Control of Alicyclobacillus acidoterrestris spore and Byssochlamys ascospore growth in ambient acid dairy products through organic acid and heat treatments

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Spore-forming microorganisms pose a significant spoilage risk in ambient acid dairy-based products. This study investigated the individual and combined effects of organic acids and heat treatments on controlling Alicyclobacillus acidoterrestris spores and Byssochlamys ascospores under conditions relevant to ambient acid dairy products (pH 4.6). Potassium Sorbate (PS) demonstrated the second highest antimicrobial efficacy among the tested organic acids, with MICs of 0.8-1.6 mg/mL against A. acidoterrestris and 0.8 mg/mL against Byssochlamys species. In broth, PS ≥ 0.5 mg/mL alone or combined with any of the heat treatments used in this study effectively controlled A. acidoterrestris spore outgrowth at 25 °C and 40 °C. Control of Byssochlamys ascospores required 0.8 mg/mL PS alone or 0.5 mg/mL PS combined with heat (85 °C for 10 min) or heat (95 °C for 30 s) when stored at 25 °C; but when storing at 40 °C, PS (0.5 mg/mL or 0.8 mg/mL) alone or heat treatment (95 °C for 30 s) alone was sufficient. Validation in drinking yoghurt confirmed that PS alone (0.5 mg/mL or 0.8 mg/mL) prevented A. acidoterrestris outgrowth at 40 °C, while only 0.8 mg/mL PS combined with 75 °C for 20 min heat treatment achieved complete inhibition of B. fulva ascospores when yoghurt was stored at 40 °C over 12 weeks. These findings provide a practical multi-hurdle strategy for ensuring the microbiological stability of ambient acid dairy products against heat-resistant spoilage organisms.