Abstract

This study was conducted to evaluate the susceptibility of the Dorper and Merino breeds to pre-slaughter condition stress at a commercial abattoir and how it affects the quality of the meat produced. The objective of this study was to investigate differences in post-mortem energy metabolites, glycolytic potential and meat quality attributes from the longissimus thoracis et lumborum (LTL) between Dorper and Merino lambs slaughtered at a commercial abattoir. Meat samples (~50 g of LTL) harvested from 100 female eight-month old of the Dorper (n = 50) and Merino (n = 50) lambs were used in this study. For measuring post-mortem energy metabolites (glycogen, lactate, glucose-6-phosphate and glucose content), sampling was done on each carcass ~30 min post-slaughter and the samples were immediately frozen (−196 °C) in liquid nitrogen to prevent further glycolysis. The pH and temperature were measured 45 min, 6 and 24 h post-slaughter, and carcass measurements were taken. Color coordinates (lightness (L*), redness (a*), yellowness (b*)) were measured at 24 h after slaughter and hue angle (H*) and chroma (C*) were calculated. Furthermore, thawing loss (TL), cooking loss (CL) and Warner Braztler Shear Force (WBSF) were measured after 7 days post-slaughter storage (−20 °C). The Dorper had lower glycogen levels and thus produced meat with a high ultimate pH and tougher meat compared to the Merino breed. The relationships observed between post-mortem muscle metabolites, glycolytic potential and meat quality attributes indicate that meat quality is affected by glycogen levels at slaughter. The results indicate that the Dorper breed was more susceptible to pre-slaughter stress and thus produced meat with reduced quality compared to the Merino breed.

Highlights

  • During the conversion of muscle to meat, the amount and degree of pH drop has a considerable bearing on the overall meat quality [1]

  • Effect of breed on post-mortem energy metabolites and glycolytic potential In Table 1 differences (P < 0.001) were observed for the effect of breed on the levels of muscle glycogen where, the Merino breed had higher levels of muscle glycogen compared to Dorper

  • Glycogen concentration is affected by metabolic pathways of muscle fibres where oxidative muscle fiber types contain less glycogen compared to predominantly Type I fibers [13]

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Summary

Introduction

During the conversion of muscle to meat, the amount and degree of pH drop (from 7.4 in live muscle to 5.5 at 24 hours post-mortem) has a considerable bearing on the overall meat quality [1]. Post-mortem pH decline is reported to depend mostly on glycolysis, which is the breakdown down of glycogen (a muscle energy reserve) into lactate [2]. The anaerobic muscle conditions post-mortem favour glycolysis as a driver of lactate accumulation in muscles, lowering the pH [3]. Firm, dry (DFD) meat results when the normal pHu (~5.5) at 24 hours post-moterm is not reached, and the meat will have a high pH (>6.0), with a dark colour and reduced tenderness [6]. In order to prevent producing meat with a pHu and avoid DFD meat, there is still a need to fully apprehend the underlying mechanisms of glycolytic

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