Process optimization in the pyroconversion of native sweet potato starch: structural and functional characterization of pyrodextrin

Abstract

AbstractThis work aims to produce dextrin from sweet potato (Ipomoea batatas) starch by pyroconversion. The effect of dextrinization process (roasting time, temperature, and hydrochloric acid concentration) on properties (structural and functional) of starch have been studied using central composite design of experiment. Reaction conditions included: roasting time (55 and 94 min), temperature (127 and 152 °C), and hydrochloric acid concentration (0.17 and 0.43 M). The temperature (quadratic effect X22) is highly significant on the three measured responses (p < 0.05) (Color Index (CI), Turbidity (Turb), and Saccharification Percentage (SP)). Also, the findings indicated that the two most important parameters influencing the pyroconversion of sweet potato starch in the current study were temperature (X2) and hydrochloric acid concentration (X3). The optimal conditions for dextrin production obtained are 94 min, 127 °C and 0.43 M for roasting time, temperature, and hydrochloric acid concentration respectively having 97% of solubility. The FTIR analysis revealed that OH, C-H, C-O, C–C and C-O–H were the main functional groups. These functional groups remained unaffected by the pyroconversion, since the bands extend and the spectrums of all native and pyrodextrin were similar. X-Ray Diffractometry analysis results of dextrin showed that the thermal treatment reduces the crystallinity of starch. Also, this analysis shows starch has CA-type XRD patterns. Scanning Electron Microscopy (SEM) analysis results showed that the defined optimal production maintains the morphology of starch. Differential scanning calorimetry (DSC) used for thermal analysis helps to obtain the glass transition temperature of modified starch equals to 139 °C. Optimal conditions of production of pyrodextrins from sweet potato granule starches could be easily produced with improved physicochemical properties to be used as encapsulating agent or additives in food and chemical industries.