Structural stability of lipase from wheat germ in alkaline pH

Improvement of stability and antioxidant activity of wheat germ by mixed fermentation versus single fermentation

Wheat germ is a high-nutrient by-product from the milling industry with very limited optimal consumption due to its short shelf life. The severe activity of endogenous lipase and lipoxygenase is associated with the release of fatty acids which are responsible for the rancidity and shelf-life deficiency. Reducing these enzymes activity is essential for prolonging the wheat germ shelf-life. For this purpose, the mixed and simple fermentation of different wheat germ concentrations (10, 15 and 20% w/v wheat germ in distilled water) with Lactobacillus plantarum and Lactobacillus acidophilus was investigated to improve the stability of wheat germ by restraining the activity of the enzymes. Fermentation noticeably reduced the activity of the enzymes in all samples (ranges from 50 to 82.15% for lipase and 55.34 to 72 for lipoxygenase in different treatments), but the mixed-fermented wheat germ with the maximum concentration (20%) achieved the highest reduction level in both enzymes inactivation. Fermentation also resulted in an obvious increase in antioxidant activity from 51.18% in raw wheat germ to more than 72.73% in different samples, which mixed fermentation of 20% wheat germ suspension with the value of 89.76 was ranked first.

Wheat germ lipase: isolation, purification and applications

In recent years, wheat germ lipase (WGL) is attracting considerable interest. To date, several WGL applications have already been described: (i) fats and oils modification; (ii) esterification reactions in organic media, accepting a wide range of acids and alcohols as substrates; (iii) the asymmetric resolution of various chiral racemic intermediates; (iv) more recently, the promiscuous activity of WGL has been shown in carbon-carbon bond formation. To date, no crystallographic structure of this enzyme has been published, which means its activity, catalytic potential and substrate scope is being assessed empirically. Therefore, new catalytic activities of this enzyme are constantly being discovered. Taking into account the emergency and the current interest in environmentally sustainable processes, this review aims to highlight the origin, isolation, stabilization by immobilization and applications of the wheat germ lipase.HIGHLIGHTSWheat germ as an inexpensive source of biocatalystsWheat germ lipase an efficient catalyst for various chemical transformationsWheat germ lipase in food productionIndustrial applications of wheat germ lipaseWheat germ lipase as a promiscuous biocatalystImmobilization of wheat germ lipase as a method of stabilization.

Enzymatic process of rice bran: a stabilized functional food with nutraceuticals and nutrients

Rice bran (RB), a byproduct of rice milling industry, is a rich source of nutraceuticals and nutrients. However its utility is limited due to the presence of lipase and lipoxygenase which initiates rancidity on milling. The aim of this investigation is to prevent oxidation of free fatty acids by enzymatic approach for its effective utilization. The enzymatic treatment comprised of alcalase treatment for complete inactivation of lipase along with reduction in lipoxygenase (LOX) activity and endoglucanase for improving the soluble fiber content. The enzyme treated rice bran was drum dried for further use. The nutraceutical molecules like γ-oryzanol, α-tocopherol and polyphenols were retained in the range of 68 to 110 % and the total antioxidant activity was improved. By the action of endoglucanase the complex carbohydrate was converted into glucose (72.28 %), cellobiose (18.36 %) and cellotriose (9.36 %). The prebiotic effect of enzyme treated rice bran was evaluated by the action of lactobacillus which was measured through the release of the short chain free fatty acids (SCFAs) analyzed by HPLC. The SCFAs; acetic acid and propionic acid increased by 1.72 folds and 2.12 folds respectively. B-complex vitamins showed maximum retention with vitamins like B1 (66.3 %), B2 (68.3 %) and B3 (55.0 %) after enzyme treatment. At different humidity levels, storage studies showed no change in LOX activity and also retained ubiquinol-10 in reduced state in enzyme treated RB for a period of 3 months. A stabilized RB has been developed enriched with short chain prebiotics and antioxidant molecules.

Phenylboronic acid--a potent inhibitor of lipase from Oryza sativa

The kinetics of inhibition of rice bran lipase (RBL) by phenylboronic acid (PBA) was studied to elucidate the nature of inhibition and the effect of the inhibitor on the structure-function of RBL. The effectiveness of an inhibitor is normally expressed by the constant K(i), which is calculated from the Lineweaver-Burk plot and found to be 1.7 mM at pH 7.4. The kinetics of inhibition by PBA was competitive, indicating the presence of serine in the active site of the enzyme. The loss of activity of RBL was concentration dependent on the inhibitor (PBA), and the inactivation followed a pseudo-first-order kinetics. Fluorescence emission measurements indicated a decrease in the fluorescence emission intensity and a red shift in the emission maximum as the inhibitor concentration was increased. The inhibition of the enzyme by PBA was also confirmed by thermal denaturation measurements, which indicated a shift in the thermal denaturation temperature of the enzyme toward lower temperatures. The far-UV-CD data suggest that there were no significant changes in the conformation of the enzyme as a result of binding of PBA. These results indicate that PBA is a potential inhibitor of RBL and binds to the enzyme in bringing about inhibition without any structural alterations.

Protein adsorption at the oil/water interface: characterization of adsorption kinetics by dynamic interfacial tension measurements

The dynamics of protein adsorption at an oil/water interface are examined over time scales ranging from seconds to several hours. The pendant drop technique is used to determine the dynamic interfacial tension of several proteins at the heptane/aqueous buffer interface. The kinetics of adsorption of these proteins are interpreted from tension/log time plots, which often display three distinct regimes. (I) Diffusion and protein interfacial affinity determine the duration of an initial induction period of minimal tension reduction. A comparison of surface pressure profiles at the oil/water and air/water interface reveals the role of interfacial conformational changes in the early stages of adsorption. (II) Continued rearrangement defines the second regime, where the resulting number of interfacial contacts per protein molecule causes a steep tension decline. (III) The final regime occurs upon monolayer coverage, and is attributed to continued relaxation of the adsorbed layer and possible build-up of multilayers. Denaturation of proteins by urea in the bulk phase is shown to affect early regimes.

Preferential interaction of denaturants with rice bran lipase

The catalytic stability of rice bran lipase has been determined in the presence of three denaturants viz, urea, GuHCl and GuHSCN. The enzyme is completely inactive above 7 M urea, 4 M GuHCl and 2 M GuHSCN concentration. The extent of denaturant interaction has been determined by the partial specific volume measurements of the enzyme. The preferential interaction parameter (xi 3) has values of 0.042, 0.064 and 0.075 g/g, and the denaturation volume changes are -180, -240 and -270 ml/mol in presence of 8 M urea, 6 M GuHC1; and 3 M GuHSCN, respectively. The experimental values of number of denaturant molecules bound (A3) are 0.418, 0.566 and 0.320 g/g and the calculated values are 0.321, 0.511 and 0.632 g/g in presence of 8 M urea, 6 M GuHCl and 3 M GuHSCN, respectively. Fluorescence emission measurements indicated a decrease in the fluorescence emission intensity and a red shift in the emission maximum as the denaturant concentration is increased indicating the gradual exposure of aromatic chromophores. The instability of the enzyme in the presence of these denaturants has been indicated by a decreased value of apparent thermal denaturation temperature (Tm) of the enzyme from a control value of 67 degrees C. The results obtained in the present study explain the extent of inactivation/stability of rice bran lipase in presence of these denaturants at different concentrations.

Structural stability of lipase from wheat germ

Purified lipase from wheat germ was used for the determination of preferential interaction parameters under different stabilizing cosolvent conditions. The partial specific volume of the enzyme was measured under both isomolal and isopotential conditions in phosphate buffer at pH 7.0, 0.02 M, and the value was found to be 0.730 +/- 0.001 and 0.731 +/- 0.002 mL/g, respectively. The partial specific volume measurements with different cosolvents indicated that the enzyme has a (delta g3/delta g2)T,mu1,mu3 values of -0.119 +/- 0.012, -0.073 +/- 0.009 and -0.141 +/- 0.020 g/g, respectively, in 25% glucose, 25% sucrose and 25% DMSO. The (delta g3/delta g2)T,mu1,mu3 values in 10 and 20% glycerol were -0.054 +/- 0.012 and -0.073 +/- 0.016 g/g, respectively. Based on these values it is clear that the enzyme is stabilized in the presence of these cosolvents by increasing its hydration, of which DMSO is stabilizing to the maximum extent. The stabilization of the enzyme was also confirmed by the thermal denaturation measurements in the presence of these cosolvents which indicated a shift in the apparent thermal denaturation temperature of the enzyme towards higher temperatures. The data are supported further by the ultraviolet difference spectral as well as fluorescence measurements in the presence of these cosolvents. The stabilization has been attributed to the preferential hydration of the enzyme in the presence of these cosolvents.