G. B. Oguntimein

Lipase catalysed synthesis of sugar ester in organic solvents

SummaryThe synthesis of sugar esters catalysed by lipase in organic solvents was studied. Immobilized Candida and Mucor miehei lipase catalysed the synthesis of fructose and glucose esters of stearic acid in tertiary butyl alcohol with yields of 10 to 24 %. In the presence of phenyl or butyl boronic acid synthesis of glucose ester was achieved in hexane, heptane, benzene and toluene. The only positive reaction on disaccharides was found with palatinose.

Synthesis of geraniol esters in a solvent-free system catalysed by Candida antarctica lipase

SummaryCandida antarctica lipase was investigated for the synthesis of short chain fatty acid esters of geraniol in a solvent-free system. Maximal activity occurred at 60°C. High yields (about 100%) were obtained with propionate and butyrate, while acetate showed much lower reactivity. The enzyme was used in four consecutive batch reactions with only a 10% loss of activity.

Production of cellulolytic enzymes by Neurospora sitophila grown on cellulosic materials

Abstract Cellulases and β-glucosidase were produced by Neurospora sitophila cultured in media containing corn stover or sugar cane bagasse as carbon sources. The effects of initial medium pH, organic nitrogen source and Tween 80 on enzyme activity were investigated. Values of pH above 6·5 were found to favour enzyme production. Defatted sesame seed flour increased both carboxymethyl-cellulase and filter-paper activities, while yeast extract enhanced β-glucosidase activity. Tween 80 at a concentration of 0·1% (v/v) increased all the enzyme activities.

Production and properties ofβ-glucosidase byNeurospora sitophila.

Growth at 25°C and pH 5.50 favour the production ofβ-glucosidase. De-fatted oilseed flour and Tween 80 enhanced the production ofβ-glucosidase, Lactose, gentibiose, gentibiose-acetate, laminarabiose and xylobiose inducedβ-glucosidase activity. Precipitation of the culture filtrate with (NH4)2SO4 resulted in 26-fold purification with 67% recovery. The optimum pH and temperature for activity were 5.0 to 5.4 and 55°C respectively. The enzyme was stable at 40°C with half-life at 12 h at 50°C. TheKm andVmax for the hydrolysis ofp-nitrophenyl-β-d-glucoside at 40°C H 5.0 are 0.28mm and 0.60 U/mg protein, respectively.

Regulation of aspartokinase in Lactobacillus plantarum

As a rational approach to the genetic development of a stable lysine overproducing strain of Lactobacillus plantarum for the fermentation of ‘ogi’, a Nigerian fermented cereal porridge, regulation of lysine biosynthesis in this species was investigated. Spontaneous lysine overproducing mutants of Lact. plantarum were obtained and their aspartokinase activities compared with those of wild‐type strains under different conditions. Results showed that aspartokinase activity of Lact. plantarum cell extracts was not inhibited by either lysine, threonine, methionine or combinations of lysine and threonine. Instead, methionine enhanced aspartokinase activity in vitro. Results indicated that lysine biosynthesis in Lact. plantarum could be regulated by lysine via the control of aspartokinase production in a way different to that described for other bacteria.