Post-mortem metabolism and meat quality properties in five lamb muscles : A Dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science at Lincoln University

Abstract

The objective of this study was to analyze pH changes within five lamb muscles and correlate those to the physical and biochemical characteristics of the muscles, meanwhile, to understand what drives the changes and determine the strength of the correlation in pH changes with meat quality properties. Semimembranosus (SM), semitendinosus (ST), longissimus dorsi (LD), infraspinatus (IS), and supraspinatus (SS) from six animals were analyzed. Muscles from the left side of the carcasses were excised at 4 hours post-mortem to measure the fiber type by electrophoresis, while muscles from the right side of the carcasses were used to measure pH and temperature at 1.5, 6, 8, and 24 hours, and color was measured after the muscles were excised at 24 hours. After that, muscles from the right side were aged for 7 days and checked for cooking loss and tenderness. SM, ST, and LD muscles presented predominantly type-IIa and -IIx fibers, while SS was more abundant in type-Ifiber, and IS presented more type-Ifiber than SM, ST, and LD, but less than SS. Temperature of all muscles decreased and reached 3°C. All the muscles followed the normal trend of post-mortem pH decline, with the largest extent in LD and relatively higher ultimate pH in IS and SS. ST was the lightest (P < 0.05) muscle, while SS was the reddest (P < 0.05) muscle in this study. After aging and cooking, SM presented the highest (P < 0.05) loss of water and was the toughest (P < 0.05) muscle, while IS had the lowest (P < 0.05) cooking loss and was the most tender (P < 0.05) muscle. These data show that the different muscles varied in their on post-mortem biochemical and physical changes, and the gel results indicate that the methodology developed is suitable for observing fiber types in lamb muscles.