Is the rate and extent of pH fall correlated across the muscles in sheep? : A Dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science in Food Innovation at Lincoln University

Abstract

The pattern of pH decline in animals has been related to several factors such as electrical simulation, rapid chilling, and/or meat tenderness. The main objective of this study was to analyse the factors that affects the change in pH in sheep carcasses, and to compare the change among different muscles during the post slaughter period. For this, an experimental trial was carried out using 5 muscles, namely the Longissimus dorsi (LD), Semitendinosus (ST), Gracilis (G), Sternomandibularis (StM), and Platysma (P) from 6 sheep carcasses. Muscles from the right-hand side were used for assessing the biochemical characteristics and meat quality. The other side was used to measure the pH and temperature changes. The pH and temperature of the five different muscles on the carcasses was measured at time interval of 90m, 3h, and 24h post-mortem, and off the carcasses was measured at 45m and 48h post slaughter. The rate of decline in pH was correlated to different biochemical characteristics such as muscle fibre typing, lactate content and glycogen content, and meat quality characteristics such as colour, cooking loss, and shear force. The effect of pH and temperature change, colour, cooking loss, shear force, muscle fibre typing, lactate, and glycogen content across different muscles in sheep was investigated. The study provided evidence to prove that there is a constant decline in muscle pH with Platysma showing the highest and Semitendinosus and Longissimus dorsi muscles showing the lowest pH values. The colour measurements showed that Sternomandibularis had the highest chroma, and Longissimus dorsi muscles hsd the highest hue value. Cooking loss was measured on the 2nd day and 7th day for the muscles, and it was studied that Longissimus dorsi muscles had the highest cooking loss and Gracilis had the lowest. Muscle shear force values was also measured on 2nd and 7th day, which provided evidence to prove that Gracilis had the highest and Semitendinosus and Longissimus dorsi muscles muscles had the lowest shear force values. However, day 7 measurements showed that G and ST muscles had the highest sheat force whereas LD muscles had the lowest. The muscle fibre typing provided evidence to prove that all the five muscle samples showed the presence of MCH IIx (MHC-1), IIa (MHC- 2), IIb (MHC-4), and MHC-7 (slow/1). The glycogen analysis provided evidence to prove that the concentration of muscle glycogen followed the order P>> ST=G>>SM=LD. This in turn suggested the correlation of glycogen concentration with pH, temperature, and fibre typing.