Experimental cookery

Samec states: "Esterification with phosphoric acid, thus introducing a group with ability to ionize, greatly increases the hydration capacity and does not essentially decrease the tendency to association. ''If a starch paste be heated under pressure to 120°C., the high viscosity of the paste, the proportion of the undialysable phosphoric acid, the quan- tity of substance which can be transported by the electric current in a given time, and the precipitability by alcohol diminish, whilst the electrical con- 406 FLOUR AND BREAD ductivity of the solution rises but the magnitude of the molecular aggregates does not change in the same degree." Therefore Samec believed there was some correlation between the phos- phoric acid content and the high viscosity of starch pastes. Hence he tried phosphating potato amylose with the following result : P2O5 Relative viscosity of Color with content a 1-per cent solution iodine Amylose 0.00 1.008 Pure blue Phosphated amylose 2.06 43.1 Pure blue From these results it appears that phosphoric acid may have some rela- tion to the viscosity of starch pastes. Other factors affecting viscosity will be discussed later. Fatty acids. Taylor and Morris make a further distinction between the two starch fractions from the fact that the insoluble residue carries certain high molecular-weight fatty acids combined with its carbohydrate. This insoluble fraction is called alpha-amylose and the soluble fatty-acid free portion is designated as beta-amylose. In potato starch pastes or solutions all the starchy material may be dispersed and, because potato starch con- tains no fatty acids, Taylor and associates question the existence of alpha- amylose in potato starch as it exists in cornstarch. They state that because the beta-amylose retrogrades on standing to a residue which resembles alpha-amylose except in its fatty-acid content, many investigators report the presence of alpha-amylose in potato starch. The fatty acids may be split from the carbohydrate by long acid hydrol- ysis or with lipase-free amylase. Taylor and associates report that un- saturated fatty acids are liberated before the saturated ones. Samec states that "careful researches concerning the colloidal changes which occur because of esterification of the starch substance with fatty acids are not as yet available, but we assume that the hydration capacity will thereby be decreased since longer chains of C-Ho are introduced into the molecule. The hydration capacity is also decreased by compounds con- taining phosphorus and nitrogen." Cereal starches contain a relatively higher percentage of fatty acids. Potato starch contains no fatty acids but has a relatively high phosphorus content. Wheat also has a relatively high phosphorus content. Taylor states that roughly, those starches having a relatively high fatty-acid content may have a relatively low phosphoric-acid content and vice versa. Starch paste. Starch granules added to cold water swell slightly. According to Alsberg the axes may increase as much as 15 per cent. Such swelling is not like that in hot water inasmuch as there is no change in structure observable under the polarizing microscope. If the starch is dried rifts may appear in the granule, and the dried starch granules are deprived of their power to reassume their former volume when wetted. When a small quantity of starch is mixed with cold water, a thin, milky, non- GELATINIZATION 407