2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

Soybean hulls contain peroxidase, an enzyme used in the European bread baking industry as a replacement for potassium bromate. Hulls contain a low percentage of nitrogen where fiber and carbohydrates are the major components. Our objective was to determine whether air classification of milled hulls can be used to fractionate and enrich peroxidase. Hulls were milled either one or three times at 18,000 rpm with an Alpine pin mill followed by air classification to yield 5 fractions with particle size distributions: <15 micrometers (um), 15-18 um, 18-24 um, 24-30 um, and >30 um. Protein shift for 1 passage at 18,000 rpm was 38% whereas that for 3 passages was 47%. For each grinding and classification, nitrogen was concentrated in the first three fractions. Assays for aqueous extracts of all 10 fractions showed that peroxidase resides mainly in the coarser, high carbohydrate fractions from 18 to >30 um. Scanning electron microscopy demonstrated an abundance of protein bodies in both the <15 and 15-18 um fractions, concentration of hour glass cells in the 18-24 um fraction, and a composite of partially disintegrated palisade cells, hour glass cells, parenchyma cells and aleurone cells in the last two fractions. Peroxidase, as previously claimed in the literature, is associated with the hourglass cells which appear to be concentrated in the last 3 coarse fractions.