Preparation and In vitro Digestibility of Corn Starch Phosphodiester

Purpose: To optimize the process conditions and analyze in vitro digestibility of corn starch phosphodiester prepared by sodium trimetaphosphate (STMP).
Methods: By using response surface method, the effects of STMP concentration, pH, esterification temperature, and urea addition on digestion resistance of corn starch phosphodiester were investigated and optimal conditions were determined. Corn starch phosphodiester was identified by Fourier transform infrared spectroscopy (FT-IR) and an in vitro digestibility method was applied to investigate starch digestion performances of corn starch phosphodiester.
Results: The optimum conditions for the preparation of corn starch phosphodiester were as follows: STMP, 3.3 %; pH 9.07; esterification temperature, 42 °C; and urea, 2.3 %. Under these conditions, corn starch phosphodiester with a digestion resistance of 66.02 % ± 1.63 % was obtained. Compared with corn starch, the digestible starch content of corn starch phosphodiester decreased sharply (from 86.6 to 10.9 %), while digestion-resistance starch content increased significantly from 1.9 to 66.0 % (p < 0.05), and its digestibility was reduced. FTIR spectrum showed new absorption peaks at 1028 cm-1 indicating that an esterification cross-linking reaction occurred between corn starch and sodium trimetaphosphate.
Conclusion: The corn starch phosphodiester obtained has a lower digestbility and therefore, can potentially be used as a medium glycemic index food for diabetic patients.

Keywords
Corn starch phosphodiester; Digestion resistance; Sodium trimetaphosophate; In vitro digestibility; Glycemic index