Cereal Chem 49:508 - 513.  |  VIEW ARTICLE
The Effect of Chlorogenic, Quinic, and Caffeic Acids on the Solubility and Color of Protein Isolates, Especially from Sunflower Seed.

C. M. Cater, S. Gheyasuddin, and K. F. Mattil. Copyright 1972 by the American Association of Cereal Chemists, Inc. 

Chlorogenic (CGA), quinic (QA), and caffeic (CA) acids have been identified as components of sunflower seed. CGA in particular has been indicted as causing the discoloration of sunflower meal at alkaline pH and the broad pH range (3 to 7) of minimum solubility and maximum precipitability of sunflower protein. The objective of this research was to test the validity of these indictments. Two approaches were used in evaluating the solubility effect. First, pH-solubility and precipitation profiles of sunflower meal freed from CGA, QA, and CA were compared with the original meal. Second, samples of a commercial soybean- protein isolate were treated with the organic acids individually, and their solubility profiles compared with that of untreated soybean-protein isolate. The results indicate that the unusual solubility profile is a characteristic of the sunflower protein, and not induced by interaction with any of the three organic acids. To measure the chromophoric effects of the three acids, soybean-protein isolate treated with each was extracted with water at pH values ranging from 2.0 to 11.0, and the colors noted visually. For comparison, sunflower meal was treated in a similar manner. The CGA-treated soybean meal exhibited color changes similar to the sunflower meal, although the colors obtained were lighter. QA had no effect on the color; and CA produced a slight pink, rather than the green to brown of CGA. The lyophilized CGA-treated soybean meal had a grayish color, whereas those treated with QA and CA were similar to the control. This suggests that chlorogenic acid per se darkens the protein.