Wet media planetary ball milling remarkably improves functional and cholesterol-binding properties of okara

The utilization of okara, an important byproduct of soybean industry, has attracted increasing interests, due to its good nutrition and potential health effects. This work investigated the influence of a wet media planetary ball milling on some physicochemical and functional properties and cholesterol binding capacity (CBC) of okara from defatted soy flour. The tested properties included particle size, ζ-potential, water holding and swelling capacities (WHC and WSC), oil binding capacity (OBC), cation exchange capacity (CEC), emulsifying ability and emulsion stability indices (EAI and ESI), foaming ability (FA) and foam stability (FS). The results indicated that a milling with increasing time from 5 to 15 h resulted in a progressive decrease in z-average diameter (up to 270 nm) of okara particles, and thus improved their water dispersibility. In general, the milling progressively increased WHC, WSC, OBC, CEC, EAI, FA and CBC, in a milling time dependent way. Especially for the okara milled for 15 h, its EAI became comparable to that of soy protein isolate (SPI), while its ESI was considerably higher than SPI. The CBC of okara at pH 7.0 increased by 3-folds, after the milling for 15 h. Such improvements of functionalities were largely attributed to the transformation of insoluble components into water-dispersible, highly functional colloidal nanoparticles, as well as disruption of crystalline polysaccharides for milled okara. The findings are of interest not only for guiding the highly-added-value utilization of okara, but also for the development of a kind of highly functional and health-benefiting food functional ingredients with a great potential to be applied in food formulations.