Abstract
The gelatinization of potato starch and the effect of NaCl on starch gelatinization were monitored successfully in situ by 1H NMR spectroscopy. Variable temperature (VT) 1H NMR measurement, from 316 K to 340 K, was conducted on a suspension of potato starch and deuterium water as well as a mixture of potato starch, NaCl and deuterium water. The hydration level of starch was determined with the increase of temperature. In the presence of NaCl, the initial gelatinization temperature of potato starch was decreased from 331 to 328 K. Meanwhile, in situ1H NMR spectroscopy as a function of time was also carried out to monitor the gelatinization with a time resolution of 90 s per spectrum. Furthermore, the effect of using different processing methods during gelatinization, including varying the temperature or time duration, was investigated in detail. It was confirmed that protons from different groups of starch showed different accessibility for water during hydration of starch granules. In comparison with temperature, gelatinization time as the major factor for reaching complete gelatinization was confirmed. We expect that this research, as a continuing effort to apply NMR spectroscopy for characterizing starch, will pave a new way in the structural elucidation of starch.
Highlights
As one of the most abundant and attractive natural biopolymers, starch is the main constituent used to manipulate the quality of food in the human diet, and can be widely found in various botanical sources such as potato, corn, wheat and so on.[1,2,3,4,5,6] The structure of starch has been investigated extensively during the last decades
Gelatinization, when starch was heated in water, is one of the most signi cant processes in the industrial application and development of starch.[17,18,19]
To real-time monitor the detailed gelatinization process of potato starch in situ at atomic-levels, the variable temperature 1H NMR measurements at T 1⁄4 316–340 K were conducted upon the suspensions of potato starch and deuterium water with the weight ratio of 1 : 7.5 (Fig. 1a)
Summary
Considerable effort has been devoted to monitor the process and discovered the mechanism of gelatinization, using a variety of microscopic, diffraction and spectroscopic techniques, including scanning electron microscope (SEM), powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR) and NMR spectroscopy.[29,30,31,32,33,34,35,36,37] most of these methods were carried out depending on the post treatment, which usually processed samples with several preparation steps. It was found that the addition of NaCl decreased the initial temperature of starch gelatinization
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