A Hybrid Dry And Aqueous Fractionation Method To Obtain Buckwheat Protein Concentrate With Its Functional Characterization

Buckwheat especially tartary buckwheat contains a mount of nutrients including proteins,bioactive polyphenols,minerals and so on.Besides,buckwheat has great adaptability,so it can grow in harsh environment such as area with high altitude and extremely cold climate.The conventional wet fractionation method involves an alkali to solubilize the protein from the defatted flour and acid to purify the protein via precipitation.However,this method consumes large amounts of water and energy,and even leads to denaturation of the protein.Therefore,it's necessary to find a new way to obtain functional protein-rich fractions of buckwheat in order to satisfy the demand of the marketing.Besides,traditional protein production focuses on high purity and yield only,resulting in energy-and resource-intensive fractionation processes,but nowadays we have to focus on functionality and optimal resource use.Combination of dry and aqueous fractionation is investigated to obtain different functional properties protein-rich fractions from buckwheat milder and more sustainable way compared to conventional wet fractionation.The protein extraction method has a major impact on its properties in food.In this study,three ways were explored to prepare three different kinds of buckwheat protein concentrate and evaluate their functional properties.The research results mainly include the following aspects.(1)Buckwheat protein concentrate(BPC)enriched with polyphenols was prepared from hulling tartary buckwheat grain by extrusion fractionation and double-enzyme extraction in combination with membrane separation.Compared to alkaline extraction-acid precipitation,double-enzyme extraction shown a high protein recovery(57.93%),with a protein content of 49.07%.Furthermore,double-enzyme extraction method displayed high polyphenols contents(11.35%)and recovery(70.89%),compared to those of the alkaline extraction-acid precipitation method(3.65% and 8.58%,respectively).Similar results from the SDS-PAGE analysis of BPC prepared by these three methods were observed after the in vitro digestion.Additionally,the nitrogen release of BPC from double-enzyme extraction method was only 43.3%,suggesting that the buckwheat protein concentrate prepared from double-enzyme extraction possessed a high resistibility for digestion.(2)Buckwheat protein concentrate(BPC)removed polyphenols and trypsin inhibitor were prepared from hulling tartary buckwheat grain by extrusion fractionation and salt extraction combined with resin absorption.The physicochemical and functional properties of BPC were evaluated.The product demonstrates superior characteristics such as light color,little polyphenols(0.43%),good solubility and good digestibility.Because it was removed 10.0 kDa proteins inclusive trypsin inhibitor,the maximum nitrogen release was 72.88% after in vitro digestion.These results suggest that the buckwheat protein concentrate is a potential food ingredient,particularly in amino acid supplements.(3)Dry fractionation of buckwheat involved fine milling during which starch granules are liberated from a protein matrix that breaks in small fragments.During subsequent airclassification,the protein fragments were separated from the starch granules on the basis of their size.A buckwheat protein concentrate was obtained with 36.32 g protein/100 g and 5.51 g polyphenols/100 g.These results indicate promising development of buckwheat's dry fractionation.Unlike conventional wet isolates,dry-enriched buckwheat fractions consist of a mixture of protein,fibre and polyphenols,and have advantages that protein retains its native state and the fine granule is particularly well-proportioned.