Control of Listeria monocytogenes by low-dose irradiation in combination with refrigeration in the soft whey cheese ‘Anthotyros’

Abstract

Soft whey cheese ‘Anthotyros’ has the following characteristics: moisture content 65%, protein content 9·6%, fat content 16·6%, salt concentration in the aqueous phase below 1% and pH 6·4. The average counts of the product were 4·54, 3·80, and 1·2 log cfu g−1 for aerobic mesophilic bacteria, yeasts and Enterobacteriaceae, respectively. The feasibility of gamma radiation for eliminating Listeria monocytogenes Scott A inoculated into the freshly produced product, and following its counts during refrigerated storage at 4 and 10°C under vacuum packaging was investigated. Cheese samples were exposed to doses of 0·5, 2 and 4 kGy of gamma irradiation at 4°C. Irradiation at 0·5 kGy slightly reduced the aerobic mesophilic bacteria counts, while irradiation doses at 2 and 4 kGy reduced the microbial load by approximately 1–2 log cycles. Enterobacteriaceae could not be detected in irradiated samples. Irradiation decreased the yeast population which was detected during later stages of storage. Molds were not detected in any of the samples. The calculatedD10 -value for L. monocytogenes was 1.38 kGy. Surviving microbial cells could be detected throughout the entire period of 42 days storage. Sensory scores indicated that irradiation doses up to 4 kGy do not adversely affect ‘Anthotyros’ sensory properties.