The aim of the present study was to characterize the multiscale structures of ternary complexes of a model system of starch, fatty acid (FA), and β-lactoglobulin (βLG) prepared using a Rapid Visco Analyzer (RVA). The addition of βLG to starch-lauric acid or starch-oleic acid RVA pastes resulted in the increased intensity or occurrence of a new viscosity peak during cooling when the RVA protocol was repeated. The viscosity peak was attributed to the formation of starch-βLG-FA complexes. Differential scanning calorimetry (DSC) results showed clearly that the starch-βLG-FAs complex was formed as gelatinized starch was cooled in the presence of βLG and FAs. The results of Raman, FTIR, and X-ray diffraction analyses showed that starch can interact with βLG and FAs to form a ternary V-type crystalline complex, which had a greater short-range molecular order and higher relative crystallinity compared with those of the binary starch-FA complex. The present study provided insights into the structure of a model starch-protein-fatty acid complex as an example of what might occur during food processing.

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A thorough understanding of starch gelatinization is extremely important for precise control of starch functional properties for food processing and human nutrition. Here we reveal the molecular mechanism of starch gelatinization by differential scanning calorimetry (DSC) in conjunction with a protocol using the rapid viscosity analyzer (RVA) to generate material for analysis under conditions that simulated the DSC heating profiles. The results from DSC, FTIR, Raman, X-ray diffraction and small angle X-ray scattering (SAXS) analyses all showed that residual structural order remained in starch that was heated to the DSC endotherm end temperature in starch:water mixtures of 0.5 to 4:1 (v/w). We conclude from this study that the DSC endotherm of starch at a water:starch ratio of 2 to 4 (v/w) does not represent complete starch gelatinization. The DSC endotherm of starch involves not only the water uptake and swelling of amorphous regions, but also the melting of starch crystallites.

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Recently, the use of ionic liquids as promising “green solvents” in starch chemistry has gained extensive interest, especially in the areas of chemical modification of starch and the development of starch-based materials.

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The molecular disassembly of starch during thermal processing is a major determinant for the susceptibility of starch to enzymatic digestion. In the present study, the effects of thermal processing on the disassembly of the granular structure and the in vitro enzymatic digestibility of rice and lotus starches were investigated. After heating at 50 °C, rice and lotus starches did not show significant changes in granular morphology, long-range crystallinity and short-range molecular order. As the temperature increased to 60 °C, rice starch underwent a partial gelatinization followed by an incomplete disruption of granular morphology, crystallites and molecular order. In contrast, lotus starch was almost completely gelatinized at 60 °C. At 70 °C or higher, both starches were fully gelatinized with complete disruption of the micro and macro structures. Our results show that gelatinization greatly increased the in vitro enzymatic digestibility of both starches, but that the degree of disassembly of the starch structure during thermal processing was not a major determinant of the digestibility of gelatinized starch.

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