Effects Of Microwave Treatment On The Properties And Bioactivity Of Germinated Tartary Buckwheat Protein

Tartary buckwheat protein is one of the main bioactive components of Tartary buckwheat(Fagopyrum tataricum),with rich and balanced amino acid content and has biological functions such as lowering cholesterol,lowering blood pressure and antioxidation.Tartary buckwheat protein is very popular as a natural plant protein with high safety and nutritional value.After germination,the amino acid composition of Tartary buckwheat is more reasonable,and the protein properties and biological activity are also improved to a certain extent.Recently,studies have found that microwave pretreatment can safely and effectively promote plant germination and activate a variety of enzymes in seeds,so as to change the structure of biological macromolecules and affect the physiological and biochemical characteristics and biological functions of plants.Therefore,using microwave to stimulate plant germination can be an effective strategy to improve the content of plant bioactive metabolites,plant nutritional value and biological activity.In this study,Tartary buckwheat seeds were used as experimental materials to study the effects of microwave treatment of different power and treatment time on the physicochemical properties,functional properties and biological activities of Tartary buckwheat protein after germination.Based on proteomics,the mechanism of Tartary buckwheat germination and flavonoid accumulation induced by microwave treatment was revealed,in order to provide a theoretical basis for the development of nutritional and functional Tartary buckwheat protein foods.The primary research results are as follows:The changes of physicochemical properties of germinated Tartary buckwheat protein after microwave treatment were studied.The results showed that microwave treatment could change the protein content of Tartary buckwheat during germination but the effect of different microwave treatments on its content was not significant(P≥0.05).Moderate microwave treatment could promote the synthesis of amino acids in Tartary buckwheat during germination,improve the nutritional value of germinated Tartary buckwheat protein,and be more conducive to the absorption and utilization of Tartary buckwheat protein by human body.The contents of total amino acids,essential and non-essential amino acids in Tartary buckwheat protein germinated for 5 d after 300 W/50 s microwave treatment were the highest,which increased by 26.41%,30.26%and25.34%respectively compared with CK group,and the amino acid score(AAS)values of various essential amino acids were the highest except methionine+cystine,and the in vitro digestibility of germinated Tartary buckwheat protein was the highest under this condition,which was 5.56%higher than CK.Under different microwave power and microwave time,the free sulfhydryl content of germinated Tartary buckwheat protein increased significantly compared with CK(P<0.05),indicating that microwave treatment could promote the extension of the molecular structure of germinated Tartary buckwheat protein.Infrared spectrum analysis showed that microwave pretreatment could change the secondary structure of germinated Tartary buckwheat protein from order to disorder and increase the flexibility of protein,the ultraviolet spectroscopic analysis showed that microwave pretreatment could change the spatial conformation of germinated Tartary buckwheat protein,expand protein molecules and expose the internal chromogenic groups.The changes of protein functional properties of germinated Tartary buckwheat after microwave treatment were studied.The results showed that 300W/50 s microwave treatment had the best effect on improving the solubility and water holding capacity of Tartary buckwheat protein at 5 d of germination,which increased by 24.37%and 38.95%respectively compared with CK.Under200 W/50 s treatment,the oil holding capacity of Tartary buckwheat protein at 5d of germination reached the maximum,which increased by 5.57%compared with CK,but the effect of microwave treatment on the oil holding capacity of germinated Tartary buckwheat protein was not significant(P≥0.05).When the microwave power was 300 W and the microwave time was 50 s,the emulsifying ability(18.64 m~2/g)and foaming ability(80.00%)of Tartary buckwheat protein were the best at 5 d of germination,and the emulsion stability and foam stability reached the peak at 7 d of germination,which were 67.04%and 78.02%respectively.The thermal stability of Tartary buckwheat seed protein was the highest,while the absorption peak temperature of germinated Tartary buckwheat protein decreased in varying degrees after microwave pretreatment,indicating that microwave reduced the thermal stability of germinated Tartary buckwheat protein.The changes of antioxidant capacity of germinated Tartary buckwheat protein after microwave treatment were studied.The results showed that the antioxidant capacity of germinated Tartary buckwheat was improved to a certain extent with moderate microwave power and treatment time.After 300 W/50 s microwave treatment,the Tartary buckwheat protein had the strongest scavenging capacity for free radicals of 1,1-diphenyl-2-picrylhydrazyl(DPPH)and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)at 5 d of germination,which increased by 32.35%and 41.95%compared with CK,respectively.After microwave treatment at 200 W/50 s,300 W/50 s and 300W/70 s,the total reducing power of germinated Tartary buckwheat protein increased significantly,especially when it germinated for 5 d after microwave treatment at 300 W/50 s,the total reducing power of germinated Tartary buckwheat protein reached the maximum(17.83μmol TE/g),increased by41.46%compared with CK.The proteome of germinated Tartary buckwheat after microwave treatment was deeply analyzed by Label-free quantitative proteomics technology to reveal the mechanism of Tartary buckwheat germination and flavonoids enrichment under microwave treatment.Label-free quantitative proteomic analysis showed that there were 7,5 and 5 differentially expressed proteins(DEPs)in Tartary buckwheat germinating for 3,5 and 7 d after 300 W/50 s microwave treatment compared with CK.These DEPs were mainly related to energy metabolism,gene expression and flavonoids biosynthesis.KEGG analysis showed that DEPs were mainly enriched in the metabolic pathways of photosynthesis,RNA polymerase,flavonoid biosynthesis,phenylalanine metabolism and phenylpropanoid biosynthesis.In addition,microwave treatment also promoted the germination and accumulation of flavonoids in Tartary buckwheat by up-regulating the expression of enzymes such as phenylalanine ammonia-lyase and flavonol synthase.The mechanism of Tartary buckwheat germination and enrichment of flavonoids under the action of microwave was revealed,which provided a scientific basis for the development of germinated Tartary buckwheat functional food.