Study On The Methods For Decoloring Zein

Zein has many industrial uses and which can be incorporated into food and pharmaceutical industries because of its film forming, biocompatibility, self-assembly and hydrophobic property. However, commerial zein looks yellow and smells odorous due to the extraction of xanthophylls and beta-carotene, which limits the zein’s deep appilication in pharmaceutical, cosmetic and food fields. Thus, we studied the decolorization process of yellow zein with activated carbons. In order to reveal the decolorization mechanism, we also studied thermodynamics and kinetics during the decolorization process. Besides, we researched another method to decolor yellow zein by freezing precipitation. The main research contents and results are summarized as follows:1. Absorption efficiencies of activated carbon P(ACP) and Draco activated carbon(ACD) were compared based on pigment adsorption rate and zein loss rate.And, the difference of absorption efficiency was studied when zein extract or solution as adsorbate. The results showed that ACP can absorb more than 76% pigment and less than 25% zein in zein solution, prior to ACD. Both ACP and ACD can remove the most part of the pigment.And, ACP absorb less protein than ACD. As adsorbate, zein solutin and zein extract have no significant difference on pigment adsorption rate and protein loss rate.2. The microstructures of ACD and ACP were analyzed by scanning electron microscopy(SEM), surface area analysis, pore size analysis, grain size analysis and the analysis of surface functional groups. Structure characterization results of ACP and ACD showed that ACP had higher specific surface area(>1400m2/g) and total pore volume(>1.3m3/g) than ACD(779.809 m2/g and 0.626 cm3/g, respectively).ACD’s surface had rich arboxylic acids and inter-esters oxygen-containing functional groups, which leads to the almost equal absorption efficiency of ACP and ACD. Thus,the adsorption capacities of activated carbons were affected by not only the surface structure, specific surface area, but also chemical groups on the surface of activated carbons. ACP’s particle size distributed around 150 nm and 250 nm, and ACD’s particle size distributed around 300 nm. ACD’s particle size is advantageous to remove. ACD is ideal absorbent for zein decolorization.3. The adsorption behavior and decolorization mechanism of pigment and zein onto ACD were studied by thermodynamics and kinetics. Langmuir and Freundlichmodels fitted the adsorption data quite reasonably(R2>0.99), which illustrated that adsorption of pigment and protein onto activated carbon had both monolayer and multilayer adsorption. Thermodynamics parameters showed that the adsorption of pigment and zein onto ACD was spontaneous(△G0<0) and endothermal(△Ha0>0).Adsorption entropy △ S0>0 indicated that adsorption of pigment and protein is affinity adsorption. Lagergren quasi secondary rate equation was suitable to describe the dynamics of adsorption of pigment and protein onto ACD, which illustrated that adsorption of pigment and protein onto activated carbon had both physical and chemical adsorption Fitting results of Weber and Morris particle diffusion equation showed that the rate of protein and pigment adsorption process was controlled by liquid film diffusion and particle diffusion at the same time. And, particle diffusion is the primary rate control step during.the latter adsorption prccess.4. The single factor tests and response surface optimization experiment were carried on the research of zein freezing precipitation decoloring process. Single factor test results showed that anhydrous ethanol was the ideal precipitant for freezing decoloring research. The key factors affecting zein freezing decolorization were volume ratio of zein solution to precipitating agent(liquid-liquid volume ratio),precipitating agent temperature and pH of decoloring liquid and Through the response surface analysis, the best decoloring process parameters as follows: zein concentration10%, the precipitant ethanol concentration 100%, liquid-liquid volume ratio 2.4:1,precipitant ethanol temperature-30 ℃, pH of decoloring liquid 6.91, and and decoloring 1 times. And, in the above optimum decoloring process conditions, the pigment content was 6.55×10-2 μg/mg and zein recovery rate was 86.41%.