Effects of sodium pyrophosphate on moisture characteristics and texture evolution of indica rice gel during short-term retrogradation at low-temperature

Abstract

Starch retrogradation is a common phenomenon of quality deterioration in indica rice gel (IRG)-based products, and is closely related to the state and dynamic behavior of water molecules in the system. This research investigated how tetrasodium pyrophosphate (TSPP) delayed IRG retrogradation during short-term low-temperature storage. The texture analyzer, LF-NMR, FTIR, XRD and SEM were used to elucidate the moisture characteristics, texture parameters, and starch inner conformational changes from macroscopic properties to microstructural perspectives. Results demonstrated that 0.6 % TSPP significantly increased IRG's water content, elevating the water solubility index (WSI), water absorption index (WAI), and swelling power (SP) to 7.20 %, 3.26 %, and 7.45 % respectively, while reducing hardness by 18.06 %. TSPP hindered the rearrangement of starch molecules and suppressed the reconstruction of short-range ordered structures in low-moisture regions, thus affecting the degree of starch retrogradation. Additionally, TSPP affected water-starch matrix binding and altered the distribution of gel hydrogen bonds, thereby changing the water migration and ordered arrangement of starch molecules. The microstructure characterization showed that the IRG treated with TSPP shows a larger pore structure. This study revealed that TSPP retarded IRG retrogradation through dual synergistic effects involving water-starch-phosphate interactions. These findings provide technical references for developing high-moisture gel rice products with low additive content and lower retrogradation.

Keywords: Indica rice gel; Moisture characteristics; Retrogradation; TSPP.