Structural characterization and in vitro digestibility of rice starch processed with the combination of ultra-high pressure homogenization, debranching, and temperature-cycled crystallization

Abstract

This study examined the structural characterization and in vitro digestibility of rice starch processed with the combination of ultra-high pressure homogenization (UHPH), debranching, and temperature-cycled crystallization under various pressures (0–160 MPa). After UHPH treatment, the degree of branching (DB) of processed starches (0.65%–2.03%) was lower than that of the native rice starch (NS, 2.96%). Assessment of chain length distribution suggested that the considerable amylose was produced after treatments. Processed starches exhibited an irregular fragmented structure, and the crystalline structure was transformed from A-type (native rice starch) into B + V-type (processed starches). Moreover, the relative crystallinity (RC) and the absorbance ratio of 1047/1022 cm⁻¹ (R_1047/1022) of processed starches decreased from NS (RC, 22.99%; R_1047/1022, 0.79) to 13.47%–18.21% (RC) and 0.51–0.78 (R_1047/1022), respectively. Iodine binding curves revealed that processed starches possessed the higher degree of polymerization (DP). Furthermore, the contents of slowly digestible starch (SDS) and resistant starch (RS) increased in all processed starches, and the RS content of starch treated under 160 MPa (35.33%) was notably greater than that of native starch (9.37%). These results suggested that the UHPH can be used as a pretreatment strategy to reduce the digestibility of starch products.

Practical applications

UHPH pretreatment disrupts starch molecular chains to produce the large amounts of short linear amylose. Debranching followed by temperature-cycled crystallization can increase the content of resistant starch (RS), yielding a raw material suitable for boosting the health of the digestive system and overall health. Therefore, UHPH pretreatment has a high application value in the field of starch modification.