Use of γ-irradiation to reduce high levels of Staphylococcus aureus on casein-whey protein coated moist beef biltong

Abstract Moist beef biltong strips (mean moisture content=53.6%, NaCl content=1.91% and a w =0.979) was inoculated with Staphylococcus aureus ATCC 9441 (10 6 –10 7  cfu/g), or sprayed with distilled water (non-inoculated controls). Both non-inoculated and inoculated biltong strips were coated with a casein–whey protein (1:1) edible coating followed by irradiation to a target dose of 4 kGy. S. aureus , aerobic plate, yeast and mould counts were performed to determine the effect of γ -irradiation and the edible coating on inoculated S. aureus and the spoilage flora of the biltong. Moisture and NaCl content, a w and pH measurements were also performed. None of the intrinsic properties were affected to a practically significant extent. Irradiation reduced all microbial counts ( P 0.05 ), i.e. inoculated S. aureus (⩾6 log cycles), aerobic plate count (5–6 log cycles) and yeast and mould counts (1–2 log cycles). Irradiation at 4 kGy is thus effective to ensure safety of moist beef biltong, and provided that initial fungal counts are not excessive, may extend the shelf-life. The edible coating had no significant effect ( P > 0.05 ) on microbial counts, possibly because the high moisture content of the biltong diminished its oxygen barrier properties.