LIPID OXIDATION IN A CHICKEN MODEL SYSTEM: ROLE OF LIPID AND PROTEIN FIBERS

Chicken muscle model systems were exposed to varying concentrations of lipid and protein fibers to clarify the role of these constituents in lipid oxidation. In this study, the lipid substrates examined included triacylglycerols, membrane phospholipid fractions, isolated phospholipid fractions, and free fatty acids. In iron-ascorbate catalyzed systems, increases in lipid concentration failed to lead to enhanced levels of oxidation at the examined times. Lipid was therefore not considered a rate limiting factor in the oxidation of muscle systems. Protein fibers accelerated oxidation only in sarcoplasmic reticulum (SR) membrane systems when catalyzed by iron-ascorbate. Enhanced interaction of the low molecular weight iron with the membrane lipids may be responsible for this unique response. Preferential oxidation of sulfhydryl groups in protein fibers, on the other hand, could account for the antioxidant effect displayed by protein fibers in methemoglobin catalyzed systems.     

SOME OBSERVATIONS ON MYOGLOBIN AND LIPID OXIDATION IN FROZEN BEEF

SUMMARY –The observed curvilinear correlation between metmyoglobin formation and lipid oxidation in beef gluteus medius samples (3 mm thick) stored in polyethylene at -5°C was dependent (P < 0.001) on initial treatment, namely freeze-thawing, delayed freezing or mincing. However, these initial treatments accelerated both metmyoglobin formation and lipid oxidation. In slices initially held in 1% oxygen at 0°C to increase the relative amount of metmyoglobin, the concentration of this pigment was first reduced during frozen storage at -5°C before increasing again. High initial metmyoglobin concentrations had no effect on the rate of lipid oxidation.     

WATER ACTIVITY AND TEMPERATURE EFFECTS ON LIPID OXIDATION IN MUSCLE FIBERS

The effects of temperature and water activity on lipid oxidation in washed muscle fibers stored at water activities ranging from 0.96 to 0.70 and at various temperatures were studied. Fluorescence measurements at −20C, revealed no significant change over 50 days at any water activity. At 4C and 20C, there was an initial increase in fluorescence for all samples over the first few days, then a more rapid decrease with no further change up to 40 days. At 80C, no change in fluorescence was seen over a 100-min period. Rancidity did develop in some samples but was not always detected by fluorescence. Through use of oxygen uptake as a measure of lipid oxidation, it was possible to see differences between samples at different water activities and temperatures. However, the limited amount of oxygen and the temperature limitation of the oxygen electrode prohibit studies over extended time periods and at high temperatures (> 50C).     

EFFECTS OF LIQUID SMOKE ON LIPID OXIDATION IN A BEEF MODEL SYSTEM AND RESTRUCTURED ROASTS

Commercially available liquid smokes were added to a meat model system and to a restructured beef product to assess their ability to suppress lipid oxidation. Aqueous hickory smoke was the most effective smoke in suppressing oxidation as reflected in 2-thiobarbituric acid reactive substances (TBARS) of microsomal lipids. Phenol was not antioxidative in the model system. Addition of liquid smoke had no significant effect on "stale, cardboardy, painty" flavor or aroma of restructured beef roast slices stored at 4C. The aroma and flavor of sliced beef deteriorated over the 7-day storage regardless of liquid smoke addition. Hexanal in the control roasts increased during storage from ∼0 to >3 ppm; those containing aqueous liquid smoke contained little (< 0.5 ppm) hexanal. Smokes, but not the phenol mix, kept TBARS near day zero (0.2 mg/kg) levels through 7 days.     

LIPID OXIDATION IN TURKEY MEAT AS INFLUENCED BY SALT,METAL CATIONS AND ANTIOXIDANTS1

Turkey breast or thigh muscle was mixed with 2% pure salt, rock salt, or pure salt plus 50 ppm of one or a combination of copper, iron or magnesium. Efficacy of 2 antioxidants was tested. Lipid oxidation was monitored during refrigerated and frozen storage of raw and cooked turkey by the thiobarbituric acid (TBA) test. TBA results indicated that the most significant prooxidant effect was caused by salt plus Cu²⁺ and Fe²⁺ followed by salt plus Fe³⁺ or Cu²⁺ alone. Tenox 6 was an effective antioxidant in the presence of copper and iron ions. Thigh meat was more susceptible to oxidation than breast meat. Cooking had a significant prooxidant effect as measured by TBA.     

LIPID OXIDATION IN RETAIL BEEF, PORK AND CHICKEN MUSCLES AS AFFECTED BY CONCENTRATIONS OF HEME PIGMENTS AND NONHEME IRON AND MICROSOMAL ENZYMIC LIPID PEROXIDATION ACTIVITY

Muscles of beef, pork and chicken purchased in two seasons were analyzed for lipid oxidation potential, concentrations of total pigments, myoglobin and nonheme iron, and microsomal enzymic lipid peroxidation activity. To determine lipid oxidation potential, thiobarbituric acid (TBA) assays with antioxidant protection were conducted on raw and cooked comminuted muscles stored at 4°C. TBA values of raw chicken muscles (white and dark) and pork muscles were low and changed little during 2–6 days of storage, whereas the values of raw beef muscles were higher and increased progressively. However, TBA values of cooked muscles of all three species increased during 2–4 days of storage with no marked differences among the species. Total pigment and mycglobin concentrations best explained the differences in TBA values of stored, raw muscles among the three species.