Influence of dietary fibre-enriched foods and of blueberry-rich diet on saliva composition in humans

The main objective of the thesis is to explore the possible “cross-talk” between the brain, intestine and specific foods components (i.e. dietary fibres and blueberry polyphenols). This objective will be achieved through a short-term study and a long-term intervention in humans, with the non-invasive analysis of saliva samples and breath compositions. The short-term study aimed at evaluating the impact of dietary fibres on salivary NAEs during mastication and in the post-prandial phase. Three types of biscuits enriched with 3% barley ?-glucan (?GB) or whole-wheat bran (WWBB) or without dietary fibre (control, CB) were developed. A crossover randomized human study with eighteen healthy and fasting participants was carried out. Saliva samples from subjects in a resting condition, upon mastication of parafilm and one of the three biscuits were collected. Subsequently, the amount of biscuits consumed in an ad-libitum breakfast was measured and post-prandial saliva samples, blood glucose, and questionnaires of appetite and food liking were collected over the following two hours. Data demonstrated that salivary NAEs concentration increased only upon food mastication instead of mastication itself, independently from dietary fibre composition of the food. The type of biscuits did not influence individual appetite nor post- prandial blood glucose; on the contrary it influenced the persistence of NAEs in saliva over 30 min after consumption. Future studies will clarify the mechanisms behind this finding and the role of salivary NAEs in food liking and appetite cues after food consumption. The aim of long-term intervention study was to test the influence of a one week-consumption of blueberries on the volatile organic compounds (VOCs) of breath and saliva in humans. Fourteen healthy volunteers participated in this three-week single blind study with a two- week cross over design. After a one-week of baseline period with a low polyphenol-diet (BL), subjects were grouped randomly to continue the same diet (control diet, CT) or to add 200 g/day of fresh blueberries (intervention diet, INT) for one week. In the following week they switched to the other arm. At the end of each week, fasting subjects reached the laboratory to collect saliva samples and to have on-line analysis of breath by PTR-ToF-MS. After INT and CT, difference was found neither in VOC fingerprints nor in single VOC of breath and saliva samples. Nevertheless, a significant correlation was shown between saliva and breath composition for methanol, formaldehyde, ethanol, acetone and propanol. Numerous previous studies focused on VOCs composition of breath of patients and of healthy subjects, but very few studies focused on salivary VOCs. Therefore the link found in this study between saliva and breath VOCs may open a new research path to clarify the mechanisms behind the metabolic effect of the dietary intervention in humans.