Swadesh Ranjan Biswas

Production and Characterization of Nisin-Like Peptide Produced by a Strain of Lactococcus lactis Isolated from Fermented Milk

An isolate of Lactococcus lactis from fermented milk was found to produce a bacteriocin peptide. The isolate could grow in a medium with an initial pH of 11.0, in which it produced the bacteriocin extracellularly at the highest level. The level of the bacteriocin in the medium increased in parallel to the bacterial growth and reached its peak during the late exponential phase; thereafter it plateaued. The bacteriocin had a broad antibacterial spectrum similar to that of nisin and inhibited several related species of lactic acid bacteria and other Gram-positive bacteria. The inhibitory activity of the bacteriocin was found to be stable over a wide range of pH and temperature. The molecular weight of the peptide was judged to be 2.5 kDa by SDS-polyacrylamide gel electrophoresis.

Identification of the allergenic proteins of Ipomoea fistulosa pollen: Partial characterization and sensitivity test

Total soluble proteins were extracted from the pollen of Ipomoea fistulosa and subjected to ammonium sulphate precipitation at 80% saturation. Total protein was separated on SDS Polyacrylamide gel. Each band was recovered from the gel by electroelution avoiding the time‐consuming and expensive biochemical methods of column chromatography. The allergenic proteins were identified by skin tests. The fourth and the fifth band in the protein profile of I. fistulosa, IF4 (47 kDa) and IF5 (42 kDa) were the two major allergenic components of I. fistulosa. The protein profiles showed slight variations in the pollen collected from different geographical regions.

Potential application of the nisin Z preparation of Lactococcus lactis W8 in preservation of milk.

Aims:  The aim of the study is to evaluate the effectiveness of the preparation of nisin Z from Lactococcus lactis W8‐fermented milk in controlling the growth of spoilage bacteria in pasteurized milk.

Cloning, overexpression, and characterization of a novel alkali-thermostable xylanase from Geobacillus sp. WBI

An endo‐β‐1,4‐xylanase gene xynA of a thermophilic Geobacillus sp. WBI from “hot” compost was isolated by PCR amplification. The gene encoding 407 residues were overexpressed in E. coli and purified by Ni‐NTA chromatography. The purified enzyme (47 kDa) had a broad pH optimum of 6.0 to 9.0, and was active between 50 and 90 °C. The enzyme retained 100% of its activity when incubated at 65 °C for 1 h under alkaline condition (pH 10.0) and retained 75% activity at pH 11.0. The Km and Vmax of the enzyme were 0.9 mg ml−1 and 0.8 µmol ml−1 min−1, respectively. In molecular dynamics simulation at 338 K (65 °C), the enzyme was found to be stable. At an elevated temperature (450 K) specific α‐helix and β‐turns of the proteins were most denatured. The denaturation was less in WBI compared with its highest homolog G. stearothermophilus T‐6 xylanase with difference of six residues. The results predict that these regions are responsible for the improved thermostability observed over related enzymes. The present work encourages further experimental demonstration to understand how these regions contribute thermostability to WBI xylanase. The study noted that WBI produces a xylanase with unique characteristics, specifically alkali‐thermostability.

A foodgrade preparation of nisin from diluted milk fermented with Lactococcus lactis W8.

Lactococcus lactis strain W8, which contains the nisin Z gene in its genome, grew well and produced nisin in cows milk at temperatures of 30 to 37 degrees C. Maximum production of nisin was achieved at 6 h and was 4,000 activity units (AU) per ml in skim milk and 2,400 AU/ml in 3% fat milk. The organism produced nisin even in 20 times diluted skim milk and 3% fat milk at 1,000 and 600 AU/ml, respectively. Boiling of the fermented milk (pH 4.2) made with this culture allowed the separation of the liquid part (whey) from the curd. When 20 times diluted skim milk was fermented and the whey derived from it was lyophilized, the yield of nisin was 60,000 AU/g. The antimicrobial activity of the nisin preparation was stable for at least 1 year at refrigeration temperature. L. lactis W8 may have significant applications in the food industry for a cost-effective natural nisin preparation.