Influence of Different Ultrasonic Treatments on Physicochemical Properties of Sea Red Rice Starch-Lauric Acid Complex

This study aimed to investigate the effects of different ultrasonic treatments on the physicochemical properties of the starch-lauric acid complex. The starch-lauric acid complex between the sea red rice starch (SRS) and lauric acid (LA) was prepared using three ultrasonic treatment methods: pre-treatment, co-treatment, and post-treatment. The complex index, particle morphology, crystalline structure, pasting properties, thermal properties and in vitro digestibility of the complexes were systematically analyzed. The results showed that the complex index of the starch-lauric acid complex without ultrasonic treatment (LA-SRS) was 5.66%. Ultrasonic pre-treatment starch-lauric acid complex (LA-USRS) and ultrasonic co-treatment starch-lauric acid complex (ULA-SRS) significantly increased the complex index to 9.95% and 14.24%, respectively, while ultrasonic post-treatment starch-lauric acid complex (LA-SRS-U) decreased to 4.78%. Ultrasonic treatments complex showed significant decrease in the degree of short-range order structure and relative crystallinity (P<0.05). In terms of gelatinization properties, all ultrasonic treatments complex significantly elevated the gelatinization temperature (P<0.05) and reduced the breakdown value, setback value, and final viscosity (P<0.05). Thermogravimetric analysis indicated that ultrasonic treatments enhanced the thermal stability of complex, with the peak temperature increasing from 305.5 ℃ to 317.0 ℃. Additionally, in terms of in vitro digestibility, LA-USRS showed an increase to 37.65% in resistant starch content, compared to SRS. In contrast, ULA-SRS and LA-SRS-U had significantly higher contents of rapidly digested starch and slowly digested starch than SRS (P<0.05). Correlation analysis revealed that the complex index was significantly positively correlated with gelatinization temperature and peak temperature (P<0.05), and significantly negatively correlated with the degree of short-range ordering and relative crystallinity (P<0.05). Overall, the physicochemical properties of the starch-lauric acid complex were significantly influenced by different ultrasonic treatments. These findings would provide theoretical basis for the development of starch-based foods with tailored digestive behaviors.