By: Aamarpali Puri
The sugar crystallization is the diffusion-controlled process followed by the deposition of sucrose molecules lattice on to the nuclei. The higher is the temperature, the more is the sugar that can be held in the solution. In sufficiently concentrated solution, there is formation of aggregates among the sucrose molecules. The sugar crystal grows only in a supersaturated solution with the degree of supersaturation defined as the ratio between the total solid content in a supersaturated solution to that in the saturated solution. As the solution enters the supersaturation zone, there is an even higher probability that these aggregates reach dimensions to originate a stable three-dimensional nucleus, which, increasing will form, the sucrose crystals. During crystallization of the sucrose from the mother liquor and it’s subsequent development to produce uniform size and shape of the crystal, there is need to monitor the degree of supersaturation. Supersaturation is an unstable state. In this state the sucrose molecules begin to crystallize back into a solid at the least provocation. Stirring or jostling of any kind can cause the sucrose to begin crystallizing. For achieving optimum crystal growth without forming any false grain, supersaturation has to be kept within the metastable zone (1.05<SS<1.25). An automatic laboratory vacuum pan (Kishihara and Fujii, 1994) was also developed. It was (Kishihara et al., 1993) reported that overall coefficient of the growth rate of sucrose crystals from the ultra filtrate of factory syrup is 1.2 fold greater than that from the original syrup. Sucrose solubility is highly influenced by the presence of both organic and inorganic compounds, which are normally present in the industrial solution. The effect of non-sugars on sucrose solubility depends on both their type and the concentration. The (Maurandii et al., 1982 and 1984; Vanhook, 1983) presence of the impurities in sugar solution has effect analogous to the one exerted by an increase of temperature: a concentration increase promotes an increase of the volume diffusion influence on the overall crystal growth process. Sucrose crystal growth (Guimaraes et al., 1995) rate is sensitive to the variation in the crystal size and slightly influenced by the surface integration, with the diffusion step in crystal growth a significant factor in determining the over all rates. Sucrose crystallization takes place by layer upon layer deposition at the crystal surface and is affected by the non-sugars present. Powers (Powers, 1970) study revealed that if structural affinity with a single face exists, or there is possibility of bond formation, the molecule of impurity could statistically remain on the surface for a period. The increase in the viscosity due to presence of the impurities affects the crystal movement in the bulk of massecuite. The non-sugars present affects the deposition of sugar at different sugar crystal faces and hence the sugar crystal’s growth and quality. All the polysaccharides (Kaur et al., 2004) increase the viscosity of sugar liquor and decrease the rate of sugar crystallization. The growth rate of sucrose crystals increases with the increase in the level of phosphate but decreases with the increase in the level of silica in sugar solution (Puri, A.R and S.Kaur., 2005). The impurities that are added in the form of a dye tracer (methylene blue) and KCl show no effect on the growth rate.
To obtain sugar both from beet or cane, rather complex processing schemes are followed which depend on the quality and quantity of non-sucrose compounds present in the solutions at the end of the extraction stage. Till now no general applicable theory exists which predicts effects of all the factors that govern the process of crystallization from the solutions, accurately and completely. In the present investigation the growth rate of sugar crystals is studied as a function of supersaturation, temperature and the seed size. So the effect of alanine on growth rate of sucrose crystals is studied at two degrees of supersaturation, at two temperatures and at two different seed sizes of sucrose crystal.
The crystal growth rate depends on the viscosity, which further depend on the nature and amount of the impurities. Impurity gets attached to the sugar crystal by adsorption, occlusion or co-crystallization and influences the spin of the crystal in the solution. Hence, it is found to affect the final colour, shape and size of the crystal.
The sugar cane industry is a major user of nitrogen fertilizer and has an interest in efficient fertilization practice to limit costs and ensure a sensitive environment, which is not exposed to excessive N losses. Amino acid (Chen, 1985) and amides are present in raw cane juice and molasses. Excessive urea application in fields without potassium and phosphate use is responsible for higher amino compounds in juices. The free Amino acids accumulate in molasses and contribute to sucrose loss when amino acids are linked together to form proteins. In sugar cane plant the total content of nitrogen ranges from 0.036 up to 0.05%. Cane juice contains nitrogenous bodies such as albuminoids, ammonia, amino acids (alanine and glycine) and amides varying from 0.5 to 1.0%. Amino acids are of importance as they along with other nitrogenous bodies reacts with reducing sugars and form colored compounds. In industry, so many efforts are done to remove color. Analyzing amino acids in a sample can help solving color problem in sugar to some extent.
Alanine is a non-essential amino acid and was first isolated in 1879. It is one of the 20 amino acids used to synthesize proteins in terrestrial living organisms. It is an inhibitory or calming neurotransmitter in brain. Alanine (Molecular formula C3H7NO2) is the major amino acid present in cane juice. As percentage dry solids, the alanine is 0.06% free and is 0.05% as protein. It is one of the 20 most common natural amino acids. It is hydrophobic, with a methyl group side chain, and is the second-smallest of the 20 after glycine. It is also known as 2-aminopropanoic acid. As shown (Fig .1), its alpha carbon atom is bonded to a carboxyl group (COO–), an amino group (NH3+), a methyl group (CH3), and a hydrogen atom.
It exists as two distinct enantiomers, L-alanine and D-alanine, the former of which is used in protein synthesis. In the present study growth rate of sugar crystals in the presence of alanine has been studied.
Abbemat digital automatic refractometer was used for determining Brix. The rate of sugar crystallization was studied using two-litre laboratory vacuum pan.
Sucrose crystallization is a mass transfer process, sucrose molecules migration from solution, to crystal, driven by concentration differences between the mother liquor and the crystal surface. The rate of sugar crystallization was studied at two temperatures 328 and 338K in the laboratory vacuum pan in the presence of varying concentrations of alanine at the two seed sizes 850 μm and 600 μm The increase in alanine content in the sugar solution decreases the growth rate of sugar crystals. The growth rate was found to increase both with the increase in the supersaturation and 100C rise in temperature. However, the increase was more significant with the increase in supersaturation then with 100C rise in temperature. It can be concluded that the presence of alanine impedes the growth of sucrose crystals.
Chen, C.P. (1985). “Cane Sugar Handbook 11th Edition”. A Wiley-Interscience publication. John Wiley & Sons, New York., 34-35.
Honing, P. (1963). “Principals of Sugar Technology”. Vol II Elsevier Publishing Co. London.
Kaur, S.; Kaler. R.S.S and Aamarpali. (2004). “Effect of polysaccharides on rate of crystallization of sucrose”. Ind. Sug. July, 265-268.
Kishihara, S.; Tamaki, H.; Wakiuchi, N and Fijis, S. (1993). “Effect of Ultra filtration of factory sugar solution on growth of sucrose crystals”. Int. Sug. J., 95, 1135, 273-276.
Kishihara, S and Fuji, S. (1994). “Development of an automatic laboratory boiling pan”. Int. Sug. J. 96, 1151, 451-455.
Mathur, R.L. (1986b). “Handbook of cane sugar technology IInd Edition”. Oxford and IBH Publishing Co., India, 26.