Endogenous alpha-amylase explains the different pasting and rheological properties of wet and dry milled glutinous rice flour

Wet-milled glutinous rice flour (WMF) and dry milled glutinous rice flour (DMF) have different pasting and rheological properties but the underlying mechanism has not been defined. Dry milling methods can result in glutinous rice flour (GRF) with higher residual alpha-amylase activity and damaged starch content compared to flours prepared by wet milling methods. The addition of alpha-amylase significantly increased starch hydrolysis and reduced the peak, trough, and final viscosity of GRF gels. The pasting viscosity and dynamic modules of WMF-Water gels were significantly higher than those of DMF-Water gels. Inhibiting amylase activity significantly reduced the differences in paste viscosity and dynamic modules between WMF and DMF. Scanning electron microscopy (SEM) showed that alpha-amylase affected the microstructure of the DMF. FT-IR spectra results indicated no new formation of covalent bonds in GRF-Water or GRF-Ag gels. These results suggested that endogenous alpha-amylase influenced starch hydrolysis and subsequently the viscoelastic property of GRF gels, indicating that residual endogenous alpha-amylase explains the differences in pasting and rheological properties between WMF and DMF.

Automated summary

The presence of residual endogenous alpha-amylase in wet-milled and dry-milled glutinous rice flour plays a significant role in influencing the pasting and rheological properties, starch hydrolysis, and gel characteristics. The differences in these properties between wet-milled glutinous rice flour and dry-milled glutinous rice flour can be attributed to the activity of residual alpha-amylase.