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Title of Thesis

Shah Ali Qader
Institute/University/Department Details
University of Karachi, Pakistan
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
dextransucrase, dextran, leuconostoc mesenteroides, glucose molecules, fermentation process

Dextran is a long chain polymer of D- Glucose in which glucose molecules are linked with a-1†’6 and a-1†’3 linkages. Strains of Leuconostoc mesenteroides is involved in the production of dextran through fermentation process. Nine strains of L. mesenteroides were isolated from different vegetables and fruit sources.L. mesenteroides PCSIR was selected for studies due to its high enzyme activity and dextran production with reference to commercial strain L. mesenteroides NRRL B-512F different media compositions used for dextran production showed that medium containing CaCI2 (media-4) produced dextran in high quantity compared with other media. Dextran production in medium-4 clearly showed that the presence of magnesium and calcium salts in the medium not only effects the dextran production but also the enzyme activity.The viscosity of dextran produced in different media varied depending on the nature ofdextran. Dextran production is also effected by sucrose concentration in the media, higher the sucrose concentration higher is the yield of dextran per unit volume; however, the percentage conversion of sucrose to dextran decreased with increase in sucrose concentration. A continuous drop in pH was associated with growth and dextran production. The yield of dextran increased during the growth phase and maximum yield was obtained at the end of exponential phase.

Time course study of dextransucrase showed that 18 hours incubation is the optimum time for obtaining maximum enzyme activity, after which there was a progressive decline in the enzyme activity. Maximum dextransucrase production was obtained when medium of pH 7.5 was incubated at 26°C for 18 hours. Maximum enzyme production was obtained when sucrose (2%) was used as a carbon source in medium. Effect of reaction time, temperature, substrate concentration, pH and buffer were performed for extracellular dextransucrase maxima. It was found that 15 minutes is the optimum time for maximum enzyme activity instead of 1 hour reported earlier. It was also noted that the dextransucrase from L. mesenteroides PCSIR more thermostable. A loss of 86% activity was observed at 40°C in 240 minutes as compared to previously reported 100% loss of activity enzyme from other strains in just 125 minutes at the same temperature.

The activity loss at -18°C was very low and enzyme retained its activity even after 120 days.Cells of L. mesenteroides PCSIR-4 were immobilized on two supports, acrylamide and alginate beads. Alginate beads showed high yield of dextran as compared to acrylamide in a fermentation reactor. Dextran yield was found to be higher at 26°C as compared to 35°C when 10% sucrose was used as a substrate. Size of the beads, sucrose concentration and temperature play an important role in dextran production by immobilized cells on alginate beads. Bead size of 0.6 mm, sucrose (10%) and 30°C provide optimal conditions for dextran production from alginate immobilized cells.

Partial purification of dextransucrase was achieved by 36% chilled ethanol on addition of CaCI2 ho Partially purified enzyme was immobilized on alginate beads and it was found that 1 hour is the optimum time for maximum enzyme activity. A substrate maximum of 200 mg/ml, optimum temperature of 35°C, pH maxima of 5.00 were observed for immobilized enzyme.

Molecular mass distribution of L. mesenteroides PCSIR-4 dextran from immobilized enzyme was compared with blue dextran and a high molecular mass dextran was obtained by immobilized enzyme.

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3554.15 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
465.34 KB
2 1 Introduction 1
988.88 KB
  1.1 Dextran 1
  1.2 Dextransucrase
  1.3 Immobilization 29
3 2 Plan Of Work 48
31.05 KB
  2.1 Materials And Methods 52
  2.2 General Section 53
  2.3 Experimental 58
  2.4 Analytical 71
4 3 Results And Discussion 87
673.64 KB
  3.1 Dextran And Dextransucrase 88
  3.2 Characteristics Of Organism 88
  3.3 Production Of Dextran 90
  3.4 Dextransucarse 99
5 4 Immobilization 119
1198.24 KB
  4.1 Immobilization Of Cells 119
  4.2 Immobilization Of Enzyme 131
6 5 Molecular Mass Distribution Of Dextran 141
54.97 KB
7 6 Conclusion 145
74.33 KB
8 7 References 149
231.43 KB
9 8 Abbrevations 160
19.04 KB
10 9 Publications 160
42.11 KB