Insights into the structural, thermal, crystalline and rheological behavior of various hydrothermally modified elephant foot yam (Amorphophallus paeoniifolius) starch

Starch isolated from elephant foot yam (Amorphophallus paeoniifolius) was modified by heat moisture treatment (HMT) using various heating sources viz. hot air oven (HAO), autoclave (AL), and microwave (MW). Morphology, surface roughness, thermal, structural, and dynamic rheological properties of native and HMT modified elephant foot yam starch (EFYS) were evaluated. Surface cracks, pitting, and scratching were prominent on the granules after modification, leading to an increase in surface roughness. HAO treated EFYS exhibited the highest formation of agglomerations and an increase in particle size compared to other treatments. All the modified EFYS samples had a significant increase in amylose content, and the highest was observed in HAO treatment. An increase in gelatinization temperature and reduction in gelatinization enthalpy were observed in HMT EFYS. Relative crystallinity was reduced in HMT modified EFYS which varied in the range of 35–41% as compared to native EFYS of 43%. A decrease in molecular weight from native 6.39 × 107 g/mol to HMT modified EFYS was observed which varied in the range 4.51–5.37 × 107 g/mol. Interestingly, the increase in elastic behavior was noticed in all modified EFYS compared to native EFYS and the highest increment was noted in HAO treated EFYS, suggesting the formation of a strong gel network under high shear. The Pearson correlation studies showed that particle size and short amylopectin chain fractions have significant positive correlation with dynamic moduli of EFYS. HMT using HAO treatment resulted in improved characteristics of EFYS and extended the range of its use in food processing.