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Aims:  This work aimed at clarifying the physiological responses of Lactobacillus delbrueckii subsp. bulgaricus CFL1 cells after exposure to acidification at the end of fermentation, in relation to their cryotolerance. Methods and Results:  Cells acidified at the end of the fermentation (pH 5·25 for 30 min) had their cryotolerance improved as compared to the reference condition (pH 6·0). By analyzing the cytosolic proteome, it was established that changes occurred in the synthesis of 21 proteins, involved in energy metabolism, nucleotide and protein synthesis and stress response. Acidification also induced a slight decrease in unsaturated to saturated and cyclic to saturated membrane fatty acid ratios. Conclusions:  Lactobacillus bulgaricus CFL1 was able to develop a combined physiological response at both membrane and cytosolic levels. This acid adaptation was referred as a cross‐protection phenomenon as it allowed the cells to become more tolerant to cold stress. Significance and Impact of the Study:  This study increased knowledge concerning the physiological mechanisms that explained the cross‐protection by acid adaptation. It may be useful for improving cryotolerance of lactic acid bacteria, either in cells banks or in an industrial context.

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In this work, we propose the reuse of apple pomace as a substrate for fungal chitosan production by liquid cultivation of Gongronella butleri CCT4274. Different concentrations of reducing sugars and sodium nitrate were added to the aqueous extract of apple pomace and the best result was obtained with 40 g/L of reducing sugars and 2.5 g/L of sodium nitrate. The results indicate the possibility of producing 1.19 g/L of chitosan per liter of culture medium after 72.5 hours of cultivation, representing around 21% of the biomass content.

This work aimed at analyzing the effect of microfiltration conditions (cross-flow velocity and transmembrane pressure) on the quality of frozen Lactobacillus bulgaricus CFL1 starters produced on pilot scale. Microfiltered cells were less resistant during the concentration process than centrifuged cells. In contrast, bacterial cryotolerance during freezing was improved after microfiltration, in a range of 28-88%, depending on the microfiltration conditions. During frozen storage, cell resistance was also affected by microfiltration conditions, either positively or negatively, compared to centrifugation. The best cryotolerance was obtained for cells microfiltered at a cross-flow velocity of 2 m/s and a transmembrane pressure of 0.15 MPa. This improvement was explained by considering membrane fatty acid composition of Lb. bulgaricus CFL1. This condition increased unsaturated to saturated and cyclic to saturated fatty acid ratios, which enhanced membrane fluidity, thus helping the cells to better resist freezing and frozen storage.

As the concentration step is usually considered to be responsible for cell damage, the objective of this work was to quantify the effect of centrifugation conditions (speed, duration, temperature, and pH) on the quality of Lactobacillus bulgaricus CFL1 starters. These effects were analyzed on the specific acidification activity of the cells, according to experimental designs. It is surprising to note that centrifugation conditions did not significantly affect the loss of specific acidification activity during the concentration step. In contrast, centrifugation speed and duration slightly altered cell resistance to freezing and frozen storage. No difference was observed when centrifugation was conducted at 4 or 15°C. Finally, combining good centrifugation conditions to an acidification of the cells in their fermented broth strongly improved their cryotolerance. These results may have an impact for industrial starter production as they allowed modifying centrifugation conditions to better match the specificity and the viscosity of the medium.

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