Characterization of black rice starch: enzymatic hydrolysis with amyloglucosidase and morphostructural, thermal, and rheological properties of native varieties from Brazil and China

This study investigated the impact of enzymatic hydrolysis with amyloglucosidase on the morphostructural, thermal, rheological, and bioactive properties of black rice starches from two origins: Brazil (SB) and China (SC). Enzymatic modification reduced the amylopectin content, increasing the amylose/amylopectin ratio, which altered the functional properties. The modified starches exhibited higher oil absorption capacity, particularly the starch Chinese modified (SCM) (171.87 g/100 g), lower bulk density, and greater gel stability (lower syneresis). Micrographs confirmed the surface erosion of the granules after hydrolysis, while X-ray Diffraction (XRD) analysis showed a reduction in crystalline. Flow properties (Carr and Hausner index) were negatively affected, indicating greater cohesiveness. The contents of free or bound phenolic compounds and anthocyanins were reduced by the extraction process. The antioxidant activity (DPPH assay) of the bioactives decreased from rice to starches, except for SCM, which maintained notable antioxidant activity. The viscosities of the modified starch pastes were reduced, with the lowest value observed for the starch Brazilian modified (SBM). The results demonstrate that geographical origin influences the initial starch properties and that enzymatic modification is an effective tool to modulate its techno-functional characteristics, enhancing its potential for food applications.