Bioactivity and chemical components of Thai rice in five stages of grain development

Tracking changes in the bioactive compounds of white (ML-W), red (ML-R) and black (RB) rice during the 5 stages of grain development were studied. Total anthocyanin (TAC) was found only in RB (stages 3-5) and proanthocyanidin (TPAC) contents were only found in ML-R (stages 2-5). Considerable amounts of total phenolic contents (TPC) were found in stages 2-4 of ML-R, while total flavonoid contents (TFC) were most detected in stages 4-5 of RB. The DPPH activity of ML-W and ML-R decreased from stages 1-5. The highest FRAP activity was found in ML-R (stages 2-3) indicating that it is highly related to the bioactive compound content. Cyanidin-3-glucoside and peonidin-3-glucoside were found in RB at stages 3-5. The cyanidin of RB in stages 4-5 was related to the amount of TAC. The proanthocyanidin compound catechin was first found and reported in stages 2-3 of ML-R. Principal component analysis indicated that antioxidant activity and the bioactive components were highly related. The data from this study suggests that ML-R at stage 2 and RB at stage 4 are the most suitable stages for harvesting to achieve the highest level of bioactive compounds, which have many health benefits.