In the production of glucose by the hydrolysis of starch, a considerable quantity of fat occurs in the glucose liquor. From the previous treatment of the raw starch this fat appears to be an inherent part of the starch itself. This investigation was undertaken to determine whether fat is really combined with the carbohydrate in the starch molecule.
It was shown that:
(a) Fat is liberated upon the hydrolysis of starch.
(b) Although no definite compound of carbohydrate and fat was isolated in pure condition, still a residue relatively high in fat content was obtained.
(c) The fatty acid of the fat was chiefly palmitic.
(d) The palmitic acid was combined with an unsaturated material, of unknown composition, as an ester.
(e) The unsaturated material served as a link between the palmitic acid and the carbohydrate part of the starch.
It has been shown that maize starch cannot be regarded as simply made up of glucose, but contains a minor constituent, a fatty substance made up of palmitic acid and an unsaturated material whose composition is still unknown.
Fat associated with starch: It is well known that the starches as they are obtained ordinarily from the plants have a certain amount of fat associated with them. It has been assumed generally that this fat can be removed by solvents, and that its presence is a contamination of the starch with other constituents which occur intimately associated with the starch in the plant.
In the manufacture of glucose commercially from corn starch an insoluble product known as “refinery mud” occurs in the sugar liquor after the hydrolysis, and is separated by filtration. This refinery mud as recovered contains about 50% of fat, chiefly the higher fatty acids, and after washing and other treatment is sold as soap stock.
Considering the process employed in the commercial hydrolysis of starch it is improbable that the source of this fatty material can be attributed to extraneous matter accompanying the starch from the kernel, since its presence is observed only during or after the destruction of the starch by hydrolysis. The occurrence of free fatty acids during the hydrolysis and disruption of the complex starch molecule leads to the
interesting question of whether the fatty material constitutes an inherent part of the starch itself.
The present article is an account of an attempt to answer this question, and the results obtained lead to the following conclusions :
I. The major part of the fatty material present in starch cannot be removed by solvents before hydrolysis.
II. Hydrolysis of corn starch freed of extraneous fat liberates fatty acids.
III. The liberated fat is principally palmitic acid, but an unsaturated substance of unknown structure also occurs with it.
IV. The fat is liberated when hydrolysis has reached the erythrodextrin stage.
V. It is possible to obtain from starch residues containing relatively large amounts of fat combined with carbohydrate.
VI. The palmitic acid apparently is attached indirectly to the carbohydrate, but directly to the unsaturated component.
VII. Starches from other sources than corn also contain combined fat.
VIII. Extraneous Fat Accompanying the Starch.
The corn starch used was the best alkali-washed product available in the open market. A 82.26 g. sample of this material was extracted, first with ether, then with petroleum ether and finally with carbon tetrachloride. The duration of the extraction in each case was 36 hours.
The amount of soluble matter, chiefly fat, obtained by means of each successive solvent was Solvent. Ether (dry) 0.057, Petroleum ether 0.012, Carbon tetrachloride 0.046, total 0.115. Further extraction gave no weighable residues upon evaporation of the solvent. The residues, obtained by evaporation of the solutions from the first extractions and the weights of which are given in the table above, were yellow and gummy.
Upon solution in alcohol and titration with alkali, the combined residues gave an acid value 1 of 95.1. A comparison of this acid number with 186.0, that of the fat described under II, indicates the presence of considerable foreign matter, probably nitrogeneous in character.
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