Functional Changes of Carboxymethyl Potato Starch by Conjugating with Amino Acids

Abstract

Amino acid-carboxymethyl starch granule (AA-CMS) conjugates were prepared by using water-soluble carbodiimide (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide) to improve the functions of starch. Slightly modified potato CMS was dispersed in a 5% water-soluble carbodiimide solution. An amino acid (Glu, Cys, Lys, Gly, Leu, or Phe) solution was added, and the reaction mixture was incubated at 24°C for 5h, resulting in the formation of an acid-amide bond between CMS and the amino acid. Each AA-CMS conjugate was recovered after thoroughly washing with distilled water and air-drying. The functional changes of the starch were investigated by microscopic observation, differential scanning calorimetry (DSC), solubility, and digestibility with α-amylase or β-amylase. The swelling and solubility of the AA-CMS conjugates were much lower than those of CMS. Data from DSC shows that the conjugates gelatinized at a higher temperature than CMS and were difficult to retrograde, especially the conjugates with hydrophobic amino acids. The digestibility of the conjugates with α-amylase or β-amylase was markedly decreased as compared with that of CMS and native starch.