Research on the Properties of Cross-Linked Polydextrin Based on Different DE Values

Polydextrin was prepared from dextrin through an esterified reaction using citric acid and sorbitol. Esterification caused the dextrin molecules crosslinked and polymerized through citric acid ester bonds. Dextrins with three different DE values obtained by enzymatic hydrolyzed corn starch were used as reaction material. The results showed that cross-linked polydextrin had an unordered crystal structure with a polymer diffraction spectrogram. The results of HPLC-MALLS-RI revealed that the weight average molecular weights of the three cross-linked polydextrin were 188 200, 106 200, and 25 270, respectively, and the number average molecular weights were 8 086, 6 517, and 3 160, respectively. Fourier infrared results showed that cross-linked polydextrin exhibited an absorption peak of carbonyl (C O) in the ester bond at 1 731.29 cm^-1. A citric acid methylene (—CH₂) signal peak appeared at σ 2.792 ppm in the ¹H NMR spectrum. Correspondingly, the ester bond (COO—) and methylene (—CH₂) signal peaks in the citric acid structure appeared in σ165.927 ppm and σ43.321 ppm in ¹³C NMR, respectively. These results indicated that poly-maltodextrin was linked by a citric acid ester bond. The moisture absorption rate of cross-linked polydextrin increased with the increase of the DE values of the raw dextrin and the relative humidity of the environment. The melt flow curve of polydextrin conformed to the power-law equation τ=kεⁿ (n< 1).