RESUMO
Lecithin-free egg yolk (LFEY) is a byproduct of the extraction of egg-yolk phospholipids, which contain approximately 46% egg yolk proteins (EYPs) and 48% lipids. The enzymatic proteolysis is the alternative to increase the commercial value of LFEY. The kinetics of proteolysis in full-fat and defatted LFEY with Alcalase 2.4 L was analyzed in terms of the Weibull and Michaelis-Menten models. A product inhibition effect was also studied in the full-fat and defatted substrate hydrolysis. The molecular weight profile of hydrolysates was analyzed by gel filtration chromatography. Results pointed out that the defatting process did not importantly affect the maximum degree of hydrolysis (DHmax) in the reaction but rather the time at which DHmax is attained. The maximum rate of hydrolysis (Vmax) and the Michaelis-Menten constant KM were higher in the hydrolysis of the defatted LFEY. The defatting process might have induced conformational changes in the EYP molecules, and this affected their interaction with the enzyme. Consequently, the enzymatic reaction mechanism of hydrolysis and the molecular weight profile of peptides were influenced by defatting. A product inhibition effect was observed when adding 1% hydrolysates containing peptides lower than 3 kDa at the beginning of the reaction with both substrates.
RESUMO
The two main challenges for industrial application of membrane distillation (MD) are mitigation of temperature polarization and reduction of high-energy consumption. Despite the development of advanced materials and the configuration improvements of MD units, membrane surface modification is still one of the alternatives to overcome temperature polarization and improve membrane performance. This work reports a novel and simple method to modify the physical and chemical properties of the polypropylene membrane in order to improve its performance in direct contact membrane distillation (DCMD). The membrane was grafted by polymerization with 1-hexene, UV irradiation, and benzophenone as a photoinitiator. A grafting degree of up to 41% was obtained under UV irradiation for 4 h. The performance of the modified membrane in DCMD was evaluated at different temperatures and salt concentrations in the feed. First, it was found that there was an increase of the vapor permeate flux in the MD process within the range of tested temperatures and salt concentrations. The results were analyzed in terms of the physical properties of the membrane, the transport phenomena, and the thermal efficiency of the process. Theoretical analysis of the results indicated that grafting increased the transfer coefficients of mass and heat of the membrane. Hence, it improved the membrane performance and the thermal efficiency of the DCMD process.
RESUMO
Lipase B from Candida antarctica (CALB) has been physically immobilized on octyl-agarose via interfacial activation. The incubation of the enzyme in 80% ethanol at pH 5 and 25°C has not significant effect on enzyme activity. Moreover, the hydrolysis of 100mM tributyrin catalyzed by this biocatalyst exhibited a quite linear reaction course. However, a new cycle of tributyrin hydrolysis showed a drastic drop in the activity. SDS-PAGE gels of the supernatant and the biocatalyst showed a significant enzyme desorption after the reaction. Similar results could be appreciated using triacetin or sunflower oil, while using 300mM methyl phenyl acetate, butyl butyrate or ethyl butyrate most enzyme molecules remained immobilized. The results show that the detergent properties of some reaction products increase the enzyme release from the hydrophobic support, and this problem increased if the concentration of the reactants increased. Using 500mM tributyrin, even in fully aqueous medium, some enzyme desorption from the support may be observed. Thus, the results show a limitation of this kind of biocatalysts that should be considered in the selection of an industrial lipase biocatalyst.
