Effect of pullulan on the digestible, crystalline and morphological characteristics of rice starch

Abstract

The in vitro enzymatic digestibility of rice starch (RiS) was investigated in the presence or absence of pullulan (PUL) using the classic Englyst method and complemented by the analysis of the digestion kinetic. PUL induced a significant increase of the sum of slowly digestible starch (SDS) and resistant starch (RS) contents from 21.24% to 38.11% with a concomitant decrease of the rapidly digestible starch (RDS) content when 0.50% PUL was added. Both of the hydrolysis kinetic parameters, C∞ and k, decreased with the increasing of PUL, indicating the deceleration of hydrolysis rate by the incorporation of PUL. As evidenced by the changes of the crystalline characteristics and morphologies of fresh starch pastes with the help of X-ray diffraction (XRD), optical microscope, and confocal laser scanning microscopy (CLSM), the inhibitory effect of PUL on gelatinization of starch and the coating effect of PUL on the surface of starch granules were hypothesized to be responsible for the reduced starch digestibility in the present work.