Characterization of Breast Meat Collected from Spent Lohmann Brown Layers in Comparison to Commercial Ross Broilers

ABSTRACT The objective of this study was to compare characteristics and properties of breast meat from spent Lohmann Brown layers (SP, 90 weeks old, n = 24) and those of commercial broilers (BR, 6 weeks old, n = 24). The breasts of both SP and BR were collected from a local processing plant, vacuum-packed in a plastic bag, and stored at -18ºC until further analyses. The SP showed a greater water-holding capacity, tougher and chewier texture (p<0.05). Both raw and cooked SP breasts comprised the greater total collagen but lower soluble collagen than those of BR (p<0.05). Muscle fibers of the SP, observed under scanning electron microscope, were small, with average fiber diameter of 37.85±1.40 μm, densely packed and surrounded by complex networks of connective tissue. The lower myofibril fragmentation index and alkaline-soluble protein fractions of the SP (p<0.05) suggested lesser degree of postmortem fragmentation and protein denaturation in SP compared to BR. Based on differential scanning calorimetry, multiple endothermic transitions were observed in both raw BR and SP breast samples. While BR thermograms comprise five transitions at 57.7ºC, 64.2ºC, 67.6ºC, 72.3ºC and 77.6ºC with total ΔH of 15.31 J/g dry meat, the SP samples exhibited four transitions at 55.1ºC, 62.1ºC, 70.5ºC and 77.7ºC and total ΔH of 17.62 J/g dry meat. Overall, the findings indicated that cooked meat toughness of SP was attributed by the high total and heat-stable collagen content, densely packing of small muscle fibers, and the superior myofibril integrity.

摘要
本研究旨在比较90周龄退役罗曼褐壳蛋鸡（spent Lohmann Brown layers，SP，n=24）与6周龄商品肉鸡（commercial broilers，BR，n=24）的胸肉品质特性。两组胸肉均采自当地屠宰加工厂，以真空塑料袋封装后于-18℃冷藏以待后续分析检测。结果显示，SP组胸肉持水性更强，质地更坚韧耐嚼（p<0.05）。生肉与熟制后的SP组胸肉总胶原蛋白含量均显著高于BR组，可溶性胶原蛋白含量则显著低于BR组（p<0.05）。通过扫描电子显微镜（scanning electron microscope）观察可见，SP组肌纤维平均直径为37.85±1.40μm，尺寸更小、排布致密，且被复杂的结缔组织网络包裹。SP组的肌原纤维碎片指数与碱溶性蛋白组分均显著更低（p<0.05），表明相较于BR组，SP组的死后肌纤维碎裂程度与蛋白质变性程度均更低。基于差示扫描量热法（differential scanning calorimetry）检测，生的BR组与SP组胸肉样品均存在多个吸热转变峰：BR组热谱图共有5个转变峰，对应温度分别为57.7℃、64.2℃、67.6℃、72.3℃与77.6℃，总焓变（ΔH）为15.31 J/g干肉；SP组则存在4个转变峰，对应温度为55.1℃、62.1℃、70.5℃与77.7℃，总焓变为17.62 J/g干肉。综合来看，SP组熟肉的高韧性归因于其较高的总胶原蛋白与热稳定性胶原蛋白含量、细小肌纤维的致密排布，以及更完好的肌原纤维完整性。