Effect of Time and Method of Aging on the Composition of the Microflora of Beef Loins and Corresponding Steaks

Abstract

Twenty-four cattle were slaughtered at a commercial packing plant. Carcasses were chilled for 72 h at 4°C, and then fabricated into wholesale cuts. Right loins were vacuum packaged and aged for 1, 3 and 5 weeks at 4°C while the left loins were aged conventionally for 1, 2 and 3 weeks at the same temperature. Core samples were removed from both ends of the conventionally and vacuum-aged loins and analyzed using standard microbiological procedures. Isolates from aerobic plates incubated at 35 and 20°C, and from gram-negative enteric plates were used to determine the composition of the aerobic (35 and 20°C) and gram-negative enteric microflora. Loins were cut into 2.54-cm thick steaks, wrapped in oxygen permeable fresh meat wrap and placed at 4°C in a simulated retail meat case. After 1, 3, 6 and 7 d, steaks were evaluated using the same microbiological techniques used for loins. Vacuum packaged loins had lower percentages of pseudomonads than conventionally aged loins after 1 and 3 w of aging. The lactobacilli were higher in vacuum packaged loins than in conventionally aged loins after 3 weeks. The aerobic (35 and 20°C) microflora of the retail cuts generally reflected the flora of the loins from which they were prepared. Enterobacteriaceae tended to be higher in vacuum packaged loins and corresponding steaks, and constituted 34% of the flora of the vacuum packaged loins after 5 weeks of aging.