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

Moist beef biltong strips (mean moisture content=53.6%, NaCl content=1.91% and aw=0.979) was inoculated with Staphylococcus aureus ATCC 9441 (106–107 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, aw and pH measurements were also performed. None of the intrinsic properties were affected to a practically significant extent. Irradiation reduced all microbial counts (P<0.05P<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>0.05P>0.05) on microbial counts, possibly because the high moisture content of the biltong diminished its oxygen barrier properties.