Understanding the change of nutritional and antioxidant content in purple brown rice grown in rice–shrimp farming systems during green germination process

Abstract

This research examined the way germination conditions influence the nutritional and antioxidant profiles of a new purple brown rice variety grown in rice–shrimp farming systems in the Mekong Delta, Vietnam. Response surface methodology was employed to optimize temperature (25–40 °C) and time (18–36 h) for the enhancement of key bioactive components, including γ-aminobutyric acid (GABA), free amino acids, total phenolic content (TPC), and anthocyanins. The findings indicated that germination markedly enhanced GABA levels (up to 0.015 mg/g) and free amino acid concentrations (up to 7.3 mg/g), which can be ascribed to enzymatic activation and stress-induced mechanisms. Anthocyanins, the primary antioxidants in purple rice, significantly decreased, retaining approximately 3 % of their original concentration, likely due to thermal and oxidative sensitivity during soaking and sprouting. The maximum TPC recorded was 37.09 °C for 22.25 h, although it decreased from the original value, suggesting partial degradation compensated by the enzymatic release of bound phenolics. Optimal germination was achieved at 35.2 °C for approximately 26 h, as the optimal condition for achieving a high germination rate (97.93 %), moderate anthocyanin retention (0.091 mg/g), and increased levels of GABA and amino acids. The findings highlight the trade-offs associated with germinating pigmented rice and present a scientifically validated protocol for producing germinated purple rice with enhanced functional value. This study advances the creation of high-value, health-promoting rice products derived from local varieties suited to integrated rice–shrimp ecosystems.