Taste perception, a key determinant of eating behavior, arises from a complex interaction between the oral cavity and the brain. Increasing evidence suggests that oral microbiota metabolism may contribute to this process. This study aimed to advance understanding of the connection between salivary bacteria and taste perception in a cohort of 108 adults by exploring the relationship between microbiota profile (16S rRNA gene amplicon sequencing), their metabolic products (lactate, acetate, propionate, and butyrate) and the salivary environment (flow rate, total protein content, antioxidant capacity) with taste perception, while accounting for biological variables (body mass index and age). The results identified 39 bacterial genera associated with the concentration of salivary acids, most of them related to oral diseases like periodontitis and dental caries. The association between short-chain fatty acids (acetate, propionate, butyrate) and salivary protein content suggests they may originate from the degradation of salivary proteins. Additionally, individuals with overweight presented higher salivary organic acids and protein content levels than the normal-weight counterparts. Twenty-nine bacterial genera were associated with the perception of basic tastes. Although taste-specific associations varied among taste modalities, members of the Clostridia class were consistently linked to all tastes. While heightened sweet, salty, and sour taste perceptions appeared to be linked to bacterial consortia associated with lower concentrations of salivary organic acids, bitter taste was associated with bacteria positively related to acids and inflammation. These findings underscore the complex interplay between oral microbiota metabolism, salivary composition, and taste perception, with potential implications for dietary behavior.

Fermented food consumption is recommended for health and environmental purposes. While it is known to impact gut microbiota, further investigation is needed to establish connections with the oral microbiota. For this purpose, we investigated the effect of daily consumption of a model cheese containing 3 Lactic Acid Bacteria (LAB) species on the oral microbiota of rats following a 3-week diet. Cheese consumption transiently modifies the oral microbiota and leads to a transient persistence of LAB in the oral cavity of 1/3 of the animals. The origin of this variability was partly explained by an overrepresentation of salivary proteins involved in the response to oxidative stress in animals without LAB persistence. These findings highlight the significance of fermented foods in shaping the diversity of the oral microbiota. Additionally, they suggest that variations in the salivary proteome among individuals may influence the permissiveness of the oral microbiota towards exogenous microorganisms.

Taste perception is crucial and impairments, which can be linked to pathologies, can lead to eating disorders. It is triggered by taste compounds stimulating receptors located on the tongue. However, the tongue is covered by a film containing saliva and microorganisms suspected to modulate the taste receptor environment. The present study aimed to elucidate the links between taste sensitivity (sweetness, sourness, bitterness, saltiness, umami) and the salivary as well as the tongue microbiota using shotgun metagenomics. 109 bacterial species were correlated with at least one taste. Interestingly, when a species was correlated with at least two tastes, the correlations were unidirectional, indicating a putative global implication. Some Streptococcus, SR1 and Rickenellaceae species correlated with five tastes. When comparing both ecosystems, saliva appears to be a better taste predictor than tongue. This work shows the implication of the oral microbiota in taste and exhibits specificities depending on the ecosystem considered.

The oral cavity hosts an important amount of microorganisms characterized by an important diversity. This diversity is partly due to the presence of various ecological niches in the oral cavity with different physicochemical and biochemical properties. The totality of these microorganisms constitutes the oral microbiota. The oral microbiota has been studied for years, especially for its implication in various oral pathologies including dental caries and periodontal disease. However, its implication in other physiological functions has started to be studied recently. Among them, we can mention taste perception. The implication of the oral microbiota in this perception appears highly credible since the surface of the tongue, which is at the interface between the oral cavity and the taste receptors, is covered by a rich and diverse microbial biofilm. Similarly, saliva, which is the fluid where sapid compounds are diluted before reaching taste receptors, is also a medium where planktonic bacteria are strongly represented. Besides the potential role of this oral microbiota, the implication of food microbiota and particularly fermented foods microbiota to taste perception is poorly known although the consumption of these products leads to the introduction of billions of exogenous microorganisms in the oral cavity. The aim of this chapter is then, in the first part, to give an overview of the characteristics of the oral microbiota. A second part will focus on the fermented food microbiota and the products of their metabolism having a potential impact on taste perception. Finally, the last part will review the potential implications of the oral microbiota in taste perception.

The Mediterranean diet (MedDiet) represents the traditional food consumption patterns of people living in countries bordering the Mediterranean Sea and is associated with a reduced incidence of obesity and type-2 diabetes mellitus (T2DM). The objective of this study was to examine differences in the composition of the oral microbiome in older adults with T2DM and/or high body mass index (BMI) and whether the microbiome was influenced by elements of a MedDiet. Using a nested case-control design individuals affected by T2DM were selected from the Seniors-ENRICA-2 cohort concurrently with non-diabetic controls. BMI was measured, a validated dietary history taken, and adherence to a Mediterranean diet calculated using the MEDAS (Mediterranean Diet Adherence Screener) index. Oral health status was assessed by questionnaire and unstimulated whole mouth saliva was collected, and salivary flow rate calculated. Richness and diversity of the salivary microbiome were reduced in participants with T2DM compared to those without diabetes. The bacterial community structure in saliva showed distinct "signatures" or "salivatypes," characterized by predominance of particular bacterial genera. Salivatype 1 was more represented in subjects with T2DM, whilst those with obesity (BMI ≥ 30 kg/m2) had a predominance of salivatype 2, and control participants without T2DM or obesity had an increased presence of salivatype 3. There was an association of salivatype 1 with increased consumption of sugary snacks combined with reduced consumption of fish/shellfish and nuts. It can be concluded that the microbial community structure of saliva is altered in T2DM and obesity and is associated with altered consumption of particular food items. In order to further substantiate these observations a prospective study should be undertaken to assess the impact of diets aimed at modifying diabetic status and reducing weight.

Fermented foods constitute a wide source of exogenous lactic acid bacteria (LAB) which could modify the endogenous microbiota of the consumer's digestive tract. This assumption depends on the ability of LAB to persist, at least transiently, in the oral cavity. The aim of this study was to evaluate the persistence of 3 LAB species, Streptococcus thermophilus, Lactococcus lactis, and Lacticaseibacillus paracasei in the oral cavity of rats by feeding them with a daily portion of model cheese containing the three bacteria for one week. Saliva samples were collected 16 h and one week after the last daily cheese intake. Their cheese bacteria contents were quantified by qPCR. When 16 h after cheese consumption, cheese bacteria were detected in the oral cavity of about 1/3 of the rats ranging from 10-3% to 10-1% of the total bacteria. One week after the last cheese intake, 1/ 8 LAB remains in the oral cavity. This study is a proof of concept showing that LAB can remain in the oral cavity several days after fermented food consumption with variability depending on individuals.

The temperature range for consuming hot drinks includes temperatures that can damage cells on the tongue. We hypothesized that the consumption of very hot drinks can lead to a decrease in the ability to perceive low concentrations of tastants. We evaluated the ability to perceive low concentrations of five prototypical sapid compounds in 42 women and 40 men aged 18–65. A questionnaire made it possible to collect the usual frequencies (number of unit/day) and consumption temperature levels (medium hot/very hot) for four very common hot drinks (coffee, tea, herbal infusions, and hot chocolate). Our results showed that subjects who consumed very hot drinks (versus medium hot) were less sensitive to sweet (p = 0.020) and salty (p = 0.046) tastes. An aggravating effect of high consumption frequencies was only shown for sweet taste (p = 0.036). Moreover, our data also showed that women were more sensitive than men to sour, bitter, and umami tastes (p values < 0.05), as well as that taste sensitivity decreases with age, especially after 50 years old (all tastes; p values < 0.05). These findings strengthen our knowledge about the influence of sex and age on taste sensitivity, and they provide knowledge on the influence of consumption habits related to hot drinks on taste sensitivity.

Objective markers of usual diet are of interest as alternative or validating tools in nutritional epidemiology research. The main purpose of the work was to assess whether saliva protein composition can reflect dietary habits in older adults, and how type 2 diabetes impacted on the saliva-diet correlates. 214 participants were selected from 2 European cohorts of community-dwelling older adults (3C-Bordeaux and Seniors-ENRICA-2), using a case–control design nested in each cohort. Cases were individuals with type 2 diabetes. Dietary information was obtained using the Mediterranean Diet Adherence Screener (MEDAS). Saliva was successfully obtained from 211 subjects, and its proteome analyzed by liquid chromatography–tandem mass spectrometry. The relative abundance of 246 saliva proteins was obtained across all participants. The salivary proteome differed depending on the intake level of some food groups (especially vegetables, fruits, sweet snacks and red meat), in a diabetic status- and cohort-specific manner. Gene Set Enrichment Analysis suggested that some biological processes were consistently affected by diet across cohorts, for example enhanced platelet degranulation in high consumers of sweet snacks. Minimal models were then fitted to predict dietary variables by sociodemographic, clinical and salivary proteome variables. For the food group «sweet snacks», selected salivary proteins contributed to the predictive model and improved its performance in the Seniors-ENRICA-2 cohort and when both cohorts were combined. Saliva proteome composition of elderly individuals can reflect some aspects of dietary patterns.

The salivary metabolome has been increasingly studied over the past ten years due to the potential of saliva as a non-invasive source of biomarkers. However, although saliva has been studied in relation to various diseases, its dynamic evolution during life is not known. This is particularly true for the first months of life. Infancy is indeed a critical period during which numerous behavioural and physiological events occur, such as dietary transitions and tooth eruption, which can lead to important biological modifications in the oral cavity. The aim of this work was therefore to study the evolution of the salivary metabolome during the first months of life by 1H NMR. Saliva of 32 infants with different milk feeding histories (breast vs formula) was collected at 6 stages, including 3 months old, 15 days before the onset of complementary feeding (CF), approximately 15 days after the onset of CF, approximately 21 days after the onset of CF and at approximately 11 and 15 months, and analysed. The longitudinal analysis showed a significant modification of the profiles of 18 metabolites over time; 14 presented an increase in abundance whereas 4 presented a decrease. These modifications seemed to be linked, for the most part, to an increase in oral microbial metabolism. Milk feeding history during the first months of life had no effect on metabolites. This work shows that the salivary metabolome should be considered when studying the changes occurring during infancy.

BACKGROUNDThere is growing evidence that the Mediterranean (Medi) diet may lower the risk of type 2 diabetes mellitus (T2DM). Whether this association is due to the Medi diet by itself or is mediated by a diet -associated lower rate of overweight is uncertain. Our aim was to disentangle these relationships among UK adults.METHODSBased on 21 585 participants from the UK Biobank cohort, the adherence to the Medi diet (high fruits, vegetables, legumes, cereals, fish, olive oil; low meat, dairy products; and intermediate alcohol intakes) was assessed (range 0-18). Data on diabetes were self-reported, and overweight was defined as a body mass index (BMI) ≥ 25 kg/m². A mediation analysis was implemented to disentangle the role of overweight in the Medi diet-T2DM relationship.RESULTSThe average baseline Medi diet score was 8.8 [standard deviation (SD) 2.6]. During a mean follow-up of 6.1 years, 473 individuals developed T2DM. A higher adherence to a Medi diet (+1 point) was associated with 14% decreased risk of T2DM [hazard ratio (HR): 0.86, 95% confidence interval (CI): 0.82-0.90]. This association split into an indirect effect of 10%, mediated by lower odds of overweight (HR: 0.90, 95% CI: 0.87-0.92), and a direct effect of the Medi diet of 4% (HR: 0.96, 95% CI: 0.93-0.99), regardless of the effect mediated by overweight.CONCLUSIONSConsidered as a single mediator, reduced overweight mainly contributes to the association between greater Medi diet adherence and lower risk of T2DM on this British subsample. However, the direct effect of the diet on the risk of T2DM, even weaker, should not be overlooked.

Épidémiologie. Au cours des dernières décennies, l’incidence du diabète de type II (DT2) a augmenté de manière significative à travers le monde, entrainant une augmentation de la morbidité et de la mortalité associées. En termes de prévention, les preuves s’accumulent quant à l’association entre l’adhérence à un régime de type Méditerranéen et un moindre risque de DT2. Dans cette étude, nous nous sommes intéressés à l’effet potentiellement médiateur de l’indice de masse corporelle (IMC) en tant que mécanisme sous-jacent à cette relation. Les participants de la UK Biobank ayant des données cliniques sur le statut diabétique et ayant répondu à au moins un questionnaire nutritionnel ont été inclus. Le statut diabétique était auto-déclaré et les participants ayant un diagnostic de diabète prévalent, gestationnel ou incertain (ç.à.d. variant au cours des suivis) ont été exclus. Le score MEDAS a été utilisé pour évaluer l’adhérence à un régime de type Méditerranéen à l’inclusion, basé sur les seuils de consommation de 11 groupes d’aliments (huile d’olive, légumes, fruits, viande rouge, beurre ou crème, boissons sucrées, vin, légumineuses, poisson, pâtisseries et noix) ainsi qu’une question additionnelle sur la consommation préférentielle de viande rouge ou blanche. Une analyse de médiation causale basée sur un modèle de Cox à risques proportionnels a été utilisé pour évaluer les relations entre MEDAS score et risque de DT2. L’échantillon d’étude était composé de 6362 participants, dont 113 ont développé un diabète incident durant une période de suivi moyenne de 4,6 ans. À l’inclusion, le score MEDAS moyen était de 4,6, variant de 0 à 11. Concernant l’effet total, l’incidence de DT2 était réduite de 12 % chez les participants ayant un score MEDAS plus élevé. Cependant, l’effet direct du score MEDAS sur le risque de DT2 n’était pas significatif après ajustement sur les potentiels facteurs de confusion dont l’IMC (RR 0,91 IC 95 % [0,82–1,02]). Les analyses de médiation ont suggéré que l’IMC expliquait environ 3 % de l’effet du score MEDAS sur le risque de diabète (RR 0,97 IC 95 % [0,96–0,97]). Les effets bénéfiques, et désormais bien connus, d’une plus grande adhérence à un régime de type Méditerranéen sur le risque de DT2 pourraient en partie être médiés par la modulation de l’IMC chez les participants de la UK Biobank.