Effect Of Ultrasound And Deamidation On In Vitro Digestibility Of Cereal Protein

Cereal protein plays an important role in human life, in all of the requirements of protein, cereal protein is the most important part. However, due to the low digestibility of some cereal proteins, such as wheat protein, rice protein, corn protein and buckwheat protein, the utilization of cereal protein is not high. It resulted in a waste of resources of raw grains. In this paper, we studied the use of ultrasound and acid deamidation for wheat gluten, rice protein, corn protein, buckwheat protein’s modification, aiming at improving the digestibility of cereal protein and for rational and efficient use of cereal protein and the development of new protein resource to provide a theoretical basis.Ultrasound was used for the modification of four grain protein and the effect of ultrasonic modification on digestibility and physicochemical properties of cereal protein were studied. The results showed that, after ultrasonic treatment, the in vitro digestibility of wheat protein, rice protein, corn protein and buckwheat protein respectively from the original 79.5%, 66.5%, 78.3% and 69.5% increased to 89.0%, 79.5%, 89.2% and 78.6%. As the increasing of ultrasound time, a significant increasing(P<0.05) in solubility at p H 7.5 of four cereal proteins were observed. The content of disulfide bonds(-SS-) was significantly decreased(P<0.05) but the free thiol(-SH) was increased. Meanwhile, the content of α-helix was increased and the β-corner was reduced. The ultrastructure of four cereal proteins becomes more porous compared with the original cereal protein.Using different concentrations of hydrochloric acid for four cereal proteins deamidation, to determine the effect of different deamidation degrees on in vitro digestibility and physicochemical properties of cereal protein. It was found with the increasing of deamidation degree, the in vitro digestibility of wheat protein, rice protein, corn protein and buckwheat protein were respectively from the original 79.5%, 66.5%, 78.5% and 69.5% increased to 89.7%, 71.5%, 89.9% and 78.5%. The solubility at p H 1.5 and p H 7.5 and surface hydrophobicity of four cereal protein were gradually increased. The inter-conversion between sulfhydryl and disulfide bonds was not significant(P<0.05), and the ultrastructure of four cereal proteins becomes loose.Comparative study of the influence on cereal protein’s digestibility of compound modification with a single ultrasound or deamidation modification was made. The results showed that the compound modification was more efficient than a single ultrasound or deamidation modification. It is synergistic effect of them.To confirm the authenticity of the in vitro results, the experiment of parallel test of rats was made. The results showed that after compound modification, the in vivo digestibility of wheat protein, rice protein, corn protein and buckwheat protein was respectively from the original 78.2% 65.1%, 76.7% and 69.3% increased to 89.1%, 86.2%, 88.7% and 80.7 %. The SDS-PAGE and Tricine-SDS-PAGE profiles of digestates of cereal protein showed that the protein is more easily digested to small amino acids molecules by gastric and small intestine. The 5% TC A soluble nitrogen content of digestion in rats was significantly(P<0.05) increased after compound modification.Using SPSS software for the correlation analysis of experimental data to explore the relationship between physical and chemical properties and the in vitro digestibility of different protein. The results showed that: the in vitro digestibility of cereal protein with the solubility was of a significant(P<0.05) positively correlation; with the surface hydrophobicity was little correlation(P>0.05); with the content of disulfide bond was significantly(P<0.05) negative correlation.