Ultrasound-assisted hydration offers a novel approach to anneal in-situ pinto bean starch

Ultrasound is considered an emerging technology capable of altering macromolecular structures linked to functionality. However, its effects vary depending on whether the ultrasound processing is applied with or without temperature control. This variability creates ambiguity regarding the effects of ultrasound on macromolecules such as starch, which is abundant in cereals and legumes. Here, the effects of temperature controlled versus un-controlled ultrasound-assisted hydration (UAH) on in-situ pinto bean starch structure and its functionality were examined. Four different treatments were designed: normal isothermal treatment (N), temperature-controlled UAH (TC), temperature-uncontrolled UAH (TuC), and high temperature treatment (HT), following the same temperature profile as during TuC. We observed the structure of TC and TuC treated starch to be very different, although N and TC were markedly similar, as were TuC and HT. The ¹H NMR analysis and size exclusion chromatography of debranched starch showed that not controlling the temperature led to minor debranching of starch (from 2.04 to 1.86) and an increase in long chain amylose content. The amounts of single and double helices remained unchanged, indicating a rearrangement of crystalline structures without the formation of new crystallites. The gelatinisation temperature increased by 8 °C, and these starches exhibited drastically different pasting properties, with the pasting temperature elevated by 15–20 °C, peak viscosity reduced by nearly 25 %, and no changes in final viscosity. Our results established that an increase in water temperature during UAH was more impactful than the physical effects of cavitation in driving changes in starch structure-functionality.