Optimization of a cryoprotective medium to increase the viability of freeze-dried Streptococcus thermophilus by response surface methodology

Selection of a galactose-positive mutant strain of Streptococcus thermophilus and its optimized production as a high-vitality starter culture

Streptococcus thermophilus is a common starter in yogurt production and plays an important role in the dairy industry. In this study, a galactose-positive (Gal+) mutant strain, IMAU20246Y, was produced using the chemical mutagen N-methyl-N'-nitro-N-nitrosoguanidine (NTG) from wild-type S. thermophilus IMAU20246, which is known to have good fermentation characteristics. The sugar content of milk fermented by either the mutant or the wild type was determined using HPLC; metabolism of lactose and galactose was significantly increased in the mutant strain. In addition, we used response surface methodology to optimize components of the basic M17 medium for survival ratio of the mutant strain. Under these optimal conditions, the viable counts of mutant S. thermophilus IMAU20246Y reached 4.15 × 108 cfu/mL and, following freeze-drying in the medium, retained cell viability of up to 67.42%. These results are conducive to production of a high-vitality starter culture and development of "low sugar, high sweetness" dairy products.

Optimization of cryoprotectant formulation to enhance the viability of Lactiplantibacillus plantarum NBC99 isolated from human origin

Freeze drying has been well applied in the preparation of high-efficiency viability probiotic powders. However, the process is generally accompanied by probiotic viability deficiency, which poses a problem for further application. In this study, various kinds of cryoprotectant formulations (skim milk, maltodextrin, and sucrose) were tested to enhance the survival of Lactiplantibacillus plantarum NBC99 after freezing and freeze-drying. An I-optimal experimental design-oriented optimization model was presented to optimize the cryoprotective medium, and the highest cell survival was observed with 25% skim milk, 8.71% maltodextrin, and 1.13% sucrose cryoprotectant as the optimum condition. L. plantarum NBC99 has been a good potential strain for the manufacture of an industrial probiotic, and this research has aimed to investigate the long-term protective effects of optimum cryoprotectant formulations on the viability of bacteria. The results showed the potential value of freeze-dried probiotic L. plantarum NBC99 culture for commercialization.

Effect of freeze-dried protectants on the survival rate and fermentation performance of fermented milk's directed vat set starters

A directed vat set (DVS) starter was proposed to improve the drawbacks of liquid starters in fermented production and enhance the survival rates of B. animalis subsp. lactis BZ11, S. thermophilus Q-1, and Lactiplantibacillus plantarum LB12. The protective agent formula was optimized using the response surface method (RSM), with the survival rate as the benchmark. The best combination of cryoprotectants was determined to be BZ11: 10 % skimmed milk powder, 3 % sodium glutamate, and 15 % trehalose; LB12: 10 % skim milk powder, 5 % glutamate sodium, and 10 % trehalose; Q-1: 10 % skimmed milk powder, 3 % sodium glutamate, and 10 % trehalose. The survival rate of BZ11 significantly increased to 92.87 ± 1.25 %. The DVS fermented milk did not differ significantly from the control group regarding cholesterol removal, live cell counts and pH (p > 0.05). All DVS can be stored for at least 2500 d at -20 °C-this DVS starter for fermented milk benefits from its large-scale and automated commercial production.

Optimizing Conditions in the Acid Tolerance Test for Potential Probiotics Using Response Surface Methodology

Acid tolerance is an important feature of probiotic development. It is one of the factors underlying the beneficial effects of probiotics in the intestine. However, the methods used by different researchers to test acid tolerance vary, causing confusion in the interpretation of the results. Therefore, in this study, we determine the optimal conditions for the acid tolerance test using response surface methodology. The factors of pH (2.5 to 3.5), exposure time (1 to 2 h), and pepsin (presence or absence) were used as independent variables, and the survival rates of seven strains (Lacticaseibacillus casei KACC 12413, Lactiplantibacillus plantarum KACC 15357, Limosilactobacillus fermentum KACC 11441, Lactiplantibacillus plantarum WCFS1, Lacticaseibacillus rhamnosus GG, Lactiplantibacillus plantarum KCTC 21024, and Lactiplantibacillus plantarum WiKim 0112) known to have probiotic properties were used as dependent variables. The results of the analysis of variance (ANOVA) indicated that the pH value and exposure time in acidic environments significantly affected the acid tolerance test model, and their interaction also had an effect (P < 0.05). Using the ANOVA results, the condition of the acid tolerance test was optimized with a target of an 85% survival rate for each strain. The optimized conditions of the acid tolerance test were as follows: pH 2.92, exposure time of 1.73 h, and presence of pepsin and pH 3, exposure time of 1.98 h, and absence of pepsin. These results can optimize strain selection with rigorous acid tolerance without confusion by unifying the conditions for the acid tolerance test. IMPORTANCE The acid tolerance test, which is the first step in selecting probiotics, is not standardized and can often cause confusion in the interpretation of results. Thus, in the present study, we optimized the conditions for the acid tolerance test using response surface methodology. These optimized conditions can be used to screen for strains with acid tolerance.

Polysaccharides can improve the survival of Lactiplantibacillus plantarum subjected to freeze-drying

Freeze-drying is one of the most commonly used methods of bacteria preservation. During this process, cryoprotectants can greatly reduce cellular damage. Micromolecular cryoprotectants have been widely adopted but have limited selectivity and protective effects. Therefore, explorations of other types of cryoprotectants are needed. This study aimed to explore the possibility of the macromolecular cryoprotectants and combinations of cryoprotectants to maintain bacterial activity. We found that the survival rate of Lactiplantibacillus plantarum AR113 after freeze-drying was 19% higher in the presence of soy polysaccharides than with trehalose, the best-performing micromolecular cryoprotectant. Moreover, a 90.52% survival rate of L. plantarum WCFS1 was achieved using the composite cryoprotectant containing soy polysaccharide and trehalose, which increased by 31.48 and 36.47% compared with adding solely trehalose or soy polysaccharide, respectively. These results demonstrate that macromolecular and micromolecular cryoprotectants have similar effects, and that combinations of macromolecular and micromolecular cryoprotectants have better protective effects. We further observed that the composite cryoprotectant can increase Lactobacilli survival by improving cell membrane integrity and lactate dehydrogenase activity. Our finding provides a new type of cryoprotectant that is safer and more effective, which can be extensively applied in the relevant food industry.

Storage stability and sourdough acidification kinetic of freeze-dried Lactobacillus curvatus N19 under optimized cryoprotectant formulation

In this study, the response surface methodology was used to optimize the cryoprotective agent (skimmed milk powder, lactose and sucrose) formulation for enhancing the viability of Lactobacillus curvatus N19 during freeze-drying and storage stability of cells freeze-dried by using optimum formulation was evaluated. Our results showed that the most significant cryoprotective agent influencing the viability of L. curvatus N19 to freezing and freeze-drying was sucrose and skim milk, respectively. The optimal formulation of cryoprotective agents was 20 g/100 mL skim milk, 3.57 g/100 mL lactose and 10 g/100 mL sucrose. Using the optimum formulation during freeze-drying, the cell survival was found more than 98%. Under the optimal conditions, although only storage of the cells at 4 °C for 6 month retained the maximum stability (8.85 log cfu/g), the employed protectant matrix showed promising results at 25 °C (7.89 log cfu/g). The storage stability of cells under optimized conditions was predicted by accelerated storage test, which was demonstrated that the inactivation rate constant of the freeze-dried L. curvatus N19 powder was 9.74 × 10^-6 1/d for 4 °C and 2.08 × 10^-3 1/d for 25 °C. The loss of specific acidification activity after the storage at 4 and 25 °C was determined.

Optimization of Production Parameters for Probiotic Lactobacillus Strains as Feed Additive

In animal nutrition, probiotics are considered as desirable alternatives to antibiotic growth promoters. The beneficial effects of probiotics primarily depend on their viability in feed, which demands technical optimization of biomass production, since processing and storage capacities are often strain-specific. In this study, we optimized the production parameters for two broiler-derived probiotic lactobacilli (L. salivarius and L. agilis). Carbohydrate utilization of both strains was determined and preferred substrates that boosted biomass production in lab-scale fermentations were selected. The strains showed good aerobic tolerance, which resulted in easier scale-up production. For the freeze-drying process, the response surface methodology was applied to optimize the composition of cryoprotective media. A quadratic polynomial model was built to study three protective factors (skim milk, sucrose, and trehalose) and to predict the optimal working conditions for maximum viability. The optimal combination of protectants was 0.14g/mL skim milk/ 0.08 g/mL sucrose/ 0.09 g/mL trehalose (L. salivarius) and 0.15g/mL skim milk/ 0.08 g/mL sucrose/ 0.07 g/mL (L. agilis), respectively. Furthermore, the in-feed stabilities of the probiotic strains were evaluated under different conditions. Our results indicate that the chosen protectants exerted an extensive protection on strains during the storage. Although only storage of the strains at 4 °C retained the maximum stability of both Lactobacillus strains, the employed protectant matrix showed promising results at room temperature.

Impact of protectants on the storage stability of freeze-dried probiotic Lactobacillus plantarum

The ability of rice protein supplemented with various prebiotics to protect probiotic Lactobacillus plantarum TISTR 2075 upon freeze-drying and subsequent storage was determined. A combination of rice protein-fructooligosaccharide (RF) provided the best storage stability with the lowest specific rate of cell death (k) of 1.20 × 10-2 and 5.79 × 10-2 1/day during subsequent storage at 4 °C for 180 days and 30 °C for 90 days, respectively. Glass transition temperatures (T g) of freeze-dried probiotic in various protectants were 14.2-25.4 and 42.9-50.1 °C after storage at 4 and 30 °C, respectively. The functional properties of freeze-dried probiotic with protectants remained stable. The presence of RF could effectively protect and enhance the probiotic functionality during exposure to gastrointestinal tract conditions. The pathogenic inhibition of freeze-dried probiotic against foodborne pathogens was not different from the active cells. Protective agents were able to maintain high degrees of cell surface hydrophobicity.