Investigating Safety and Technological Traits of a Leading Probiotic Species: Lacticaseibacillus paracasei

Lacticaseibacillus spp. are genetically close lactic acid bacteria species widely used in fermented products for their technological properties as well as their proven beneficial effects on human and animal health. This study, the first to include such a large collection of heterogeneous isolates (121) obtained from international collections belonging to Lacticaseibacillus paracasei, aimed to characterize the safety traits and technological properties of this important probiotic species, also making comparisons with other genetically related species, such as Lacticaseibacillus casei and Lacticaseibacillus zeae. These strains were isolated from a variety of heterogeneous sources, including dairy products, sourdoughs, wine, must, and human body excreta. After a preliminary molecular characterization using repetitive element palindromic PCR (Rep-PCR), Random Amplification of Polymorphic DNA (RAPD), and Sau-PCR, particular attention was paid to safety traits, evaluating antibiotic resistance profiles, biogenic amine (BA) production, the presence of genes related to the production of ethyl carbamate and diaminobenzidine (DAB), and multicopper oxidase activity (MCO). The technological characteristics of the strains, such as the capability to grow at different NaCl and ethanol concentrations and different pH values, were also investigated, as well as the production of bacteriocins. From the obtained results, it was observed that strains isolated from the same type of matrix often shared similar genetic characteristics. However, phenotypic traits were strain-specific. This underscored the vast potential of the different strains to be used for various purposes, from probiotics to bioprotective and starter cultures for food and feed production, highlighting the importance of conducting comprehensive evaluations to identify the most suitable strain for each purpose with the final aim of promoting human health.

Citrulline Accumulation Mechanism of Pediococcus acidilactici and Weissella confusa in Soy Sauce and the Effects of Phenolic Compound on Citrulline Accumulation

Citrulline is one of the major precursors of ethyl carbamate in soy sauce, and the accumulation of citrulline is attributed to the metabolism of arginine by bacteria with the arginine deiminase (ADI) pathway. However, key strains and factors affecting citrulline accumulation are not yet clear. In this study, two key strains of Pediococcus acidilactici and Weissella confusa were isolated from soy sauce moromi, and the regularity of citrulline formation was studied. Results showed that the conversion rates from arginine to citrulline (A/C rate) and the citrulline accumulation ability of W. confusa and P. acidilactici significantly increased in the presence of different concentrations of NaCl, indicating that salt stress was the main factor for citrulline accumulation. The inconsistent expression of arc genes by salt stress was the reason for citrulline accumulation for P. acidilactici, but for W. confusa, it may be due to the influence of arginine/citrulline on the transportation system: the intracellular citrulline could neither transport to extracellular space nor convert into ornithine. Environmental factors greatly influenced citrulline accumulation of the two key bacteria; A/C rate and citrulline formation in both strains decreased at low temperature (15°C) under high salt stress, but opposite effects were observed for the two key strains under anaerobic light condition. Moreover, quercetin and gallic acid significantly decreased the A/C rate and citrulline accumulation ability of the two key strains. The optimal quercetin and gallic acid as suggested by simulation experiment were 100 and 10 mg/l, respectively, and the lowest A/C rate of 28.4% and citrulline level of 1326.7 mg/l were achieved in the simulation system. This study explored the main factors for citrulline formation by the two key strains and proposed a targeted way to control citrulline in soy sauce.

Application of bamboo leaves extract to Chinese yellow rice wine brewing for ethyl carbamate regulation and its mitigation mechanism

Bamboo leaves extract (BLE) contains various effective ingredients, including phenolic compounds. In this study, the effect of BLE on ethyl carbamate (EC) formation was investigated in Chinese yellow rice wine brewing with three different fermentation starters (Saccharomyces cerevisiae, Saccharomyces cerevisiae and Lactobacillus brevis, and Chinese yeast). As a result, BLE showed significant inhibition effect on EC in multi-microbial fermented rice wine, by preventing the reactions between urea/citrulline and ethanol. We found that BLE had influence on arginine transport (GAP1, CAN1, ALP1, and VBA2 gene) in Saccharomyces cerevisiae (S. cerevisiae), which significantly up-regulated arginine uptake gene expression in vacuole (VBA2 gene) so that inhibited arginine metabolism. Besides, the presence of BLE could improve the overall quality of Chinese yellow rice wine. Consequently, it was worthwhile applying BLE to Chinese rice wine fermentation, especially the wine brewing with S. cerevisiae and Lactobacillus brevis starter.

Ethyl Carbamate Formation Regulated by Lactic Acid Bacteria and Nonconventional Yeasts in Solid-State Fermentation of Chinese Moutai-Flavor Liquor

This study aimed to identify specific microorganisms related to the formation of precursors of EC (ethyl carbamate) in the solid-state fermentation of Chinese Moutai-flavor liquor. The EC content was significantly correlated with the urea content during the fermentation process (R² = 0.772, P < 0.01). Differences in urea production and degradation were found at both species and functional gene levels by metatranscriptomic sequencing and culture-dependent analysis. Lactobacillus spp. could competitively degrade arginine through the arginine deiminase pathway with yeasts, and most Lactobacillus species were capable of degrading urea. Some dominant nonconventional yeasts, such as Pichia, Schizosaccharomyces, and Zygosaccharomyces species, were shown to produce low amounts of urea relative to Saccharomyces cerevisiae. Moreover, unusual urea degradation pathways (urea carboxylase, allophanate hydrolase, and ATP-independent urease) were identified. Our results indicate that EC precursor levels in the solid-state fermentation can be controlled using lactic acid bacteria and nonconventional yeasts.

Formation of ethyl carbamate in Goji wines: Effect of Goji fruit composition

Ethyl carbamate (EC) is a multisite carcinogen widely occurring in alcoholic beverages. In this investigation, solid-phase extraction combined with gas chromatography mass spectrometry was employed to determine EC contents during the fermentation and storage processes, and the effects of Goji varieties on its formation were also examined. The results indicated that natural and potential EC contents were significantly affected by the varied composition of Goji fruits. The analysis of chemical properties showed differences in hundred-grain weight, water contents, amino acids, and nitrogen-to-carbon ratio for Goji berries. Citrulline was completely degraded although it is routinely considered as a non-preferred nitrogen for yeasts. Due to compositional differences, Goji wines accumulated distinct urea levels that positively correlated with the potential EC contents. Furthermore, the temperature in both the production processes highly influenced EC formation. These results contribute to a more comprehensive understanding of EC formation, and in turn, controlling EC in the Goji wine matrix.

Bacterial Diversity Analysis during the Fermentation Processing of Traditional Chinese Yellow Rice Wine Revealed by 16S rDNA 454 Pyrosequencing

Rice wine is a traditional Chinese fermented alcohol drink. Spontaneous fermentation with the use of the Chinese starter and wheat Qu lead to the growth of various microorganisms during the complete brewing process. It's of great importance to fully understand the composition of bacteria diversity in rice wine in order to improve the quality and solve safety problems. In this study, a more comprehensive bacterial description was shown with the use of bacteria diversity analysis, which enabled us to have a better understanding. Rarefaction, rank abundance, alpha Diversity, beta diversity and principal coordinates analysis simplified their complex bacteria components and provide us theoretical foundation for further investigation. It has been found bacteria diversity is more abundant at mid-term and later stage of brewing process. Bacteria community analysis reveals there is a potential safety hazard existing in the fermentation, since most of the sequence reads are assigned to Enterobacter (7900 at most) and Pantoea (7336 at most), followed by Staphylococcus (2796 at most) and Pseudomonas (1681 at most). Lactic acid bacteria are rare throughout the fermentation process which is not in accordance with other reports. This work may offer us an opportunity to investigate micro ecological fermentation system in food industry.