Zein properties and alternative recovery methods

Zein, a corn protein, is a water-insoluble prolamin. It can only be dissolved in a solution with the right balance of polar and non-polar solvents. Zein properties such as solubility, viscosity, gelation, and denaturation in aqueous ethanol were studied in this research. The maximum solubility was around 50% in (mol/mol) aqueous ethanol, 40% (mol/mol) in iso-propanol, or 40% (mol/mol) in tert-butanol, respectively. Zein solutions exhibited a Newtonian behavior in aqueous ethanol. The temperature dependence for the zein solution viscosity and solubility followed Arrhenius\u27s law. Viscosity exponentially increased when zein concentration increased, while generally it decreased when ethanol concentration increased. Zein solution was unstable and tended to gel under some conditions. The gelation rate was low for zein concentrations lower than 10% (w/w). Both 12%(w/w) and 14%(w/w) zein in 88%(w/w) or 90%(w/w) ethanol solutions had a very high gelation rate. Temperature increased the denaturation rate following Arrhenius\u27s law. Shear rate was linearly proportional to the denaturation onset time. Zein was very stable when the ethanol concentration was as high as 90%(w/w). Zein denatured easily at 80%(w/w) ethanol. Two alternative zein recovery methods based on zein solubility in aqueous alcohols were considered. Pervaporation membrane technology was deemed a possible approach for zein recovery. In it water would pervaporate from a zein ethanol solution, resulting in a higher ethanol concentration thus making zein precipitate. The effects of zein concentration, ethanol concentration, circulation flow rate, and temperature were examined for pervaporation performance by checking the membrane flux and selectivity. Zein concentration had little effect on the membrane system performance. Lower flow rates, which maintained laminar flow across the membrane, had better performance than that of turbulent flow. Higher temperatures could have been used to increase the flux but the zein denaturation onset time would have decreased. The second method was addition of anhydrous alcohol directly to zein-aqueous alcohol solutions and two phases were formed. The top phase of high concentration alcohol took most oils and pigments from zein. The bottom phase of zein could be separated by centrifugation