The Correlation of Free and Bound Phenolic Acid with Antioxidant Activity Accelerated by Germination Period and Temperature

Investigation of the free and bound phenolic acid profile in malted hulled rice and the correlation to antioxidant activity were elucidated in this study. Three of free and bound hydroxycinnamic acid (FHCAs and (B)HCA); p-coumaric acid (CA), ferulic acid (FA), sinapic acid (SA), and one of hydroxybenzoic acid (HBA); vanillic acid (VA) in three rice (Oryza sativa L.) cultivars (with white, red-brown, and dark-purple kernel) were germinated under warm conditions of temperature (30 degrees C, 35 degrees C and 40 degrees C) for 5 days and analyzed for their potential antioxidant activity. The relationship of rice cultivar, malting condition, and antioxidant activity was established by PCA bi-plot analysis. The dark-purple rice malt expressed the highest phenolic acid content and antioxidant activity. The amount of (F)HCA and (F)HBA increased with germination time, which was related to the feruloyl esterase activity assayed. Among BHCAs, (B)CA was the most abundant compound and correlated positively to the antioxidant activity of the bound phenolic extract of the three rice cultivars. The (F)VA in the dark-purple rice malt was 3 to 4 times higher than that found in white and red-brown grain and led to a strong antioxidant activity of the free form extract. This research suggests that a germination temperature of 30 degrees C to 35 degrees C improved the (B)CA and (F)VA content in the malted hulled rice cultivars and conveyed a functional property for the finished product.