Ultrasound-Assisted Enzymatic Preparation of Resistant Starch from Lotus Root with Improved Structural and Anti-Diabetic Properties

Lotus root starch (LRS) is rich in bioactive compounds but has a low native resistant starch (RS) content, limiting its nutritional functionality. This study aimed to enhance the yield of type 3 resistant starch (RS3) from LRS using ultrasound-assisted enzymatic treatment. The process parameters, including pullulanase dosage, hydrolysis time, ultrasonic power density, and treatment time, were optimized through single-factor and orthogonal experiments. Under optimal conditions (36 NPUN/g pullulanase, 24 h hydrolysis, 20 W/L ultrasonic power, 15 min treatment), the RS3 content reached 24.34%. Structural and physicochemical analyses revealed that ultrasound treatment significantly increased amylose content, promoted the formation of a more ordered crystalline structure, and improved thermal stability. The resulting RS3 exhibited reduced solubility and swelling power, along with enhanced resistance to digestion. In vivo studies using a type 2 diabetes mellitus (T2DM) mouse model demonstrated that dietary supplementation with ultrasound-treated RS3 (U-RS3) effectively alleviated hyperglycemia, dyslipidemia, and body weight loss. These findings suggest that ultrasound-assisted enzymatic treatment is an effective strategy for producing high-quality lotus root RS3, suggesting its potential as a functional food ingredient for glycemic and lipid management.