- •1 Introduction and outline
- •2 Review of literature
- •2.1 Structure of dextran
- •2.2 Microbial loading in sugar factories
- •2.3 The common methods of dextran fractions determination
- •2.4 Dextran content during the process of sugar production
- •2.5 Dextrans associated with processing problems
- •2.6 Crystallization process
- •2.6.1 Growth rate of sucrose crystals
- •2.6.2 Crystallization kinetics
- •2.6.3 Parameters influencing crystallization kinetics
- •2.6.4 Crystal morphology
- •2.7 The Economic gain
- •3 Material and methods
- •3.1 Material
- •3.2 Analytical methods
- •3.2.1 Determination of dextran
- •3.2.1.1 Robert method
- •3.2.1.2 Haze method
- •3.2.2 Microbiological experiments
- •3.2.2.1 Isolation
- •3.2.2.2 Identification
- •3.2.2.2.1 Gas and acid formation
- •3.2.2.2.2 Catalase test
- •3.2.2.2.3 Gram characteristics (KOH-Test)
- •3.2.2.2.4 Identification by API 50 CHL test
- •3.2.2.2.5 L/D-Lactic acid test
- •3.2.3 Crystallization experiments
- •3.2.3.1 Measurement of growth rate of sucrose crystals
- •3.2.3.1.1 Required amount of dextran and seed
- •3.2.3.1.2 Calculation of the growth rate of sucrose crystals:
- •3.2.3.2 Dynamic viscosity
- •3.2.3.3 Crystal morphology and surface topography
- •3.2.3.4 Image analysis
- •3.2.4 Statistical analysis
- •4 Results and discussion
- •4.1 Sensitivity and accuracy of different methods for the determination of dextrans of varying molecular mass
- •4.1.1 Robert’s Copper method sensitivity
- •4.1.2 Haze method sensitivity
- •4.2 Microbial sources of dextran an identification of relevant microorganisms in sugar factories
- •4.3 Levels of dextran contents in different sugar beet factories
- •4.4 Quality of factory final products and their relationship to the levels of dextran during different industrial periods
- •4.5 Influence of dextran concentrations and molecular fractions on the rate of sucrose crystallization in pure sucrose solutions
- •4.5.1 Influence of different temperatures on growth rate of sucrose crystals in the presence of dextran
- •4.6 Elucidation of crystallization kinetics in presence of dextran molecules
- •4.7 Influence of dextran molecule fractions on sucrose solution viscosity
- •4.8 Influence of dextran on the morphology and surface topography of sucrose crystals in presence of dextran
- •4.8.1 Crystal morphology
- •4.8.2 Surface topography
- •4.9 Technical and technological consequences and future perspectives
- •5 Summary
- •6 References
- •7 Appendix
- •8 C. V. and List of Publications
Material and methods |
|
|
|
|
|
|
42 |
||
mCry |
Crystal mass |
|
|
|
|
|
|
|
|
nCry |
Number of crystals |
|
|
|
|
|
|
|
|
The growth rate of sucrose crystals (G) in g /(m2 min) was calculated as follows |
|||||||||
|
|
m |
|
|
|
1 |
|
|
|
|
|
S,Cry |
|
|
|
|
|
||
|
G = |
|
|
|
|
|
|
(3-7) |
|
|
t |
A |
|
||||||
|
|
|
|
|
|
Cry |
|
|
|
3.2.3.2 Dynamic viscosity
A capillary viscometer (Schott-Geräte, capillary no. 532 20/II, Apparatus no. 102221) was used. This viscometer is suitable to determine the kinematic viscosity of Newtonian liquids according to DIN 51 562, part 1. The instrument constant K is valid for the survey of the meniscus passage with stands type AVS/S, AVS/S-HT and AVS/SK from Schott. It was evaluated as K = 0.1028 mm2/s2.
The kinematic viscosity v (mm2/s) can be calculated using the instrument constant in the equation:
(3-8)
t Flow time in seconds corrected according to DIN 51 562, part 1. The dynamic viscosity η (mPa.s) was calculated by:
η =ν ρ |
(3−9) |
where
ρSolution density
3.2.3.3 Crystal morphology and surface topography
To examine of sucrose surface topography, a scanning electron microscope (SEM, Hitachi S-2700) was used. After crystallization experiments, the mixture of crystals and mother liquor (massecuite) was centrifuged and washed by water during centrifugation, then dried in an oven at 70°C for 3 h.
3.2.3.4 Image analysis
For accurate estimation of the crystallization speed not only the sucrose crystals quantity but also the beginning area of the sugar crystals is needed. Here, an image analysis system (IMAGE), which enables a calculation of the middle diameter and fractionation of sugar crystals was applied (Wagner, 2003).