Increased total polyphenol content, antioxidant capacity and γ-aminobutyric acid content of roasted germinated native Thai black rice and its microstructure

Abstract

The effects of roasting on the colour parameters, anthocyanin content, total polyphenol content, antioxidant activity, γ-aminobutyric acid (GABA) content, and the microstructure of germinated Thai black rice (GTBR: non-waxy) and germinated Thai black sticky rice (GTBSR: waxy) were appraised. The results revealed that both types of roasted germinated Thai black rice showed an increase in all lightness (L*), redness(a*) and yellowness (b*). For the chemical properties, only the concentration of anthocyanin slightly decreased, whereas the total polyphenol content, ABTS⁺ radical scavenging activity, and GABA content markedly increased after roasting. Moreover, images of a scanning electron microscope (SEM) displayed that both germinated black rice grains became more compact and had a tight shape in the surface structure. Additionally, small pores were found in the GTBR and large pores were present in the GTBSR rice kernel when compared with the unroasted black rice in the internal structure. Together,the roasting process was capable of enhancing the GABA and phenolic contents, and antioxidative capacity in both the GTBR and GTBSR.

Keywords:
roasting; γ-aminobutyric acid (GABA); microstructure; black rice