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Starch Acetate-Maleate Mixed Ester Synthesis and Characterization¹

¹A contribution of the University of Nebraska Agricultural Research Division, Lincoln, NE 68583. Journal Series No.14810. This study was conducted at the Industrial Agricultural Products Center. ²Industrial Agricultural Products Center and Food Science & Technology, University of Nebraska, Lincoln, NE 68583-0730, USA. ³Cadbury Adams, Inc., Morristown, NJ 07960, USA. ⁴Corresponding author. Phone: +1-402-4721634. Fax: +1-402-4726338. E-mail: mhanna1@unl.edu

A new starch acetate-maleate mixed ester with different degrees of substitution (DS) for each ester group was prepared. High-amylose (70%) corn starch was first reacted at 123°C with ≈4.5 equivalents of acetic anhydride for different times, and then the intermediate products were further reacted at 80°C with 0.27–1.1 equivalents of maleic anhydride for a fixed time. ¹H NMR and alkaline saponification were used to determine DS values of acetyl and maleate groups. Increasing the reaction time from 60 to 120 min for starch and acetic anhydride increased DS of the acetyl group, while DS of the maleate group increased with increasing amounts of maleic anhydride. There was a good agreement between the two methods for DS determination. The reaction efficiency of acetylation increased from ≈30 to 50% with reaction time, and maleation decreased from ≈30 to 20% with increasing amounts of maleic anhydride. The mixed esters were characterized by ¹H NMR, ¹³C NMR, FTIR, DSC, and TGA. Characteristic peaks in ¹H NMR, ¹³C NMR, and FTIR spectra indicated the presence of acetyl and maleate groups in starch molecules. The exothermic peak in the DSC curve and the increase in thermal stability from the TGA curve were attributed to thermal cross-linking of the double bond of the maleate group.