Experimental cookery

Viscosity of starch pastes. Viscosity of pastes made from the same concentration of starch vary (1) with different starches, (2) with its phosphoric acid content, (3) with the phosphorus salt content, (4) with the temperature to w^hich it is heated, (5) with the degree of injury or grinding of the granule, (6) possibly the proportion of beta- and alpha- amylose, and (7) with the length of the starch chain. Chain length may in turn be affected by application of dry heat, by boiling with water, or by acid and enzyme hydrolysis. Different starches. It has long been known in food preparation that starches from different sources need to be used in different concentrations, if the product to be served is stiffened to the same degree. Woodruff and Nicoli determined the stiffness of starch gels from 5 per cent concentrations of starch. The results, arranged in order of decreasing stiffness are : corn, wheat, rice, potato, arrowroot, and cassava. Other dif- ferences noted were: Of the three cereal starches, rice was the most translucent and tender when cut; corn was the firmest, the cold gel being chalky white; and wheat was intermediate between these two. For the other starches, the potato paste was ropy and too gummy to leave the mold well so that it gave a poorly formed gel, although quite transparent; arrowroot gave a still softer and more transparent gel ; and cassava starch gave only a viscous fluid. It was necessary to heat the gels to 90 °C. for maximum stiffening, but heating of any one starch to 90°, 95°, 99.5 °C. gave gels indistinguishable from each other. Phosphoric acid. Samec's results showing the increased viscosity of phos- phated starch have been given in the discussion of phosphoric-acid content of starch. From these results he concluded that the viscosity of starch pastes could be reduced in two ways : ( 1 ) by removing the phosphoric acid and (2) by reducing the size of the molecule. In general, paste formation increased with increased phosphoric acid content, but this did not hold for wheat starch. Samec believes this discrepancy may be explained on the basis that phosphoric acid in wheat starch may be present as a compound with the proteins. In general smaller granules gave richer or stiffer pastes than larger granules, which Samec ascribes to the relatively higher phosphorus content of the smaller granules. Phosphorus salt content. In separating starch by electrodialysis Samec states the amylophosphoric acid isolated in this way proved to be a diabasic acid. The solutions of various amylophosphoric acid salts not only gave pastes with differences in viscosity but also affected other properties. Thus copper and iron amylophosphate paste separated badly, the calcium amylo- phosphate tasted like chalk, magnesium and ammonium caused a slight burning and pricking sensation on the tongue, respectively, and sodium and potassium were reminiscent of wheat flour. Temperature to which the starch is heated. Although the starch may swell to a certain extent at lower temperatures, it may not reach its maxi- 410 FLOUR AND BREAD