Microbial growth and colour of minimally processed shiitake mushroom stored at different temperatures

The effect of storage temperature on the microbiological and sensory characteristics of minimally processed shiitake was investigated. Shiitake mushrooms were washed, sanitised, packed in polystyrene trays, overwrapped with plastic film and stored at 7, 10 or 15 degrees C. Microbial counts, polyphenoloxidase activity, external lightness (L*) and acceptance tests were conducted. Mesophilic, aerobic psychrotrophic bacteria, yeasts and moulds predominated during storage. Pseudomonas was detected after 10 days' storage showing an increase of, approximately, 7 log cycles at 15 degrees C. Mushroom rejection occurred when the microbial population was lower than 10(6) CFU g(-1), suggesting that, other factors, such as browning, affect mushroom spoilage more than microbial activity. Mushrooms treated with citric or ascorbic acids maintained high L* value during 10 days. The shelf life of minimally processed shiitake mushrooms was 10 days at 7 degrees C, but less than 5 days at 10 degrees C, and approximately 3 days at 15 degrees C.