Microbial and enzymatic modification of wheat bran properties at reduced water content

Cereal bran is high in dietary fibre and a good source of health promoting compounds. Enzymatic or microbiological methods offer means to improve the technological properties of bran. Water content is an important parameter in such modifications, influencing f.ex. the diffusion of components and rheological properties of the material. In studies concerning enzymatic or microbial modification of bran, the reactions have often been conducted at high water content. In industrial scale applications, low water content may be advantageous, especially in processes followed by drying as a post-treatment procedure. The aim was to study the effects of water content ranging from about 30–90%, on yeast fermentation and xylanase treatment of peeled wheat bran. Yeast was metabolically active also at low water activity, as shown by carbon dioxide production. Folate content and the amount of free ferulic acid approximately doubled in yeast fermentations at high water content, but did not markedly change in yeast fermentations at low water content. Instead, the amount of soluble arabinoxylan increased significantly also at low water content. In the enzymatic xylanase treatments, arabinoxylan solubilization was highest at the water content of about 40%, where material was transformed from powder like material into a plastic mass. The effects of water content on the kinetics of xylanase action are being further studied.