Enhancing spray-drying tolerance of Lactobacillus bulgaricus via non-sporeforming dormancy induction

Employing 0.64 mg/mL of rifampin (RFP) for dormancy induction of Lactobacillus bulgaricus sp 1.1, a 2.5-fold survival rate was achieved after spray drying, while the dried bacteria displayed delayed acidifications . Under the same condition for dormancy treatment, division analysis indicated that high proportions of cells would enter into a dormant state with around 90% of non-proliferating bacteria in the original population. Cells shrank with median diameters decreasing from 3.23 to 2.98 μm. The Raman spectrum revealed a lower ATP level, varied protein expression profiles and conformations and saccharides accumulation in bacteria. Protein aggregates formed in dormancy-induced cells may contribute to increased heat resistance which showed a 2 °C rise in the denaturing temperature in the 0.64 mg/mL group. Therefore, dormancy treatments may be developed as a protective strategy for spray-dried L . bulgaricus . Industrial relevance Enhancing the drying tolerance of bacteria is one of the crucial strategies to adapt the industrial production of spray-dried LAB . Our study proved that the non-sporeforming dormancy pre-treatment can promote the spray-dried viability of L . bulgaricus by triggering suppressed metabolism activity and protein aggregation. The non-sporeforming dormant state has potential to be exploited in industrial production of spray-dried LAB with a high viable cell density to reduce the cost of probiotics and related products.