Sensorically and antimicrobially active metabolite production of Lactobacillus strains on Jerusalem artichoke juice

Characterization of Key Aroma Compounds of Soy Sauce-like Aroma Produced in Ferment of Soybeans by Bacillus subtilis BJ3-2

Fermented soybeans are popular among many for their rich soy sauce-like aroma. However, the precise composition of this aroma remains elusive, with key aroma compounds unidentified. In this study, we screened the candidate genes ilvA and serA in BJ3-2 based on previous multi-omics data, and we constructed three mutant strains, BJ3-2-ΔserA, BJ3-2-ΔilvA, and BJ3-2-ΔserAΔilvA, using homologous recombination to fermented soybeans with varying intensities of soy sauce-like aroma. Our objective was to analyze samples that exhibited different aroma intensities resulting from the fermented soybeans of BJ3-2 and its mutant strains, thereby exploring the key flavor compounds influencing soy sauce-like aroma as well analyzing the effects of ilvA and serA on soy sauce-like aroma. We employed quantitative descriptive sensory analysis (QDA), gas chromatography-olfactometry-mass spectrometry (GC-O-MS), relative odor activity value analysis (rOAV), principal component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA), and partial least squares regression analysis (PLSR). QDA revealed the predominant soy sauce-like aroma profile of roasted and smoky aromas. GC-MS detected 99 volatile components, predominantly pyrazines and ketones, across the four samples, each showing varying concentrations. Based on rOAV (>1) and GC-O, 12 compounds emerged as primary contributors to soy sauce-like aroma. PCA and OPLS-DA were instrumental in discerning aroma differences among the samples, identifying five compounds with VIP > 1 as key marker compounds influencing soy sauce-like aroma intensity levels. Differential analyses of key aroma compounds indicated that the mutant strains of ilvA and serA affected soy sauce-like aroma mainly by affecting pyrazines. PLSR analysis indicated that roasted and smoky aromas were the two most important sensory attributes of soy sauce-like aroma, with pyrazines associated with roasted aroma and guaiacol associated with smoky aroma. In addition, substances positively correlated with the intensity of soy sauce-like aroma were verified by additional experiments. This study enhances our understanding of the characteristic flavor compounds in soy sauce-like aroma ferments, provides new perspectives for analyzing the molecular mechanisms of soy sauce-like aroma formation, and provides a theoretical framework for the targeted enhancement of soy sauce-like aroma in various foods.

Breath volatile metabolome reveals the impact of dietary fibres on the gut microbiota: Proof of concept in healthy volunteers

Background

Current data suggest that dietary fibre (DF) interaction with the gut microbiota largely contributes to their physiological effects. The bacterial fermentation of DF leads to the production of metabolites, most of them are volatile. This study analyzed the breath volatile metabolites (BVM) profile in healthy individuals (n=15) prior and after a 3-week intervention with chitin-glucan (CG, 4.5 g/day), an insoluble fermentable DF.

Methods

The present exploratory study presents the original data related to the secondary outcomes, notably the analysis of BVM. BVM were analyzed throughout the test days -in fasting state and after standardized meals - using selected ion flow tube mass spectrometry (SIFT-MS). BVM production was correlated to the gut microbiota composition (Illumina sequencing, primary outcome), analyzed before and after the intervention.

Findings

The data reveal that the post-prandial state versus fasting state is a key determinant of BVM fingerprint. Correlation analyses with fecal microbiota spotlighted butyrate-producing bacteria, notably Faecalibacterium, as dominant bacteria involved in butyrate and other BVM expiration. CG intervention promotes interindividual variations of fasting BVM, and decreases or delays the expiration of most exhaled BVM in favor of H₂ expiration, without any consequence on gastrointestinal tolerance.

Interpretation

Assessing BVM is a non-invasive methodology allowing to analyze the influence of DF intervention on the gut microbiota.

Funding

FiberTAG project was initiated from a European Joint Programming Initiative “A Healthy Diet for a Healthy Life” (JPI HDHL) and was supported by the Service Public de Wallonie (SPW-EER, convention 1610365, Belgium).

Gut microbiome modifications over time when removing in-feed antibiotics from the prophylaxis of post-weaning diarrhea in piglets

Post-weaning diarrhea (PWD) in pigs has mainly an infectious basis and control strategies are centred on antibiotics added to the diet. Given concerns on the spread of multi-resistant bacteria, it is necessary to develop alternative prophylactic approaches to control PWD in piglets. The most promising alternative strategies are based on substances that act indirectly on the bacteria by stimulating the immune system or by improving gut health. The aim of this study was to evaluate the effect on the gut microbiota of feed supplemented with a mixture of essential oils (garlic and oregano) in weaning piglets, compared to traditional PWD management (in-feed antibiotics) and to a control group without any diet supplementation. The study involved 197 piglets from 18 litters in a single farm. The piglets were followed from birth to day 58 of age and were weaned at day 26. During the experimental period, the animals were monitored for weight and growth, average daily gain, morbidity and mortality. For the metataxonomics analysis, rectal samples were collected from 17 piglets from the three experimental groups at 4 different time-points (days 1, 12, 26 and 58). Results revealed that the gut microbiota in pre- and post-weaning piglets was dominated by the phyla Firmicutes (51%), Bacteroidetes (25%) and Proteobacteria (16%), which together make up for over 90% of the entire piglet core gut microbiota. The core microbiota comprised 10 taxa before weaning and 43 taxa after weaning, with 7 taxa overlapping between timepoints: two of them (Prevotella 9, p-value = 0.00095; Solobacterium p-value = 0.00821) were significantly more abundant after weaning. All alpha diversity indexes were significantly different between pre- and post-weaning, while only Shannon and Simpson diversity and equitability were significantly different between treatments. Based on the matrix of Bray-Curtis dissimilarities, samples showed clear clustering per timepoint (before and after weaning, p-value < 0.001) and between treatments by timepoint (p-value = 0.0086). The oil-diet group showed a consistently higher F:B ratio at all timepoints. These results show that the pig gut microbiota changes significantly with weaning, and suggest that the use of essential oils as feed supplementation to control PWD does not seem to alter sgnificantly the microbiota nor the growth parameters of piglets, however modifications of specific taxa may occur.

Noninvasive monitoring of fibre fermentation in healthy volunteers by analyzing breath volatile metabolites: lessons from the FiberTAG intervention study

The fermentation of dietary fibre (DF) leads to the production of bioactive metabolites, the most volatile ones being excreted in the breath. The aim of this study was to analyze the profile of exhaled breath volatile metabolites (BVM) and gastrointestinal symptoms in healthy volunteers after a single ingestion of maltodextrin (placebo) versus chitin-glucan (CG), an insoluble DF previously shown to be fermented into short-chain fatty acids (SCFA) by the human microbiota in vitro. Maltodextrin (4.5 g at day 0) or CG (4.5 g at day 2) were added to a standardized breakfast in fasting healthy volunteers (n = 15). BVM were measured using selected ion flow tube mass spectrometry (SIFT-MS) throughout the day. A single ingestion of 4.5 g CG did not induce significant gastrointestinal discomfort. Untargeted metabolomics analysis of breath highlighted that 13 MS-fragments (among 408 obtained from ionizations of breath) discriminated CG versus maltodextrin acute intake in the posprandial state. The targeted analysis revealed that CG increased exhaled butyrate and 5 other BVM - including the microbial metabolites 2,3-butanedione and 3-hydroxybutanone - with a peak observed 6 h after CG intake. Correlation analyses with fecal microbiota (Illumina 16S rRNA sequencing) spotlighted Mitsuokella as a potential genus responsible for the presence of butyric acid, triethylamine and 3-hydroxybutanone in the breath. In conclusion, measuring BMV in the breath reveals the microbial signature of the fermentation of DF after a single ingestion. This protocol allows to analyze the time-course of released bioactive metabolites that could be proposed as new biomarkers of DF fermentation, potentially linked to their biological properties. Trial registration: Clinical Trials NCT03494491. Registered 11 April 2018 - Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03494491.

Levan from Bacillus amyloliquefaciens JN4 acts as a prebiotic for enhancing the intestinal adhesion capacity of Lactobacillus reuteri JN101

Improving intrinsic adhesion performance of the known probiotics facilitates their residence and colonization, and therefore exerts more beneficial effects on the human or animal host. In this study, through adaptive culture with levan, Lactobacillus reuteri JN101 achieved the same biomass and exhibited 2.6 times higher adhesion capacity to HT-29 cells than those grown with glucose. The mechanism study related to this adhesion enhancement showed that the elevated proportion of unsaturated fatty acids facilitated the bacterial cells to overcome repulsive forces to approach the intestinal epithelial cell. At the same time, and the greater amounts of cell membrane proteins, such as S-layer protein (3.2 folds), elongation factor Tu (2.6 folds) and phosphoglycerate kinase (2.4 folds) probably enhanced the complementary interactions to the receptor on the epithelial cell. These results presented here indicated levan could be used as a potential prebiotic to regulate the adhesion capacity of probiotics, and provide ground for developing the specific-probiotics oriented functional food.

Intestinal Microbiome-Metabolome Responses to Essential Oils in Piglets

This study investigated the effects of dietary essential oils (EOs) on intestinal microbial composition and metabolic profiles in weaned piglets. The piglets were fed the same basal diet supplemented with EOs (EO) or without EOs (Con) in the current study. The results showed that the body weight gain was significantly increased, while the diarrhea incidence was significantly reduced in the EO group. In addition, EOs could modify the intestinal microbial composition of weaned piglets. The relative abundances of some beneficial bacterial species such as Bacilli, Lactobacillales, Streptococcaceae, and Veillonellaceae were significantly increased in the EO group. Metabolomics analysis indicated that protein biosynthesis, amino acid metabolism, and lipid metabolism were enriched in the EO group. And correlation analysis demonstrated that some gut bacterial genera were highly correlated with altered gut microbiota-related metabolites. Taken together, this study indicated that dietary EOs not only altered microbial composition and function but modulated the microbial metabolic profiles in the colon, which might help us understand EOs' beneficial effects on intestinal health of weaned piglets.

Synbiotic functional drink from Jerusalem artichoke juice fermented by probiotic Lactobacillus plantarum PCS26

A probiotic strain Lactobacillus plantarum PCS26 was used to ferment Jerusalem artichoke juice. Growth kinetics of the bacterial strain was followed during juice fermentation both in flask and in laboratory fermentor. Jerusalem artichoke showed to be an excellent source of nutrients for L. plantarum PCS26 growth. The culture grew very well reaching more than 10(10) cfu/ml in just 12 h. The pH changed from the initial 6.5 to 4.6 at the end of fermentation. The culture hydrolyzed fructooligosaccharides present in the Jerusalem artichoke juice, yielding fructose which was presumably consumed along with the malic acid as energy and carbon source. Lactic acid was the main metabolite produced in concentration of 4.6 g/L. Acetic and succinic acid were also identified. Sensory evaluation of the fermented Jerusalem artichoke juice and its mixtures with blueberry juice showed that the 50/50 % v/v mixture would be very well accepted by the consumers. Above 80 % of the panelists would buy this drink, and over 60 % were willing to pay more for it. Culture survivability in the fermented juices during storage at 4-7 °C was assayed by the Weibullian model. The product shelf-life was extended from 19.70 ± 0.50 days of pure Jerusalem artichoke juice to 35.7 ± 6.4 days of the mixture containing 30 % blueberry juice.

Diacetyl: occurrence, analysis, and toxicity

Diacetyl possesses a butter-like flavor and has been widely used as a flavoring agent. It forms from sugars and lipids via various bacteria and heat treatment in various foods and beverages, such as milk. The toxicity of diacetyl, especially when inhaled, has recently attracted the attention not only of consumers but also of regulatory agencies. Even though accurate quantitative analysis of diacetyl is extremely important in evaluating its possible adverse effects, precise quantitative analysis of diacetyl in foods and beverages, as well as in ambient air, is considerably difficult because it is highly reactive and soluble in water. Among the many analytical methods developed for measuring diacetyl, preparation of 2,3-dimethylquinoxaline followed by gas chromatography has been most commonly used in the analysis of various foods, beverages, and air samples. This mini-review summarizes the formation mechanisms, analytical methods, occurrence, and toxicity of diacetyl.