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Aims To help cells to better resist the stressful conditions associated with the freeze-drying process during starter production, we investigated the effect of various osmotic conditions on growth, survival and acidification activity of Lactobacillus buchneri R1102, after freeze-drying and during storage for 3 months at 25°C. Methods and Results High survival rates during freeze-drying, but not during storage, were obtained when 0·1 mol l−1 KCl was added at the beginning of fermentation, without any change in membrane properties and betaine accumulation. This condition made it possible to maintain a high acidification rate throughout the process. In contrast, the addition of 0·6 mol l−1 KCl concentrations at the beginning of fermentation led to a high survival rate during storage that was related to high intracellular betaine levels, low membrane fluidity and high cycC19:0 concentrations. However, these modifications induced the degradation of acidification activity during storage. When a moderate stress was applied by combining 0·1 mol l−1 KCl at the beginning and 0·6 mol l−1 KCl at the end of fermentation, betaine accumulated in the cells without any membrane alteration, allowing them to maintain high acidification activity and survival rate during storage. Conclusion Specific osmotic conditions during fermentation induced intracellular betaine accumulation and modifications of membrane character-istics, thus affecting stress resistance of Lact. buchneri R1102. A slight osmotic stress made it possible to maintain a high acidification activity, whereas a high osmotic stress at the end of fermentation led to the preservation of cell survival during freeze-dried storage. Significance and Impact of the Study This study revealed that the survival and preservation of acidification activity of freeze-dried Lact. buchneri R1102 during starter production can be improved by using appropriate osmotic conditions. [ABSTRACT FROM AUTHOR]

Abstract Aim: To study the effect of casein-derived peptides, accumulated during growth of Lactococcus lactis in milk, on its oligopeptide transport (Opp) function. Methods and Results: This effect was estimated by analysing the ability of casein-derived peptides to compete for the transport of a reporter peptide by whole L. lactis cells. The transport of the reported peptide was monitored by determining the intracellular concentrations of the corresponding amino acids by means of reverse-phase high-performance liquid chromatography (HPLC). Uptake of the reporter peptide was competitively inhibited by casein-derived peptides. The competition was only because of charged casein-derived peptides, including anionic peptides. The design of specific pure peptides made it possible to evidence for a positive (or negative) influence exerted by the positively (or negatively) charged side chain of the N-terminal amino acid on the competition. Conclusions: Charged casein-derived peptides impaired the oligopeptide transport function of L. lactis . Significance and Impact of the Study: These results demonstrate an inhibition of Opp when too many peptides are produced by the proteinase. Peptide transport by Opp therefore represents a bottleneck for increasing the growth rate of L. lactis in milk. [ABSTRACT FROM AUTHOR]

Aims: The present work aimed to define a minimal chemically-defined medium which could sustain the growth of most (if not all) strains of Streptococcus thermophilus. Methods and Results: A minimal medium containing 20 components, including one carbohydrate source, six amino acids, two metallic ions, six vitamins and urea allowed for growth of 13 out of 15 Strep. thermophilus strains. Growth of the two last strains required the presence of additional amino acids, the number of which depended on the strain. Growth rates of the strains in the minimal medium ranged from 0·38 to 0·64 h–1, and final populations were about 108 cfu ml–1. Conclusions: Streptococcus thermophilus appears much less demanding than other lactic acid bacteria. Significance and Impact of the Study: The definition of such a growth medium will be very useful for metabolic flux studies as well as peptide transport studies. [ABSTRACT FROM AUTHOR]