Krishna Nand

Anaerobic digestion of fruit and vegetable processing wastes for biogas production.

Abstract The effect of feeding different fruit and vegetable wastes, mango, pineapple, tomato, jackfruit, banana and orange, was studied in a 60-liter digester by cycling each waste every fifth day in order to operate the digester as and when there was supply of feed. The characteristics of the anaerobically digested fluid and digester performance in terms of biogas production were determined at different loading rates (LR) and at different hydraulic retention times (HRT), and the maximum biogas yield of 0·6 m 3 /kg VS added was achieved at a 20-day HRT and 40 kg TS m −3 day −1 loading rate. The hourly gas production was observed in the digesters operated at 16 and 24 days HRT. The major yield (74·5%) of gas was produced within 12 h of feeding at a 16-day HRT whereas at a 24-day HRT only 59·03% of the total gas could be obtained at this time.

Production of fungal rennet by Mucor miehei using solid state fermentation

SummaryInvestigations have been carried out on the production of fungal rennet using a thermophilic strain ofMucor miehei under solid state fermentation conditions. A high milk clotting enzyme activity (58000 Soxhlet units/g) was achieved when optimum conditions were used. Further, a high ratio of 6.6:1 between milk clotting and proteolytic activities for this enzyme was obtained. Cheese prepared using this enzyme was also found to be acceptable in organoleptic quality. Large scale production of the enzyme in trays using the optimum conditions gave milk-clotting enzyme activities comparable to those in flask experiments.

Lactobacillus amylovorus as a phytase producer in submerged culture

Nineteen strains of lactic acid producing bacteria of the genera Lactobacillus and Streptococcus collected from different culture collections were screened for the production of extracellular phytase. A number of them exhibited the enzyme activity in the fermentation medium but Lactobacillus amylovorus B4552 produced the maximum amounts of phytase ranging from 125 to 146 units ml‐1 extracellularly under the submerged cultivation conditions. The optimum glucose and inorganic phosphate levels for highest phytase production were found to be 1% and 24% mg, respectively. Lactobacillus amylovorus has potential in improving nutritional qualities of cereal and pulse‐based food fermentations.

Production of thermostable cellulase-free xylanase by Clostridium absonum CFR-702

The production of cellulase-free thermostable xylanase was investigated with a locally isolated and identified strain, Clostridium absonum CFR-702 in a defined medium under anaerobic cultivation conditions at higher temperatures (above 65°C). Different fermentation conditions were standardised for the growth and xylanase activity, the optimum being 72–96 h growth at pH 8.5, and cultivation temperature at 75–80°C. Among different carbon sources tested, cellobiose, lactose, melezitose, raffinose, mannitol, sorbitol, myo-inositol, starch, pectin, cellulose and carboxymethyl cellulose (CMC) did not support any growth and enzyme activity. Xylan and xylose induced xylanase activity whereas xylobiose had less pronounced effect. The highest enzyme activity of 4300 nkatal per ml was obtained with birch wood xylan (BWX) followed by larchwood xylan (LWX) and oatspelts xylan (OSX). Glucose and β-methyl xyloside (βMEX) reduced the activity. Cultivation of the strain in 1000 ml of Hungate bottles with 1% birchwood xylan at 75°C and pH 8.5 exhibited the highest enzyme activity of 7025 nkatal per ml without filter paper degrading CMC-ase and β-glucosidase activities. Corn cob could also be utilised as a carbon source for economical production of xylanase by C. absonum CFR-702.

Jaggery: a novel substrate for pullulan production by Aureobasidium pullulans CFR-77

Abstract A locally isolated fungal strain Aureobasidium pullulans CFR-77 was used for the production of pullulan in batch fermentation employing jaggery (a traditional concentrated sugar cane juice) as a carbon source. The maximum yield of pullulan (51.9 g l −1 ) was obtained with 5% jaggery in the fermentation broth in 72 h. Jaggery supported good growth of A. pullulans and the pullulan produced was pigment free and highly viscous (160.5 cp) as compared with that of sucrose (32.0 cp). The fermentation period was reduced when jaggery was used as a carbon source as compared with sucrose. It favoured the formation of yeast like cells along with chlamydospores. The GC analysis of pullulan produced from jaggery and sucrose showed the presence of glucose as major sugar. From these results it can be concluded that Jaggery is a promising carbon source for the economical production of pullulan.

Ensilage of mangopeel for methane generation

Abstract Mangopeel is a waste product of mango processing which is available in large quantities in India during the harvest season, when disposal causes pollution problems. Ensilage of mangopeel for 6 months, the effects of ensilage on its physico-chemical characteristics and methane generation by an anaerobic digestion process were studied. Ensilage helped in the pre-treatment of polymeric constituents and the conversion of major components of carbohydrates into volatile fatty acids. The ensilage mangopeel was a useful substrate for anaerobic digestion for methane generation, and the biogas yield was as high as 0·68 m 3 /kg volatile solids (VS) added, with a methane content of 52%. This compared favourably with 0·43 m 3 /kg VS added, and a methane content of 50%, for dried mangopeel. The ensilage of feedstock could therefore eliminate pre-processing such as milling and pulverisation.

Lactobacillus farciminis MD, a newer strain with potential for bacteriocin and antibiotic assay.

A native isolate Lactobacillus farciminis MD isolated from fermenting mushroom exhibited a high degree of sensitivity to the majority of the bacteriocins produced by strains of lactobacilli, leuconostoc and pediococci. Also, the efficacy of Lact. farciminis MD as a sensitive strain for antibiotic assay was established against different antibiotics including ampicillin, cefazoline, chloramphenicol and nitrofurantoin at concentrations of 30 μg each, showing an inhibition zone of 30 mm diameter. The high degree of sensitivity towards bacteriocins and antibiotics provide potential for the exploitation of Lact. farciminis MD in establishing very well‐defined bacteriocin producers.

Influence of trace elements on biogas production from mango processing waste in 1.5 m3 KVIC digesters

SummaryThe influence of trace elements (Co2+, Ni2+ and Fe3+) in varying concentrations and combination, was studied in 1.5 m3 Khadi & Village Industries Commission (KVIC) digesters for biogas generation from mangopeel. Addition of these trace metals enhanced the biogas yield and methane content moderately, the maximum being with the iron fed digester. The digesters were always found to be stable without much variation in total volatile fatty acids (VFA), pH, total alkalinity and other parameters. A methane content of 62% and biogas yield of 0.49 m3/kg VS added was obtained with 4000 mg/L FeCl3 supplemented mangopeel fed digester as compared to control having biogas yield of 0.22 m3/kg VS added with a methane content of about 48–50%.

Control of cellulase formation by trehalose in Clostridium papyrosolvens CFR-703

The effect of different sugars on the cellulase system (total cellulase, avicelase, endoglucanase, and β-glucosidase) of Clostridium papyrosolvens CFR-703 was investigated under anaerobic fermentation conditions. Trehalose, lactose and cellobiose induced total cellulase activity of 26, 13.7 and 15.5 IU/ml, respectively. With the exception of trehalose, a concentration of >2% of these inducers inhibited production of all components of cellulase in the cultivation medium. This is the first time trehalose has been reported to be an inducer of cellulase synthesis, suggesting its industrial potential for the production of the cellulase complex especially total cellulase and avicelase required for commercial applications.

Start-up of anaerobic digestion of tomato-processing wastes for methane generation.

Abstract A good start-up of digestion of tomato-processing waste (TPW) was achieved by the stepwise addition of feedstock over 10–12 weeks of digestion. The stepped increases of TPW in the digester resulted in a steady-state gas yield of 0·597 m 3 /kg VS added with a 72% methane content. Volumetric production of gas and methane remained high after the eighth week of digestion throughout the investigation. The volatile fatty acids concentration in this system was similar to a cowdung-fed digester and never exceeded more than 150 mg/litre throughout the period.