Influence of Impurities in Sugar Technology.

By Aamarpali Puri

Starch and Dextran

Starch is a natural constituent of sugarcane. Starch gets gelatinized by heating during juice clarification and is removed to an extent of 30-35 % but the rest gets concentrated in the process stream due to evaporation of the clear juice. The resulting harmful effects of it are the increase in viscosity and poor juice filterability. Mechanical harvesting has resulted in an increase in the quantity of bacterial polysaccharides like soluble dextran in the juice. Dextran that enters the juice remains with it until crystallization of the sugar. Dextran formation causes sugar loss, processing problems and increases the viscosity manifold. This increase in the viscosity decreases the clarification rate and gives poor clarification, which in turn leads to crystal elongation and hinders the heat transfer process. It has been reported that dextran hinders the crystallization process by a temporary adsorption on especially the glucose fructose portion of the molecule.

Phosphate is natural constituent of sugarcane. In sugarcane the leaves with high phosphorous levels have more photosynthetic activity than those low in phosphorous. Shoot and root development benefits much from this element. Phosphorous deficiency causes shortening and thinning of stalks which, taper at growing point. Root system is retarded, there being very limited secondary roots. It has significant effect on the rheological characteristics of final molasses. It exhibits functional properties in a wide variety of foods produced by all segments of the processed food industry. Phosphate [Potassium dihydrogen phosphate, (KH2PO4)] is present in the form of soluble phosphate in sugar cane. Phosphate may absorb or complex with proteins and starches by virtue of their high charge. The charge and the extension of protein are altered, thereby affecting its colloidal properties. Phosphates can, therefore act to modify the processing characteristics or stability of proteins. Presence of phosphate in cane juice is essential for good clarification. If present in optimum concentration, it has beneficial effect on crystallization of sugar. It tends to form heavy precipitate of tricalcium phosphate, which not only removes the colloidal and other impurities but also absorbs much of the coloring matter and diminishes the calcium content of the clear juice.

 Cane juice is probably saturated with respect to silica. In cane juice the presence of silica creates industrial problems by the formation of scales during sugar crystallization due to silica deposition as calcium silicates (CaSiO3). Scales are hard deposits, which stick very firmly to the inner surface of the boiler. Scales are so hard and adherent that it is difficult to remove them, even with the help of hammer and chisel. There in lies the need to determine the concentration of silica in cane juice.

Alanine and Glycine

Amino acids are of importance as they along with other nitrogenous bodies reacts with reducing sugars and form colored compounds. Also it is found from the static (Wei-Jun and Wu-Chang, 1992) and dynamic analysis that different colorants such as caramel, an iron-phenolic body complex, and the browning reaction products from reducing sugars and amino acids, have different affinities for the crystals and cause different coloration under the same conditions. 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 and glycine are amino acids commonly found in sugarcane. 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 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. 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. Glycine (Molecular formula C2H5NO2) which is the other major amino acid present in cane juice is polar, uncharged, neutral and genetically coded amino acid. It is the only protein forming amino acid without a center of chirality. Its alpha carbon atom is bonded to a carboxyl group (COO-), an amino group (NH3+) and two hydrogen atoms. As percentage dry solids, the glycine is 0.01% free and 0.04% as protein in cane juice.

Oxalic acid

Oxalic acid and oxalates are mild nephrotoxic acids that are abundantly present in many plants. It is one of the major acids present in cane. The high oxalic acid content is an effective browning inhibitor in cane. More over it binds vital nutrients such as calcium, so long-term consumption of foods high in oxalic acid can lead to nutrient deficiencies. So in the present study the effect of oxalic acid on the growth rate of sucrose crystals at two degrees of supersaturation, at two temperatures and at two different seed sizes of sucrose crystal has been studied. 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.

Sulfur is a contaminant, which enters sugar during refining. Most sugar mills go through a process of sulfitation during the refining process, and the exact quantity of carry over of sulfur during the post sulfitation stages is not well known. But sulfur dioxide through bisulfite formation can form additives complexing with the aldehyde and ketonic groups of the hydrolyzed sugar moieties. Sulfur in foodstuffs is found linked to colon rectal cancer. Sulfur is believed to destroy Vitamin A, as it promotes the oxidation of the conjugated double bonds, and is also known to destroy Vitamin B1. Sulfur and sulfur dioxide are also known to promote allergies and accelerate the onset of allergy attacks.


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