Effects of konjac glucomannan on the rheological, microstructure and digestibility properties of debranched corn starch

The physicochemical properties and structure of starch can be influenced by non-starch polysaccharides. The effect of Konjac glucomannan (KGM) on retrogradation and gelatinization of debranched corn starch (DCS) was investigated. Steady rheological results indicated that KGM enhanced the viscoelasticity of DCS, the consistency coefficient (K) of DCS with 12% KGM reached 383.39 Pa.s(n). The digestion analysis showed that the total content of slowly digestible starch (SDS) and resistant starch (RS) was also improved with the concentration increase of KGM and reached 65.11% at 12% KGM concentration. Molecular weight distribution analysis showed that the proportion of amylose/amylopectin increased and the molecular weight decreased in debranched starch. X-ray diffraction (XRD) results suggested that the crystallinity of DCS containing KGM (KDCS) increased from 14.50% to 18.75% with the rising of KGM content. The crystallinities of all KDCS were lower as compared with DCS (25.67%), however, the total content of SDS and RS of KDCS in which the content of KGM exceeded 9% was higher than that of DCS. Scanning electron microscope (SEM) results showed that the compactness of the composite enhanced as KGM increasing which illuminated that the molecular weight distribution, crystallinity, viscoelasticity and digestibility of the composite were correlated to the densification of its network structure.