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Modification of bran protein solubility and quality by enzyme induced cell wall degradation and microbial fermentation
E. Arte (1), R. Coda (2), C. Rizzello (3), E. Nordlund (4), K. Katina (2), K. KATINA (5). (1) Univeristy of Helsinki, Helsinki, Finland; (2) University of Helsinki, Helsinki, Finland; (3) University of Bari, Bari, Italy; (4) VTT Technical Research Centre Finland, Espoo, Finland; (5) Univ of Helsinki, Helsinki, Finland

Wheat bran contains 15–19 % of good quality protein, compared to protein in the endosperm part of the kernel. However, protein usability is restricted for human digestion by its location inside bran aleurone cell walls. Exploiting the protein fraction of wheat bran would enable to design novel multifunctional ingredients containing both high amount dietary fibre and good quality protein. The aim of this work was to explore the influence of bioprocessing on the protein content and quality of wheat bran. Different bioprocessing methods including, impact of bran endogenous enzymes, Lb. <i>brevis</i> VTT E–95612, and C. <i>humilis</i> VTT C–96250 microbes, and cell wall hydrolyzing enzymes Depol 761P and Viscoferm were incubated for 24 h at 30 °C for degradation of the bran cell wall and releasing bran proteins to metabolic conversion. The degradation of cell wall polysaccharides was determined by analysing soluble pentosans and reducing sugar content. The results showed that by activation of endogenous enzymes solubilization of bran proteins increased significantly from 14% (without bioprocessing) up to 75 % (Kjeldahl method AACC 46–11A). Bioprocessing with endogenous and exogenous enzymes did not affect significantly on the peptide content (OPA method), the amino acid content  measured by Amino acid analyser or the digestibility of the proteins, even though the added enzymes showed degradation of cell walls by increased contents of soluble pentosan and reducing sugars. When microbial strains were used for bioprocessing, the soluble protein content increased up to 60% (strains) and with enzymes up to 52 %.The metabolic conversion of proteins by the microorganisms was shown by increased amino acid and decreased peptide contents, which lead also to an increase of the digestibility of the bran proteins (22%).

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