Effects of Hydrothermal Treatments on Physicochemical Properties and In Vitro Digestion of Starch

Starchy food items such as rice and potato with high carbohydrate content raise blood sugar. Hence, consuming low glycaemic foods is one tool to keep diabetes under control. In this study, potato and brown rice (Njavara rice) starches were subjected to hydrothermal treatments: heat moisture treatment (HMT) and annealing (ANN) to develop starch-based food products fit for consumption by diabetic patients. The effects of hydrothermal treatments on physicochemical properties and in-vitro enzymatic digestion of starch were determined. It was observed that hydrothermal treatments decreased the swelling power (SP)% and increased the water solubility (WS)% of the native starches. Native potato starch (PSN) showed a high SP of 80.33%, while annealed potato starch (PANN) and heat moisture treated potato starch (PHMT) showed SP reduced to 65.33% and 51.66%, respectively. Similarly, the SP % reduced from 64.33% in native brown rice (BRN) to 44.66% in annealed brown rice (BRANN) and 38.33% in heat moisture treated brown rice (BRHMT). WS % increased from 32.86% in PSN to 36.66% in PANN and 40.66% in PHMT. In BRN, the WS % increased from 14.0% to 14.66% in BRANN and 18.33% in BRHMT. Amylose content increased from 13.23% and 14.56% in PSN and BRN to 16.14% in PANN 17.99% in PHMT, 17.33% in BRANN, and 18.98% in BRHMT. The PSN crystallinity index reduced from 33.49 to 30.50% in PANN and 32.60% in PHMT. At 12 h of enzymatic digestion, it was found that the degree of hydrolysis (DoH) of PHMT (31.66%) and PANN (36.82%) reduced when compared to PSN (41.09%). Similarly, BRHMT exhibited the lowest DoH at 12 h compared to BRANN (29.24%) and BRN (35.48%). This study highlights the importance of hydrothermal treatments on starch in developing low glycaemic index commercial starch-based food products.