ABSTRACT

Lipid and protein oxidations are most important factors that can cause quality deterioration in fresh and cooked poultry meat during storage because many secondary compounds formed by lipid and protein oxidation can cause off-odor and off-flavor production in meat. Several synthetic antioxidants such as butylatedhydroxyanisole (BHA), butylatedhydroxytoluene (BHT), and tertiary butylhydroquinone (TBHQ) have been successfully used to prevent the oxidative changes in meat. In recent years, however, growing number of consumers are more interested in natural antioxidants than synthetic ones because of the potential carcinogenic effects of the latter.

Plant polyphenol extracts are known to have strong antioxidant and antimicrobial characteristics and have been used as preservatives in meat. Oregano essential oil and tannic acid are two examples of these polyphenol plant extracts that have strong antioxidant and antimicrobial effects. The aims of this study were: 1) to evaluate the antioxidant effect of adding oregano essential oil, tannic acid, and/or their diffrent combinations to ground chicken meat, 2) to evaluate the antimicrobial effect of oregano essential oil, tannic acid, and/or their combinations in ground chicken meat, and 3) to evaluate the sensory characteristics of combined oregano oil and tannic acid in ground chicken meat.

Ground chicken meat was prepared to study the effect of adding oregano oil and tannic acid in both raw and cooked meat patties. Several oregano oil and tannic acid concentrations were prepared to study their single and combination effects on meat quality. For the raw meat study, samples were individually packaged in oxygen-permeable bags and stored in a 4 °C cooler for up to 7 days. On the other hand cooked meat samples were packaged in oxygen-impermeable vacuum bags and then cooked in-bag reaching the internal temperature of 75 °C. After cooling to room temperature, the cooked meat was transferred to new oxygen-permeable bags and stored at 4 °C for up to 7 days. Chicken meat patties were analyzed for lipid and protein oxidation, color, and volatiles at 0, 3, and 7 days of storage. Parts of the samples prepared were also used for microbial studies.

Oregano essential oil at level 400 ppm significantly reduced (p < 0.05) lipid oxidation, protein oxidation and off-odor volatiles, but improved color stability of raw ground meat. The effects of oregano oil on cooked meat were similar to that of the raw meat but the effects were greater than the raw meat. Hexanal was the major aldehyde and was decreased significantly (P < 0.05) by oregano oil treatment in cooked meat and the differences among the treatments were clearer in cooked meat than in raw meat. Overall, the addition of oregano essential oil at 100 - 300 ppm was a good way of preserving meat and could replace the synthetic antioxidant, BHA.

Both raw and cooked chicken breast meat added with 10 ppm of tannic acid had significantly (P < 0.05) lower lipid and protein oxidation than other treatments during storage. In addition, tannic acid at 10 ppm level maintained the highest color a*- and L*-values during storage. Cooked chicken breast meat added with > 5 ppm tannic acid had significantly (p < 0.05) lower amounts of off-odor volatiles than control. Among the volatile compounds, the amount of hexanal in cooked meat increased rapidly during storage. Therefore, tannic acid at > 5 ppm could be used as a natural preservative in ground chicken meat to improve its quality during storage.

The combination of 200 ppm oregano oil and 10 ppm tannic acid showed the highest effect (P < 0.05) on TBARS, total carbonyl, and off odor volatile formation in both breast and thigh meat. The combination of 200 ppm of oregano oil and 10 ppm of tannic acid also showed the highest effect in stabilizing color values of both raw breast and thigh meats. Sensory evaluation of thigh chicken meat also indicated that 200 ppm of oregano oil and 10 ppm of tannic acid combination treatment had positive effects on most of the attributes evaluated. In conclusion, the combination of 200 ppm oregano oil and 10 ppm tannic acid could be a good replacement for the synthetic antioxidant in ground chicken meat.

Oregano oil, tannic acid, BHA treatments reduced the APC significantly (P < 0.05) when used separately. However, combination of oregano + tannic acid showed the strongest (P < 0.05) effect in reducing the APC in raw chicken breast meat during storage at 4 and 10 oC. The combination treatment also showed the strongest antimicrobial effects of all the treatments against Salmonella enterica, Listeria monocytogenes, Escherichia coli, and Enterobacteriacea (ENT) in raw meat during storage. In cooked chicken breast meat, oregano oil and oregano + tannic acid combination were efficient (P < 0.05) in suppressing the growth of aerobic bacteria in meat at all temperatures (10, 25, and 43 oC) tested. Oregano essential oil treatment was more effective than the BHA and tannic acid treatments in slowing down the growth and survival of Stapylococcus aureus in cooked meat during storage at 10, 25, and 43 oC, but oregano oil + tannic acid treatment was more effective than the oregano oil alone. Based on these results it is suggested that oregano oil has a strong antimicrobial activity but its effect can be further improved when it is combined with tannic acid. This study demonstrated that oregano oil + tannic acid combination could be a good natural antimicrobial treatment to suppress most of the food borne pathogens in chicken meat.

In conclusion oregano essential oil at > 200 ppm significantly improved meat quality and prevented meat deterioration during storage. Tannic acid at 10 ppm also improved meat quality and safety significantly during storage. However, the combination of 200 ppm oregano essential oil and 10 ppm tannic acid showed higher effect on both meat quality and safety of ground chicken meat than using them singly. This combination could be an excellent replacement for synthetic antioxidants such as BHA, BHT and TBHQ, which are commonly used for meat preservation.