School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemStructural determinants of the quality of cooked meat( 2020)The quality of cooked meat is valuable for consumers and meat industry. The aim of this research was to identify structural determinants of the quality of cooked meat. Muscle type (bovine semitendinosus, psoas major, biceps femoris), cooking temperature (45 C to 85 C), ageing time (14 vs 0 days in beef; prolonged 15 vs conventional 3 days in pork), enzyme inhibition (with/without cathepsin inhibitor) and fibre type (bovine masseter 100 percent type I; cutaneous trunci 93 percent type II) were investigated factors affecting meat quality. Methods for measuring quality (cooking loss and Warner- Bratzler shear force (WBSF)), structural changes (shrinkage) and protein denaturation [Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared (FTIR) microspectroscopy] were used. Cooking loss was higher in semitendinosus compared to biceps femoris and psoas major; and it increased with temperature in beef and pork. Cooking loss increased with ageing of beef independent of temperature and muscle type; and decreased with prolonged ageing compared to conventional ageing, of pork (cooked at 70 C and 80 C). The denaturation enthalpy of masseter and cutaneous trunci explained 58 and 59 percent of the variation in cooking loss, respectively. Reduction of WBSF in bovine muscles rich in collagen (all but psoas major) with cooking at 60 C to 65 C was attributed to collagen denaturation. The increase in WBSF in unaged beef with cooking at 70 C and 80 C was attributed to intact titin denaturation. In relation to shrinkage, 3D laser scanning was compared to caliper measurements, and was found inferior in measuring volume and predicting cooking loss. Cuboids` transverse and longitudinal shrinkage were higher in muscles with higher collagen content and sarcomere length, respectively. Transverse shrinkage started 5 C higher in psoas major fibre fragments, compared to semitendinosus and biceps femoris, likely due to predominant type I fibres. It was proven that transverse and longitudinal shrinkage of fibre fragments is caused by myosin and actin/titin denaturation, respectively. Since ageing reduced the longitudinal shrinkage of cooked beef (biceps femoris and psoas major cuboids at 80 C, semitendinosus and biceps femoris fibre fragments at temperatures greater or equal to 75 C) and pork, an important role of titin in longitudinal shrinkage was hypothesized. Cathepsin inhibition reduced the longitudinal shrinkage (semitendinosus, biceps femoris, psoas major cooked at temperatures greater than 75 C), and increased the transverse shrinkage (semitendinosus at temperatures greater or equal to 60 C) of fibre fragments. Longitudinal and transverse shrinkage were major contributors to cooking loss (beef and pork) and WBSF (beef), respectively. Cutaneous trunci had higher cooking loss (at temperatures lower or equal to 75 C), higher transverse (at temperatures lower or equal to 60 C), longitudinal (at temperatures lower or equal to 80 C) and volume shrinkage of fibre fragments (at temperatures lower or equal to 65 C); as well as lower transition temperature of myosin, higher reduction in alpha-helix and beta-sheet, and higher, compared to masseter, formation of beta-aggregated strands, random coil and aromatic side chains (at temperatures lower or equal to 60 C). The differences in protein denaturation and shrinkage between masseter and cutaneous trunci cooked at 55 C were attributed to the myosin isoform, while the differences in muscle fibre and connective tissue proteins’ denaturation at 60 C and 65 C were pH dependent. Myosin (isoform, denaturation), actin (denaturation), titin (degradation, denaturation), collagen (content, denaturation) and sarcomere length were proven or postulated, as structural determinants of the quality of cooked meat.