Thermally-induced modulations of starch and protein characteristics in sorghum grain

Abstract

Sorghum grains were processed using infrared radiation (IR), microwave (MW), and steam treatment (ST); fractionated to obtain corneous endosperm (CE), and were studied for starch and protein modifications. IR increased in vitro protein digestibility (59.31–84.45%), resistant starch content (13.02–21.21%), and decreased glycemic index (GI) (59.19–44.45%). MW increased the slowly digestible starch (SDS) (39.19–45.11%), however could not decrease GI. ST increased rapidly digestible starch (47.59–70.82%) with a drastic decrease in protein digestibility by 47.88%. Functional analyses revealed that the ST increased both water and oil absorption capacities upto 174.28 and 172.17%, respectively. Thermal, structural, and pasting profile analyses revealed limited changes in IR treated sample when compared to control. Changes in thermal properties induced more stable configuration of treated samples compared to control. Modulations in the starch and protein characteristics suggested that the IR promoted binary complexing between starch and protein via hydrogen bonding. This binary complex imparted low GI to CE and hence could be used in food formulations for obese and diabetic populations. However, the dipolar movements in MW caused transglycosidation that increased the SDS content, which needs to be explored for further utilization. ST resulted in honey-comb like structure of starch resulting in the superior techno-functional qualities that could be used as texture modifier in food products. This study highlights that the method of thermal treatment plays a pivotal role in enhancing the value of modified grains, tailoring them into consumer-specific products.