Histochemical, histological and physicochemical characteristics of bovine muscle from four quality groups

Abstract

Twenty-four steer beef carcasses of A maturity and similar grade were selected postmortem to represent four quality groups. These were: normal in color, firmness and exudate (NOR); normal in color but soft and exudative (NSE); pale in color, soft and exudative (PSE); and dark cutting (DC). Selection was based on longissimus muscle properties. The longissimus muscle (LD), psoas major muscle (PM), gluteus medius muscle (GM), inner and outer semimembranosus muscle (ISM and OSM) and inner and outer semitendinosus muscle (1ST and OST) were studied. The objective of the investigation was to characterize the histochemical, histological, physico-chemical and sensory properties of the NOR muscles and to compare muscles among the four groups. Histochemically the PM was the reddest muscle and the OST was the whitest muscle examined. The LD and GM muscles were similar in fiber types. The 1ST had more red fibers than the OST but the ISM had more anaerobic fibers than the OSM. Histological and numerous physico-chemical characteristics of bovine tissues varied among muscles and within cross-sectional areas of the muscle. Muscles from the NOR and NSE groups were similar in color and those from the PSE and DC groups were the palest and darkest, respectively, of the four groups. Muscles from the NSE, PSE and DC quality groups had more myoglobin and hemoglobin than those from the NOR group. However, myoglobin levels of all muscles from all quality groups were of normal magnitude. Hemoglobin level in the LD from the NSE, PSE and DC groups was three times greater than in the LD of the NOR group. Muscles from the NSE and PSE groups were softer, more exudative, higher in transmission values and lower in water-holding capacity compared to muscles of the NOR group. Muscles from the DC group had the highest pH, firmness and exudate values, the highest water-holding capacity and the lowest transmission values compared to muscles from the other three groups. Palatability characteristics of steaks from the three aberrant quality groups were as desirable as those of steaks from the NOR group; however, cooking and total weight losses were greater in steaks from the NSE and PSE groups than those from NOR and DC steaks. Areas of all fiber types from the DC group were larger than those from the NOR, NSE and PSE groups and ATPase aWhite fibers in muscles of all the groups were considerably larger than either the 6 Red or aRed fibers. Giant fibers were observed in all muscles from all four quality groups and were distinctly round, tended to exhibit more crenation and were usually aWhite and NADH negative. Occasionally the giant fibers stained aRed and NADH positive or aWhite and NADH positive. More anaerobic type fibers were observed in muscles of the NSE, PSE and DC groups than in muscles from the NOR group. The observed increase in anaerobic potential of muscles from the three aberrant quality groups indicates this muscle characteristic is conducive to and associated with undesirable chemical and physical muscle properties.