABF Replacement of fat with ABF especially at 50% (w/w) in the production of reduced fat meatballs resulted with acceptable sensory and better physicochemical properties compared to original meatballs

| Traditional cooking methods
The cooking methods used in meatball processing mainly include boiling, oven cooking, frying, and a new processing approach. In general, the BMs are precooked in water (45°C) for 20 min and then heated to 80°C. In this process, meatballs are gelatinized at low temperature and then cooked slowly at high temperature. However, myosin formed a complex and weak network structure when BMs were directly exposed to high temperature. Besides, the BMs should be fetched on time and placed in cold water at 10°C after heat treatment. The BMs could be cooled to reabsorb the water lost during the cooking process, which could prevent the surface of the meatballs from wrinkling and browning. Different cooking methods may lead to different effects. Table 4 shows the advantages and disadvantages of BMs cooked by different traditional cooking methods.

| Novel cooking methods
The new cooking methods include ohmic heating, ultrasonic-assisted (US) processing, and infrared final cooking, moderate electric field (MEF), and so on. Ultrasonication is a useful tool for preparing meat products (José et al., 2019). US can also improve the stability and technological quality of meat emulsions. Besides, it promotes the dissolution and penetration of flavor substances into raw materials, thereby improving the flavor of meat products. In addition, the application of ultrasound-aided processing is conducive for improving the tenderness and water retention of meatballs. Wang et al. also (Sengun et al., 2014). Infrared cooking is of interest to the food ingredients and the processed meat sector. Infrared radiation has intrinsic advantages such as keeping oven temperatures and humidity at low values.
A further advantage of this method is the ease with which heat can be applied evenly over a broad surface area (Sheridan & Shiton, 1999).
Kendirci indicated that precooking followed by infrared cooking may be regarded as a safe cooking method of meatballs from a polycyclic aromatic hydrocarbon (PAH) contamination point of view (Perihan et al. (2014). In addition, the use of moderate electric field (MEF) heating as an emerging cooking inactivation technology has gained considerable attention in more recent times. Therefore, it is necessary to consider the combination of cooking methods in further research (Sengun et al., 2014). Table 5 shows the principles, advantages, and disadvantages of different novel cooking techniques. Further studies should be carried out that optimize parameters for meatball cooking while putting into practice ohmic and infrared heating combination system. In addition, it is advisable to set the optimum cooking parameters and the improvement of the quality of meatballs into practice when meatballs were prepared.

| Antistaling agent
The addition of antistaling agent is one of the acceptable methods used to delay and/or prevent the oxidative deterioration in processed meat products. Extracting nisin lactate, sodium lactate, TA B L E 3 The principles, advantages, and disadvantages of different beating methods

Beating
The beating process formed more continuous and compact structures at the same salt content compared with chopping. Beating process allowed for the production of lowsalt and higher quality kung-wans When the beater beating machine speed is too fast, the meat is rapidly increased, and the amount of dissolution of myoblast protein is reduced, which is not conducive to the formation of the gel structure  Chopping Meatballs produced by the vacuum bowl cutter have better softness and tenderness Chopping process resulted in worse texture than beating at the same salt level  butylated hydroxytoluene, butylated hydroxyanisole, and extraction of the plant materials (including herbs, perfumes, fruits, and vegetables) are widely used in meatballs to improve the quality and prolong Recently, many researchers have focused on applying natural active substances to the antioxidant activity of beef meatballs. Table 6 shows the processing methods and the results of common preservatives used in BM production.
These results indicated that the addition of preservatives in the processing of meatballs could effectively inhibit the oxidative deterioration of beef meatballs, and prolong the shelf-life of products without affecting the sensory characteristics. Future research may consider the combination of a variety of natural preservatives.
Besides, the application of natural antioxidant instead of synthetic antioxidants can be considered at both industrial and small-scale levels to enhance the quality of BMs.

| Packing material
Packaging meatballs can reduce the incidence of foodborne diseases and significantly extend the storage period of meatballs. In addition, the packaging system can affect MP associated with beef tenderness. Edible packaging is generally used to improve the mechanical properties of the food. Edible composite packaging materials can be applied to meatball packaging because of its green pollution-free TA B L E 4 The principles, advantages, and disadvantages of different traditional cooking methods

Advantages Disadvantages Reference
Boiling This may be results in the sufficient time for the reaction between protein molecules at lower temperature. The elasticity of beef meatballs gradually increases with the increase of temperature Texture profile analysis (TPA) hardness of meatballs with fiber, cooked in boiling water, was lower compared to oven-baked and pan-fried Behannis et al. (2020) Oven The highest cooking yield was found in samples cooked in the oven. Loss of nutrients after cooking was lower for oven-baked compared to boiling It took more time to achieve the same level of inactivation in the oven compared with the fryer Mena et al. (2020) Porto et al. (2016) Frying Compared with the deep-fat frying group, hot airfried giant salamander meatballs had higher L * , elasticity, and hardness Compared with the deep-fat frying group, hot air-fried giant salamander meatballs had lower fat content, b * value, a * , and yield Mena et al. (2020) TA B L E 5 The principles, advantages, and disadvantages of different novel cooking techniques

Advantages Disadvantages Reference
Ohmic cooking In ohmic cooking, heat generation was homogeneous, a uniform temperature increase within the meat sample could be obtained.
Ohmic cooking seems to be the best cooking method in terms of retaining fatty acid in meatballs enriched with flaxseed flour The distinctive crust layer was not formed at the meatball surface during ohmic cooking, so physical retention of fat and water was difficult Turp (2016) Ultrasonicassisted frying The application of ultrasonic-assisted frying could accelerate the speed of free fatty acids' (FFAs) oxidation and would further promote the generation of volatile flavor compounds and improve the flavor quality of meatballs Longer ultrasound (40 min) treatment resulted in a decrease in hardness, G′ value, and water-holding capacity (WHC) of meat batter (MB) Zhang, Zhao, et al. (2020);  Infrared final cooking Infrared cooking, which was mainly effective for surface heating, could be applied as a final cooking method to improve the quality characteristics of ohmically precooked beef meatballs The cooking loss rate of the meatballs increased at the extended application duration of infrared heating Turp et al. (2016); Perihan et al. (2014) Moderate electric field Moderate electric field could be used to cook meat in a shorter time and with a reasonably low energy input while producing a product which was comparable in quality to conventionally cooked meatballs Further work was required to investigate the effect of moderate electric field cooking methods on consumer acceptance, sensorial properties, and the availability of nutrients in the food products under investigation Bedane et al. (2021)  and good preservation effect (Desvita et al., 2020). Many different substances have suitable properties for use as a coating or film. Table 7 shows the results of meatballs treated with different packaging materials.

Active ingredients
Thus, it is a feasible method to select some useful packaging materials in the production of meatballs. Packaging meatballs effectively inhibit the growth of microorganisms and the oxidative deterioration of meatballs, without affecting the sensory characteristics of meatballs.

| Packaging method
At present, many researchers have studied the effect of different packaging methods on meatball quality

| CON CLUS I ON AND FORE S I G HT
With the increasing demand of convenience, and nutritious foods, beef products have become a popular food in the meat industry.
This demand initiates the development of BMs in industry. In this

Results Reference
Edible chitosan (1) Buy commercial shrimp shell chitosan, with a minimum deacetylation degree of 90% (2) Twenty grams of chitosan was mixed with 1000 ml of distilled water and stirred for 10 min at 60°C (3) Ten milliliters of glacial acetic acid was added to the mixture, which was stirred for 1 h Note: ↑, increased after packaging materials' addition; ↓, decreased after packaging materials' addition; →, unchanged after packaging materials' addition.
paper, the effects of different factors which include ingredients, beating, cooking methods, and storage and preservation on the quality of BMs were comprehensively explained. Various factors on sensory, physical, chemical, nutritional, and safety attributes of beef meatballs were discussed. Beating, salt, starch, the order of ingredients, and cooking play a significant role in gel formation of MP, and emulsification stability of BMs with a unique taste profile, and better water-fat binding. This is vital to assure the quality of BMs. However, some BMs on the market showed low quality, which limited the rapid development of BM in meat industries. Therefore, in a follow-up study, BMs from the following aspects will be/need to be considered: (1) modification of MP by nonthermal processing technology to improve the gel properties of beef; (2) detecting adulteration in beef meatballs, and doing market research to look for deficiencies in the BMs industry; (3) assay sensory analysis of BMs, and establish the suitable sensory evaluation system of BMs by consumer preference experiments; (4) explore the beating mechanism during the process of meatballs and excavate the fast and efficient processing methods of BMs; (5) study the combined effect of novel techniques (ultrasonication +ohmic heating) during the cooking process on the yield and quality of BMs. Further research will also be done to investigate the combined application of different packaging methods and antistaling agent in BMs. Finally, this review may create new opportunities for providing guidance for the industrial production and quality assurance of beef meatballs.

ACK N OWLED G EM ENTS
This study was supported by grants from High-level Talent Program of Yangzhou University (137012132), Qinglan Project of Yangzhou University, and Leading Talent Funding Project of "lu yang jinfeng plan" in Yangzhou City.

CO N FLI C T O F I NTE R E S T
We declare that there are no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.