Impact of the fermentation parameters pH and temperature on stress resilience of Lactobacillus reuteri DSM 17938

Abstract

This study was undertaken to investigate the impact of culture pH (4.5–6.5) and temperature (32–37 °C) on the stress resilience of Lactobacillus reuteri DSM 17938 during freeze-drying and post freeze-drying exposure to low pH (pH 2) and bile salts. Response-surface methodology analysis revealed that freeze-drying survival rates were linearly related to pH with the highest survival rate of 80% when cells were cultured at pH 6.5 and the lowest was 40% when cells were cultured at pH 4.5. The analysis further revealed that within the chosen temperature range the culture temperature did not significantly affect the freeze-drying survival rate. However, fermentation at pH 4.5 led to better survival rates when rehydrated cells were exposed to low pH shock or bile salts. Thus, the effect of pH on freeze-drying survival was in contrast to effects on low pH and bile salts stress tolerance. The rationale behind this irreconcilability is based on the responses being dissimilar and are not tuned to each other. Culturing strain DSM 17938 at pH values higher than 5.5 could be a useful option to improve the survivability and increase viable cell numbers in the final freeze-dried product. However, the dissimilar responses for the process- and application parameters tested here suggest that an optimal compromise has to be found in order to obtain the most functional probiotic product possible.

Antimicrobial and Antibiofilm Activities of Probiotic Lactobacilli on Antibiotic-Resistant Proteus mirabilis

“…We tested pH-adjusted supernatants of Lactobacillus , which is a commonly used approach in Lactobacillus probiotic studies to reduce the acidity of the Lactobacillus supernatants and thus assess if the antimicrobial activity of Lactobacillus products is pH-dependent [ 23 , 24 , 25 , 26 , 27 ]. This is significant given that studies showed that the acidic pH (due to lactic acid secretion) contributed only a small part of the activity [ 28 ], or did not contribute any additional activity (activity was pH-independent) [ 29 ].…”

Autolysis and Cell Death Is Affected by pH in L. reuteri DSM 20016 Cells

“…Predictably, when uMRS was used, pH values remained steady over time ( Figure 2 D). Presumably, this was because uMRS no longer contained the nutrients for the L. reuteri cells to generate further quantities of lactic acid [ 20 ]. This hypothesis is also consistent with data showing that depleting glucose from the media leads to both a higher pH and an increase in autolysis in L. lactis, and that excess glucose led to the inverse outcome of low pH and inhibition of autolysis [ 21 ].…”

“…In addition, UAD was already known to be a poor environment for bacterial lactic acid production compared to UAD’s sugar sweetened alternatives [ 22 ]. Moreover, lactic acid production ceases when the sugar in the culturing media is consumed [ 20 ]. In addition, fermented products made with sweetened almond drink lose substantial viability during storage [ 13 , 23 , 24 ].…”

Production of Probiotic Passion Fruit (Passiflora edulis Sims f. flavicarpa Deg.) Drink Using Lactobacillus reuteri and Microencapsulation via Spray Drying

“…It was observed that the sample with pH 3.18 when fermented at 30 • C showed the shortest generation time, followed by samples with pH adjusted to 5.5 at 20 • C and pH 6.5 at 10 • C. Although Lactobacillus reuteri showed excellent growth in the samples with pH 3.18 at 30 • C and 20 • C, the generation time (t g ) was greater than 2 h. Under optimal conditions, bacteria are the microorganisms with the highest growth rate and may have a generation time (t g ) of less than 1 hour. Hernandez and co-workers found higher growth rates and lower generation times when Lactobacillus reuteri DSM 17938 was cultured under commercial medium [31]. In terms of this, it is important to recognize that our study had as its aim the development and optimization of variables in the passion fruit pulp extracted from Passiflora edulis Sims f. flavicarpa Deg.…”

“…In our study, we designed a set of batch conditions to investigate and optimize the production of an innovative probiotic product, using both passion fruit pulp and Lactobacillus reuteri. In terms of lactic acid bacteria specifically, Lactobacillus reuteri is known as a culture that presents optimal growth between 25 and 40 • C, and that the growth development is dependent upon fermentation medium [31]. Here, for the first time, the passion fruit pulp (Passiflora edulis Sims f. flavicarpa Deg) was used as a medium for fermentation of Lactobacillus reuteri.…”