FUNCTIONAL-CHANGES OF CARBOXYMETHYL POTATO STARCH BY CONJUGATION WITH WHEY PROTEINS

Potato starch granules and whey protein were conjugated with a covalent bond to improve the function of starch. Slightly carboxymethylated starch (CMS) was prepared and dispersed in a water-soluble carbodiimide [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide] solution. Whey protein isolate (WPI) was added, and the reaction mixture was incubated at 24 degrees C for 5 h, resulting in the formation of an acid-amide bond between CMS and WPI. WPI-CMS conjugate was recovered after thorough washing with a 0.9% NaCl solution and distilled water and then air-drying. The conjugation of WPI to the CMS granules was demonstrated by Coomassie Brilliant Blue staining, the WPI content of the conjugate being estimated to be about 6%. Conjugation markedly decreased the solubility and swelling of starch granules. DSC data revealed that the conjugate gelatinized at a higher temperature than CMS and ceased retrogradation. The digestibility of the conjugate with alpha-amylase and beta-amylase decreased as compared with that of CMS and native starch. The retinol binding activity of the conjugate was confirmed by fluorescence titration.