Effects of yeast extract and different amino acids on the dynamics of some components in cabbage juice during fermentation with Bifidobacterium lactis BB-12

The growth-promoting effects of protein hydrolysates and their derived peptides on probiotics: structure-activity relationships, mechanisms and future perspectives

Lactic acid bacteria (LAB) are the main probiotics currently available in the markets and are essential for maintaining gut health. To guarantee probiotic function, it is imperative to boost the culture yield of probiotic organisms, ensure the sufficient viable cells in commercial products, or develop effective prebiotics. Recent studies have shown that protein hydrolysates and their derived peptides promote the proliferation of probiotic in vitro and the abundance of gut flora. This article comprehensively reviews different sources of protein hydrolysates and their derived peptides as growth-promoting factors for probiotics including Lactobacillus, Bifidobacterium, and Saccharomyces. We also provide a preliminary analysis of the characteristics of LAB proteolytic systems focusing on the correlation between their elements and growth-promoting activities. The structure-activity relationship and underlying mechanisms of growth-promoting peptides and their research perspectives are thoroughly discussed. Overall, this review provides valuable insights into growth-promoting protein hydrolysates and their derived peptides for proliferating probiotics in vivo or in vitro, which may inspire researchers to explore new options for industrial probiotics proliferation, dairy products fermentation, and novel prebiotics development in the future.

Effect of the initial pH of the culture medium on the nutrient consumption pattern of Bifidobacterium animalis subsp. lactis Bb12 and the improvement of acid resistance by purine and pyrimidine compounds

AIMS

During fermentation, the accumulation of acidic products can induce media acidification, which restrains the growth of Bifidobacterium animalis subsp. lactis Bb12 (Bb12). This study investigated the nutrient consumption patterns of Bb12 under acid stress and effects of specific nutrients on the acid resistance of Bb12.

METHODS AND RESULTS

Bb12 was cultured in chemically defined medium (CDM) at different initial pH values. Nutrient consumption patterns were analyzed in CDM at pH 5.3, 5.7, and 6.7. The patterns varied with pH: Asp + Asn had the highest consumption rate at pH 5.3 and 5.7, while Ala was predominant at pH 6.7. Regardless of the pH levels (5.3, 5.7, or 6.7), ascorbic acid, adenine, and Fe2+ were vitamins, nucleobases, and metal ions with the highest consumption rates, respectively. Nutrients whose consumption rates exceeded 50% were added individually in CDM at pH 5.3, 5.7, and 6.7. It was demonstrated that only some of them could promote the growth of Bb12. Mixed nutrients that could promote the growth of Bb12 were added to three different CDM. In CDM at pH 5.3, 5.7, and 6.7, it was found that the viable cell count of Bb12 was the highest after adding mixed nutrients, which were 8.87, 9.02, and 9.10 log CFU ml-1, respectively.

CONCLUSIONS

The findings suggest that the initial pH of the culture medium affects the nutrient consumption patterns of Bb12. Specific nutrients can enhance the growth of Bb12 under acidic conditions and increase its acid resistance.

Fermentation optimization and kinetic model for high cell density culture of a probiotic microorganism: Lactobacillus rhamnosus LS-8

To develop a practical food-grade medium and optimal fermentation process for the cost-effective fermentation of Lactobacillus rhamnosus LS-8, both culture medium and conditions were optimized by combining single-factor experimental design, Plackett-Burman design and Box-Behnken design. The medium was simplified to five ingredients (g/L): whey powder (62.5), maltose syrup (50), corn steep liquor (55), NaCl (1) and lysine (0.05), and the optimal culture conditions were initial pH (6.28), constant fermentation pH (4.7), neutralizing agent (NaOH), aeration rate (0.2 v/v/min) and stirrer speed (200 rpm). After culturing in this optimized medium and conditions, the cell density of L. rhamnosus LS-8 was improved to 4.5 × 10⁹ CFU/mL, which was elevated about 9 times higher than that obtained in MRS medium. Moreover, cell growth and substrate consumption kinetic constants were determined by the logistic equation and Luedeking-Piret model, and the R² values from the model equation were 0.9900 and 0.9971, respectively, indicating that these models were able to simulate the growth and substrate consumption of L. rhamnosus LS-8 accurately. In addition, a high-efficient production process of L. rhamnosus LS-8 was developed by repeated-batch operation, which was verified by five cycles of fermentation with good stability and repeatability. In conclusion, the efficiency of L. rhamnosus LS-8 fermentation was greatly improved as well as the reduction of the cost using the medium and process developed in the present study.