Microbiological Evaluation of Cultivated Oyster Mushrooms (Pleurotus ostreatus) During Storage.

Abstract

Globally, the cultivation of Pleurotus ostreatus has risen tremendously due to their ability to grow on a wide range of cheaply available agricultural wastes. However, they are highly perishable and susceptible to contamination by microorganisms. Contamination of dried food by microorganisms has become a major health concern. The aim of this study was to evaluate the microbiological properties of dried cultivated Pleurotus ostreatus during storage. Fresh cultivated P. ostreatus were dried in hot air oven at 55℃ for 72 hours. A portion was sun dried for five days to constant weight. Samples were taken at day 0, 30, 60, 90, and 120. Moisture content (MC) was determined using standard methods. MC of sun dried varied between 9.00% and 12.20%. MC of oven dried varied from 7.00% and 10.00%. The MC of the sun dried and oven dried samples were within the acceptable limit for dried mushrooms. Isolation, enumeration and identification of microorganisms were done using standard microbiological techniques. Mean total bacterial count (TBC) of sun dried varied from 2.8 x 105 CFU/g to 6.5 x 105 CFU/g. TBC for oven dried varied from 1.1 x 105CFU/g to 4.2 x 10CFU/g. Frequency of occurrence of bacteria: Escherichia coli 4(20%), Staphylococcus aureus 7(35%), and Pseudomonas aeruginosa 9(45%). Mean total fungal count (TFC) for sun dried varied from 2.3 x 102CFU/g to 6.2 x 102CFU/g. TFC for oven dried was 1.1 x 102 CFU/g to 2.0 x 102CFU/g. Frequency of occurrence of fungi: Aspergillus sp 15(75%), Fusarium sp 3(15%), and Rhizopus sp 2(10%). Microbial load of sun and oven dried increased with storage time. Post-harvest losses, shortened shelf life and health risk can be ameliorated by evaluating and understanding the microbiological properties of microbial isolates during storage.