Effect of Combined Ultrasound-Autoclaving Pretreatment Followed by Acetylation Modification on the Structural and Functional Properties of Loquat Kernel Resistant Starch

A combined physical and chemical modification strategy involving ultrasonic and autoclaving pretreatment followed by acetylation was applied to improve the functional properties of loquat kernel resistant starch (RS). The effects of different modifications on the multiscale structure and functional properties of RS were systematically investigated. The results showed that ultrasound-autoclaving pretreatment effectively disrupted the structure of RS, reduced the relative crystallinity from 30.1% to 19.9%, and decreased the short-range molecular order. The treated starch exhibited significantly enhanced solubility (16.5%) and swelling power (2.0 g/g) at 95 ℃ compared with the control group (P < 0.05), and its acetylated product (UHARS) showed the highest degree of acetyl substitution (0.069). Different modifications affected the freeze-thaw stability of RS, and single autoclaving or ultrasonic treatment was the most effective in improving this property, with a syneresis rate of approximately 10% after 5 freeze-thaw cycles. Conversely, acetylation treatment reduced the freeze-thaw stability of RS. In vitro digestion experiments demonstrated that combined modifications enhanced the enzymatic resistance of RS; the RS content of UHARS was 82.0%, which was significantly higher than that of the untreated group (64.0%) (P < 0.05). This study elucidates the synergistic mechanism of “physical disruption sensitization and chemical modification enhancement”, providing a theoretical basis for the high-value utilization of loquat by-products and the development of functional starch ingredients.