Effects of dual modification by cold plasma and heat-moisture treatment on the structure and in vitro digestibility of waxy maize starch

Cold plasma technology with potential clean-label attributes applying in starch modification has gained intensive interest. In this study, waxy maize starch was subjected to cold plasma treatment at different discharge current (0.8 & 1.2 A), followed by heat-moisture treatment (HMT) under heating moisture of 20 % similar to 30 %. The effects of dual modification on starch structural orders, functional characteristics and in vitro starch digestibility were investigated. X-ray diffraction and Fourier transform infrared spectroscopy revealed that plasma treatment disrupted crystallinity and double-helix order, whereas the structural orders was slightly increased when subjected to HMT under 20 % similar to 25 % moisture, without altering the diffraction patterns or FTIR spectra of starch. The gel permeation chromatography observed that dual modification produced lower molecule weight with smaller radius of gyration. The prior plasma treatment was responsible for the loss of structural orders and chain depolymerization, whereas the sequential HMT contributed to restore impaired packing orders, mainly due to the molecular chain rearrangement. In addition, the dual-modified starch exhibited biphasic endothermic profile with distinct crystalline perfections and enhanced thermal stability. In vitro starch digestibility showed that the overall starch digestion rate and extent were significantly enhanced, in which the granular roughness and reduction in molecule weight played important roles. This study indicated that plasma-HMT modification could be a new strategy to fabricate starch with lower viscosity and enhanced hydrolysis susceptibility, which would broaden applications of plasma-involved starch modification in food industry.