This study explores the ability of lactic acid bacteria (LAB) to ferment soy juice. The ability of 276 LAB strains from 25 species to ferment the principal soy carbohydrates, sucrose, raffinose or stachyose was tested in synthetic media and a soy juice. Fermented soy juices (FSJs) were characterized for their odor. Selected FSJs were characterized by targeted metabolomics. All Streptococcus, 83% of Leuconostoc and Lactobacillus and 41% of Lactococcus strains were sucrose-positive, while only 36% of all the LAB strains tested were raffinose-positive and 6% stachyose-positive. Nearly all (97%) the sucrose-positive strains fermented soy juice, indicating that an ability to use sucrose is a good criterion to select strains for soy juice fermentation. Among the most efficient acidifying strains, 46 FSJs had an odor deemed to be acceptable. FSJ composition was dependent on both species and strains: 17/46 strains deglycosylated soy juice isoflavones, the 27 S. thermophilus strains converted a mean 4.4 ± 0.1 g/L of sucrose into 3.0 ± 0.1 g/L of lactic acid versus 5.2 ± 0.1 g/L into 2.2 ± 0.1 g/L for the 18 Lactobacillus and one Lactococcus strains. This study highlights the diversity of the metabolic profiles of LAB strains in soy juice fermentation.

The formation of cheese flavor mainly results from the production of volatile compounds by microorganisms. We investigated how fine-tuning cheese-making process parameters changed the cheese volatilome in a semi-hard cheese inoculated with Lactococcus (L.) lactis, Lactiplantibacillus (L.) plantarum, and Propionibacterium (P.) freudenreichii. A standard (Std) cheese was compared with three variants of technological itineraries: a shorter salting time (7 h vs 10 h, Salt7h), a shorter stirring time (15 min vs 30 min, Stir15min), or a higher ripening temperature (16 °C vs 13 °C, Rip16°C). Bacterial counts were similar in the four cheese types, except for a 1.4 log₁₀ reduction of L. lactis counts in Rip16°C cheeses after 7 weeks of ripening. Compared to Std, Stir15min and Rip16°C increased propionibacterial activity, causing higher concentrations of acetic, succinic, and propanoic acids and lower levels of lactic acid. Rip16°C accelerated secondary proteolysis and volatile production. We thus demonstrated that fine-tuning process parameters could modulate the cheese volatilome by influencing specific bacterial metabolisms.

Amyloid-β (Aβ) plays a critical role in Alzheimer’s disease (AD) and its accumulation in the brain is pivotal to disease progression and precedes memory and neuronal loss. Besides the severely handicapping brain symptoms, AD patients display early gastro-intestinal (GI) manifestations such as upper and lower GI dysmotility, in particular constipation. Although there is increasing evidence of Aβ accumulation in the gut, its pathogenic effects on enteric nervous system (ENS) connectivity and gut function as well as underlying pathophysiological mechanisms are poorly understood. Furthermore, studies have reported a gut to brain transmission of Aβ that causes memory deficits in mice. Therefore, identifying therapeutics which can reduce Aβ accumulation in the gut at an early stage of the disease could have the advantage of slowing or even reversing disease progression before severe alterations or irreversible damages at both intestinal and brain levels. Hence, in this study, we investigated the capacity of the short-fatty acid butyrate to restore Aβ-driven alteration of ENS connectivity and gut-brain functions in the SAMP8 mouse model of AD. Here we show that SAMP8 mice display a gut amyloid pathology, an alteration of ENS connectivity and gut defects prior to memory decline. BACE1, an Aβ-producing enzyme, expression and activity are increased whereas neprilysin, an Aβ-degrading enzyme, is decreased in the gut of SAMP8 mice, indicating a rise in the Amyloid Precursor Protein (APP) holoprotein processing and a reduction of Aβ clearance which promote an amyloidosis. In primary ENS cultures, Aβ causes a degradation of synaptic-associated proteins EphB2 and synaptophysin, leading to an alteration of ENS connectivity. In wild-type mice, intra-colon delivery of Aβ alters ENS connectivity and causes subsequent GI symptoms, recapitulating the phenotype of the SAMP8 mouse model of aging and AD. Moreover, Aβ impairs ENS connectivity in human induced pluripotent stem cell (iPSC)-derived intestinal organoids and explant cultures of human colon, indicating that Aβ causes ENS lesions in models of the human gut. Butyrate, a short-chain fatty acid derived from bacterial metabolism, reduces Aβ secretion and preserves enteric neuronal connectivity in vitro and in vivo, and blocks Aβ accumulation in the gut, brain and plasma in SAMP8 mice. In addition, butyrate ameliorates neuroinflammation and prevents gut dysfunction and memory deficit. Collectively, these findings suggest that Aβ promotes gut symptoms through alteration of ENS connectivity and butyrate counteracts these impairments with an amelioration of neuroinflammation and memory function in AD model.

In Algeria, Smen is a fermented butter produced in households using empirical methods. Smen fermentation is driven by autochthonous microorganisms; it improves butter shelf-life and yields highly fragrant products used as ingredients in traditional dishes as well as in traditional medicine. The present study is aimed at investigating microbial diversity and dynamics during Algerian Smen fermentation using both culture-dependent and culture-independent approaches, as well as by monitoring volatile organic compound production. To reach this goal, fifteen Smen samples (final products) produced in households from different regions in Algeria were collected and analyzed. In addition, microbial and volatile compound dynamics at the different stages of Smen manufacturing were investigated for one Smen preparation. The results showed that Smen is a microbiologically safe product, as all hygiene and safety criteria were respected. The dominant microorganisms identified by both techniques were LAB and yeasts. Lactococcus spp. and Streptococcus thermophilus were the main bacterial species involved in spontaneous raw milk fermentation preceding butter-making, while lactobacilli and enterococci were the only bacteria found to be viable during Smen maturation. Regarding fungal diversity, yeast species were only recovered from two mature Smen samples by culturing, while different species (e.g., Geotrichum candidum, Moniliella sp.) were identified in all samples by the culture-independent approach. Using microbial analysis of a single batch, many of these were found viable during manufacturing. Concerning the volatile profiles, they were highly diverse and characterized by a high prevalence of short chain fatty acids, methylketones, and esters. Correlation analysis between microbial diversity and volatile profiles showed that several yeast (Moniliella sp., K. marxianus) and LAB (e.g., Lactococcus spp., S. thermophilus) species were strongly correlated with one or more volatile organic compound families, including several ethyl esters and methyl ketones that can be linked to pleasant, sweetly floral, fruity, buttery, and creamy odors. This study clearly identified key microorganisms involved in Smen fermentation and maturation that could be used in the future for better fermentation control and improvement of quality attributes.