Sudhir B. Sawant

Shear Deactivation of Cellulase, Exoglucanase, Endoglucanase, and β‐Glucosidase in a Mechanically Agitated Reactor

Shear deactivation of cellulase and its major component enzymes, viz., exoglucanase (exo‐1,4‐β‐D‐glucan‐4‐cellobiohydrolase), endoglucanase (endo‐1,4‐β‐D‐glucanhydrolase), and 1,4‐β‐glucosidase, was carried out by exposing cellulase to shear in a mechanically agitated reactor in the presence as well as in the absence of the substrate cellulose. Cellulase was found to undergo deactivation when subjected to shear, and the extent of deactivation increased with increasing speed of agitation. Among the three major component enzymes of cellulase, exoglucanase showed rapid deactivation and contributed the most to cellulase deactivation. The presence of a substrate did not affect the deactivation of cellulase.

Rice bran lipase: extraction, activity, and stability

A simple procedure for the extraction of the lipolytic activity from rice bran has been developed. Various conditions of extraction have been optimized so as to obtain maximum yield of the lipase. It was found that high enzyme activity could be obtained by first defatting the rice bran to remove the lipid component. This was followed by five cycles of aqueous extraction (potassium phosphate buffer, 50 mM and pH 7, containing 0.5 mM of CaCl2). The stability of the rice bran lipase under storage and operative conditions was investigated. Further, the influence of glycerol as a stabilizer has been assessed. It was found that further purification using micro‐ and ultrafiltration yielded an enzyme preparation with higher activity and specific activity and better stability.

Development of methanol selective membranes for separation of methanol–methyl tertiary butyl ether mixtures by pervaporation

Several copolymers of acrylonitrile (AN) were synthesized. Methanol selective membranes were prepared from these copolymers of AN. The other monomers in the copolymers were selected on the basis of their solubility parameter values relative to those of methanol. These were hydroxyethyl methacrylate, methacrylic acid, and vinyl pyrrolidone. Thus, pervaporative separation of methanol from its mixture with methyl tertiary butyl ether over the entire concentration range of 0-100% methanol was studied using these copolymer membranes of AN. For each copolymer of AN three different membranes with different copolymer compositions were prepared. Copolymers of AN with hydroxyethyl methacrylate and methacrylic acid showed high selectivity and moderate flux for methanol (2561, 773, 0.057, and 0.045 kg/m 2 h, respectively, with a membrane of 50-μm thickness for a feed mixture containing 5% methanol at 30°C). A copolymer of AN with vinyl pyrrolidone showed comparable flux, but methanol selectivity of this membrane was poor.

Solar-assisted photocatalytic degradation of benzoic acid using titanium dioxide as a photocatalyst

The photocatalytic degradation of benzoic acid using titanium dioxide (Degussa P-25) as a photocatalyst has been studied. The effects of various anions, which are common in industrial wastewater, and of the initial pH were also studied. The effect of the presence of low concentration of cations was also studied. From the intermediates detected a photocatalytic degradation pathway for benzoic acid has been proposed.

Ammonia Removal from Mammalian Cell Culture Medium by Ion-Exchange Membranes∗

Abstract Metabolites such as ammonia and lactic acid formed during mammalian cell culture can frequently be toxic to the cells themselves beyond a threshold concentration of the metabolites. Cell culture conducted in the presence of such accumulated metabolites is therefore limited in productivity. This work demonstrates with laboratory data that a nonporous ion-exchange membrane of the perfluorinated sulfonic acid type can be used to contact the culture medium, and ammonia removed selectivity from the medium without disturbing the process. The technique of pervaporation showed particular promise in this regard. The pervaporation used with inert gas sweep on the permeate side was found superior to that used with vacuum application. ∗The experimental work presented here was completed at the National Institute of Standards and Technology, Boulder, Colorado. Being the product of a US Government agency, the work is not subject to US copyright.