Quality of muscle foods : effects of feed and storage time

Sammanfattning: The overall aim of this thesis was to investigate the effects of feed and storage time on meat quality. To study the effect of feed, chicken were fed seven steam-pelleted or nonpelleted rapeseed (RS) diets with different RS inclusion levels (0, 80, 160, and 240 g/kg) for 34 days, and the dietary effects on meat yield, fatty acid composition in meat, and the expression of lipid metabolism-related genes in liver were determined. Feeding with steam-pelleted diets with high inclusion of RS (160 or 240 g/kg) significantly increased the content of n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) in meat, without compromising the meat yield and total fatty acid content. The increased intake of α-linolenic acid enabled higher conversion into n-3 LC-PUFA. Therefore, feeding broiler chicken steam-pelleted diet with high RS inclusion can be a feasible strategy to increase human intake of n-3 LC-PUFA without compromising meat yield. The effect of storage time on meat color, microbial growth, and lipid oxidation was studied on beef steaks from Longissimus thoracis et lumborum muscles overwrapped with polyvinyl chloride (PVC) film and stored at 4°C for 0, 4, 7, and 10 days. Microbial spoilage of beef occurred at day 10 as indicated by the total viable count exceeding the threshold of 7 log10 CFU/cm². Pseudomonas spp. and Brochothrix spp. were the prevailing bacteria species when meat was spoiled. Moreover, Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis showed the successive changes in the incidences of different bacteria over time. At day 10, the a' and Chroma decreased and hue angle increased significantly, indicating meat discoloration. Concentrations of spermine, tyramine, and cadaverine were found to be potential spoilage indicators of meat freshness. Lipid oxidation occurred only slightly, which could be attributed to the high content of α-tocopherol in meat. In contrast, the degree of lipid lipolysis increased with storage time as reflected by the increase in the relative content of free fatty acids and decrease in relative content of triacylglycerols.

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