Effects of Different Feeding Regimes on Deer Meat (Venison) Quality Following Chilled Storage Condition

All animal-based procedures were performed in accordance with the standard guidelines for the Care and Use of Experimental Animals provided by the National Institute of Animal Science, RDA, Republic of Korea. Twelve elk stags were raised for 4 months at the Animal Genetic Resources Research Center, National Institute of Animal Science (NIAS), Namwon, Republic of Korea.

Twelve 5-year-old elk stags were stratified by weight and randomly assigned to one of four treatments (three elks per treatment): concentrate at 1.5% of body weight (T1), concentrate at 1.8% of body weight (T2), concentrate ad libitum (T3), and home-mixed ration ad libitum (T4).

The ingredients and chemical compositions of the experimental diets are presented in Table 1. Concentrate feed was provided twice a day in equal amounts, and animals were provided free access to freshwater and mineralized salt blocks. A portion of each diet samples was collected for proximate analysis using the modified methods of the Association of Official Analytical Chemists (AOAC, 2005).

Upon reaching an average live weight of about 350 kg, elks were slaughtered at the NIAS slaughterhouse using standard NIAS procedures. Carcasses were then held in cold storage (4°C) for 24 h prior to carcass dissection. After boning, excised loin muscle samples were vacuum-packed and stored at 4°C until further analysis.

After slaughter, samples were stored at 4°C for 2, 7, 11, 15, 18, or 21 days post mortem, and quality characteristics were then measured. All determinations were carried out on homogenized samples in triplicate.

The pH of each sample was determined using a pH meter (Model 520A, Orion, USA). The pH values of samples were measured by blending a 10-g sample with 90 mL distilled water for 60 s in a homogenizer [T25-B, IKA Works (Asia) Sdn. Bhd., Malaysia].

For assessment of cooking loss, samples in vacuum-sealed plastic bags were weighed and cooked for 1 h at 80°C in a water bath (SB-1000, EYELA, Japan). Cooked samples were cooled at 24°C for 30 min, and then they were dried and re-weighed. Cooking loss percentage was calculated based on the difference between the raw and final cooked weights.

Shear force values were analyzed using the method described by Wheeler et al. (2000). Shear force values per core were obtained for each animal from 30-mm-thick steaks that had been cooked to an internal temperature of 70°C and then cooled rapidly in cold water. The cooled samples (cylinders 0.5 inches in diameter) were cut perpendicular to the muscle fiber and assessed with a texture analyzer (Waner-Bratzler shear meter, G-R Elec. Mfg. Co., USA).

Color measurements were taken with a Minolta chromameter (Model CR-301, Japan), and the Commission Internationale de l’Eclairage color values for L*, a*, and b* were measured. The chromameter was standardized using a white calibration plate (Y=92.4, x=0.3136, y=0.3196) after 30 min of blooming at room temperature. Color measurements were recorded for three replicates of each sample.

All determinations were carried out on the homogenized sample. The chemical composition was determined on samples using a slightly modified method of AOAC (AOAC, 2000).

Total fat for fatty acid analysis was extracted according to the method of Folch et al. (1957). After thawing the samples, the lipids in a 5 g sample were extracted in chloroform/methanol (2:1), with 10% dibutyl hydroxyl toluene as an antioxidant. The fatty acid methyl esters (FAMEs) were formed using a KOH solution in methanol and extracted with water and hexane. The top hexane layer containing FAME was dehydrated through anhydrous NaSO₄. The extracted and dehydrated hexane was transferred to a vial to be analyzed. Separation and quantification of the fatty acid methyl esters was carried out using a gas chromatograph (GC, Aglient 7890N, Aglient Technologies Seoul, Korea) equipped with a flame ionization detector, automatic sample injector (HP 7693). The column was unsed DB-WAX fused silica capillary column (30 m, 0.25 mm i.d., 0.2 m film thickness, Agilent Techonologies, Seoul, Korea). Helium was used as carrier gas at linear flow of 1 mL/min and the injection volume was 1 mL. The oven temperature was initially held at 180°C for 1 min then increased at 2.5°C/min to 230°C for 12 min. The injector (split mode) and detector temperatures were maintained at 280°C. Linoleic acid (C18:2) was used as an internal standard (H3500, Sigma-Aldrich Inc., USA). The FAMEs in the total lipids were identified by comparison of the retention times with those of a standard FAME mixture (Supelco TM 37 component FAME mix, Sigma-Aldrich Inc., USA). Fatty acid were expressed as a percentage of total fatty acids (MUFA) and polyunsaturated fatty acid (PUFA). PUFA/SFA rations were calculated.

An analysis of variance for all variables was performed using the GLM procedure in the SAS 9.1 statistical package (SAS Institute Inc., USA). Differences among treatment means were identified using Duncan’s multiple range tests.

Changes in the pH values of meat samples following various durations of storage at 4°C are presented in Table 2. There was no difference in average pH value among treatments. However, there were significant increases in the average pH values of T1 and T4 samples with an increasing duration of cold storage (p<0.05), consistent with previous reports (Tesanovic et al., 2011). It is well documented that meat pH values influence the color, tenderness, water-holding capacity, and packaging processes of meat (Boles et al., 1993; Hofmann, 1986). A previous study reported that an increase in pH during maturation was associated with proteolytic changes in muscle proteins (Wiklund et al., 1995). It was also associated with an increase in the content of alkaline compounds formed during autolysis (Feidt et al., 1998).

Different feeding regimes and cold storage durations had no significant effects on the cooking loss of elk meat under T1, T2, or T3 treatment (Table 3). However, in the T4 treatment group, cooking loss increased with increased storage duration. Cooking loss in meat is related to water-holding capacity. Bengtsson et al. (1876) reported that loss of water in the form of purge or drip loss attributes to an increase in meat temperature. Cooking loss and water-holding capacity are important factors in the evaluation of meat quality and affect the juiciness of cooked meat (Wiklund et al., 2003).

A previous study reported that cooking loss changes associated with increased storage times could be due to physical factors, including changes in muscle structure, rather than biochemical factors (Huff-Lonergan and Lonergan, 2005). Manipulation of the physical properties of meat by altering muscle fiber and fiber bundle alignment results in meat with high drip losses in the raw and cooked states (Farouk et al., 2007), which did occur in our study. Thus, the observed increase in cooking loss with longer storage times in the T4 treatment may be related to changes in muscle structure with different sources of feed and feed intake.

The shearing forces of elk meat resulting from the different feeding regimes and storage durations are presented in Table 4. Shear force is associated with the connective tissue contribution to cooked meat toughness and also affects meat flavor and preference (Beilken et al., 1986; Savell et al., 1987). In the present study, increased storage times resulted in significantly decreased shear forces under T2 and T3 treatment (p<0.05). This is consistent with numerous studies that have reported that increased storage periods are associated with decreases in shear forces and juiciness of deer meat due to increasing proteolytic degradation of myofibrillar protein within muscles (Bouton et al., 1972; Bureš et al., 2015). The activity of proteolytic enzymes (μ-calpain and m-calpain) leads to the degradation of cytoskeletal proteins responsible for maintaining the structural integrity of the muscle fibers (Farouk et al., 2007; Koohmaraie, 1996). It has also been reported that the degradation of muscle fibers increases the tenderness of deer meat during aging (Piaskowska et al., 2016).

In our study, the significant decrease in the shear force value of deer meat stored at 4°C for 18 d following T4 treatment compared with that following T1 treatment may result from differences in feed and energy level intake. However, further study is required to determine the relationship between concentrate feed intake and shearing force with increasing aging periods.

Different feeding regimes had no significant effect on the color parameters of deer meat samples (Table 5). Maintaining color stability is a major challenge in the optimization of meat storage conditions and is affected by the myoglobin content within the meat (Anchía et al., 1992; Kang et al., 1999). In the present study, significant increases in the color parameters a* and b* were observed under T1 and T4 treatments with increasing storage periods (p<0.05). This may be related to residual oxygen levels within packaged meat samples. A previous study reported that use of a vacuum with an anaerobic gas mixture prevented changes in the color of red meat during aging and storage periods. Nonetheless, under industrial conditions, oxygen is incompletely eliminated and low partial pressures of residual oxygen exist within meat, contributing to oxidation of meat myoglobin (Mancini and Hunt, 2005; Piaskowska et al., 2016).

There were no significant differences in chemical composition of deer meat on different feeding regimes (Table 6). Moisture, Crude protein and fat contents were in the range of 74% to 75%, 22% to 23% and 1% to 2%, respectively. The above finding is consistent with Kim et al. (2016), who found that the moisture, protein and fat content of elk was 73 to 75%, 22% and 1 to 2%, respectively. Previous study venison could fulfill the expectations and dietary requirements of the modern consumer, due to a low content of fat with a desirable fatty acid composition and high levels of protein (Hoffman and Wiklund, 2006). In our study, the high protein content and low fat content in the Korean elk meat obtained indicating a similar result to the previous findings.

Previous studies have shown that the changes of deer meat quality during storage time is more commonly affected in physicochemical composition than fatty acid composition (Piaskowska et al., 2016). In our study, predominant saturated fatty acids were palmitic and stearic acid, the predominant MUFA was oleic acid, and the predominant polyunsaturated fatty acid was linoleic acid. These results are consistent with those from previous studies with deer and elk (Purchas et al., 2010; Wiklund et al., 2003). Levels of oleic acid in beef are usually greater than 30% of total fatty acid (Purchas et al., 2010). The elk contains lower proportions of oleic acid than beef in this study. This may be a reflection of the very low level of intramuscular fat in venison, as the proportion of this oleic acid usually increases as fat levels increase within meat (Purchas et al., 2010). The PUFA/SFA (P/S) ratio is a key indicator of the nutritional value of food products, and its low values contribute to the development of cardiovascular diseases (Daszkiewicz et al., 2012). The normal P/S ratio in ruminant meat is around 0.1 because dietary unsaturated fatty acids are hydrogenated by rumen microorganisms, which did occur present study.

Overall, different feeding regimes had no significant effect on meat quality, which is correlated with consumer appeal, during 4°C storage. In contrast, increased storage duration increased pH values, cooking loss, and the meat color parameters of redness and yellowness, accompanied by a decrease in the shear force value of deer meat (venison). This change in deer meat quality may be associated with protein degradation within the meat muscle. Therefore, further study needed to examine effect of different storage condition on deer meat quality using microbiological analysis.