Microbiological quality assessment of gamma irradiated fresh and dried mushrooms (Pleurotus ostreatus) and determination of D10 values of Bacillus cereus in storage packs

Abstract

The microbiological food contamination in Ghana is alarming. Gamma radiation was used to decontaminate and preserve fresh and dried mushrooms (Pleurotus ostreatus). Fresh mushrooms were irradiated with doses of 0 kGy (control), 1 kGy and 2 kGy and stored in polythene and polypropylene storage packs at 20 oC for a period of 5 days. Dried mushrooms were also irradiated at doses of 0 kGy, 0.5 kGy, 1 kGy, 1.5 kGy and 2 kGy and stored in the same packs and temperature for 12 months. The samples were analysed for aerobic plate counts, total coliforms, Bacillus cereus, Staphylococcus aureus, Salmonella spp, yeasts and molds counts using standard microbiological methods at intervals of 0 and 5 days for fresh mushrooms while dried mushrooms were monitored at 0, 3, 6 and 12 months. The D10 values of Bacillus cereus were calculated for fresh and dried mushrooms using a linear regression model after gamma irradiation. Generally fresh mushrooms counts ranged 3x103- 7.5x108, 5x101- 4x102 and 8x101- 9x104 for aerobic mesophiles, Bacillus cereus, yeasts and molds respectively. Dried mushrooms recorded count ranges of 2.8x102- 8.3x105, 1x101- 5x103 and 1x101- 3x103 for same. Salmonella spp, coliforms and Staphylococcus aureus were not detected on both fresh and dried mushrooms. The mean D10 values for Bacillus cereus on fresh mushrooms were 3.21±0.81 kGy (polypropylene), 0.76±0.04 kGy (polythene) while dried mushrooms recorded 2.40±0.90kGy (polypropylene) and 1.80±0.85 kGy (polythene). Low dose radiations were effective in reducing the contaminants to acceptable standards