Changes of Bacterial Growth and Water Activity Values of Sliced Cabbage, Sandwich, and Tofu Stored under Various Temperatures and Humidity Conditions

Introduction: Temperature may have both direct and indirect impact on food safety hazards in food chain at any stages, from production through consumption. Although temperature and humidity are supposed to have direct impacts on microbes growing in foods, researches related to these factors are limited.

Purpose: The objective of this study was to investigate changes of bacterial growth and water activity of sliced cabbage, sandwich, and tofu stored under different temperature and relative humidity with or without sealing air-tightly for 7 days storage.

Methods: Water activity, total viable counts, total coliforms, Escherichia coli, Staphylococcus aureus, Bacillus cereus, and Salmonella spp. in sliced cabbage, sandwich, and tofu were analyzed under different temperature (20, 30, and 40°C) and humidity (30%, 50%, and 75%) during storage. The significance was verified through ANOVA.

Results: Initial A_w of sliced cabbages, sandwiches, and tofu were 0.999, 0.979, and 0.996, respectively. Storage temperatures, relative humidity, and air tight sealing did not significantly (P > 0.05) change A_w of sliced cabbage during storage. A_w of sandwiches increased significantly (P < 0.05) with increasing relative humidity and temperature during storage. In tofu, A_w ranged from 0.972 to 1.000 and were not significantly (P> 0.05) influenced by temperature and relative humidity during storage.

Storage time and temperatures affected significantly (P < 0.05) aerobic plate counts and coliforms in sliced cabbage and tofu, while relative humidity and sealing did not change significantly (P > 0.05) aerobic plate counts of sliced cabbage during storage. In case of sandwich, storage temperatures, relative humidity, and sealing did not affect coliforms forming. Staphylococcus aureus and Bacillus cereus were not detected in sandwich and tofu during study.

Significance: Thorough supervision of temperature and time is required regardless of whether sealing or not for the safety of ready-to-eat foods due to climate conditions; however, relative humidity did not affect significantly the A_w of the foods which contained high A_w originally.