Effects of Extrusion Conditions on Starch Ordered Structure, Functional Components, and Physicochemical Properties of Black Highland Barley Flour

This study investigated the effects of different extrusion temperatures and feed moisture contents on starch structure, functional components, and physicochemical properties of extrusion modified black highland barley flour. An X-ray diffractometer, a Fourier transform infrared spectrometer, a colorimeter, a rapid viscosity analyzer, and a dynamic rheometer were used to characterize the ordered structure of starch and physicochemical properties of the extrudate. Changes in functional components were examined, and the correlations between starch structure, functional components, and physicochemical properties were explored. The results showed that increasing the extrusion temperature significantly increased the degree of gelatinization and the short-range order of starch in extrudates, while decreasing the long-range order of starch. Extruded flour produced at high temperatures had lower polyphenol and β-glucan contents. Moreover, it had lower pasting characteristic values such as trough viscosity, final viscosity, and setback value, and higher water absorption index, swelling power, peak viscosity, and breakdown value. At lower extrusion temperatures, the degree of order of starch molecules decreased more slowly, more polyphenols were retained, and the contents of soluble dietary fiber and β-glucan increased significantly. Increased feed moisture content significantly reduced specific mechanical energy (SME), decreased storage and loss moduli, and resulted in weaker elastic solid-like behavior. The correlation analysis indicated that the extrusion temperature was highly significantly positively correlated with gelatinization degree, insoluble dietary fiber content, peak viscosity, and breakdown value, but highly significantly negatively correlated with polyphenol and β-glucan contents as well as relative crystallinity; feed moisture content was extremely significantly negatively correlated with SME. The above findings provide a theoretical basis for the industrial production of extruded black highland barley flour and the development of functional foods based on it.