Vasanthy Arasaratnam

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.

Reversibly soluble biocatalyst: optimization of trypsin coupling to Eudragit S-100 and biocatalyst activity in soluble and precipitated forms

Eudragit S-100, a copolymer of methacrylic acid and methyl methacrylate is soluble at pH above 5 and insoluble at pH below 4.5. pH-dependent solubility of the polymer is used for the development of reversibly soluble biocatalyst, which combines the advantages of both soluble and immobilized biocatalysts. Activity of trypsin, covalently coupled to Eudragit S-100, was improved by protecting the active site of the enzyme with benzamidine and removing the noncovalently bound proteins with Triton X-100 in 0.15 M Tris buffer (pH 7.6). Accurate choice of coupling conditions combined with proper washing protocol produced highly active enzyme-polymer conjugate with no noncovalently bound protein. Two conjugates with 100-fold difference in the content of trypsin coupled to Eudragit S-100 were studied when the preparations were in soluble and precipitated forms. The K(m)values of the soluble enzyme to the lower molecular weight substrate was less than that of the free enzyme, whereas that to the higher molecular weight substrate was closer to that of the free enzyme. Activities of the soluble and precipitated immobilized trypsin with higher molecular weight substrate were completely inhibited by soy bean trypsin inhibitor, whereas complete inhibition with soy bean trypsin inhibitor was never achieved with lower molecular weight substrate, indicating reduced access of high-molecular weight substrate/inhibitor to some of the catalytically active enzyme molecules in trypsin-Eudragit conjugate.

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.

Biochemical changes associated with germinating rice grains and germination improvement.

Abstract To determine biochemical changes during the germination of rice grains ( Oryza sativa L. subsp. indica var. Mottaikaruppan) and to improve germination rate using gibberellic acid and surfactants [sodium dodecyl sulfate (SDS) (1.0 g/L) and Triton-X−100 (1.0 mL/L)], whole rice grains soaked in distilled water for 12 h at 30°C were germinated in the dark at 30°C for five days. The highest germination rate (77.1%) was obtained on the 5 th day. An increase in the content of reducing sugars from 7.3 to 58.1 mg/g DM (dry matter) was observed from the 1 st day of germination. Free amino acids and soluble protein contents increased to 3.69 and 5.29 mg/g DM, respectively on the 5 th day of germination. Total protein content decreased from 100.5 to 91.0 g/kg DM during germination. Increases in amylolytic (1.1 to 190.0 U/g DM) and proteolytic (0 to 0.12 U/g DM) activities were observed during germination. Effects of different concentrations of gibberellic acid on the germination of rice grains were evaluated and 0.1 g/L was found to promote germination. When effects of gibberellic acid (0.1 g/L) and surfactants were evaluated individually and together, higher germination rate was observed in the control experiment (grains germinated in distilled water), whereas giberellic acid and surfactants decreased the germination rate. Therefore, the flour obtained from the grains germinated for four days using distilled water to obtain high content of soluble materials and enzyme activities can be used in preparation of bakery items.

Paddy Husk as Support for Solid State Fermentation to Produce Xylanase from Bacillus pumilus

To optimize culture conditions for xylanase production by solid state fermentation (SSF) using Bacillus pumilus, with paddy husk as support, solid medium contained 200 g of paddy husk with 800 mL of liquid fermentation medium (xylan, 20.0 g/L; peptone, 2.0 g/L; yeast extract, 2.5 g/L; K2HPO4, 2.5 g/L; KH2PO4, 1.0 g/L; NaCl, 0.1 g/L; (NH4)2SO4, 2.0 g/L, CaCl2·2H2O, 0.005 g/L; MgCl2·6H2O, 0.005 g/L; and FeCl3, 0.005 g/L) at pH 9.0 was applied. The highest xylanase activity (142.0 ±0.47 U/g DM) was obtained on the 6 th day at 30°C. The optimized paddy husk to liquid fermentation medium ratio was 2:9, and the optimized culture temperature was 40°C. When commercial Birchwood xylan was replaced with different concentrations of corncob, xylanase production was maximized (224.2 U/g DM) in the medium with 150 g/L corncob. Xylanase production was increased by sucrose, fructose and arabinose, whereas reduced by glucose, galactose, lactose and amylose. When organic nitrogen sources were replaced with locally available nitrogen sources such as groundnut powder or sesame seedcake powder or coconut seedcake powder or soy meal powder, the highest xylanase production (290.7 U/g DM) was obtained in the medium with soy meal powder and 16.0 g/L of soy meal powder was the optimum (326.5±0.34 U/g DM). Based on the optimization studies, B. pumilus produced 2.3 times higher xylanase activity. The medium cost was reduced from 2 458.3 to 178.3 SLR/kg and the total activity which could be obtained from 1 kg of the medium was increased from 48 624 to 220 253 Units.

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.

Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour

Abstract The feasibility of partially replacing wheat flour with malted rice flour in bread making was evaluated in several formulations, aiming to find a formulation for the production of malted rice-wheat bread with better nutritional quality and consumer acceptance. The whole grains of a local rice variety ( Oryza sativa L. subsp. indica var. Mottaikaruppan ) were steeped in distilled water (12 h, 30°C) and germinated for 3 days to obtain high content of soluble materials and amylase activity in bread making. The quality of bread was evaluated by considering the physical and sensorial parameters. When the wheat flour was substituted with malted rice flour, 35% substitution level and the malted rice flour from 3 days of germination was the best according to the physical and sensory qualities of bread. The quality of bread was improved by the addition of 20 g of margarine, 20 g of baking powder and 20 g of yeast in 1 kg of flour. Among different ratios of yeast and baking powder, 2:1 was the best. Bread improver containing amylases and oxidizing agents at the concentration of 40 g/kg was selected as the best concentration. When comparing the final formulation made in the bakery with wheat bread, malted rice-wheat bread contains more soluble dietary fiber (0.62%), insoluble dietary fiber (3.95%), total dietary fiber (4.57%) and free amino acid content (0.64 g/kg) than those in wheat bread (0.5%, 2.73%, 3.23% and 0.36 g/kg, respectively).

Physical, chemical and microbial analysis of bottled drinking water

INTRODUCTION People rely on the quality of the bottled drinking water, expecting it to be free of microbial contamination and health hazards. OBJECTIVES To evaluate the quality of bottled drinking water sold in Jaffna peninsula by analysing the physical, chemical and microbial contents and comparing with the recommended Sri Lankan Standard (SLS) values. METHODS All bottled water samples sold in Jaffna peninsula were collected. Electrical conductivity, total dissolved solid, pH, calcium, nitrate, total aerobic and anaerobic count, coliform bacterial count and faecal contamination were checked. RESULTS These are 22 brands of bottled drinking water sold in Jaffna peninsula. The sample had very low electrical conductivity when compared with SLS (750 μS/ cm) and varied from 19 to 253 μS/cm with the mean of 80.53 (±60.92) μS/cm. The pH values of the bottled drinking water brands varied from 4.11 to 7.58 with a mean of 6.2 (±0.75). The total dissolved solid content of the bottled drinking water brands varied from 9 to 123.67 mg/l with a mean of 39.5 (±30.23) mg/l. The calcium content of the bottled drinking water brands varied from 6.48 to 83.77 mg/l with a mean of 49.9 (±25.09) mg/l. The nitrate content of the bottled drinking water brands varied from 0.21 to 4.19 mg/l with the mean of 1.26 (±1.08) mg/l. Aerobic bacterial count varied from 0 to 800 colony forming unit per ml (cfu/ml) with a mean of 262.6 (±327.50) cfu/ml. Among the 22 drinking bottled water brands 14 and 9% of bottled drinking water brands showed fungal and coliform bacterial contaminants respectively. The water brands which contained faecal contamination had either Escherichia coli or Klebsiella spp. CONCLUSIONS The bottled drinking water available for sale do not meet the standards stipulated by SLS.

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.