Bioprocessing as a tool to improve bioavailability of phytochemicals of wheat bran

Background: Health effects related to the consumption of wholegrain foods are assumed to be partly derived from the phenolic compounds of the bran fraction of grain [1, 2]. In wheat bran, ferulic acid (FA) is the most abundant phenolic compound. FA is a structural component in cell walls, cross-linking cell wall polysaccharides, such as lignin and arabinoxylan. Most of FA is covalently bound to the cell wall structures, and thus the bioavailability of FA in physiological conditions is suggested to be low [3]. Aim: The objective was to improve the biological availability of phenolic acids of wheat bran by bioprocessing, using a treatment by cell wall degrading enzymes and yeast fermentation. Experimental: Five different wheat breads, 1) white wheat bread, 2) wholemeal bread, 3) wholemeal bread with native wheat bran, 4) wholemeal bread with fermented wheat bran and 5) wholemeal bread with fermented and enzymatically treated wheat bran, were prepared and analyzed in their phenolic acid bioaccessibility in vitro. The release of FA from the wheat to be available for absorption was determined in a dynamic in vitro model of upper gastro-intestinal tract [3]. To monitor the technological functionality of wheat bran, the instrumental texture and chemical composition of breads were also analysed. Results: The processing of wheat bran by fermentation together with hydrolytic enzyme treatment increased bioaccessibility of FA five-fold as compared to native bran. In a dynamic in vitro model of colon, it was also found that the pre-treatment of bran increased the amount of FA colonic metabolites (phenylpropionic acids) which have been reported to have anti-inflammatory properties. Pre-treatment of bran by bioprocessing improved also the volume and shelf-life of wholemeal wheat breads supplemented with bran. Both nutritional and textural improvements of wholemeal bread fortified with bran are suggested to be based on enzyme- and fermentation-induced degradation of bran cell wall structures. Synergetic effects of enzymatic and microbial activities resulted in solubilisation of cell wall carbohydrates and release of covalently bound FA. Conclusion: The results show that both bioaccessibility and colonic metabolism of phytochemicals of wheat bran, and also the technological quality of the whole meal wheat bread fortified with bran, can be improved by pre-processing of the bran by hydrolytic enzymes and fermentation. Bioprocessing thus offers the possibility to make nutritionally boosted wholemeal cereal products with high sensory quality.