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Changes in Distribution of Isoflavones and β-Glucosidase Activity During Soy Bread Proofing and Baking

¹The Ohio State University, Department of Food Science and Technology, 2015 Fyffe Road, Columbus, OH 43210. ²Department of Food Science and Technology, Seoul National University of Technology, Seoul, Korea. Phone: +82 2 970 6739. E-mail: JHLee@SNUT.ac.kr ³Corresponding author. Phone: 614-292-2934. Fax 614-292-4233. E-mail: zhang.363@osu.edu

Bread made partially with soy may represent a viable alternative for increasing soy consumption in populations consuming Western diets. The potential health-promoting activity of soy isoflavones may depend on their abundance and chemical form. The objective of this study was to characterize the changes in isoflavone distribution and β-glucosidase activity during the soy breadmaking process. Soy bread ingredients were combined and mixed to form a dough that was subsequently proofed at 48°C for 1–4 hr and baked at 165°C for 50 min to produce breads. The isoflavone composition and β-glucosidase activity in bread ingredients, doughs, and breads were monitored. Soy ingredients and wheat flour (not bread yeast) were the major contributors of the β-glucosidase activity in bread. No degradation of isoflavones was observed during breadmaking but the isoflavone distribution was largely altered. Proofing and baking have important but different roles in changing the isoflavone distribution. Proofing converted isoflavone β-glucosides to aglycones by highly specific β-glucosidase activity. Thermal treatment during baking significantly decreased the isoflavone malonylglucosides and increased isoflavone β-glucosides. Enzyme activity during proofing and the balance between formation and deconjugation of isoflavones during baking determine the isoflavone content and composition in the final product.