Problems of Lipid Oxidation in Minced Meat Products for a Ready-made Meal during Cooking, Processing, and Storage

Abstract

In 2019, the market for ready-made meals in Japan has increased by 27% in the past ten years and was valued at around 10 trillion yen. Minced meat is one of the most convenient ingredients for ready-made meals because it can be used in a wide variety of dishes, either by itself, or in combination with other ingredients. Processes that are necessary to obtain minced meat increase the area in contact with air. Consequently, these processes can compromise the quality of minced meat products, which tend to be more damaged compared to chopped meat or steak. Therefore, it is necessary to select an appropriate processing method to prevent lipid oxidation in meat. Lipid oxidation is a major cause of meat deterioration. Several factors, such as the degree of unsaturation of fatty acids, exposure to light and heat, and the presence of molecular oxygen as well as pro-oxidant and antioxidant components, affect lipid oxidation. Suppressing lipid oxidation is important for inhibiting the damage to meat products. Radical scavengers donate hydrogen to lipid radicals, stop the chain reaction, and suppress the progression of lipid oxidation. Chelating agents trap metal ions, thereby inhibiting the progress of lipid oxidation. Furthermore, a combination of the two methods to suppress lipid oxidation has also been reported. In light of this, combining chelating agents with other chemicals is expected to inhibit lipid oxidation.

1. Introduction

Meat and meat products are good sources of proteins, fat-soluble vitamins, minerals, and bioactive compounds. Lipids are also important components in all types of meat, they significantly influence the flavor of the meat, and also contribute to its tenderness and juiciness. The muscles in meat have been reported to be extremely variable, differing considerably in size, weight, components, and meat quality due to muscle fiber composition [1]. For example, early studies demonstrated that animal muscles differ in their protein, fat, and moisture contents [2, 3, 4]. Lipid oxidation affects the color, texture, nutritional value, taste, and aroma of meat, leading to rancidity [5]. In combination with oxygen, free radicals usually initiate oxidative chain reactions, which primarily target the lipids, pigments, proteins, and vitamins in meat products. Several factors, such as the fatty acid composition and pro-oxidant agents (e.g., free iron and myoglobin in muscles), influence lipid oxidation in meat and its derivatives.

This review introduces the trend of meat intake in Japan, primarily focusing on ready-made meals, namely minced meat, which is one of the main ingredients of ready-made meals. In this review, we introduce the advantages and disadvantages of meat preservation methods again lipid oxidation and indicate the basic mechanism of lipid oxidation to deepen our understanding towards developing preservation systems for meat and meat products. Focus is placed on secondary oxidation products because they affect the color and odor of meat. In addition, our review describes the role of lipid oxidation in meat product deterioration. Finally, we introduce methods that inhibit lipid oxidation in meat products.

2. Trend of meat intake in Japan including ready-made meals

In Japan, legislation implemented in 1961 to stabilize the price of livestock products has resulted in the establishment of a carcass evaluation system with five quality grades. The Japanese Meat Grading Association (JMGA) was established in 1975 to administrate grading activities. Another reason for establishing a national system was a common terminology for price comparison and market reporting when describing carcasses produced and sold in different locations. The carcass grading standards were revised in 1976, 1979, and 1988, and separate meat quality and yield grades were adopted during each revision.

The intake of meat in Japan has been recently increasing. According to the National Health and Nutrition Survey in 2019, the average value of meat intake per day was 103.0 g, which is the highest value in the past ten years. Typical meats cooked at home include beef, pork, and chicken. The annual supply per capita is 6.5 kg for beef, 12.8 kg for pork, and 13.9 kg for chicken. Notably, chicken meat consumption has been increasing compared to pork and beef.

Ready-made meals in Japan are sold in the delicatessen section of supermarkets, butchers, and convenience stores. In recent years, the market for replacing home-cooked meals has been valued at around 10 trillion yen and increased by 27% in the past ten years. Meat is sold in ready-made meals, such as boxed lunches, fried chicken, hamburgers, and meat dumplings. Minced meat is one of the most important ingredients in ready-made meals in Japan

3. Minced meat products

The sequence for preparing meat for the market is shown in Fig. 1. Many processes are performed before the meat is ready for the market: first, the carcasses are deboned and exsanguinated; second, the meat is divided into portions, such as the arms, thigh, and loin; finally, each portion is cut into blocks and sliced; in the case of minced meat, grinding is required after obtaining the blocks of processed meat.

Minced meat has been used in a wide variety of dishes, either alone or combined with other ingredients. Furthermore, minced meat can be formed into patties that are either grilled, fried, or braised. Additionally, minced meat that is derived from a tough section of meat can be easily cooked. However, as the number of manufacturing processes increases, such as those for minced meat products, the meat quality tends to deteriorate compared to meat subjected to fewer processes, such as chopped meat or steak. Therefore, it is necessary to select an appropriate storage method (refrigeration and freezing).

Figure 1: Flowchart of the process for meat preparation

4. Methods of storing processed meat products

Cooked meat is more susceptible to lipid oxidation than raw meat during refrigeration and frozen storage because heating accelerates the oxidative reactions of lipids in meat [5, 6]. In this section, we introduce the quality of meat products during refrigeration and freezing storage.

4.1 Refrigeration

Refrigeration is one process that uses cooling without freezing to preserve food. Since it is difficult to completely inhibit microorganism growth at low temperatures, it is difficult to preserve raw meat via refrigeration for long periods. Furthermore, during refrigeration, the color of the raw meat changes due to undesirable reactions. Park et al. [7] investigated the lipid oxidation and color stability of minced beef and pork. They reported that without antioxidants, the a* value (red color) of minced beef products at 4 °C decreased over the course of two weeks. Min et al. [8] investigated the susceptibility of different animal meats to lipid oxidation. That study demonstrated that the thiobarbituric acid reactive substances (TBARS) in raw pork, chicken breast, and chicken thigh did not change during storage for seven days; comparatively, the TBARS values of raw beef increased significantly during storage because of high heme iron content, high lipoxygenase-like activity, and low 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. Additionally, they evaluated the ferric ion-reducing capacities of all the raw meat samples and confirmed that the ferric ion reducing capacities were different. Tang et al. [9] evaluated the antioxidant activity of tea catechins on the susceptibility of cooked and overwrapped red meat (beef and pork), poultry (chicken, duck, and ostrich), and fish (whiting and mackerel) to lipid oxidation. In their study, the patties were prepared from treated and untreated minced meat, cooked until the core temperature reached 75 °C, cooled to room temperature, and refrigerated (4 °C) for ten days. The lipid oxidation of the cooked patties was closely related to the lipid content, concentration of unsaturated fatty acids, and presence of different iron species.

Lipid oxidation, associated with a rancid odor, led to the deterioration of food quality. When food safety and quality are considered, refrigeration is suitable for short-term storage but unsuitable for long-term storage.

4.2 Freezing

Generally, freezing suppresses the growth of microorganisms compared to refrigeration. Cooked minced meat tends to undergo lipid oxidation during refrigeration, while freezing suppresses the progress of lipid oxidation. Huang et al. [10] reported the effects of the storage temperature and duration on oxidation and flavor changes in frozen pork dumpling fillers. Freshly prepared dumplings were stored for 0, 30, 60, 90, and 180 d at −7 °C and −18 °C, and with oscillation between −7 °C and −18 °C. The samples stored at −7 °C for 180 d had significantly higher levels of TBARS and protein carbonyls than those stored at −18 °C and those stored with temperature fluctuations (between −7 °C and −18 °C). The percentage of unsaturated fatty acids in the total lipids decreased with increasing storage time. Volatile compounds with pleasant odors decreased with time, while those with pungent tastes and smells increased. That study suggested that oxidation was the primary cause of deterioration in the quality of pork dumpling fillers during frozen storage. Soyer et al. [11] examined the effect of different freezing temperatures (−7, −12, and −18 °C) on lipid oxidation in the leg and breast of chicken meat. After six months of frozen storage, the freezing temperature had no significant effect. Based on these results, the lipid content in the sample was found to be an important factor for lipid oxidation. In general, the lipid content in pork was higher than that in chicken, and the lipid oxidation in pork was temperature-dependent.

Although freezing suppresses lipid oxidation, the freeze-thaw processes affect the quality of meat products. Ali et al. [12] determined the effects of repeated freeze-thaw cycles (0–6) on the physicochemical changes and lipid and protein oxidation in chicken breast. Evaluations of the meat color showed that the redness (a*) and yellowness (b*) values decreased, while the lightness (L*) values increased with increasing cycle numbers. Increasing the number of freeze-thaw cycles resulted in a greater degree of lipid and protein oxidation, evidenced by the higher content of malondialdehyde and carbonyl compounds and the lower content of sulfhydryl groups. The nuclear magnetic resonance relaxometry profile confirmed that the structural changes in the proteins caused by oxidation directly affected the ability of muscles to retain water. In that study, multiple freeze-thaw cycles increased lipid and protein oxidation and decreased the water holding capacity and color stability of broiler chicken breast.

5. Lipid oxidation in processed meat products

Lipid oxidation is one of the causes of meat and meat product deterioration. Lipids are one of the most chemically unstable food components. Several factors that involve complex mechanisms induce oxidation reactions in lipids. The major factors in lipid oxidation reactions include the structure of the lipid and the environment. Factors that promote lipid oxidation include the degree of unsaturation of fatty acids, exposure to light and heat, as well as the presence of oxygen and metal ions [5, 13]. Secondary oxidation products, such as aldehydes and ketones, impart a rancid odor and deteriorate food quality. In addition, an increase in secondary oxidation products decreases the nutritional value of meats. First, we outline the mechanisms underlying lipid oxidation. Thereafter, the factors that promote lipid oxidation are explained, and examples of lipid oxidation in meat from the peer-reviewed literature are highlighted. Finally, examples of methods for suppressing lipid oxidation are introduced.

5.1 Mechanism of lipid oxidation (Autoxidation)

Lipid oxidation is a chain reaction, which consists of three primary steps [14, 15]. The process is shown in Fig. 2. In the initiation step, a carbon-centered lipid radical (alkyl radical) is generated after a hydrogen atom is abstracted from a polyunsaturated fatty acid molecule. Heat, light, and transition metals can catalyze the initiation reaction [14]. The alkyl radical is stabilized by molecular rearrangement to form a conjugated diene [13]. In the propagation step, the alkyl radical reacts with molecular oxygen at a very high rate to form a peroxyl radical. The peroxyl radical can attack another polyunsaturated fatty acid molecule. The initial peroxyl radical is able to abstract hydrogen atoms from another polyunsaturated fatty acid and is subsequently converted to hydroperoxide. This process produces a new alkyl radical, which is rapidly converted into peroxyl radicals. In the termination step, the chain reaction continues until the chain-carrying peroxyl radical combines with another radical to form stable lipid oxidation products [14]. Although hydroperoxide is stable at physiological temperatures, it is decomposed by heating at high temperatures or by exposure to transitional metal ions [13]. Hydroperoxides can decompose to generate a wide range of volatile and nonvolatile compounds, such as carbonyls (e.g., ketones and aldehydes), alcohols, hydrocarbons (e.g., alkane and alkene), and furans that contribute to the deterioration of flavor in many foods [16]. For example, n-6 fatty acids deteriorate to form hexanal, 1-octen-3-ol, 2-nonenal, and 4-hydroxy-2-trans-nonenal (HNE), while n-3 fatty acids deteriorate to form propanal, 4-heptenal, 2,4-heptadienal, 2-hexenal, 2,4,7-decatrienal, 1,5-octadien-3-ol, 2,5-octadien-1-ol, 1,5-octadien-3-one, and 2,6-nonadienal [13]. The primary aldehydes, namely propanal, pentenal, hexanal, and 4-hydroxynonenal (HNE), are formed during the lipid oxidation of stored minced beef [17]. Hexanal is the most common volatile compound generated from cooked meat [13]. The effect of different cooking methods (roasting, grilling, microwaving, and frying) on the lipid oxidation and volatile compounds in foal meat was investigated [18]. The content of volatile compounds in the meat after roasting was higher than after cooking by other methods. The aldehydes (pentanal, hexanal, 2-hexanal, heptanal, benzaldehyde, octanal, and nonanal) in the cooked foal meat comprised 53–65% of the total volatile compounds. Hexanal was the most abundant aldehyde in the cooked foal samples. Hexanal, total aldehydes, and total volatile compounds in the cooked foal meat were highly correlated (p<0.01) with the TBARS value. Ismal et al. [19] investigated the effect of irradiation at 0 or 2.5 kGy on minced beef stored for 14 d at 4 °C. Because of microbial growth, the production of alcohol greatly increased in non-irradiated minced beef. Irradiation increased both lipid oxidation and the total volatiles, especially aldehydes, during storage. The total aldehydes and hexanal increased after irradiation and storage. Minced beef with a low fat content (10%) produced more significant amounts of aldehydes than those with higher fat content (20%). Lynch et al. [17] reported that aldehydes produced from lipid peroxidation form adducts with proteins, which may be associated with the deterioration of protein stability and functionality.

Figure 2: Schematic of formation of hydroperoxide and reaction for generating secondary oxidation products

5.2 Factors affecting the development of lipid oxidation

Lipid oxidation of meat products is promoted by fatty acid composition, metal ions, myoglobin, sodium chloride and so on. In this section, the factors affecting the development lipid oxidation are focused on.

5.2.1 Lipid composition

Triglycerides are formed from the esterification of glycerol with three fatty acids and are considered the main cause of rancidity because lipid oxidation primarily occurs in fatty acids [5, 20, 21].

Lipid oxidation is enhanced with an increase in the number of unsaturated groups (double bonds). For example, polyunsaturated fatty acids (PUFAs) with more double bonds oxidize more rapidly than monounsaturated fatty acids. Linoleic acid (C18:2) is oxidized ten times faster than oleic acid (C18:1). Linolenic acid (C18:3) oxidation occurs 20 to 30 times faster than the oxidation of oleic acid (C18:1), primarily because more energy is required to remove hydrogen from a methyl carbon than to remove hydrogen from a carbon double bond, especially when the carbon is between two double-bonds. The formation of lipid oxides is not only affected by the fatty acid chain length, but lipid oxidation increases with the number of bis-allylic positions [5, 22, 23]. Yang et al. [24] investigated the effect of only pasture feeding with vitamin E supplementation and compared the findings with those obtained for grain-fed diets (with and without supplementation). Pasture-fed beef had more linolenic acid and the polyunsaturated fat content was higher than grain-fed beef. Pasture-feeding with vitamin E increased the lipid oxidation of beef when compared to grain-feeding with vitamin E. Lee et al. [25] investigated the effects of n-3 PUFA oil, emulsion form, and antioxidants on lipid oxidation in meat products fortified with n-3 PUFA. An emulsion of n-3 PUFAs was prepared and incorporated into fresh minced turkey and fresh pork sausage (20% fat) to achieve a concentration of 500 mg n-3 PUFA/110 g meat. The TBARS and lipid hydroperoxides in both n-3 PUFA-enhanced meat products increased with storage (p<0.05).

5.2.2 Metal ions (Iron)

Metal ions, such as copper and iron, can trigger lipid oxidation in meat. Metal ions can easily donate electrons, leading to an increased rate of free radical production [5, 22].

Iron is the most abundant transition metal in biological systems and has various oxidation states, reduction potentials, and electron configurations. Iron plays an important role in lipid peroxidation as the primary initiator and catalyst. Iron can catalyze the generation of hydroxyl radicals via the Fenton reaction [5, 13, 26] (Eq.1).

  

$$\mathrm{\text{Complex}}-\mathrm{\text{Fe}}\left(\text{Ⅱ}\right)+{\text{H}}_2{\text{O}}_2\to \mathrm{\text{Complex}}-\mathrm{\text{Fe}}\left(\text{Ⅲ}\right)+{\text{OH}}^{-}+•\text{OH}$$(1)

Iron is found in five different pools in biological systems: transferrin, ferritin, heme pigments (hemoglobin/myoglobin), iron-dependent enzymes, and small iron chelates (also called “free iron”). Free ionic iron that is released from heme pigments and ferritin are considered major catalysts for lipid oxidation in raw and cooked meat [5, 13].

5.2.3 Myoglobin

Myoglobin is a pigment and a major catalyst for lipid oxidation in meat [13, 26]. The oxidation of oxymyoglobin to metmyoglobin generates intermediates that can further enhance the oxidation of oxymyoglobin and/or unsaturated fatty acids. This process specifically occurs following the formation of a superoxide anion, which further generates hydrogen peroxide. The hydrogen peroxide generated from this oxidation sequence can react with metmyoglobin to form an activated metmyoglobin complex, ferryl myoglobin, which can increase lipid oxidation [27].

5.2.4 Sodium chloride

Sodium chloride (NaCl) is one of the most important components in meat and meat products, where it is used to enhance preservation, flavor, softness, and water holding capacity. However, depending on its concentration, NaCl has been reported to promote lipid oxidation in meat and meat products [5]. Additionally, NaCl increases the concentration of non-heme iron [26]. Kanner et al. [28] investigated the pro-oxidant effects of NaCl in minced turkey. The results of the study revealed that increasing the NaCl concentration in raw minced turkey enhanced lipid oxidation. The addition of FeCl3 to minced turkey promoted lipid oxidation, which was further accelerated after the addition of NaCl (0.3 M). Rhee and Ziprin [29] investigated minced beef mixed with 0–5% NaCl that was aerobically refrigerated for 0–6 d. NaCl increased the TBARS values of the stored beef. Additionally, the TBARS content of beef increased or tended to increase with storage time at each NaCl concentration. Beltran et al. [30] evaluated the lipid oxidation in pressurized (300 and 500 MPa for 30 min at 20 °C) and cooked (90 °C for 15 min) minced chicken breast and slurries. Mechanical processing, which was used to make the meat slurry, and the addition of NaCl before and after pressurization and cooking were tested as pro-oxidant factors. TBARS and hexanal were quantified at 1, 3, 6, and 9 d of storage at 4 °C. NaCl and processing had a significant pro-oxidant effect on the pressurized samples. Hernández et al. [31] compared the effect of NaCl and KCl at varying strengths on the catalase and glutathione peroxidase activities and lipid oxidation in refrigerated minced pork muscles. The glutathione peroxidase activity was decreased to a greater extent by NaCl than by KCl. The type of salt had no consistent effect on the catalase activity. The TBARS increased more with NaCl than with KCl. Additionally, the glutathione peroxidase activity decreased at the highest ionic strength of NaCl, while the TBARS increased.

5.3 Inhibition of lipid oxidation

Radical scavengers and chelating agents are known as antioxidants. In addition, the effects of radical scavengers and chelating agents as antioxidants have been reported. In this section, typical antioxidants against the lipid oxidation in meat products are introduced. Furthermore, the effects of the combination of the antioxidants are also introduced.

5.3.1 Effect of radical scavenger

A radical scavenger, such as α-tocopherol, supplies hydrogen to lipid radicals and stops the chain reaction, which suppresses the progress of lipid oxidation. For example, Yamauchi reported the effect of α-tocopherol on lipid oxidation [14]. α-Tocopherol inhibits the propagation step and therefore breaks the chain of autoxidation. During this process, α-tocopherol donates its phenolic hydrogen atom to a peroxyl radical and converts it to hydroperoxide. The α-tocopheroxyl radical that is formed is sufficiently stable and becomes unable to continue the chain reaction. Instead, the stabilized radical is removed from the cycle after reaction with another peroxyl radical to form an inactive, non-radical product. Grau et al. [32] used a factorial design to determine the influence of dietary fat sources (linseed, sunflower, oxidized sunflower oils, and beef tallow) and dietary supplementation (α-tocopheryl acetate (225 mg/kg of feed) and ascorbic acid (110 mg/kg)) on the oxidation of dark chicken meat (lipid hydroperoxide, TBA values, and the content of oxidation products from cholesterol). They found that α-tocopheryl acetate protected ground and vacuum-packaged raw or cooked meat from fatty acid and cholesterol oxidation after storage for 0, 3.5, or 7 months at −20 °C. Additionally, it has been reported that sinapic acid, taxifolin, and vinylsyringol have an inhibitory effect on lipid oxidation in cooked pork stored at 5 °C [33].

5.3.2 Effect of metal chelating agent

Chelating agents, such as EDTA, citric acid, and tea catechins trap metal ions. Therefore, they suppress the progress of lipid oxidation. For example, depending on EDTA concentration, lipid oxidation was suppressed when EDTA was added to ground minced meat samples (beef, pork, and chicken) stored at 40 °C [34]. It was also reported that lipid oxidation was suppressed in a concentration-dependent manner when EDTA was added to uncooked turkey stored at 4 °C [28]. Ke et al. [35] investigated the oxidative stability of beef after injection and marination with citric acid as an acidulent and with sodium carbonate or sodium tripolyphosphate, which increased the pH. Lipid oxidation was inhibited in the cooked blocks of beef and in the minced meat that was acidified with citric acid. Contini et al. [36] also reported that citric acid affected lipid oxidation. That study investigated the effect of packaging on reducing lipid oxidation in cooked turkey meat. Antioxidant active packaging was prepared by coating with a citrus extract, which consisted of a mixture of carboxylic acids and flavanones on polyethylene terephthalate trays. The antioxidant-active packaging led to a significant reduction in lipid oxidation. Citric acid has also been reported to be a major element with antioxidant activity among citrus extract components. Mitsumoto et al. [37] investigated the effects of adding tea catechins (TC) and vitamin C (VC) on the sensory evaluation, color, and lipid stability in cooked or raw beef and chicken meat patties during refrigeration. Beef and chicken patties were assigned to one of the following five treatments: control, meat plus 200 mg TC/kg muscle, meat plus 400 mg TC/kg muscle, meat plus 200 mg VC/kg muscle, meat plus 400 mg VC/kg muscle. The addition of tea catechins reduced lipid oxidation in the cooked and raw beef patties when compared to the control. Tea catechin treatments inhibited the lipid oxidation in raw beef to a greater extent than VC treatment. The inhibitory effects from the chelating action of phytic acid on lipid oxidation have also been reported. Stodolak et al. [38] investigated the addition of phytic acid on the TBARS and metmyoglobin levels of cooked or raw pork and beef homogenates after storage for 3 d at 4 °C. The addition of phytic acid (IP6) decreased the TBARS in raw and cooked meat. The effect of IP6 was more pronounced in cooked meat than in raw meat and in cooked beef than in pork.

5.3.3 Combination of antioxidants

This section evaluates the effect of combining antioxidants. Georganteils et al. [39] investigated the effect of rosemary extract, chitosan, and α-tocopherol, which were added separately or in combination, on the lipid oxidation and color stability of frozen beef burgers (18 °C) that were stored for 180 d. Whether used separately or combined with either the rosemary extract or α-tocopherol, chitosan had the best antioxidative effect compared to rosemary extract or α-tocopherol alone. Nonetheless, compared to the controls, there were significant differences in the antioxidative effects when rosemary extract or α-tocopherol was used separately. Karpińska-Tymoszcztk [40] studied the effect of oil-soluble rosemary extract and butylated hydroxytoluene (BHT) in turkey meatballs, separately or in combination. BHT, oil-soluble rosemary extract, and their combination significantly decreased the TBA values after the samples were air- and vacuum-packaged, then frozen for 90 d. A mixture of BHT and oil-soluble rosemary extract stored in air, and BHT in the vacuum-packaged samples, most effectively inhibited lipid oxidation. Lund et al. [41] investigated the effect of rosemary extract or ascorbate-citrate (1:1) in combination with modified atmosphere (100% N₂, and 80/20 O₂:N₂) packaging on lipid oxidation in minced beef patties during storage at 4 °C. Both antioxidant systems inhibited lipid oxidation. The rosemary extract increased the stability of α-tocopherol, while ascorbate-citrate protected the fresh red meat color. Sampaio et al. [42] studied the effect of combining sage, oregano, and honey on lipid oxidation in cooked chicken meat during refrigeration at 4 °C. That study demonstrated the effectiveness of natural antioxidants in reducing the rate of lipid oxidation in cooked chicken thighs and breasts. The treatments with the lowest hexanal values after 96 h were oregano + sage + honey (5%) and oregano + sage + honey (10%).

5.3.4 Other antioxidants

This section presents several natural antioxidants and their mixtures that inhibit lipid oxidation in meat, although the detailed mechanisms remain unknown. Pateiro et al. [43] investigated the effect of adding natural antioxidants (tea, chestnut, and grape seed extracts) or BHT on the oxidative stability of refrigerated pig liver pâtés, which were stored at 4 °C. At the end of sampling, lower TBARS values were obtained in samples that contained the tea extract and grape seed extract. Additionally, lipid-derived volatile compounds, which evolved during storage, increased after refrigeration; however, samples with the tea extract and grape seed extract showed the lowest values. Prommachart et al. [44] investigated the effect of water extracts from black rice on lipid oxidation in minced meat patties. The meat patties were stored for 0, 3, and 6 d. The water extract from black rice decreased the TBARS levels in the meat patties after 3 and 6 d. Additionally, the water extracts from black rice (0.8% and 1.2%) inhibited lipid oxidation. Ozturk et al. [45] studied the effect of wheat sprout flour on lipid oxidation in beef patties. The beef patties were stored at 4 °C for 6 d or at −18 °C for 180 d. The wheat sprout flours inhibited lipid oxidation in beef patties stored at 4 °C and −18 °C. Zhang et al. [46] investigated the antioxidant of effect soy protein hydrolysates produced from Bacillus subtilis (neutral proteases, NP), Aspergillus oryzae (validases, Val), and Bacillus licheniformis (alkaline proteases, AP). The soy protein hydrolysates from NP, Val, or AP were incorporated into minced beef. The beef mixtures were cooked to an internal temperature of 71 °C in a water bath. After cooling to room temperature, the cooked meat samples were stored at 4 °C. The soy protein hydrolysates from AP or NP inhibited lipid oxidation in the meat products during storage for 15 d. Hamed et al. [47] investigated the antioxidant activity of crude water-soluble polysaccharides, which were isolated from the hot-water extract of pistachio hulls. A powdered sample of these crude polysaccharides was added to the minced meat. The carbohydrate fraction of this crude polysaccharide isolate was mainly composed of rhamnose, glucose, galactose, mannose, xylose, arabinose, and galacturonic acid. Lipid oxidation was suppressed in the minced beef during storage at 4 °C for 9 d when the crude polysaccharides from the pistachio hulls were externally added. Turgut et al. [48] investigated effect of pomegranate peel extract (PE) in beef meatballs during frozen storage at −18 °C. Concentrated and freeze dried aqueous extract of pomegranate peel was incorporated into prepared meatball mix, and compared with BHT and control (without any antioxidant). In high PE concentration, peroxide, malondialdehyde and carbonyl formation were significantly lower than control after 6 months. Elhadef et al. [49] investigated effect of Ephedra alata aqueous extract (EAE) on minced beef meat during storage at 4 °C for 14 d. EAE significantly delayed the formation of thiobarbituric acid reactive. Burri et al. [50] was investigated lipid oxidation inhibiting capacity of diverse horticultural plant materials in the meat model system. In the model, heme-containing sarcoplasmic proteins from the meat water-phase were homogenized with linoleic acid and thiobarbituric reactive substances (TBARS) were measured. In the high concentration sets, summer savory freeze-dried powder, beetroot leaves extracted with 50% ethanol, and an olive polyphenol powder extracted from wastewater, inhibited lipid oxidation. In the low concentration set, spray dried rhubarb juice inhibited lipid oxidation after two weeks at 5 ppm.

6. Conclusion

The intake of meat in Japan has been increasing recently, and the market size of home-cooked meal replacements has increased over the past ten years. In Japan, minced meat is one of the most important ingredients in ready-made meals. Lipid oxidation in processed meat products affects their color, texture, nutritional value, taste, and aroma, leading to rancidity. Lipid oxidation damages the quality of minced meat products during a number of manufacturing processes, such as cooking and distribution. Therefore, it is necessary to select an appropriate storage method (refrigeration and freezing). Although refrigeration is a process of preserving food, the growth of microorganisms is not completely inhibited. Therefore, it is difficult to use refrigeration to preserve raw meat for a long time. Freezing suppresses the growth of microorganisms when compared to refrigeration. Therefore, freezing is suitable for long-term storage. Furthermore, cooked minced meat tends to undergo lipid oxidation during refrigeration, but freezing suppresses the progress of lipid oxidation.

Lipid oxidation is a chain reaction that involves polyunsaturated fatty acids. Several factors, such as the fatty acid composition and pro-oxidant agents (e.g., free iron and myoglobin), can influence lipid oxidation. Furthermore, in the case of minced meat products, there are greater huge the specific surfaces due to grinding process. The surfaces would contribute to develop the lipid oxidation. Although the mechanism of lipid oxidation is complex, understanding this mechanism is important for reducing the damage to meat products from lipid oxidation. Radical scavengers that donate hydrogen to lipid radicals stop the chain reaction and suppress the progress of lipid oxidation. For example, chelating agents can inhibit the progress of lipid oxidation. However, adding antioxidants to minced meat products changes the meat texture. Suppressing lipid oxidation is important for inhibiting food damage. Studies have been conducted on food additives and processing methods to suppress lipid oxidation. However, studies on the appropriate amounts and types of chelating agents are insufficient. Therefore, it is necessary to develop additives and processing methods that control lipid oxidation and the texture of minced meat products.

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