Lactic acid bacteria viability in different refrigerated food matrices: a systematic review and Meta‑analysis

The aim of this systematic review and meta-analysis was to determine which variables affect the viability of lactic acid bacteria (LAB) added to different types of refrigerated foods during the first 28 days. Scopus, ScienceDirect, PubMed and Cochrane Central Register of Reviews databases were searched from 1997 to April 2022. A total of 278 studies, which showed randomized and controlled experiments published in peer reviewed journals, were included. The viability of LAB in different moments during the storage process was synthesized as mean point estimate (MPE) via random-effects meta-analyses and the effect of multiple factors on the LAB´s viability was evaluated by multiple meta-regression. The meta-analysis showed that the decrease in LAB viability will be more abrupt the greater the initial dose. The physical structure of food may influence bacterial viability. Fruit was the type of product that most quickly lost viability. Co-culture of two or more species did not affect viability. Preservation methods had an unfavorable effect and prebiotics had a beneficial effect on bacterial viability. Viability was genus dependent. The data obtained in this study provide an overview of the factors to be taken into account for the design of new foods.

Optimization of cultural conditions for enhancement of anti-quorum sensing potential in the probiotic strain Lactobacillus rhamnosus GG against Pseudomonas aeruginosa

Disruption of quorum sensing (QS) system, which is a central regulator for pathogenesis of Pseudomonas aeruginosa, is referring to as quorum quenching (QQ). This study was undertaken to evaluate and enhance the anti-quorum sensing (AQS) potential of probiotic strain Lactobacillus rhamnosus GG. The cell-free supernatant (CFS) of this probiotic strain showed anti-quorum sensing activity against Pseudomonas aeruginosa, which was determined using well-diffusion agar-plate assay. Anti-quorum sensing potential of L. rhamnosus GG was enhanced by optimization of various cultural conditions using classical and statistical optimization approaches. Six variables were optimized using one-variable-at-a-time (OVAT) method. Four significant variables, viz., temperature, pH, incubation time, metal ion, and its concentration, were chosen for further optimization by response surface methodology (RSM) using central composite design (CCD). Analysis of variance (ANOVA) demonstrated that the regression model is highly significant, as indicated by F test with a low probability value (p  < 0.0002) and high value of coefficient of determination (0.8738) and also had significant influence on the generation of anti-quorum sensing effector molecules. Maximum production of anti-quorum sensing activity, in terms of zones of inhibition, was achieved under the following optimized conditions such as 37 °C temperature, pH 6.5, incubation time 24 h, and 2.5 mM concentration of zinc sulfate (ZnSO₄). The quadratic model predicted 1.3-fold increase anti-quorum sensing activity production over un-optimized cultural conditions. The present research is the first report representing the enhancement of anti-quorum sensing potential of L. rhamnosus GG.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03187-2.

Co-Culture Probiotic Fermentation of Protein-Enriched Cereal Medium (Boza)

Objective: Boza is a fermented cereal beverage which is produced by co-culture fermentation of lactic acid bacteria and yeasts. In addition to the nutritional properties of cereals used in the production, it is also suitable to be gaining functional properties by fermenting with probiotic microorganisms.Methods: In this study, protein content of probiotic boza was increased by the addition of gluten, zein and chickpea flour and the volatile compounds formed during co-culture fermentation of the cereal medium with Lactobacillus acidophilus, Bifidobacterium bifidum and Saccharomyces boulardii were determined.Results: It was determined that chickpea added boza provided the highest cell counts of Lactobacillus acidophilus (7.92 logs CFU/g), Bifidobacterium bifidum (7.32 log CFU/g) and Saccharomyces boulardii (3.26 log CFU/g) during storage. With the addition of gluten, the protein content of the sample was enriched four times more when compared with control boza. During fermentation and storage, a total of 36 different compounds were identified with the major compounds as 9,12-octadecadienoic acid, 9-octadecenoic acid, hexadecanoic acid and hexadecanoic acid, 2-hydroxy-1-(hydroxymethyl)ethyl ester. The concentration of volatile compounds generally decreased during storage of samples. According to Principle Cluster Analysis results, enriched protein samples had similar projections due to their fatty acid contents and the main difference was shown in the control sample.Conclusions: The results of this study indicate that chickpea, single or mixture with cereals, can be a good substrate for probiotic microorganism production for acceptance as probiotic foods.