Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Abstract Only
Publication Acceptance Date: March 26, 2000
Publication Date: N/A
Technical Abstract: Citric acid (CA), also known as 2-hydroxy-1,2,3 propane tricarboxylic acid, is a cross-linking agent used to enhance some of the physical properties of zein films and fibers. It has been proposed that the carboxyl groups of CA or its anhydride will interact with the nucleophilic hydroxyl or amino groups of protein to generate ester and/or amide derivatives. FTIR data of fzein/CA products generated in a semi-dry state showed evidence of ester bond formation. To access amide bond formation we reacted zein with CA dissolved in 80% ethanol either in the presence or absence of the catalysts: N-hydroxy succinimide and 1-[3-(dimethylamino)propyl]-3-ethyl- carbodiimide hydrochloride. A dye, fluorescein isothiocyanate, that will bind free amino groups was used to qualitatively demonstrate that zein/CA under our reaction conditions in the absence of catalyst still possessed free amino groups. Hence, no amide bonds were generated. However, the catalyzed zein/CA reaction products possessed no free amino groups. There fore, catalyst is essential to achieve amide bond formation with zein/CA.