EFFECT OF FREEZE STORAGE ON THE QUALITY OF LAMB MEAT TREATED WITH TOMATO PEEL AND SUMAC EXTRACTS

The study was conducted to investigate the influence of natural antioxidants extracted from tomato (Solanum lycopersicum) peel extract (TPE) and sumac (Rhus coriaria) extract (SE) on the quality of lamb meat stored for (6) months at freezestorage (– 18 °C). Treated samples (TS) with these extracts showed a significant values (p<0.05) of drip loss and water holding capacity (WHC) compared to untreated samples (UTS). The UTS demonstrated a significant increase (p≤0.05) of cooking loss values compared to TS. Peroxide values (POVs) have been decreased steadily with TS until 2 months of storage, unlike the POVs of UTS were ongoing increase until the end of storage, however no POV significant differences were obtained through the storage period. TS with TPE and SE have continuously showed less volatile base nitrogen values (VBNs) (p≤0.05) compared to UTS. Free fatty acid values (FFAs) showed little differences within the first 3 months of storage for UTS and TS, however, after the 3 months of storage, FA of UTS were significantly increased (p≤0.05) by the end of storage period.


INTRODUCTION
Sheep are among the animals that have great importance in the Iraqi economy, as they supply the local market with large quantities of red meat. Sheep are one of the main sources of red meat of the desired quality in Iraq for its palatability and preference by the consumer compared to other meat, as its numbers reached (6,900) thousand heads and its annual contribution to the production of red meat was estimated at 30,930 tons (FAO, 2000). In a study by Raes et al. (2004), it was found that lamb meat is ideal in containing long-chain polyunsaturated fatty acids compared to those found in beef, and this can be concluded that lamb is a good source for humans.
The juiciness, along with the tenderness of the meat, are of the main factors affecting consumer acceptability when consuming the meat (Kosar et al., 2006). It is evaluated in various ways, either subjectively (by consumption) or instrumentally, to measure the ability of meat to hold water. As with other organoleptic properties, keeping lean meats in the presence of oxygen, generally results in lower quality compared to anaerobic packaging, which increases the shelf life (Aaslyng et al., 2010). Moeller et al. (2010) showed that the values of tenderness and juiciness were highly related to its pH and to a lesser extent to the temperature used in the cooking process.
Fats play an important functional part in foods, as they affect the productivity of texture and cooking in moisture retention ability (Pizzale et al., 2002). However, ‫الــرافـديــن‬ ‫زراعـــة‬ ‫مـجـلـــة‬ ( ‫المجلد‬ 49 ( ‫العدد‬ ) 1 ) 2021 due to fat oxidation during storage, the flavor, color, texture and nutritional properties of the food are usually reduced (Eriksson, 1982). Fat oxidation can severely reduce the quality of food, because it can lead to unacceptable quality and loss of nutritional value. In addition, oxidation can cause health problems, such as atherosclerosis and cancer (Bashash et al., 2014).
Freezing technology can lower the temperature of the food product below the freezing point, thereby extending the shelf life of the food (Mahmoud et al., 2017) and to preserve its fresh properties (Musa, 2003). It is necessary to use the appropriate method of storing food when it is harvested and transported over long distances (Jeremiah, 2004). The method of freezing food has been widely used due to its great advantages, including preserving its flavor, organoleptic properties, and inhibiting bacterial growth (Masuda et al., 2001). Several freezing methods are used in food, and the standard freezing temperature used is (-18°C) (Farouk et al., 2004). However, conventional freezing will cause some problems, making the quality of frozen food easily degraded, especially when large ice crystals are formed, which will lead to a decrease in quality parameters. (Musa, 2003;and Zhang et al., 2006). It is found that the shape and size of ice crystals depends on the rate of freezing, so it is necessary to form ice crystals both outside and inside the cell quickly to prevent cell damage (Masuda et al., 2001).
There are internal factors (such as natural antioxidants associated with animal feeding, spices, age, etc.) in the muscles of the body to prevent fat oxidation (Sallam et al.,2004). Antioxidants are usually added to food to prevent oxidation chain reactions in the formation of free radicals, and they function by inhibiting the delayed initiation and propagation steps of initiating the reaction and terminating oxidation. (Bursal and Koksal, 2010;Shan et al., 2005;and Surh, 2002). Natural antioxidants obtained from natural sources are among the substances that have increased circulation in food processing, as the market for food products demands the addition of natural antioxidants that are free of artificial additives and have the ability to reduce oxidation processes in meat and its products (Lawrie, 1998). It was found that many herbs and spices have antioxidant effects on foodstuffs, of which they contain phenols that have an inhibitory effect on oxidation (Shan et al., 2005;and Sen et al., 2014). Upon oxidative stress reactions, the antioxidants will interact with free and non-free radicals to initiate defense mechanisms to protect all compounds inside or outside cells. Due to the increasing demand for natural foods in food processing, it is considered to add natural antioxidants to various foods to delay the oxidative decomposition of fats, improve the quality and nutritional value of fats, and replace them with synthetic antioxidants that have negative effects on human health (Fasseas et al., 2007;Camo et al., 2008;and Yang et al., 2013). The presence of antioxidants in the diet has a beneficial effect on human health, because it can protect biologically important cellular components (such as DNA, proteins and cell lipids) from the attack of reactive oxygen species (ROS (Surh, 2002). Synthetic antioxidants have been used to delay or reduce the oxidative degradation of food, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ) (Fasseas et al., 2007), but they were not desired by the majority of consumers due to their pathogenicity to cause carcinogenicity (Altmann et al., 1986;and Wojdylo et al., 2007). Thus, the advantages of natural antioxidants ‫الــرافـديــن‬ ‫زراعـــة‬ ‫مـجـلـــة‬ ( ‫المجلد‬ 49 ( ‫العدد‬ ) 1 ) 2021 in foods prompted consumers to prefer them for their safe use in foods. Various herbs and spices and their extracts are added to various foods to improve their sensory properties and extend their shelf life (Shan et al., 2005). According to reports, herbs of the Lamiaceae family, especially oregano (Origanum vulgare), rosemary (Rosmarinus officinalis) and sage (Salvia officinalis) have significant antioxidant capacity (Su et al., 2007;Yang et al., 2013). Many herbs and spices and their extracts have antioxidant effects (Zheng and Wang, 2001). Tomatoes are one of the most popular plant sources on earth and an important part of many foods. Tomatoes and tomato products, such as tomato juice, tomato sauce, and tomato soup are usually consumed (Clinton, 1998). Tomatoes contain hydrophilic antioxidants such as ascorbic acid and phenolic compounds such as caffeic acid and quercetin (Van Esch, 1986). Ascorbic acid and phenolic compounds can be considered as the main contributors to hydrophilic antioxidant activity (Arnao et al., 2001), and these compounds are affected by many factors, such as maturity, temperature, variety, and storage atmosphere (Giovanelli and Paradiso, 2002;Hart and Scott, 1995). On the other hand, Sumac (Rhus coriaria) has economic importance due to its increasing use in the food, cosmetics, pharmaceutical, coloring or food preservation industries and veterinary practices (Koohmaraie et al., 2002). The chemical composition of sumac (Rhus coriaria) consists of hydrolysable tannins, which are the highest in sumac fruits, followed by flavonoids, of which this confirms the ability of sumac to contain antioxidants (Ardalani et al., 2016). Other research indicated that the antioxidant activity of sumac extract may be due to a polyphenol compound (Nerin et al., 2006). Sumac is traditionally used as a table spice, and it is recommended for adjusting blood lipid content in diabetics, and it has been indicated that its fruit has antioxidant properties (Giancarlo et al., 2006;and Kumar et al., 2015). Al-Muwaly et al., (2010) found that Iraqi sumac extracted by water and alcohol methods contains a large amount of phenols and flavonoids which have a high scavenging ability for oxidation, because they are resistant to ROS. The purpose of this research is to study the natural antioxidants present in tomato peel and sumac fruits to maintain the characteristics of lamb meat under frozen storage conditions at (-18°C).

MATERIALS AND METHODS Experimental samples
Local lamb ribs of 6 month old were bought from the local market. After trimming the visible fat and connective tissue, the meat was cut into 3x10x3 cm 3 . The fresh meat was divided by 6 groups of 3 sample each used for freezing study and 2 samples being used for fresh meat properties. After sample being perforated through different sample sites, the samples were dipped in sumac and tomato rind powder extracts for 4 hours. The meat samples were then vacuum packaged with poly-nylon pouches. The samples were then conditioned in a refrigerator at 2°C, and then frozen in a freezer (Hitache, Ltd Japanese) at (-18°C) for (6) months. One sample in each group was inserted with a thermocouple (Elitech Tayp, China) at the geometric center of the sample. During freezing, the temperature of the sample is recorded through the connected thermocouple. The phase transition time is defined by the time from the initial freezing point -1.2°C to -5°C of the geometric center of the sample. After each month of storage, the frozen samples were thawed in a refrigerator at 4°C until the  (1) 2021 core temperature of the meat reached 0°C. All chemicals used in this study are of analytical grade. The thawed samples were tested for drip loss, cooking loss, water holding capacity (WHC), peroxide value (POV), free fatty acid (FFA) and volatile basic nitrogen (VBN).

Drip loss
Drip loss is calculated as a percentage of weight loss.

Water holding capacity (WHC)
After thawing, 1 gram of minced meat sample was put into a test tube, wrapped it in a metal clip and suspend it in the test tube, and then placed it in a 3000 xg centrifuge (Nuve, J2-21, Turkey) for 10 minutes. The WHC of the sample is calculated as the ratio of the water remaining after centrifugation to the initial water content of the sample as follows: Where w1 is the water amount of the sample before centrifugation, and w2 is the difference in the water amount of the sample after centrifugation (Rahman et al., 2015).

Cooking loss
The meat sample was put in a polyethylene bag, sealed it under vacuum, and cooked it at 80°C for 30 minutes. The sample was then placed at room temperature for 30 minutes. The cooking loss is calculated as follows: cooking loss(%) = w1 − w2 w1 × 100 Where w1 and w2 are the weight of the sample before cooking the weight of the sample after cooking respectively (Rahman et al., 2015).

Volatile base nitrogen (VBN)
This test is used to measure meat tenderness and the degree of spoilage due to microbial contamination. The total volatile basic nitrogen (VBN) is determined by micro-diffusion method (Conway, 1950). The method is to take 5 grams of meat samples, put them in a plastic bag containing 20 mL of distilled water, shaken for 3 minutes, then filtered the sample with Whatman No. 1 filter paper. One mL of the filtrate was put on the outer part of the Conway dish. A mixture of 1 mL of 0.01 N Boric acid (H3BO3) and 100μL of Conway solution (0.066% methyl red: 0.066% bromocresol green, 1:1 using 99.99% alcohol as solvent) as an indicator were added to the inner part of the Conway dish. Then the Conway unit was immediately closed after adding 1 mL of K2CO3 (50%) to the outer side of the dish. The dish was incubated at (37 °C) for (2) hours. VBN was measured by titrating with (0.02 N) H2SO4 of the inner part of the Conway dish. A blank test was conducted following the same process without adding sample. S Where A is the titer of the sample (mL), B is the titer of the blank (mL), F is the normality of H2SO4 (0.02 N), S is the sample weight (gm), and C is the dilution rate.

Peroxide value (POV)
POV is estimated by the method of Sallam et al., (2004).Five meat samples were put into (250) mL glass stopper flasks, then heated in a (60°C) water bath for (3) minutes to melt the fat. After adding (30) mL of a mixture of acetic acid and chloroform (2:3 v/v) to dissolve the fat, the flasks were shaked for (3) minutes. The mixture was filtered with filter paper Whatman No. 1 to remove meat residue. 0.5 mL saturated potassium iodide solution was added to the filtrate, while adding starch solution as an indicator. Titration was pursued with sodium thiosulfate standard solution. POV is calculated by the following equation and expressed as milliequivalent of O2 peroxide per kilogram of sample (meq O2/kg): POV (meq O2 / kg) = {(S × N) / W} × 100 Where S is the titration volume (ml), N is the standard solution of sodium thiosulfate solution (0.01 N), and W is the sample weight (gm).

Free fatty acids (FFA)
The method of Rukunudin et al. (1998) was used to determine FFA value. The meat sample of 5 gm was mixed with 30 mL of chloroform in a mixer for (1) minute. The mix was filtered with a whatman No.1 to remove meat residue from leachate. 5 drops of 1% ethanolic phenonphthalein are added to the filtrate with a solution of (0.01N) ethanolic potassium hydroxide (KOH). The amount of free fatty acids is estimated as follows:

FFA = mL of titration x KOH N x 28.2 gm of sample Tomato peel extract
Local fresh tomatoes were purchased from the local market. After washing with tap water, they were mixed in an electric mixer and filtered through cheesecloth to separate the skin and seeds (precipitate) from the tomato juice. The precipitate was then dried in an air dryer (Brabender, Germany) at (50°C) until a moisture content of (5%) was reached. The dried material is ground in a laboratory grinder (Silver Crest, Model :223fs, China) to obtain fine particles of tomato peel powder. A solution of (10%) tomato peel powder was prepared with distilled water and used to soak meat samples (Kim and Chin, 2013). Sumac extract Sumac extract was prepared using the method of Al-Muwaly et al. (2013). The sumac fruits were washed with tab water and dried at a temperature of (50 °C ) for (2) hours. Dried sumac fruits were then grinded with a laboratory grinder and a solution of grinded sumac and distilled water was prepared at a ratio of (4.2 g / 100 mL). Then the meat samples were soaked in the sumac solution for (2) hours.

STATISTICAL ANALYSIS
The data was analyzed according to Complete Randomized Design using Duncan Test among the treatments.

RESULTS AND DISCUSSION Drip loss
The initial drip loss of fresh lamb meat was (19.65 mL/100 gm). Although the drip loss was increased for all UTS and TS with TPE or SE, but it showed higher increase (p≤0.05) with the UTS than TPE and SE at the end of storage period (6 months), as 40.57, 32.42, and 29.90 mL/100 gm respectively (Fig. 1).
Drip loss is in going process involving the transfer of water from myofibrils to the extracellular space of which it can be higher with decreasing the pH values of meat (Tayler, 2004). Therefore, within the first 4 month of storage, it can be noticed that samples treated with SE (of higher pH) showed a higher (p≤0.05) of samples treated with TPE (of lower pH). On other hand, the lower pH of muscle proteins, the lower their ability to bind water (den Hertog-Meischke et al., 1997). Further, Lawrie (1985) indicated that meat freshness is high when the pH of a high value leading to high moisture content and water retention capacity in muscle proteins.

WHC
The WHC of meat is defined as the affinity with meat to maintain its own moisture during processing, and is considered one of the important indicators of quality, such as eating quality, juiciness, tenderness, and cooking loss (Choi et al., 2018). The initial WHC of fresh sample was (55.33%). Frozen lamb of treated and untreated samples showed a significant decrease (p≤0.05) during the storage period of 6 months. Comparing with UTS, the initially soaked samples in either TPE or SE have had a higher WHC (p≤0.05) after the first month of storage (Fig. 2). Although lamb samples stored at (-18°C) showed a gradual decrease in the continuous storage period of WHC, it showed a significant decrease (p<0.05) after (3) months of storage in all WHC values. These results were coincided with those obtained by Choi et al. (2018). However, Das et al. (2011) showed that adding curry leaves to minced meat did not significantly affect WHC, but it was observed that WHC was significantly reduced in untreated meat samples. It is speculated that the presence of natural antioxidants in meat products will reduce the percentage of WHC or have a high water retention capacity (Vallverdú-Queralt et al., 2011;and Mohmoud et al., 2017). However, the effect of antioxidants on the hydrolysis of meat protein has been studied by increasing the hydrolysate of short peptides, which may be the reason for the reduction of WHC value (Kim, et al., 2001;Zhang, et al., 2010;and Tounkara, et al., 2013) Cooking loss Figure 3 shows the effect of freezing storage at (-18 °C) for (6) months on cooking loss of UTS and TS of lamb meat with soaking in TPE or SE. After the first month of storage, the cooking loss of all the lamb samples studied increased significantly (p≤0.05), which were 43.70, 43.20, and 40.26 mL/100gm for UTS and TS with TPE and SE respectively. During the continuous storage period, the reduction of the cooking loss value of all samples was small, although the cooking loss value of UTS at the end of the storage period was significantly higher (p≤0.05) than that of TS. Meat samples treated with certain plant extracts can improve cooking loss, thereby combining water and fat (Rinaudo, 2006). In contrast with the work of Choi et al. (2018) who examined the freezing temperature of (-18 °C) of lamb meat stored for (5) months, they reported higher cooking loss values than the results obtained in this study when TPE and SE were experimented.

POV
POV of fresh lamb meat was (0.94) meq O₂/kg. POVs have been decreased steadily with treated lamb meat samples when TPE and SE were used until 2 months of freezing storage at  (-18 °C), as (0.80) and (0.83) meq O₂/kg respectively, then they were kept increasing to the end of storage period (6 months), unlike the POVs of UTS were ongoing increase until the end of storage period (Fig. 4). Both untreated and treated lamb meat samples with TPE and SE showed the same POV of (1.3) meq O2 /kg at the end of 6 months storage at (-18°C). However, in the first three months of storage, the POV difference of TS using TPE or SE is lower than that of the UTS. As mentioned by Masuda et al. (2001) and Kumar et al. (2015) natural antioxidants can donate hydrogen free radicals to pair with other available free radicals, and inhibit the propagation reaction during the entire lipid oxidation process. This can be accrued to a certain extent, until all the hydrogen radicals of the endogenous antioxidants in the lamb meat sample and the natural antioxidants present in TPE and SE are used up within (2-3) months of storage at (-18°C), as shown in Figure 3.

VBN
It is well known that the increase in VBN is related to the reaction of microbial spoilage. Initially, the VBN value of fresh lamb was a VBN (14.07) mg/100 gm. Although UTS and TS using TPE or SE followed the same increasing trend of VBN value during the entire (6) months of storage at (-18 °C), both TS with these extracts have continuously shown significantly (p≤0.05) fewer VBN values compared to UTS (Fig. 4). Although at the end of storage at (-18 °C) for (6) months of UTS and TS with TPE and SE have had VBN values of 18.28, 17.53, and 17.34 mg/100 gm respectively, these values were lower than the spoiled level (35 mg/100 gm) suggested by Connell (1990). FFA Generally, FFA is formed from lipids. They are not only the products of enzymatic degradation, but also the microbial degradation of lipids. FFA provides ideas about the stability of lipids during storage. The initial FFA value of fresh lamb is 1.09%. During the first three months of storage of untreated and treated lamb meat samples at (-18°C), the FFA value showed no significant difference (p≤0.05) (Fig. 5). After 3 months of storage at (-18 °C), UTS were significantly increased (p≤0.05) until the end of storage period compared with TS with TPE and SE as the FFA values reached 2.52, 1.99, and 1.94 % respectively. At the end of the storage period of lamb meat samples treated with TPE and SE, the decrease in FFA value may be due to their ability to inactivate enzymatic degradation to form FFA, which is more unstable to the oxidation process of lamb meat. As mentioned earlier, many plant extracts have antioxidant effects on food, and the phenolic substances contained therein have an inhibitory effect on oxidation. (Schwarz, et al., 2001;and Pizzale, et al., 2002).
CONCLUSSION Frozen storage at (-18°C) for (6) months affected the drip loss, WHC, cooking loss, POV, VBN and FFA values of lamb meat. Nevertheless, soaking lamb meat samples in either tomato peel or sumac extracts before freezing storage can improve the quality characteristics of lamb meat in terms of those determined values. Regardless the little differences among the experimented values of lamb meat samples treated with tomato peel or sumac extracts, they showed the same trend when testing the various values studied, but, they have had less influence on the studied values untreated lamb meat samples (control).