Impact of Fermentation Duration of Okara on Dough and Bread Properties

Okara, a nutrient dense by-product of soymilk and tofu processing, serves as a high potential fiber source in various food application. Nevertheless, the high insoluble fiber fraction in okara might negatively affect product characteristics. Several measures have been proposed to increase soluble fiber fractions such as via physical and chemical modifications. In this study, wet okara has been fermented at various duration (0, 4, 8 and 20 hours) with S. cerevisiae and the fermented okara powder was incorporated in high-fiber bread making. Physicochemical characteristics of dough and bread, namely dough expansion and stickiness, bread loaf volume, textural properties, and degree of retrogradation were determined. Control samples are bread made without addition of okara (C1) and with addition of 10% non-fermented okara (C2). Addition of okara significantly decreases dough expansion, but increases dough stickiness perhaps due to higher fiber content and increase in soluble fiber content in the dough, respectively. However, bread made with okara fermented at longest duration, FO20 (20 h) had the highest increment in dough expansion. Similar improvement was observed for dough stickiness, with FO20 creates dough with the lowest stickiness. Fermentation of okara improved bread loaf volume, with increasing fermentation duration enhanced the value. Similarly, longer fermentation duration resulted in okara enriched bread with lower firmness. A 5-days storage of the bread at room temperature showed that FO20 has the lowest degree of staling, therefore able to maintain the bread softness. The observed findings of bread-enriched fermented okara was an interplay of less disruption on gluten network, improved gas holding capacity and enhanced moisture absorption. In conclusion, manipulating fermentation duration of fiber source can be an alternative for enhancement for soluble fiber content in developing high-fiber products with improved quality.