Storage Temperature Effects on <i>Bacillus</i> Spores and <i>Lactobacillus acidophilus</i> Viability

This study investigated the impact of various storage temperatures on the viability of four commercial probiotic strains: <i>Lactobacillus acidophilus</i> (<i>LA-1</i>) vegetative cells, <i>Bacillus subtilis</i> 1 spores, <i>ProSilience Bacillus subtilis HU58</i> (<i>HU58</i>) spores, and <i>Bacillus coagulans GBI-30</i>, <i>6086</i> (<i>BC30</i>) spores. These probiotics were incorporated into cookies and crackers, which were then stored at 25°C, 4°C, and -18°C for 12 months. Evaluations were conducted at eight different time points throughout the storage period. Among the probiotics tested, the <i>B. subtilis</i> spores exhibited the greatest stability, showing < 2 log reductions under all conditions over the 12 months. In contrast, <i>LA-1</i> cells were the least stable, falling below the minimum therapeutic level for probiotic microorganisms in a food product (10⁶ CFU/g) after just 2 months in crackers and 4 months in cookies. <i>BC30</i> spores were more sensitive to temperature changes than the other <i>Bacillus</i> strains (<i>B. subtilis 1</i> and <i>HU58</i>), with > 4 log reductions. This study also revealed that different probiotics have distinct optimal storage conditions. However, storage temperature had no significant effect on the viability of <i>B. subtilis</i> 1 spores, <i>BC30</i> spores, and <i>LA-1</i> vegetative cells. In contrast, <i>HU58</i> spores were notably affected by temperature during the final months of storage. Specifically, samples held at 25°C showed significantly higher log reductions compared to those stored at cooler temperatures, highlighting HU58's sensitivity to temperature, particularly with longer storage periods. Throughout the storage period, both <i>BC30</i> spores and <i>LA-1</i> cells experienced substantial increases in log reductions. Overall, this study highlights the importance of selecting appropriate storage conditions for different probiotic strains to maintain their viability in food products over extended periods.