Kandiah Balasubramaniam

Supplementation of whey with glucose and different nitrogen sources for lactic acid production by Lactobacillus delbrueckii

Abstract Lactobacillus delbrueckii was grown at room temperature in static culture. When whey (total sugar 30 g l −1 ) was supplemented with different concentrations of yeast extract, lactic acid production increased. When glucose (20 g l −1 ) was added to whey, 20 g l −1 yeast extract supplementation was found to be most suitable. Among the different nitrogen sources supplemented to whey [yeast extract, peptone, soya flour, and (NH 4 ) 2 SO 4 , having the same elemental nitrogen level of 3.1 g l −1 ], yeast extract was the best. The effect of yeast extract could be due to its vitamin B content. Therefore, whey was supplemented with different nitrogen sources and vitamin B complex, and no significant improvement in lactic acid production was observed. As yeast extract supplementation was not economically attractive, we decided to use a proportion of (NH 4 ) 2 SO 4 and yeast extract. When the elemental nitrogen ratio of (NH 4 ) 2 SO 4 to yeast extract was 3:1, the substrate use and efficiency of lactic acid production were same as in whey supplemented with 20 g l −1 yeast extract.

Isolation and improvement of a thermotolerant Saccharomyces cerevisiae strain

The ambient temperature is a drawback in industrial ethanol production in Jaffna due to heat killing of yeast during fermentation. Thus a search was initiated for thermotolerant organisms suitable for fermentation in hot climates. The screening of the best wild-type organisms was undertaken as the first step. Thermotolerant strains were selected from environments where there are chances of organisms being exposed to high temperature. The samples were enriched and screened for thermotolerant organisms which survived at 45 °C for 15 h. Among the yeast strains selected from different sources, thermotolerant strains with the capacity to withstand 45 °C for 15 h were found in samples collected from the compost heap and distillery environments. Three colonies from the distillery environment were selected for further studies and named p1, p2 and p3. Exponential phase (18 h) cultures of p1, p2 and p3 were subjected to 15 temperature treatment cycles (at 50 °C each for 3 h) and thermally adapted strains pt1, pt2 and pt3 were obtained, showing 100, 30 and 20% viability at 50 °C for 30 min respectively. The initial round of thermal adaptation cycles increased the duration of 100% viability from 20 h (p1) to 68 h (pt1) when incubated at 40 °C. Very little benefit was obtained when pt1 was treated with u.v. and ethyl methanesulphonate. The selected strain was identified and designated as Saccharomyces cerevisiae S1. The ethanol produced from 100 g glucose l−1 by S. cerevisiae S1 was 46 g l−1 (36 h), 38 g l−1 (48 h) and 26 g l−1 (48 h) at 40, 43 and 45 °C respectively in rich nutrient medium.

Channelling of glucose by methanol for citric acid production from Aspergillus niger

Citric acid produced by Aspergillus niger was increased from 4.6g l-1 to 7.8gl-1 by supplementing basal medium with methanol (30mll-1). While stimulating citric acid production, methanol did not improve membrane permeability of the fungus for citric acid. Methanol inhibited the germination of Aspergillus spores. An increase in glucose concentration from 50gl-1 to 100gl-1 in the presence of methanol (30mll-1) improved citric acid production (1.6-fold) while at higher levels of glucose concentration methanol had no effect on citic acid production.

Formulation of medium and recycling of biomass for glucoamylase production by Botryodiplodia theobromae

Abstract Botryodiplodia theobromae grown in manioc starch medium supplemented with ammonium phosphate, peptone, tri potassium phosphate, calcium carbonate and soy bean powder, produced 1950 U ml −1 glucoamylase in shake flasks at pH 6·0. Fungal biomass could be recycled at least four times without significant loss in enzyme production.

Sugar syrup (DE 50-70) from corn flour.

Starch in corn flour (22% solids, w/w) was hydrolyzed by different concentrations of α-amylase and 12 KNU/100g Suspension produced a sugar syrup with dextrose equivalent (DE) of 58%. As tap water contained calcium, addition of calcium acetate did not improve starch hydrolysis. To increase total solids, either corn flour or corn flour suspension was added during liquefaction. Among the different conditions studied, addition of corn flour suspension (30g of 33%, w/w) to liquefying starch (22%, w/w) produced a sugar syrup with highest DE (DE 60) at 3.0 h. To increase the DE, malt extract rich in β-amylase was added to liquefied starch preparations supplemented with either corn flour (10 g) or corn flour suspension (33%, w/w) and DE increased from 50 and 60 to 62.2 in both, respectively. Then malt powder suspension (25%, w/w) equivalent to malt extract was added directly and DE obtained were 57.0 and 55.21, respectively. These results indicate that glucose syrups of DE 50 and 70 can be prepared using α-amylase alone without malt β-amylase.

The use of monochloroacetic acid for improved ethanol production by immobilized Saccharomyces cerevisiae

Saccharomyces cerevisiae adsorbed on acid-treated glass beads produced 5.4 g I -l ethanol at 96 h in batch process. Precoating the acid-treated glass beads with gelatin (25 g I -l ) before immobilization of the cells increased ethanol production to 26.3 g I -1 at 72 h. Cell leakage into the medium was decreased when the immobilized cells were crosslinked with increasing concentrations of glutaraldehyde (0-100 g I -1 ). Although monochloroacetic acid inhibited ethanol production and cell multiplication at concentrations greater than 0.1 g I -1 , at a concentration of 0.01 g I -1 it not only increased the ethanol production to 52.1 g I -1 but also shortened the ethanol production time to 48 h. In a semi-continuous batch process with the feed containing 0.01 g I -1 monochloroacetic acid, immobilized cells showed no significant change in ethanol-producing ability for 40 days when incubated with nutrient medium intermittently.

Thermal stabilization of immobilized α-amylase by coupling with proline

Abstract α-Amylase was immobilized to Sepharose-4B activated by electrophilic method using cyanogen bromide. The α-amylase coupled was 77% of the total protein added. Further l -proline was covalently linked to the immobilized α-amylase by carbodiimide. Optimum carbodiimide concentration for the coupling of proline to the immobilized α-amylase and the suitable proline concentration for the coupling were determined. Activity of immobilized α-amylase was not altered after coupling to proline. The thermal stability of soluble α-amylase, immobilized α-amylase and immobilized α-amylse-proline conjugates (samples coupled to two different proline concentrations) were studied at 45 and 60°C. Soluble α-amylase lost its total activity in 4 days and 1 day at 45 and 60°C, respectively. Immobilized α-amylase lost its total activity on the 30th and 16th days at 45 and 60°C, respectively. Immobilized α-amylase-proline conjugate (85·35 μg proline/g gel) lost only 78% activity at 45°C on the 30th day while the same preparation took 20 days at 60°C to lose the total activity. On the other hand the immobilized α-amylase-proline conjugate (785·32 μg proline/g gel) lost only 30% of its original activity at 45°C on the 30th day and took 30 days at 60°C to lose its total activity. These results show that the coupling of proline to immobilized enzymes increases their thermal stability.

Improved Performance of Amberlite IRA-904 Immobilized Glucoamylase

When the glucoamylase protein immobilized to Amberlite IRA-904 was estimated by direct (Kjeldhal), indirect (measuring the protein left in the supernatant) and elution methods, direct and indirect methods gave almost same results while the elution method gave a protein concentration of only 68.9% of that obtained with the Kjeldhal method. When the activity of the soluble and immobilized glucoamylase were compared with different substrates, the activity yield increased with decreasing molecular size of the substrate. However when the immobilized glucoamylase containing Amberlite IRA-9004 was ground, it showed increase in activity with increasing molecular weight of the substrates.

Large scale preparation of crystalline glucose from raw starch in corn flour

Starch in considerable amount is lost during its purification from raw materials. Further, purification costs energy and time. To avoid these, starch in corn flour was hydrolyzed by the synergistic action of α-amylase and glucoamylase while avoiding high temperature gelatinization and liquefaction processes. When 1600 g (16%, W/W suspension) and 4000 g (40%. W/W suspension) corn flour was hydrolyzed and purified, 76.0% and 50.2% glucose yields were obtained. The residues obtained were rich in protein and minerals.