Friday, February 19, 2010

Miscellaneous Starch

Amylose occurs to the extent of 27% in cornstarch, the other 73% being amylopectin. Amylase is a linier chain of dextrose units and resembles cellulose, which it can supplant for many uses, such as in film, starch adhesive, and paper. Waxy corn is almost all amylase and is being grown in increasing amounts. However, there are a number of process for separating the two starches. One process beats the cornstarch slurry under pressure to prevent boiling, whereupon the mixed starch dissolves; upon slow cooling to about 49oC the amylase crystals form and are recovered, leaving the amylopectin to be precipitated upon further cooling.

White Potato Starch

White potatoes contain 10 to 30% starch. Upon being received at the factory, the potatoes are washed and disintegrated to a water pulp, using a hammer mill. The pulp is treated with sulfur dioxide gas, in ratio 0,5 kg per kg of starch and sent to the continuous horizontal centrifuge with an imperforate conical bowl and a continuous spiral ribbon starch remover. The protein water mixture is separated from the starch, cellulose and skims, and the later three substance are resuspended in water. The suspension is sieved, and the pulp from the sieves is reground and resieved. The liquor from the second sieving is again passed through a centrifuge, suspended in water, and sent to the separation devices. From this point on operation are similar to those used for the manufacture of corn starch. Two other process are also used. In the batter process, which is similar to the Martin’s process, the dough formed is dispersed in water and the dispersed gluten collected on a sieve. Using alkali in a similar process disperse the gluten sufficiently that the starch settles out on standing.

Rise Starch

This is made from cargo rice, which still has the brown outer cuticle attached or from broken white grains rejected as foodstuff. The rice is steeped for 24 h with dilute caustic soda solution (1.005 specific gravity) in tanks with perforated false bottoms. At the end of the period the liquor is withdrawn, the rise washed, fresh liquor added, and steeping solution to a specific gravity of 1.24, and the mash to centrifuged. The solids obtained include all sorts of fibrous material, starch, and gluten. These are resuspended, a small amount of formaldehyde is added to inhibit fermentation and they are centrifuged and washed. A bleaching or bluing agent may be added at this point. The liquor is screened, adjusted to a specific gravity of 1.21 and sent to disk centrifuges. The resulting starch is dried for 2 days at 50 to 60oC.

Cassava (Tapioca Starch)

This starch is obtained from the roots and tubers of the manioc plant. Imports are mainly from Thailand, Indonesia and brazil. The average starch content varies from 20 to 30%. In general, the roots are pulped and washed on sieves to obtained the starch. Separating and purifying operations are similar to those described for potato starch.