Food-Grade Efficient Pickering Stabilizers From Okara:Strategies And Mechanisms Investigation

The added-value-utilization of agricultural byproducts is one of important research subjects in the agri-byproduct processing and food science fields.Okara,as the major byproduct during the processing of soybean products,e.g.,soymilk and soy protein isolate(SPI),is produced at a mass scale globally,which is rich in dietary fibers and proteins with benefiting effects to health,and can thus be utilized as starting materials for a variety of functional ingredients.To date,okara is mainly utilized as feedstuff.The main objective of the work was to investigate the effective strategies,mainly through high energy ball milling and ultrasonication treatments,to transform okara or its insoluble polysaccharide components into a kind of functional ingredients,with a great potential to be applied in food formulations.Using okara from the SPI production as the starting material,the work not only demonstrated that the nanoparticles formed through ball milling or ultrasonication can act as outstanding Pickering stabilizers for emulsions,and but also proposed a facile process to prepare high quality holocellulose nanofibers from okara.The main results of the work include but not limited to as following:Firstly,the effects of wet-media ball milling on physicochemical,functional properties,as well as cholesterol-binding capacity,were investigated.The results indicated that,as the milling time increased from 5 to 15 h,the average particle size of okara progressively decreased up to 270 nm,and accordingly,its hydration properties,oil-binding capacity,cation-exchange ability,emulsifying and foaming activities,and cholesterol-binding capacity were significantly and persistantly improved.After 15 h of the milling treatment,the cholesterol-binding capacity of okara increased by 3-folds,and the emulsifying properties of the milled okara were comparable to,or even better than SPI.By the microfluidization as the emulsification process,the emulsions stabilized by milled okara exhibited a high tendency to form a bridging structure,and good stability against coalescence and creaming.The droplet size,flocculation extent,stability(against coalescence and creaming)and rheological behavior of the as-obtained emulsions can be well modulated by varying particle concentration(c)and/or oil fraction(?).Thus,the results showed that the ball milling treatment could be used to transform okara into a kind of highly functional nanoparticles with strong cholesterol binding capacity,which can act as a kind of outstanding Pickering stabilizers.Secondly,the transformation of insoluble polysaccharides of okara(ISP)into a kind of nanoparticles by high energy ultrasonication,as well as their potential and effectiveness to act as Pickering stabilizers,was investigated.The results indicated that,the ultrasonication treatment(only several minutes)of the ISP dispersions in water could lead to formation of a kind of water-dispersible nanoparticles,which exhibited excellent emulsifying properties and interfacial stabilization.Using the as-prepared nanoparticles as sole stabilizers,a kind of unique Pickering emulsions with highly flocculated droplets with sizes at the nanoscale could be obtained using the microfluidization as the emulsification technique.The droplet size,microstructure and rheological behavior of the resultant emulsions could be also modulated by adjusting the c and/or ?.The results confirmed that the ultrasonication could effectively transform the ISP of okara into a kind of highly efficient Pickering stabilizers.Next,the effectiveness of using the above-fabricated nanoparticles to stabilize high internal phase emulsions(HIPEs),as well as the characteristics of the resulting HIPE gels,was evaluated.The results indicated that,using these nanoparticles as stabilizers,a kind of HIPE gels which were not disrupted by 6 M urea could be facilely fabricated using a ‘one-pot' shearing homogenization,at a particle concentration as low as 0.25 wt%.The corresponding HIPE gels could be effectively formed over a wide range of pH(2.0-12.0)or ionic strength(0-500 mM).These HIPE gels not only exhibited outstanding stability against a long-term storage and heating,as well as a good reversibility of freeze-thawing/re-homogenization,but also could act as good protective containers for hydrophilic bioactives.Lastly,the possibility to prepare high quality holo-cellulose nanofibers(hCNFs)from okara was investigated.The results indicated that,using the ISP as the starting material,a kind of hCNFs could be highly efficiently and facilely obtained using a mild alkali(1.0 wt% NaOH)ball milling process(10-25 h).The as-prepared hCNFs contained a high content of crystalline cellulose(as high as 81%),and possessed outstanding water dispersibility and emulsifying properties,with the emulsifying performance and emulsion stability better than a commercial CNFs.The Pickering emulsions stabilized by such hCNFs were highly prone to droplet flocculation,with the extent of flocculation increasing with the c,or decreasing with the ?,but exhibited good stability against creaming and coalescence.The results of the in vitro digestion experiments showed that,as compared to other conventional emulsions,the as-fabricated Pickering emulsions exhibited much lower rates of fatty acid release,as well as much lower bioaccessibility of encapsulated ?-carotene.Thus,these Pickering emulsions may be used as a kind of delivery systems with sustained release and targeted delivery function.In summary,it was demonstrated that okara was not only a kind of excellent materials with a great potential to be developed into a kind of highly effective and biocompatible food-grade Pickering stabilizers,but also was a kind of potential ingredients for the development of functional foods.The findings of the work would be of crucial importance for guiding the highly-added-utilization of okara.