Screening of an efficient cholesterol-lowering strain of Lactiplantibacillus plantarum 54-1 and investigation of its degradation molecular mechanism

Active induction: a promising strategy for enhancing the bioactivity of lactic acid bacteria

Lactic acid bacteria (LAB), as key probiotic, play crucial roles in maintaining human health. However, their survival and functionality in diverse habitats depend on their ability to sense and respond to environmental stresses. Notably, active induction has emerged as a promising strategy for regulating the biological activity of LAB, potentially enhancing their health benefits. Therefore, this review summarizes the beneficial effects of active induction, including acid, bile, oxidation, ethanol, heat, cold, and radiation induction on the functional activities of LAB. In addition, omics methods, in silico analysis, and gene editing technologies have greatly facilitated the profound exploration of the stress regulatory network in LAB, thereby aiding the identification of active components and stress adaptors. Through these advancements, LAB provide health benefits by regulating stress-related genes and proteins, as well as inducing bioactive metabolite production. As a result, they could enhance stress tolerance, cross-protection, intestinal colonization, adhesion properties, and provide antialcohol and liver protection in vitro or in vivo. This study highlights the potential of active induction strategies in enhancing the functional role of LAB in food applications.

Accumulation of Water-Soluble Polysaccharides during Lychee Pulp Fermentation with Lactiplantibacillus plantarum Involves Endoglucanase Expression

In the current work, lychee pulp was subjected to Lactiplantibacillus plantarum ATCC 14917 fermentation, leading to a substantial increase (2.32-2.67-fold) in water-soluble polysaccharides (WSP). Concurrently, a significant degradation occurred in water-insoluble polysaccharides (WISP) composed of glucose (28.73%), arabinose (28.25%), galacturonic acid (25.07%), and galactose (11.00%). To clarify polysaccharide conversion and its relevant mechanism, carbohydrate-active enzyme encoding sequences in the L. plantarum ATCC 14917 genome and structural alterations of two polysaccharide fractions were dissected. By integrating the transcriptional assay, prokaryotic expression, and enzymic hydrolysis, three endoglucanases were demonstrated to catalyze WISP degradation, leading to WSP accumulation during lychee pulp fermentation with L. plantarum ATCC 14917. Reductions in proportions of galactose and galacturonic acid in WSPs were partly attributed to the actions of multiple galactosidases. These findings provide an enzyme-based explanation for WSP accumulation during Lactobacillus fermentation and serve as a practical foundation for directional polysaccharide conversion.

Effect of ultrasonic pretreatment with synergistic microbial fermentation on tenderness and flavor of air-dried duck under low nitrite process

The tenderness and flavor of meat products are critical factors influencing consumers' purchasing decisions. This study investigated the effects of ultrasonic pretreatment with synergistic microbial strain fermentation on tenderness and flavor of air-dried duck under low nitrite process. The results demonstrated that ultrasonic pretreatment combined with microbial strain fermentation improved water retention and tenderness of duck meat by disrupting the muscle microstructure, increasing muscle fiber spacing, and facilitating water migration and distribution. This primarily concerns the cavitation and mechanical effects of ultrasound and the role of lactic acid bacteria and yeasts in muscle protein hydrolysis. A total of 34 and 55 volatile flavor compounds were detected by HS-SPME-GC-MS and GC-IMS, respectively. The results indicated that acetaldehyde (stimulating, fruity, green apple), ethyl acetate (sweet, fruity, pineapple), and 3-hydroxy-2-butanone (sweet, creamy) were responsible for the improved flavor during this process, which was primarily related to the increased activity of neutral lipase (0.38 U/g protein), acidic lipase (0.48 U/g protein), and phospholipase (0.09 U/g protein). This study provides valuable insights into the synergistic effects of ultrasonic pretreatment and microbial co-fermentation, offering a theoretical basis for optimizing air-dried duck production and enhancing flavor quality.

Limosilactobacillus fermentum CGMCC 1.7434 and Debaryomyces hansenii GDMCC 2.149 synergize with ultrasound treatment to efficiently degrade nitrite in air-dried ducks

Nitrites in meat products are important food additives with coloring, antibacterial and antioxidant effects, but excessive intake of nitrites can pose health risks, including an increased risk of cancer due to the formation of carcinogenic nitrosamines. In the present study, Limosilactobacillus fermentum CGMCC 1.7434 was screened and the effects of it and Debaryomyces hansenii GDMCC 2.149 and their combination on nitrite degradation were investigated. It was found that the co-culture of L. fermentum CGMCC 1.7434 and D. hansenii GDMCC 2.149 significantly enhanced nitrite degradation (99.58%). The findings on salt and ethanol tolerance suggest suitability for application in meat fermentation processes. Scanning electron microscopy and additional data indicate that D. hansenii GDMCC 2.149 facilitates the growth, acid production, adhesion, secretion of AI-2 signaling molecules, and biofilm formation of L. fermentum CGMCC 1.7434. Metabolomics analysis suggests that these microorganisms reduce nitrite levels by converting NH3 derived from nitrite into L-glutamine, which is further transformed into N-nitroso compounds and their downstream derivatives through the ABC transporter pathway, the TCA cycle, and the amino acid metabolism pathway. Microbial community analyses showed that L. fermentum CGMCC 1.7434 and D. hansenii GDMCC 2.149 were successfully inoculated into air-dried ducks, becoming dominant strains and effectively inhibiting the growth of pathogenic bacteria. Furthermore, during the processing of air-dried duck, the combination of ultrasonic cavitation (250 W, 4 min, 30°C, 40 kHz) with the co-fermentation of L. fermentum CGMCC 1.7434 and D. hansenii GDMCC 2.149 effectively reduced nitrite content (84.55%) and TVB-N levels in the meat, without compromising color or TBARS values. This is crucial for understanding the mechanism of nitrite degradation by LAB in synergy with yeast and for the advancement of low-nitrite air-dried duck products.

The Role of Autochthonous Levilactobacillus brevis B1 Starter Culture in Improving the Technological and Nutritional Quality of Cow's Milk Acid-Rennet Cheeses-Industrial Model Study

In the study, an attempt was made to develop an innovative technology for cheese manufacturing. It was hypothesized that selected autochthonous lactic acid bacteria as a starter culture are more suitable for the production of acid-rennet cheeses of good technological and sensory quality. The study aimed to assess the possibility of using the strain Levilactobacillus brevis B1 (L. brevis B1) as a starter culture to produce acid-rennet cheeses using raw cow's milk. Two variants of cheese were manufactured. The control variant (R) was coagulated with microbial rennet and buttermilk, and the other variant (B1) was inoculated with rennet and L. brevis B1 starter culture. The effect of the addition of these autochthonous lactic acid bacteria on selected physicochemical characteristics, durability, the composition of fatty acids, cholesterol, Iipid Quality Indices, and microbiological and sensory quality of acid-rennet cheeses was determined during a 3-month period of storage. The dominant fatty acids observed in the tested cheeses were saturated fatty acids (SFA) (68.43-69.70%) and monounsaturated fatty acids (MUFA) (25.85-26.55%). Significantly higher polyunsaturated fatty acid (PUFA) content during storage was observed for B1 cheeses. The B1 cheeses were characterized by lower cholesterol content compared to cheese R and showed better indexes, including the Index of atherogenicity, Index of thrombogenicity, DFA, OFA, H/H, and HPI indexes, than the R cheese. No effect of the tested L. brevis B1 on sensory quality was observed in relation to the control cheeses during 3 months of storage. The results of the research indicate the possibility of using the L. brevis B1 strain for the production of high-quality, potentially probiotic acid-rennet cheeses.