Abstract
Wheat bran is the main co-product of the milling industry, resulting from the transformation of wheat grains into flour or semolina. It represents the outer layer of the grain containing various tissues; mainly pericarp, testa and aleurone. Wheat bran is produced every year in considerable quantities and is mainly used for animal feed. However, given its nutrient composition and availability, it could also be used for human food. Several studies have shown the beneficial effect of wheat bran consumption on human health, particularly in reducing the risk of obesity, cardiovascular disease, diabetes and others.Ferulic acid (FA) (-cis and -trans) and its dimers (8,5′-diFA, 8,5 ′- benzo-diFA, 8-O-4'-diFA and 5,5'-DiFA) account for about 95% of the phenolic acids in wheat bran, concentrated mainly in the aleurone layer and the pericarp. FA is known for its antioxidant, anti-microbial and anti-inflammatory properties. It is also able to be transformed into aromatic derivatives such as vanillin or 4-vinylguaiacol in the presence of microorganisms. In connection with the bakery industry, the main objective of this phD work is to study the effect of certain practices on the content of FA and its derivatives in bran and/or bread. The study of the variations in FA content from wheat to bread showed an effect of terroir and wheat varieties on the FA content of bran as well as an effect of the type of ferment on the FA content of bread. In a synthetic fermentation medium, the behavior of FA was studied in the presence of sourdough yeasts and lactic acid bacteria, alone or in combination. We found that FA metabolism varied among strains and that yeast/bacteria interactions had an effect on the consumption and conversion of FA. Indeed, the transformation of FA into dihydroferulic acid is favored in co-cultures compared to monocultures, to the detriment of the production of 4-vinylguaiacol. Overall, our results clarify the evolution of FA from grain to bread by highlighting the important role of fermentation microorganisms and their interaction in its transformation, and are discussed in view of their interest in baking.