Abstract: In this study, changes in the multi-scale structure and physicochemical properties (digestibility and pasting properties) of highland barley starch before and after dry heat treatment (DHT) under alkaline conditions at different pH levels were explored by scanning electron microscopy, particle size and distribution analysis, small-angle X-ray scattering, X-ray diffraction and gel permeation chromatography. The results indicated that with the increase in pH value, DHT decreased the viscosity and retrogradation value but increased the paste stability of the starch paste. These changes resulted from an increase in starch highly-ordered structures and crystallinity and the rearrangement of degraded starch molecules. Moreover, the DHT starch possessed greater proportions of slowly digestible starch (SDS) and resistant starch (RS). The degraded starch with a molecular molar mass below 2 × 107 g/mol showed increased helix content, greater crystallinity with a more ordered crystalline lamellae, promoting SDS and RS formation. Overall, these results suggest that DHT is a promising approach for the regulation of starch digestibility with suitable pasting properties, which can provide valuable information for the rational design of highland barley starch-based products.

Key words: highland barley starch, dry heat treatment, multi-scale structure, pasting properties, digestibility