EFFECT OF HOUSEHOLD STORAGE, THAWING AND COOKING PRACTICES ON THE SURVIVAL OF SALMONELLA AND ESCHERICHIA COU IN BEEF PATTIES

摘要

Food Safety authorities worldwide have issued general guidelines for the proper handling of ground beef in households. However, these recommendations may not sufficiently cover all the commonly applied practices, because the latter depend on the convenience and personal preferences of the consumers for handling and consuming foods. The objective of the study was to evaluate the survival of Salmonella and Escherichia coli O157:H7 during frozen storage, thawing and cooking of beef patties, simulating common consumer-style practices. Portions (400 g) of ground beef were inoculated (6.5 log CFU/g) with a five-strain composite of Salmonella or a three-strain composite of E. coli O157:H7 and stored at -22°C. After 5 and 75 days of frozen storage, thawing took place (i) in refrigerator at 4°C for 16 hours; (ii) at 20°C for 12 hours, simulating thawing on counter, or (iii) in microwave for 22-24 minutes. Following thawing 90 g beef patties were shaped and cooked in Double-Broil (DB) or Pan-Grill (PG) until the internal temperature reached 60°C (simulating undercooking) or 71°C (recommended cooking temperature). In addition, the survival of the two pathogens after direct cooking of frozen patties was studied, simulating commercial cooking practices in catering services and restaurants. Storage of beef patties at -22°C resulted in 0.5 - 0.7 log CFU/g reduction (p<0.05) of the two pathogens, while 1.0 log increase (p<0.05) was observed following thawing under kitchen counter conditions (20°C). Cooking in DB was more effective for the elimination of the pathogens compared with cooking in PG, especially when cooked at 71°C. These findings showed that the survival of the pathogens was highly affected by the rate and the direction of heat transfer into the beef patties, during cooking, regardless of the thawing method applied before. E. coli O157:H7 showed an increased survival during cooking after frozen storage for 75 days, compared to 5 days of storage, while the opposite was observed for Salmonella. The results may be used to instruct the consumers and catering services for the appropriate defrosting or cooking practices of beef patties, taking into account the variability that might occur for practical purposes in different establishments (i.e. households, food caterings, restaurants).