EFFECT OF GLUCOSE ON THE BACTERIAL SPOILAGE OF BEEF

Ground beef with less than 2% added glucose showed typical spoilage characteristics by gram-negative psychrophiles during refrigerated storage. In samples containing 2–10% glucose, acids produced at the expense of the carbohydrate lowered the meat pH from 5.8 to 5.0–5.2. This low pH persisted in the meat until all glucose was depleted. During this period growth of the predominant nonpigmented Pseudomonas organisms was hindered, and no spoilage characteristics such as slime and off-odors were observed. When the glucose disappeared the meat pH started to rise. Incipient spoilage (off-odors and tackiness) became apparent when a pH value of 6.0 was exceeded. Lactobacilli counts were slightly higher in glucose-treated meat than in the control, but no bacterial shift was observed. Instead, the added glucose caused a shift in nutrient utilization by the spoilage microflora. Normally these bacteria attack the nitrogenous compounds in meat, resulting in production of alkaline by-products and elevated meat pH. In the presence of glucose, the same microorganisms utilized the carbohydrate preferential to other compounds in the meat. The oxidatively formed acids lowered the meat pH, affected the growth rate of the spoilage bacteria and hence retarded spoilage. The addition of 2% glucose to ground beef prolonged its average shelf life at refrigerated temperatures from 5 days to 8–10 days.