The micronization process for improving the dietary value of okara (soybean residue) by planetary ball milling

Okara, a perishable and useless byproduct, is mainly discarded or used as feed. This study focused on increasing its valuable components using a safe and straightforward process to resolve the overproduction problems and improve the utilization value of okara. Because of its tough fibers and richness in phytochemicals, it could be applied to the planetary ball milling, a powerful technique to embellish its structure and characterization. After treatment using a ball size of 5 mm and a rotation speed of 750 rpm, the particle size was significantly decreased from 161 to 15 mu m, and 43 g/100 g of the insoluble dietary fiber was converted into soluble dietary fiber with a change in the crystalline and functional groups. The released amounts of phenolics and flavonoids increased from 29 to 45 mg gallic acid equivalent/g and from 9 to 262 mg quercetin equivalent/g, and the conversion of soy isoflavone glycosides to aglycone was observed. This study suggests that ball-milled okara is a good option as a supplemental materials or nutritional additives for the food industry.