The effects of microwave heating on the molecular arrangements in potato starch, including single and double helices and amorphous structures, were studied using a 13C CP/MAS NMR method combined with X-ray diffraction.
In the food industry, research into the characteristics of microwave-heated materials has focused on dielectric properties. However, the lack of studies on microwave-absorbing properties has hindered the application of microwave technology. The aim of the present study was to investigate the microwave-absorbing properties of rice starch. It should be noted that this was the first time that the improved arch method was used to measure the microwave reflection loss (RL) of the starch dispersion. The results showed that the microwave absorption of the liquid system corresponded to the classical quarter-wavelength resonator model. When the concentration of the native starch was increased from 1% to 30%, the RL decreased from´5.1 dB to´1.2 dB at 2.45 GHz. Therefore, the absorption rate of microwave, γ ab , decreased from 69.1% to 24.1%. At 1.7 to 2.6 GHz, the interference effect of pregelatinization rice starch in an aqueous system on the microwave absorption properties became weak compared to native starch.
The aim of this work was to investigate the role of microwave parameters and moisture content on the free volume (FV) changes of rice starch by positron annihilation lifetime spectroscopy analysis (PALS) and to explore the potential relationship between the changes of FV and physicochemical properties of rice starch. Microwave heating and water molecules lead to the increasing of FV of starch. However, this result is largely influenced by the plasticization of water molecule. The anti-plasticization caused by water evaporation resulting in a decrease in the size and concentration of FV during microwave heating. Significant decrease (p < 0.05) in the thickness of amorphous region of microwave-heated rice starch was found by small angle X-ray scattering (SAXS), and the glass transition temperature (
Tg
) and gelatinization temperature significantly increase (p < 0.05) after microwave heating. According to correlation analysis, the power intensity and heating time were correlated negatively with the lifetime of o-Ps. In addition, the changes of amorphous region and
Tg
of rice starch were strongly related to FV changes. These results provided a theoretical basis for further research on the directional regulation of FV and improvement the quality of starch-based food by using microwave treatment.
The effect of microwave heating on the lamellar ultrastructure of potato starch granules was studied using small-angle X-ray scattering (SAXS), and the linear correlation function was generated from SAXS data to obtain the parameters of the lamellar repeats architecture. To investigate how the molecular vibration of the microwaves influences the lamellar structure during heating, rapid convection heating was applied through an oil bath for comparison. The results showed that the samples subjected to the microwave and the rapid convection heating displayed similar data, which could demonstrate that the effect of microwave heating on submicroscopic structure of potato starch may be mainly due to its rapid heating effect.
In this short communication, based on Renyi entropy measure, a new Renyi information based clustering algorithm A is presented. Algorithm A and the wellknown fuzzy clustering algorithm FCM have the same clustering track. This fact builds the very bridge between probabilistic clustering and fuzzy clustering, and fruitful research results on Renyi entropy measure may help us to further understand the essence of fuzzy clustering.
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