Biosci. Biotech. Biochem. 59 : 2203-2206 (1995)

Functional Changes of Carboxymethyl Potato Starch by Conjugation with Amino Acids

W. Yang, M. Hattori, and K. Takahashi

Department ofApplied Biological Science,
Faculty of Agriculture,
Tokyo University of Agriculture and Technology
Tokyo 183, Japan

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. Amino acid (Glu, Cys, Lys, Gly, Leu or Phe) solution was added and the reaction mixture was incubated at 24ÁC for 5 h, resulting in the formation of acid-amide bond between CMS and amino acid. AA-CMS conjugates were recovered after washing with distilled water thoroughly and air-drying. The functional changes of starch were investigated by microscopic observation, differential scanning calorimetry (DSC), solubility, and digestibility with alpha-amylase or beta-amylase. The swelling and solubility of the AA-CMS conjugates were much lower than those of CMS. Data from DSC exhibited that the conjugates gelatinized at higher temperature region than CMS and were hard to retrograde, especially the conjugates with hydrophobic amino acids. The digestibility of the conjugates with alpha-amylase or beta-amylase markedly decreased as compared with those of CMS and native starch.