Dj. Sessa et Re. Wing, THERMOCHEMICALLY-MODIFIED SOYBEAN AND CORN PROTEIN PRODUCTS WITH ENHANCED METAL-BINDING PROPERTIES, Die Nahrung, 42(3-4), 1998, pp. 266-268
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.