Effets Of Radio Frequency Heating Treatment On Functional Properties And Structure Changes Of Soy Protein Isolate

Protein is one of the most important components of food,and its functional properties are very important to the quality of the food.The main protein modification methods include chemical,enzyme,physical and genetic engineering.Compared with other methods,physical modification gets lots of advantages such as low cost,safety,short treatment time and smaller effects on nutrition.Whereas,the effects of novel food processing methods have advantages such as generally offer low energy cost,low treatment temperature,high product quality,low consumption waste-free technologies for quality enhancements and energy efficiency in protein modification.Due to fast heating,uniform heating,high penetration depth and low energy consumption,radio frequency(RF)has great potential in protein modification as a new electromagnetic heating technology.This research mainly researched the influence of RF heating on the functional properties and structure of soybean protein isolate(SPI),in order to obtain a better understanding of physicochemical effects of RF heating on SPI which may lead to improving the soy products and protein modification applications in the food industry.In this paper,the dielectric properties of SPI and the effects of radio frequency treatment on the structure and functional properties of soy protein isolate were studied.The main conclusions are as follows:(1)The value of dielectric constant(??)and loss factor(??)were decreased as the increasing of the frequency.The change in the value of ?? with temperature and concentration at low frequencies were different with it's at high frequencies.All temperature,pH and concentration can significantly affect the dielectric properties of SPI.The 2nd polynomial model of dielectric properties affected by pH,concentration and temperature were found to have good correlations(R2adj ? 0.850).The dielectric parameters(dielectric constant and loss factor)had an irregular change at temperatures near the denaturation temperature of SPI.All temperature,concentration and frequency can significantly affect the dp value.(2)The results suggested that under the same electrode gap,heating rate of SPI dispersion gradually decreased as the increasing of concentration.The difference of dielectric constant and loss factor increased as the increasing of concentration.The closer ?? and ?? value,the bigger heating rate of SPI dispersion under RF heating.The heating rate of SPI dispersion by using RF heating was negatively affected by the electrode gap.(3)The results suggested that solubility,Emulsifying properties,foaming properties and heat stability of SPI were increased by RF heating.Both of solubility,Emulsifying properties,Foaming properties and heat stability were increased with the increasing of electrode gap of RF heating system and was found highest when the electrode gap was 200 mm.Whereas,the foaming stability was decreased after RF heating.Compared with the electrode gap at 120 mm,the reduction of foaming stability of RF heated SPI was smaller than that at 160 and 200 mm.(4)The results showed that RF heating significantly influenced free sulfhydryl groups and surface hydrophobicity of SPI.Free sulfhydryl groups increased with the increase of final temperature.The hydrophobicity of the RF heated samples was higher than that of original SPI without RF treatment.The highest hydrophobicity of the RF heated SPI was found with electrode gap of 200 mm at 90 °C.RF heating treatment resulted in the decrease of ultraviolet absorption of SPI indicating change of three-dimensional positions of soy protein,but did not modify the protein primary structure of SPI.The Fourier transform infrared spectroscopy implied that hydration of SPI was decreased by RF heating.The self-reassembly from random coil structure to ?-sheet structure suggested that RF heating treatment can change secondary structure of soy protein to be more orderly.