Holocellulose nanofibers from insoluble polysaccharides of okara by mild alkali planetary ball milling: Structural characteristics and emulsifying properties

The added-value utilization of okara, a major byproduct of soybean processing, has attracted increasing interests, due to its good nutrition, functionalities and health-promoting effects. This work reports a facile and green process to prepare highly functional holocellulose nanofibers (hCNFs) from the insoluble polysaccharides (ISP) of okara, using a mild alkali planetary ball milling technique. The ball milling for 10–25 h in the presence of 1.0 wt% NaOH could efficiently transform the ISP into water dispersible hCNFs with highly crystalline cellulose contents reaching around 80%. The crystallinity of cellulose in these hCNFs was around 60%. The surface hydrophobicity of these hCNFs progressively decreased with increasing the milling time from 0 to 25 h, and their ζ-potential was independent of milling time. The hCNFs were demonstrated to perform as outstanding Pickering stabilizers for oil-in-water emulsions, with much better emulsification performance and emulsion stability than the ISP. All the emulsions at an oil fraction of 0.2 could be well stabilized by these hCNFs at a particle concentration in the aqueous phase of 0.1 wt%. Among all the hCNFs, those obtained after the milling of 10–20 h had highest potential to stabilize fine emulsions. All the emulsions stabilized by the hCNFs were prone to fast creaming, but the creamed emulsions exhibited excellent storage stability. The emulsifying properties of the hCNFs were closely associated with their interfacial adsorption at oil-water interface. The findings would be of importance not only for guiding the added-value utilization of underutilized byproducts of agricultural products, but also for providing a facile and green process to prepare highly functional hCNFs from okara.