Effects of different sodium periodate/TEMPO oxidation sequences on the structural and functional properties of insoluble dietary fiber from okara

Herein, the effects of different oxidation sequences of NaIO₄ (sodium periodate, O) and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical,. T) on the structure and functional properties of insoluble dietary fiber (IDF) in okara were investigated. IDF was oxidized using NaIO₄ (1:1 w/w, 6 h, dark) and TEMPO/NaBr/NaClO (15 mmoL, pH 10.5, 4 h) systems. The results show that after T oxidation, the IDF exhibits significantly higher carboxyl group content and a substantial reduction in particle size to the nanoscale. The smallest can reach 288.35 ± 11.75 nm. Significantly improved thermal stability was observed in the modified IDF, and both T-treated and T-co-treated samples exhibited unique fiber structures. The sequence of oxidation significantly influenced the surface functional groups of the samples, consequently affecting their functional properties. Specifically, OT-IDF (IDF oxidized by NaIO₄-TEMPO) demonstrated a significantly enhanced oil-holding capacity and optimal nitrite ion adsorption capability, 143 % and 147 % of the IDF, respectively. However, the degradation of lignin during oxidation led to a significant decrease in the antioxidant capacity of the IDF, only 33.1 % of the IDF. However, the degradation of lignin during oxidation led to a significant decrease in the antioxidant capacity of the IDF. In conclusion, OT-IDF synergistically optimized the functional properties of IDF, offering a viable approach for the high-value utilization of okara.