36E-2 |
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N. CHIKTHIMMAH1, R. B. Beelman, and L. F. LaBorde. (1) Dept. of Food Science, Pennsylvania State Univ., 111 Borland Lab., University Park, PA 16802-2504 In mushroom growing, peat soil amended with calcium carbonate is added on top of mushroom mycelia-colonized compost. This layer is called the casing soil. The casing soil promotes mushroom fruitbody formation. The microbial food safety of fresh mushrooms as influenced by the casing soil is unknown. Also, the survival characteristics of Listeria monocytogenes on fresh mushrooms is not known. The objectives of this study were to understand the microbial ecology of the casing soil, and determine the survival of L. monocytogenes in casing soil and on fresh mushrooms under pre and postharvest conditions, respectively. Batches of casing soil were either untreated, or sterilized (by autoclaving at 121º C for 45 min). The soils were inoculated with L. monocytogenes and maintained under simulated growing conditions (80 % moisture, 22° C). In postharvest experiments, mushrooms were inoculated by dispensing a 15- microliter drop of L. monocytogenes suspension and spreading it over the fruitbody surface. The inoculated mushrooms were packaged and stored at 12º C. Casing soil and mushrooms were periodically sampled for microbial enumeration. A 6.8 log CFU of L. monocytogenes per gram of untreated casing soil was reduced to undetectable levels in 10 days in the presence of indigenous microflora comprised predominantly of the Penicillium sp., Aspergillus sp., and the Pseudomonas bacterial genus. During this time period, populations of L. monocytogenes remained unchanged in sterilized casing soil and survived even after 5 weeks. L. monocytogenes did not grow on mushrooms during postharvest storage. Over a thirteen day storage period, populations of L. monocytogenes in mushrooms reduced by 1.6 log units. The microbial ecology studies indicate that the indigenous microbial populations present in casing soils and fresh mushrooms may play a significant role in the inhibition of L. monocytogenes.
Session 36E, Fruit & Vegetable Products: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |