THERMOCHEMICALLY-MODIFIED SOYBEAN AND CORN PROTEIN PRODUCTS WITH ENHANCED METAL-BINDING PROPERTIES

Citric acid (CA), also known as 2-hydroxy-1,2,3 propane tricarboxylic acid, was thermo-chemically reacted with food quality soy protein isol ate (SPI), distillers' dried grains (DDG), produced from corn dry mill ing, and corn gluten meal (CGM), produced from corn wet milling, to ge nerate acid-stable products with enhanced metal-binding properties. CA dehydrates at high temperature to form an anhydride that can interact with nucleophilic functional groups of protein or carbohydrate to gen erate ester or acyl derivatives. Effects of temperature, CA concentrat ion, pH and reaction lime were evaluated to show that SPI, DDG, and CG M, when heated in the range 110-120 degrees C with CA at 1:1 w/w ratio , under endogenous acidic conditions for 24 h. yielded reaction produc ts with reaction efficiencies >60% which possessed 4.13, 4.19 and 4.26 mmol COOH/g, respectively. FTIR data of original heated protein compa red with their respective CA products demonstrated additional absorban ces indicative of ester and carboxyl Linkages. The SPI/CA, DDG/CA, and CGM/CA products effectively bound 1.18, 1.07, and 0.9S mmol Cu2+/g, r espectively, when analysed by ion plasma spectrometry. Solid state Al- 27 NMR supported the metal binding characteristics of CA reaction prod ucts and demonstrated that Al3+ was bound ionically to carboxyl groups present on the reaction product. Amino acid composition studies showe d diminished amounts of amino acids with nucleophilic reactive groups in all three CA reaction products. The CA reaction products are highly resistant to acid hydrolysis with 6 N HCl for 4 h at 145 degrees C. T he biobased products generated in this study possess cation-exchange c apability and potential biodegradability that may have an outlet for i ndustrial wastewater treatment.