Studies on the Structure and Digestive Qualities of Cooked Black Beans after being Soaked in NaCl with the Assistance of Ultrasonography

The structural and digestive characteristics of black beans under ultrasound-assisted NaCl treatment were studied. Scanning electron microscopy, infrared spectroscopy, and X-ray diffraction were used to characterize the effect of NaCl on the structure of black beans. Thermal properties, water absorption, and swelling were used to clarify the changes in the properties of the black beans during the ripening process and to analyze the in vitro starch digestive properties. 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. The swelling rate of black bean particles with different concentrations of NaCl increased by 28%, 48%, and 56%, respectively, and the degree of pasting increased by 40%, 43%, and 45%, respectively, compared with that of water soaking, indicating that NaCl soaking made the black beans more easily pasted. In addition, the hydrolysis rate of black bean starch decreased significantly with increasing NaCl concentration, indicating that Na⁺ could inhibit starch digestion. Therefore, NaCl treatment as a new technology could provide a theoretical basis for the development of low GI functional foods.