Biological modification of functional properties of orange-fleshed sweet potato flour by spontaneous fermentation and its possible utilization

This study evaluated some functional properties of the orange-fleshed sweet potato flour modified by spontaneous fermentation at different times. This information can further be used to assess its potential application in food processing. Under anaerobic conditions, the peeled slices of orange-fleshed sweet potatoes were fermented at 30°±2°C spontaneously. Samples were taken at 0, 24, 48, and 72 hours and processed into flour. Observations were performed on the pH, residual starch yield, water retention, expansion rate, solubility, and sensory evaluation of the color. Starch granules were observed on samples of 48 h and 72 h using a scanning electron microscope (SEM). Results showed that the properties of the flours were modified by fermentation time. There were linear decreases of pH from 4.87 to 4.16, residual starch yield from 62.12% to 47.88% (db), and color score from 3.6-3.7 (brownish yellow) to 1.6-1.7 (yellowish white). A quadratic decrease in solubility at both 85ºC and 90ºC from 16.92% to 16.74% and 13.07% to 12.45%, respectively, was observed. However, a quadratic increase was found in water retention from 2.55 to 2.72 and linear expansion rate from 13.54 to 16.59. Starch granules changed with fermentation time. With these functional properties, the orange-fleshed fermented sweet potato flour can be applied as raw material for producing baking products with a distinct acidic taste.