Protective effects of non-catalytic proteins on endoglucanase activity at air and lignin interfaces.

The manner in which added non-catalytic proteins during enzymatic hydrolysis of lignocellulosic substrates enhances hydrolysis mechanisms is not completely understood. Prior research has indicated that a reduction in the non-specific adsorption of enzymes on lignin, and deactivation of enzymes exposed to air-liquid interface provide rationale. This work investigated root causes including effects of the air-liquid interface on non-catalytic proteins, and effects of lignin on endoglucanase. Three different experimental designs and three variables (air-liquid interfacial area, the types of lignin (acid or enzymatic lignin), and the presence of non-enzymatic protein (bovine serum albumin [BSA] or soy proteins ) were used. The results showed that acid isolated lignin adsorbed almost all endoglucanase activity initially present in supernatant, independent of air interface conditions (25 or 250 ml flasks) with the presence of BSA preventing this effect. Endoglucanase lost 30%-50% of its activity due to an air-liquid interface in the presence of lignin while addition of non-enzymatic protein helped to preserve this enzyme's activity. Langmuir and Freundlich models applied to experimental data indicated that the adsorption increases with increasing temperature for both endoglucanase and BSA. Adsorption of the enzyme and protein were endothermic with an increase in entropy. These results, combined, show that hydrophobicity plays a strong role in the adsorption of both endoglucanase and BSA on lignin.

Caffeine removal using Elaeis guineensis activated carbon: adsorption and RSM studies.

The palm (Elaeis guineensis), known as dendê, is an important oleaginous Brazilian plant with a high performance of oil production. In this work, a 23 full experimental design was performed and the response surface method (RSM) was used to indicate the optimum parameter of caffeine adsorption on Elaeis guineensis endocarp activated carbon, since the endocarp is the main by-product from dendê oil production. It was set the adsorbent point of zero charge (pHpzc), and the material was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The RSM results indicate removal efficiency (%) at the optimal conditions, 0.20 g of adsorbent, and caffeine initial concentration of 20 mg/L, and acidic medium was about 95%. Based on ANOVA and F test (Fcalculated > Fstandard), the mathematical/statistical model obtained fits well to the experimental data. The overall kinetic studies showed time was achieved after 5 h and caffeine adsorption followed the pseudo-second-order model suggesting chemisorption is a predominant mechanism. Redlich-Peterson and Sips models best represented the experimental data (0.967 < R2 < 0.993). Thermodynamic revealed that caffeine adsorption was spontaneous at all temperatures studied, exothermic, and probably with changes in the adsorbate-adsorbent complex during the process. The tests conducted in different water matrixes corroborate the suitability of this adsorbent to be used in caffeine removal even in a complex solution.