Lacticaseibacillus casei K11 exerts immunomodulatory effects by enhancing natural killer cell cytotoxicity via the extracellular regulated-protein kinase pathway.

PURPOSE: Probiotics can serve as immunomodulators that regulate the activation of immune cells. This study aimed to screen potential probiotic strains that can enhance NK cell toxicity to improve host immunity. METHODS: In this investigation, we examined three potential probiotic strains, namely Lactiplantibacillus plantarum YZX21 (YZX21), Bifidobacterium bifidum FL-276.1 (FL-276.1) and Lacticaseibacillus casei K11 (K11), to assess their capacity in modulating NK cytotoxicity both in vitro and in vivo, while elucidating the underlying mechanisms involved. RESULTS: The findings demonstrated that K11 exhibited superior efficacy in enhancing NK cytotoxicity. Subsequent analysis revealed that K11 significantly augmented the secretion of perforin and granzyme B by NK cells through activation of receptors NKp30 and NKp46 via the extracellular signal-regulated kinase (ERK) pathway. Furthermore, heat-inactivated K11 also enhanced NK cell activity to an extent comparable to live bacteria, with lipoteichoic acid from K11 identified as a crucial factor mediating the activation of NK cell cytotoxicity. CONCLUSION: Our study suggests that K11 may have potential applications as probiotics or postbiotics for regulating NK cell cytotoxicity to enhance immunity.

Protective effects of Bifidobacterium bifidum FL-228.1 on dextran sulfate sodium-induced intestinal damage in mice.

PURPOSE: Numerous studies have found that probiotics benefit the intestinal barrier. However, the prophylactic effects of probiotics on the intestinal barrier, i.e., if probiotics exert protective effects in healthy individuals to defend them against harmful elements, have seldomly been reported. The present study aimed to investigate the possible mechanisms of potential strains with the function of preventing intestinal barrier damage. METHODS: This study investigated nine potential probiotic strains using in vitro and in vivo models on their intestinal barrier-protecting properties. Transcriptomic was then employed to decipher the underlying mechanisms of action of the strains. RESULTS: The results showed that the strains, to varying degrees, regulated the ratio of interleukin (IL)-10 and IL-12 in peripheral blood mononuclear cells (PBMCs), increased the transepithelial electrical resistance (TEER) values, and decreased Caco-2 cell monolayers permeability. Correspondingly, the strains showed different prophylactic efficacies in protecting mice from dextran sulfate sodium (DSS)-induced intestinal barrier damage. Remarkably, Bifidobacterium bifidum FL-228.1 (FL-228.1) showed the best prophylactic efficacies in protecting mice from DSS-induced intestinal barrier damage. Further research suggested that FL-228.1 exerted its prophylactic effects by enhancing mucin 2 (Muc2) production and Claudin (Cldn)-4 in the colon. Furthermore, the transcriptomic and protein-protein interactions (PPI) analyses indicated that the inhibition of NLRP3 and the activation of PPARγ and TLR2 could be involved in protecting the intestinal barrier by FL-228.1. CONCLUSION: Bifidobacterium bifidum FL-228.1 may be developed as a promising probiotic for the prevention of intestinal barrier damage via PPARγ/NLRP3/ TLR2 pathways by enhancing Muc2 and Cldn-4.

Lactobacillus derived from breast milk facilitates intestinal development in IUGR rats.

AIM: The intestinal microbiota contributes to infant's intestine homeostasis. This study aimed to analyse how probiotics derived from breast milk promote infant intestinal development in rat pups. METHODS AND RESULTS: The effect of potential probiotics derived from breast milk on development of intrauterine growth retardation (IUGR) newborn rats' intestine was investigated. Limosilactobacillus oris ML-329 and Lacticaseibacillus paracasei ML-446 exhibited good hydrophobicity percentages (p < 0.05). ML-446 showed a significant effect on intestinal length and weight (p < 0.05). Meanwhile, the villus height of the IUGR newborn rats fed with ML-329 was significantly higher compared with those fed with Lacticaseibacillus rhamnosus GG (p < 0.05). Moreover, ML-329 and ML-446 both significantly stimulated the proliferation and differentiation of intestinal epithelial cells by increasing the number of ki67-positive cells, goblet cells, and lysozyme-positive Paneth cells (p < 0.05) through Wnt and Notch pathway. CONCLUSIONS: The proliferation and differentiation stimulating effects of ML-329 and ML-446 on IECs in the jejunum, ileum, and colon were mediated by activating the Wnt pathway with increased expression of wnt, lrp5, and ß-catenin genes and accumulation of ß-catenin, and by downregulating the Notch signalling pathway with decreased expression of the activated notch protein. SIGNIFICANCE AND IMPACT OF THE STUDY: Lactobacillus could facilitate IUGR rat pups' intestinal development and enhance the proliferation of Paneth cells and goblet cells. These findings provide further insights into promotion of the intestinal development by breast milk-derived beneficial microbes in early life of the IUGR newborn rats.

Breast milk contains probiotics with anti-infantile diarrhoea effects that may protect infants as they change to solid foods.

Infants often experience complementary food-induced diarrhoea (CFID), which occurs when infants switch from breast milk to solid foods. The relative abundances of Prevotella and Rothia were higher in stools of infants with CFID, while the relative abundances of Enterococcus and Escherichia were higher in healthy infants. The abundance of Lactobacillus spp. normally found in breast milk fed to infants with CFID was significantly reduced, and Enterococcus spp. were less abundant when diarrhoea occurred. Furthermore, Lactobacillus and Enterococcus were present as shared bacteria in both mother and infant, and they were considered potential anti-CFID probiotics as their relative abundances in breast milk were negatively correlated to infant CFID. Kyoto encyclopedia of genes and genomes (KEGG) functional analysis showed that the function of amino acid metabolism differed between infants with CFID and healthy infants. Therefore, CFID might be related to the decomposition of proteins in food supplements. The screening revealed seven hydrolytic casein and five hydrolytic casein and rice protein isolates from 320 suspected Lactobacillus and Enterococcus isolates. The animal experiments demonstrated that a mixture of five isolates effectively hydrolysed the casein and rice protein and prevented diarrhoea in young rats. Thus, the occurrence of CFID was found to be closely related to the intestinal and breast milk microbiota, and bacteria that could assist in the digestion of cereal proteins were involved in CFID.

Lactobacillus casei YRL577 combined with plant extracts reduce markers of non-alcoholic fatty liver disease in mice.

Probiotics and plant extracts are considered to prevent the development of non-alcoholic fatty liver disease (NAFLD). The present study explores the effects of using both probiotics and plant extracts on NAFLD. The present study evaluated the effects of plant extracts on lipid droplet accumulation and the growth of probiotics in vitro. A C57BL/6 mouse model was used to examine the effects of probiotics and plant extracts on NAFLD. Body weight and food intake were measured. The levels of serum lipids, oxidative stress and the liver injury index were determined using commercial kits. Haematoxylin and eosin staining, GC and real-time PCR were also used for analysis. The results revealed that administration of Lactobacillus casei YRL577 and L. paracasei X11 with resveratrol (RES) or tea polyphenols (TP) significantly reduced the levels of total cholesterol, TAG and LDL-cholesterol and increased the level of the HDL-cholesterol. The groups of L. casei YRL577 with RES and TP also regulated the liver structure, oxidative stress and injury. Furthermore, L. casei YRL577 with TP exhibited a more positive effect towards improving the NAFLD and increased the concentrations of the butyric acid than other three combined groups. L. casei YRL577 with TP up-regulated the mRNA levels of the farnesoid X receptor and fibroblast growth factor 15 and decreased the mRNA levels of the apical Na-dependent bile acid transporter. These findings showed that L. casei YRL577 + TP-modified genes in the intestinal bile acid pathway improved markers of NAFLD.

Lactobacillus casei YRL577 ameliorates markers of non-alcoholic fatty liver and alters expression of genes within the intestinal bile acid pathway.

Non-alcoholic fatty liver disease (NAFLD) has become the main cause of end-stage liver disease. Probiotics have the potential effect of alleviating NAFLD. The aim of this study was to explore functional probiotics and their underlying mechanisms. The bile salt hydrolase (BSH) activity in thirty-four strains was determined in vitro. Then, C57BL/6 mice were used to explore the effects of probiotics on NAFLD. Body weight and food intake were measured, and serum lipid concentrations, oxidative stress and proinflammatory cytokines levels were determined using commercial kits. The expressions of intestinal bile acid pathway genes were evaluated via real-time PCR. The results showed that Lactobacillus casei YRL577 and L. paracasei X11 had higher BSH activity. L. casei YRL577 significantly reduced liver weight and liver index and could regulate the levels of lipid metabolism, oxidative stress and proinflammatory cytokines as compared with L. paracasei X11. Furthermore, the results indicated that L. casei YRL577 up-regulated the mRNA levels of farnesoid X receptor and fibroblast growth factor 15, whereas down-regulated the mRNA level of apical Na-dependent bile acid transporter. These findings suggested that L. casei YRL577 modified genes in the intestinal bile acid pathway which might contribute to the alleviation of NAFLD.

In vitro and in vivo investigations of probiotic properties of lactic acid bacteria isolated from Chinese traditional sourdough.

A total of 88 lactic acid bacteria (LAB) strains were isolated from Chinese traditional sourdough and five of them were selected based on their bile resistance. All the five strains were identified as Lactobacillus plantarum by 16S rRNA gene sequencing. In vitro probiotic properties of the L. plantarum strains including tolerance to simulated gastrointestinal conditions, aggregation activity, and cholesterol removal ability were assessed. Two representatives, L. plantarum ZJUFT34 and L. plantarum ZJUFT17, were intragastrically administered to male C57BL/6J mice of 4-week age for 6 weeks to evaluate their in vivo health-promoting effects. The results indicated that L. plantarum ZJUFT34, L. plantarum ZJUFHN9, and L. plantarum ZJUFAH5 could survive the 3-h incubation in simulated gastric juice with a pH value of 2.0, while L. plantarum ZJUFT32 and L. plantarum ZJUFT17 exhibited better autoaggregation activities and coaggregation activities with pathogens. All the strains showed a cholesterol removal ability in vitro. However, L. plantarum ZJUFT34 or L. plantarum ZJUFT17 administration did not significantly change the serum total cholesterol in vivo. But the ratio of high-density lipoprotein cholesterol to low-density lipoprotein cholesterol was significantly increased by the L. plantarum administration. Besides, L. plantarum ZJUFT17 significantly lowered serum tumor necrosis factor (TNF)-α concentrations. Furthermore, the administration of the LAB strains showed significant influences on lipid metabolism-related gut microbiota. These findings suggested that the L. plantarum strains may benefit the prevention of metabolic syndrome.

New mechanistic insights into the motile-to-sessile switch in various bacteria with particular emphasis on Bacillus subtilis and Pseudomonas aeruginosa: a review.

A biofilm is a complex assemblage of microbial communities adhered to a biotic or an abiotic surface which is embedded within a self-produced matrix of extracellular polymeric substances. Many transcriptional regulators play a role in triggering a motile-sessile switch and in consequently producing the biofilm matrix. This review is aimed at highlighting the role of two nucleotide signaling molecules (c-di-GMP and c-di-AMP), toxin antitoxin modules and a novel transcriptional regulator BolA in biofilm formation in various bacteria. In addition, it highlights the common themes that have appeared in recent research regarding the key regulatory components and signal transduction pathways that help Bacillus subtilis and Pseudomonas aeruginosa to acquire the biofilm mode of life.

Oral Milk-Derived Extracellular Vesicles Inhibit Osteoclastogenesis and Ameliorate Bone Loss in Ovariectomized Mice by Improving Gut Microbiota.

Milk-derived extracellular vesicles can improve intestinal health and have antiosteoporosis potential. In this paper, we explored the effects of bovine raw milk-derived extracellular vesicles (mEVs) on ovariectomized (OVX) osteoporotic mice from the perspective of the gut-bone axis. mEVs could inhibit osteoclast differentiation and improve microarchitecture. The level of osteoporotic biomarkers in OVX mice was restored after the mEVs intervened. Compared with OVX mice, mEVs could enhance intestinal permeability, reduce endotoxin levels, and improve the expression of TNF-α, IL-17, and IL-10. 16S rDNA sequencing indicated that mEVs altered the composition of gut microbiota, specifically for Bacteroides associated with short-chain fatty acids (SCFAs). In-depth analysis of SCFAs demonstrated that mEVs could restore acetic acid, propionic acid, valeric acid, and isovaleric acid levels in OVX mice. Correlation analysis revealed that changed gut microbiota and SCFAs were significantly associated with gut inflammation and osteoporotic biomarkers. This study demonstrated that mEVs could inhibit osteoclast differentiation and improve osteoporosis by reshaping the gut microbiota, increasing SCFAs, and decreasing the level of pro-inflammatory cytokines and osteoclast differentiation-related factors in OVX mice. These findings provide evidence for the use of mEVs as a food supplement for osteoporosis.

Probiotics induce intestinal IgA secretion in weanling mice potentially through promoting intestinal APRIL expression and modulating the gut microbiota composition.

Intestinal infections are strongly associated with infant mortality, and intestinal immunoglobulin A (IgA) is important to protect infants from intestinal infections after weaning. This study aims to screen probiotics that can promote the production of intestinal IgA after weaning and further explore their potential mechanisms of action. In this study, probiotics promoting intestinal IgA production were screened in weanling mouse models. The results showed that oral administration of Bifidobacterium bifidum (B. bifidum) FL228.1 and Bifidobacterium bifidum (B. bifidum) FL276.1 significantly enhanced IgA levels in the small intestine and upregulated the expression of a proliferation-inducing ligand (APRIL) and its upstream regulatory factor toll-like receptor 4 (TLR4). Furthermore, B. bifidum FL228.1 upregulated the relative abundance of Lactobacillus, while B. bifidum FL276.1 increased the relative abundance of Marvinbryantia and decreased Mucispirillum, further elevating intestinal IgA levels. In summary, B. bifidum FL228.1 and B. bifidum FL276.1 can induce IgA production in the intestinal tract of weanling mice by promoting intestinal APRIL expression and mediating changes in the gut microbiota, thus playing a significant role in enhancing local intestinal immunity in infants.

Thermal, Electrical, and Environmental Safeties of Sulfide Electrolyte-Based All-Solid-State Li-Ion Batteries.

The next generation of all-solid-state lithium-ion batteries (ASLIBs) based on solid-state sulfide electrolytes (SSEs) is closest to commercialization. Understanding the overall safety behavior of SSE-ASLIBs is necessary for their product design and commercialization. However, their safety behavior in real-life situations, such as battery exposure to high temperature, overcharge, mechanical rupture, and air exposure, remains largely unknown. Herein, we report preliminary but needed evidence of (i) significantly improved resistance to electrical shorting at high temperatures, (ii) reduced heat generation when subjected to excessive heat, (iii) tolerable harmful gas generation when subjected to air exposure followed by high-temperature heating, and (iv) high-voltage charge stability when a battery is overcharged (5.5 V charge) in SSE-based ASLIBs compared to commercial liquid electrolyte-based LIBs (LE-LIBs). Furthermore, the result shows that SSEs can self-induce a fast and effective battery shut-down capability in ASLIBs and avoid thermal runaway upon mechanical damage and exposure to air.

Metagenomic insights into bacterial communities and functional genes associated with texture characteristics of Kazakh artisanal fermented milk Ayran in Xinjiang, China.

The complex microflora of traditional fermented milk is crucial to milk coagulation mainly through acid and protease production; however, it is still unclear which microbes and proteases significantly influence the texture of Ayran, a Kazakh artisanal fermented milk in Xinjiang, China. In this study, fifty-nine samples of Ayran were collected and investigated on texture properties. Finally, six Ayran samples with different texture features were screened out, and the taxonomic and functional attributes of their microbiota were characterized by metagenomics. The results showed that the hardness of the fermented milk in Yili Kazakh Autonomous Prefecture was significantly higher than that in other pasture areas. Lactobacillus and Lactococcus were the core genera that affected the coagulation quality of milk. Furthermore, we found that the proline iminopeptidase pip (EC 3.4.11.5) gene of Lactobacillus helveticus and Limosilactobacillus fermentum and the dipeptidase E pepE (EC 3.4.13.21) gene of Lactococcus lactis were most associated with the coagulation quality of fermented milk. Furthermore, positive correlations were observed among the hardness of fermented milk, the activity of the proteases, and the corresponding functional gene expressions.

Probiotics Alleviate Food Protein Allergy in Mice by Activating TLR4 Signaling Pathway.

SCOPE: Food allergy has become a world recognized public health problem due to its versatility and lack of efficacious methods for its treatment. Probiotics supplement is a potential way to prevent food allergy. METHODS AND RESULTS: In this study, potential strains are screen out by peripheral blood mononuclear cells (PBMCs), and their abilities of alleviating food allergy are examined using a mouse model induced by ovalbumin (OVA). The results show that six strains increase ratio of interferon-γ (IFN-γ)/interleukin (IL)-4 secreted by PBMCs with good abilities in intestinal adhesion and gastrointestinal tolerance. Oral administration of Bifidobacterium animalis KV9 (KV9) and Lactobacillus vaginalis FN3 (FN3) attenuates allergic responses in allergy mice, including allergic symptoms, mast cells aggregation and activity, serum OVA-special-immunoglobulins E (OVA-sIgE) production. KV9 and FN3 upregulate the production of IFN-γ/IL-4 in splenocytes, increase the genes and proteins expression of toll-like receptor 4 (TLR4), myeloid differentiation primary response 88 (Myd88) and interferon regulatory factor (IRF)-1 in allergic mice spleen, and decrease the IRF-4. CONCLUSION: The study demonstrates that KV9 and FN3 possess anti-allergic activities via activation of TLR4 pathway and modulating the expression of IRF-1 and IRF-4 which leads to T helper type 1 (Th1)/T helper type 2 (Th2) cell immunology balance.

Insight into the molecular-level details of αs1 casein interactions with IgG: Combining with LC-MS/MS and molecular modelling techniques.

αs1-Casein (αs1-CN) is a major cow milk allergen, while the tertiary structure of αs1-CN and conformational epitopes of αs1-CN have not been clarified. Here, a reasonable three-dimensional structure of αs1-CN was established using ab initio methods, and hot-spot residues and epitopes were investigated by combining molecular dynamics simulation, peptides synthesis, and ELISA. Obtained results demonstrated that the binding mechanism between αs1-CN and IgG was located on three main regions: a helical structure zone (E77-Q97), the flexible loop zone (Y154-T174), and a flexible C-terminal (N190-L198), mainly connecting via hydrogen bond and ionic bonds. The hydrolysates produced by papain with lowest antigenicity (12.43%), which could considerably destroy the essential epitopes of αs1-CN confirmed by epitope synthesis, and LC-MS/MS. The results reported herein would provide novel insights into the interface interactions between αs1-CN and IgG, and prove valuable for developing hypoallergenic infant-formula and peptide vaccines for allergen-specific immunotherapy.

Bifidobacterium animalis sup F1-7 Acts as an Effective Activator to Regulate Immune Response Via Casepase-3 and Bak of FAS/CD95 Pathway.

Intestinal microecology was closely related to immune regulation, but the related mechanism was still unclear. This study aimed to reveal how microorganisms improved immune response via casepase-3 and Bak of FAS/CD95 pathway. Bifidobacterium animalis F1-7 inhibited the melanoma B16-F10 cells in vitro effectively; had a potent anticancer effect of lung cancer mice; effectively improved the spleen immune index and CD3+ (75.8%) and CD8+ (19.8%) expression level; strengthened the phagocytosis of macrophages; inhibited the overexpression of inflammatory factors IL-6 (319.10 ± 2.46 pg/mL), IL-8 (383.05 ± 9.87 pg/mL), and TNF-α (2003.40 ± 11.42 pg/mL); and promoted the expression of anti-inflammatory factor IL-10 (406.00 ± 3.59 pg/mL). This process was achieved by promoting caspase-8/3 and BH3-interacting domain death agonist (Bid), Bak genes, and protein expression. This study confirmed the B. animalis F1-7 could act as an effective activator to regulate immune response by promoting the expression of caspase-8/3, Bid and Bak genes, and proteins and by activating the FAS/CD95 pathway. Our study provided a data support for the application of potentially beneficial microorganisms of B. animalis F1-7 as an effective activator to improve immunity.

Lactobacillus rhamnosus MN-431 Metabolic Tryptophan Alleviates Complementary Food-Induced Diarrhea through PXR-NF-κB Pathway and AHR-Th17 Cell Response Pathways.

SCOPE: Lactobacillus rhamnosus MN-431 tryptophan broth culture (MN-431 TBC) can prevent complementary food-induced diarrhea (CFID). However, it is not clear whether this effect is related to indole derivatives. METHODS AND RESULTS: In this study, the anti-CFID effects of different components in MN-431 TBC including MN-431 cells, unfermented tryptophan broth, and supernatant of MN-431 TBC (MN-431 TBS) are investigated. Only MN-431 TBS can significantly prevent CFID, indicating that indole derivatives produced by MN-431 can exert antidiarrheal effects. Intestinal morphological analysis reveals that MN-431 TBS can increase the number of goblet cells, height of ileal villi, and length of rectal glands while also increasing the expression of ZO-1 in colon. Furthermore, HPLC analysis reveals the indole derivatives in MN-431 TBS are IAld and skatole. Cell experiments demonstrate that MN-431 TBS promotes the transcription of aryl hydrocarbon receptor (AHR) and pregnane X receptor (PXR), comparable to the synergistic effect of IAld and skatole. MN-431 TBS can activate AHR and reduces the concentrations of Th17 cell-inflammatory factors IL-17A and IL-21 in intestine and IL-17F, IL-21, and IL-22 in serum. MN-431 TBS can also activate PXR and reduces the concentrations of TNF-α and IL-6 in intestine and serum. CONCLUSION: MN-431 TBS, containing IAld and skatole, can exert anti-CFID effects through the AHR-Th17 and PXR-NF-κB pathways.

Bifidobacterium bifidum Ameliorates DSS-Induced Colitis in Mice by Regulating AHR/NRF2/NLRP3 Inflammasome Pathways through Indole-3-lactic Acid Production.

In this study, the effectors and mechanisms of Bifidobacterium bifidum FL-276.1 and B. bifidum FL-228.1 in alleviating dextran sulfate sodium (DSS)-induced colitis were investigated. Both FL-276.1 and FL-228.1 significantly alleviated DSS-induced colitis, whether they were supplemented from the beginning of the experiment (whole course intervention) or after the DSS induction started (partial intervention). Aryl hydrocarbon receptor (AHR) and the nuclear factor erythroid 2-related factor 2 (NRF2) pathways were activated in mice colons, while the NLR family pyrin domain containing 3 (NLRP3) was downregulated under the whole course intervention modes. Indole-3-lactic acid, an AHR ligand produced by FL-276.1 and FL-228.1, could regulate the AHR/NRF2/NLRP3 pathway in Caco-2 monolayers, thus upregulating the tight junction proteins and protecting the integrity of the epithelial barrier. These results are conducive to promoting clinical trials and product development of probiotics for alleviating colitis.

Milk-derived extracellular vesicles protect intestinal barrier integrity in the gut-liver axis.

Milk-derived extracellular vesicles (mEVs) have been proposed as a potential nanomedicine for intestinal disorders; however, their impact on intestinal barrier integrity in gut inflammation and associated metabolic diseases has not been explored yet. Here, mEVs derived from bovine and human breast milk exert similar protective effects on epithelial tight junction functionality in vitro, survive harsh gastrointestinal conditions ex vivo, and reach the colon in vivo. Oral administration of mEVs restores gut barrier integrity at multiple levels, including mucus, epithelial, and immune barriers, and prevents endotoxin translocation into the liver in chemical-induced experimental colitis and diet-induced nonalcoholic steatohepatitis (NASH), thereby alleviating gut disorders, their associated liver inflammation, and NASH. Oral administration of mEVs has potential in the treatment of gut inflammation and gut-liver axis-associated metabolic diseases via protection of intestinal barrier integrity.

The Mutual Influence of Predominant Microbes in Sourdough Fermentation: Focusing on Flavor Formation and Gene Transcription.

The interplay between microorganisms generally plays a vital role in food fermentation. In this study, the mutual influence of Saccharomyces cerevisiae and Fructilactobacillus sanfranciscensis, the two predominant microbes in the sourdough ecosystem, were investigated in situ during fermentation. Doughs fermented with S. cerevisiae, F. sanfranciscensis, or their combination were compared regarding acid production, microbial density, and volatiles. Furthermore, in situ gene expressions were investigated using RNA-sequencing. The results showed that the presence of S. cerevisiae had no visible influence on F. sanfranciscensis, whereas F. sanfranciscensis facilitated the growth of S. cerevisiae but affected its volatile production since metabolites such as 3-methyl-1-butanol decreased. The RNA-sequencing demonstrated that S. cerevisiae significantly changed the gene transcripts implicated in amino acid metabolism in F. sanfranciscensis and may stimulate its growth suggested by the enrichment of the KEGG pathway of peptidoglycan biosynthesis.

Aroma classification and characterization of Lactobacillus delbrueckii subsp. bulgaricus fermented milk.

The aroma of the fermented milk produced by twenty-eight Lactobacillus delbrueckii subsp. bulgaricus strains was evaluated via quantitative descriptive analysis. According to the sensory analysis results, the fermented milks were grouped into milky-type, cheesy-type, fermented-type and miscellaneous-type. The representative samples of cheese-type and fermented-type were analyzed by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and flavoromics. A total of 95 volatile compounds were identified and particularly, 12 aroma-active compounds were detected by using gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Among the different aroma types, 2,3-butanedione, δ-decalactone, acetaldehyde, butanoic acid, acetic acid and hexanoic acid were finally screened out as the key aroma-active compounds by quantitative and odor activity value (OAV) analysis combined with aroma recombination, omission and addition experiments. These findings were valuable in developing specific fermented milk products with different aroma profiles.