Production of resistant starch type III (RS3) from anthocyanin-rich flour

Abstract

This research study was aimed to investigate the production of resistant starch type III (RS3) from anthocyanin-rich flour. The raw materials including purple rice, purple sweet potato, and purple corn were studied. The study consisted of all 3 types of raw materials that contain flour as the main component. The purple flours through the process of extracting protein and lipid to be starch. The studied on the chemical composition, it was found that the carbohydrate content of all 3 types of starches was 80.28-81.52%. The highest amylose content in purple sweet potato starch (20.64%), followed by purple rice starch (9.36%) and purple corn starch (6.27%). The 3 types of purple starches were selected for further study. The studied on the production of resistant starch type III (RS3), after modification by dual-retrogradation treatment (DART), the resistant starch (RS) content of purple rice starch (34.13 %) was higher than that of purple sweet potato (26.15%) and purple corn starch (20.73%). While the dual enzyme treatment (DET) modification was conducted to study the optimum conditions of the α-amylase enzyme, the optimum conditions revealed that the hydrolyzed time was 15 min, pH 5.5, temperature 90°C, enzyme concentration 4 U/g, and initial starch was 25% (w/v) for purple corn, and purple rice starch and 20% (w/v) for purple sweet potato starch. The optimum conditions of pullulanase were 16 h, pH 4.5, temperature 50°C, maximum enzyme concentration of 12 U/g for purple corn starch, 10 U/g for purple rice starch, and 8 U/g for sweet potato starch. After retrogradation at 4°C for 24 h, it was found that the maximum resistant starch content was purple corn starch (54.27%) was followed by purple sweet potato (53.36%) and purple rice (51.34%). RS obtained from purple starches were significantly higher levels of RS content (p<0.05) compared with native purple starches. The studied on the characterization of RS including structure by SEM, physical and thermal properties, and enthalpy of gelatinization (∆H). It was found that the structure of starch granules was changed, swelling and solubility index decreased, the viscosity decreased. In addition, the crystalline pattern from XRD were changed when compared with native purple starch. For antioxidant activity assay, DPPH, ABTS, and FRAP assay were studied. From this study found that RS obtained from purple starches still had lower antioxidant activity compared with native purple starches. The % hydrolysis of RS obtained from purple starches by human saliva, gastric condition, and intestinal condition were decreased when compared to the native purple starches, the result showed that RS obtained from purple starches has similar physiological effects as dietary fiber.