Involvement of Heat Shock Proteins in Tenderness Development and Oxidative Stability of Postmortem Muscle
Heat shock proteins are widely recognized for their cytoprotective properties, including direct chaperoning and antioxidative function. Their relevance to meat quality has been of recent interest to the industry, as evidence shows meat with increased heat shock protein expression and abundance is prone to increased toughness. However, the full extent of their effects and the mechanisms by which they affect meat quality are unknown. Therefore, the overall objective of this thesis was to investigate the role of heat shock proteins in meat quality, especially in terms of proteolytic tenderization and oxidative stability. The first chapter of this thesis is a literature review that covers heat shock proteins and apoptosis, the mechanism of programmed cell death, and the implications thereof in meat quality. The second chapter is an investigation into the correlations between small heat shock proteins and callipyge lamb meat toughness. The objective of this study was to determine if heat shock proteins (HSPs) involve in tenderness development of loins from callipyge lambs. Loin samples (M. longissimus thoracis) from sixteen lambs across four genotypes were collected throughout postmortem aging. The higher concentration of HSP27 in callipyge was coincided with higher levels of intact desmin and troponin T, less calpain-1 autolysis, and higher shears force values compared to other non-callipyge phenotype lambs (P < 0.05). There were positive correlations between anti-apoptotic activities (shown by elevated HSP27 and procaspase 3, and less cytochrome c) and increased toughness in callipyge lamb loins (P < 0.05). The third chapter was focused on oxidative stability and meat quality in broiler chickens. Two hundred forty male Ross 708 broilers were assigned to 48 pens in two temperature-controlled rooms. Using a 2 x 2 factorial design, broilers were kept at either 32 °C (heat stressed, HS) or the thermoneutral condition at 21 °C. The broilers were fed either regular diets or the diets mixed with probiotic (Sporulin, 250 ppm; containing three strains of B. subtilis). Forty-eight chickens (12 birds/treatment) were randomly harvested at day 46, and pH decline was immediately measured for 4.5 hours. At l day postmortem, paired breast muscles (M. pectoralis) were collected for the meat quality analyses such as, drip loss, cook loss, Werner-Bratzler shear force, and display color. 2-thiobarbituric acid reactive substances (TBARS), 2,2- diphenylpicrylhydrazyl (DPPH), and antioxidant enzyme activity, such as catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx), were measured. Western blots for HSP70 and HSP27 were performed. Data were analyzed using the PROC MIXED procedure of SAS, and means were separated using least significant differences (P < 0.05). Probiotic feeding significantly decreased TBARS and phospholipid contents in HS chicken breast (P < 0.05). DPPH was increased with heat stress (P < 0.0001), but diet had no significant impact within HS broilers.
Kim, Purdue University.
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