Structure and Digestive Qualities of Cooked Black Beans after Soaked in NaCl with the Assistance of Ultrasound

To investigate the effect of ultrasound assisted NaCl soaking on the structure and digestive characteristics of black beans, the scanning electron microscopy, infrared spectroscopy analysis, X-ray diffraction and other methods were used to analyze the mechanism of NaCl on the structure of black beans. And the thermal properties, water absorption, and swelling rate were used to clarify the changes in the properties of the black beans during the ripening process, and the in vitro digestive properties of starch were analyzed. The results showed that ultrasound-assisted NaCl soaking decreased the densification of black bean powder particles and made the gap between particles larger while reducing the damage to the starch crystallization region. With the increase of NaCl concentration, the swelling rate of black bean particles increased by 28%, 48%, and 56% compared to water soaking, and the hardness significantly decreased. The gelatinization degree increased to 40%, 43%, and 45%, and the hydrolysis rate of black bean starch decreased to 19.05%, 17.93%, and 17.48%, respectively. This indicated that sodium ions could inhibit starch digestion, the NaCl soaking treatment in this study would provide a theoretical basis for the development of low GI functional foods.