Survival of Salmonella on Dried Fruits and in Aqueous Dried Fruit Homogenates as Affected by Temperature

摘要

A study was done to determine the ability of Salmonella to survive on dried cranberries, raisins, and strawberries and in date paste, as affected by storage temperature. Acid-adapted Salmonella, initially at 6.57 to 7.01 log CFU/g, was recovered from mist-inoculated cranberries (water activity [a_w] 0.47) and raisins (a_w 0.46) stored at 25℃ for 21 days but not 42 days, strawberries (a_w 0.21) for 42 days but not 84 days, and date paste (a_w 0.69) for 84 days but not 126 days. In contrast, the pathogen was detected in strawberries stored at 4℃ for 182 days (6 months) but not 242 days (8 months) and in cranberries, date paste, and raisins stored for 242 days. Surface-grown cells survived longer than broth-grown cells in date paste. The order of rate of inactivation at 4℃ was cranberry ＞ strawberry ＞ raisin ＞ date paste. Initially at 2.18 to 3.35 log CFU/g, inactivation of Salmonella on dry (sand)-inoculated fruits followed trends similar to those for mist-inoculated fruits. Survival of Salmonella in aqueous homogenates of dried fruits as affected by fruit concentration and temperature was also studied. Growth was not observed in 10% (a_w 0.995 to 0.999) and 50% (a_w 0.955 to 0.962) homogenates of the four fruits held at 4℃, 50% homogenates at 25℃, and 10% cranberry and strawberry homogenates at 25℃. Growth of the pathogen in 10% date paste and raisin homogenates stored at 25℃ was followed by rapid inactivation. Results of these studies suggest the need to subject dried fruits that may be contaminated with Salmonella to a lethal process and prevent postprocess contamination before they are eaten out-of-hand or used as ingredients in ready-to-eat foods. Observations showing that Salmonella can grow in aqueous homogenates of date paste and raisins emphasize the importance of minimizing contact of these fruits with high-moisture environments during handling and storage.