Ready-to-eat meat requires particular attention because it is less likely to be re-heated by consumers compared to raw products, which will be cooked. The new research suggests that processors will also have to monitor humidity to ensure their final products are safe to eat, even though cooking once is a known effective method of killing salmonella. Authors of the study, from Texas Technical University, US, have called for a minimum humidity level to be set for processors producing ready-to-eat beef. Their study used raw beef top round roasts purchased from a commercial supplier. The samples were then contaminated with a seven-strain mix of heat-shocked salmonella and then processed until the internal temperature reached 62.8C at humidity ranging from 0 to 90 per cent. The thin agar layer method was used to determine the salmonella counts on the samples. The tests found significant differences in the salmonella counts between roasts processed at 30 per cent humidity and those processed at 15 per cent humidity or lower. At a humidity of 30 per cent or less, salmonella reductions were less than the US regulatory performance standard of 6.5 log units. The results indicate that cooked ready-to-eat roast beef can be safely processed under conditions outside of the current US Department of Agriculture (USDA) Food Safety and Inspection Service "safe harbor" guidelines. However, one of these current safe harbor guidelines for safe ready-to-eat beef production, which allows humidity to be introduced for at least half the cooking time at internal temperatures of 62.8C, could result in a finished product that falls below USDA performance standards, claims the study. The study recommended that this specific guideline should be clarified with a minimum relative humidity requirement to ensure the production of a safe product. Other research has also shown that bacteria can develop a higher heat tolerance when their moisture levels decrease because of the increased concentration of solutes, including sugars. Moisture on the surface of meat releases energy as it evaporates which increases the effectiveness of killing salmonella and other bacteria that may otherwise survive.
