Abstract
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.
Highlights
Multiple analytical tools to be used to examine simultaneous structural changes of starch during Differential scanning calorimetry (DSC) heating over a wide range of water content
The present study has shown that ordered structures and morphology of starch are still present at Tc of the starch gelatinization endotherm at these high water contents, indicating that the constant DSC endotherm obtained at a water:ratio of 2:1 or higher does not represent complete gelatinization of starch
Lamellar structure and granular morphology have been reported at Tc of the DSC endotherm of starch at a water content of 60% or 66%17,21–24.The results of the present study, together with the previous findings, show clearly that the DSC endotherm obtained at water:starch ratios used in many experiments (2:1 to 4:1) do not represent the complete gelatinization behavior of starch
Summary
Multiple analytical tools to be used to examine simultaneous structural changes of starch during DSC heating over a wide range of water content. To the best of our knowledge, this is the first time the RVA has been used to simulate DSC heating profiles for the preparation of gelatinized starch samples over a wide range of water content to probe the molecular mechanism underlying gelatinization. For the freeze-dried starch samples, prepared as described subsequently using an RVA instrument, a ratio of water:starch of 4 (v/w) was used in the DSC measurements. To obtain sufficient material to characterize structural changes of starch during DSC heating, samples were prepared by heating starch-water systems in a RVA instrument without stirring under the same heating profile described above for DSC measurements. 2.5 g of native starch (10.6% moisture) were weighed accurately into an RVA canister and distilled water was added with a pipette to obtain the water:starch ratios of 0.5, 0.75, 1.0, 1.5, 2.0, 3.0 and 4.0 (v/w). A water:starch (4:1, v/w) mixture that was freeze-dried without prior heating was used as a control
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