| In this study,soybean protein isolate(SPI)and xylo-oligosaccharide(XOS)were used as the main raw materials.On the basis of the selection and optimization of physical modification methods,glycosylation products were prepared by dry-heating Maillard reaction at high temperature and short time.The effects of ultrasonic treatment with dry-heating Maillard reaction on the functional properties of SPI were investigated.Functional properties such as emulsifying properties,emulsion stability,oil absorption,and water holding capacity were used as evaluation indexes.According to the weight of each index,calculated modified protein synthesis membership and thus determine the optimum modified conditions for the final evaluation.And the structure and morphology of the SPI before and after modification were also compared.The glycosylation products were applied to the pound cake.The palatability and storage resistance of the product were guaranteed.Through single factor and orthogonal experiments,the ultrasonic modification process and glycosylation modification process were optimized.The results showed that the ultrasonic modification conditions were solution pH 9.0,ultrasonic power 250 W and ultrasonic time 20 min.Under these conditions,the comprehensive membership value of functional properties of SPI(Ult)was 0.55.The optimum conditions for dry-heating Maillard reaction were:SPI(Ult):XOS mass ratio 1:2,Maillard reaction time 135 min,Maillard reaction temperature 130?,and the comprehensive membership value of functional properties of XOS-SPI(Ult)was 0.54.FT-IR,ultra-violet absorption spectroscopy,endogenous fluorescence spectroscopy,exogenous fluorescence spectroscopy,surface hydrophobicity index and SEM were used to analyze the structure of SPI after ultrasound treatment and dry-heating Maillard reaction.The secondary structure of SPI was changed obviously in the range of 1700-1600 cm-1 and 1500-800 cm-1 after ultrasonic treatment.The content of random curl structure was increased by 3.82%.The molecular structure of SPI became disordered.The surface hydrophobicity index was increased by 20.42.Because the tight spatial structure was destroyed,more chromogenic groups were exposed and the protein aggregated slightly.On this basis,it was proved that the SPI(Ult)reacted with XOS by dry-heating Maillard reaction.The significant changes in the range of 3700-3200 cm-1,1700-1590 cm-1 and 1260-1000 cm-1 were showed by FT-IR spectroscopy.The content of random curl structure of glycosylated products increased by 3.54%.and the secondary structure became more disordered.The surface hydrophobicity index increased by 146.24.The results showed that xylo-oligosaccharides had more chromophores in the glycosylation products after the grafting reaction,and exogenous fluorescence spectra proved that xylo-oligosaccharides and soybean protein isolate treated by ultrasonic had covalent grafting reaction.The above structural analysis results shown that the structure of SPI had undergone a large change after ultrasonic-glycosylation modification.XOS was grafted with SPI(Ult)and the glycosylated product was formed.XOS-SPI(Ult)was applied to pound cakes with directional carbohydrate supplementation and high energy efficiency.By adding 4%glycosylated products to the basic formula of heavy oil cake,through the determination of specific volume,baking loss rate and color difference,sensory evaluation and texture analysis,it was concluded that the heavy oil cake with XOS-SPI(Ult)was easy to be accepted in sensory and texture.The shelf life of heavy oil cake was predicted by ASLT experiment.It was concluded that the shelf life of heavy oil cake with glycosylation products could reach more than 2 years at 20? and 55%humidity.The results showed that the modified protein could be used in heavy oil cake to meet the needs of carbohydrate and the first limiting amino acid directional supplementation of special population. |
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