Mechanistic insights into solubilization of rice protein isolates by freeze-milling combined with alkali pretreatment.

The solubilization of rice protein isolates (RPIs) has been regarded as one of the critical and challenging processes affecting commercial availability. Simultaneous treatment with freezing and milling (freeze-milling) combined with alkali pretreatment can remarkably increase the maximum achievable amounts of soluble RPIs by up to 42 times. This study investigates the mechanism of solubilization of RPIs by freeze-milling (RPI(fm)). Structural analyses reveal that milling causes proteins to unfold with ice crystals formed inside protein bodies. Fluorescent and Fourier transform infrared spectra show that RPI(fm) possesses disrupted hydrophobic surface and exposed hydrophilic inner groups. Size exclusion chromatography results reveal that RPI(fm) exhibits disaggregation and strong water-protein interactions. These results indicate that freeze-milling may be a promising manufacturing technique in food industry.