Study On The Enrichment Of Flavonoids In Germinated Tartary Buckwheat Treated With Microwave Combined With Exogenous L-phe

In recent years,the non-thermal effect of microwave has been widely used in many fields of food processing,such as freshness preservation,sterilization and blunt enzyme.Microwave irradiation of seeds can significantly stimulate the germination of seeds and activate various enzymes in the seeds,thus transforming macromolecular bioactive substances such as proteins and polysaccharides into small molecules that are more easily absorbed by the human body.And at the same time,the morphological and structural characteristics,physiological and biochemical characters of seeds were changed.Fagopyrum tataricum(Fagopyrum tataricum L.Gaertn.)is a dicotyledonous plant of genus buckwheat in Polygonum family,commonly known as Tartary buckwheat.Tartary buckwheat is not only of high nutritional value but also rich in flavonoids with health care effect.It is a typical edible and medicinal plant in China,and is known as "natural golden partner".After the germination of Tartary buckwheat,carbohydrate,vitamin,flavonoids and other substances were significantly increased,the amino acid composition was more reasonable,and its nutritional value was greatly improved.However,L-Phe is a precursor of the flavonoid synthesis pathway,and studies have shown that the addition of precursor substances during plant growth can effectively enrich specific secondary metabolites.Therefore,in this experiment,Tartary buckwheat was used as the experimental material,microwave time,microwave power and L-Phe concentration were used as factors,and the optimal process conditions of Tartary buckwheat germinating to enrich flavonoids were determined by response surface optimization test.The aim is to provide reference for clarifying the molecular mechanism of flavonoid enrichment in Tartary buckwheat sprouts by microwave and L-Phe treatment.The main results are as follows:The effects of microwave time,microwave power and L-Phe concentration on the content of total flavonoids in Tartary buckwheat seedlings after germination were studied.The optimal conditions for promoting the concentration of flavonoids in Tartary buckwheat were determined as follows:microwave time 90 s,microwave power 250 W,L-Phe concentration 2.90 mmol/L.Under these conditions,the content of flavonoids in Tartary buckwheat sprouts was 6.26±0.15 g/100 g DW.In addition,the changes of nutrient content and structure of Tartary buckwheat after germination treated with L-Phe and microwave were investigated.The results showed that with the germination of Tartary buckwheat seeds,the contents of soluble sugar and soluble protein decreased gradually,while the contents of reducing sugar and amino acid increased.Among them,the content of reducing sugar and total amino acid in sprouts after 7 days of germination were 8.88 and 1.11 times higher than that in seeds,respectively(CK).The contents of reducing sugars and amino acids in T3 group(250 W,90 s,2.9 mmol/L)were 1.13 and 1.12 times of those in CK,and increased by 4.00%and 5.84%(7 d),respectively,compared with those in T1 group(250 W,90 s,0 mmol/L).The starch granules were damaged and the surface of Tartary buckwheat appeared pits and holes after germination by SEM,and the damage was the most serious after 3 d of germination.On the 7th day of germination,there were many fragments around the starch granules treated by microwave and L-Phe,but the surface of the seed and CK starch granules was smooth.According to the FTIR spectra,microwave treatment had a certain effect on the protein structure of seeds,and the contents and structures of various nutrients were changed after germination.The effects of microwave and L-Phe treatment on the contents of total flavonoids,total phenols,antioxidant capacity and enzyme inhibitory activity of germination Tartary buckwheat were studied.The correlation between antioxidant capacity,enzyme inhibitory activity and the contents of total flavonoids and total phenols in germination of Tartary buckwheat was further analyzed.The results showed that germination of Tartary buckwheat could increase the contents of total phenols and flavonoids,enhance the antioxidant capacity and the inhibitory activities of tyrosinase and acetylcholinesterase.The contents of total phenols and total flavonoids in Tartary buckwheat sprout of treatment group were significantly higher than those of CK(P<0.05).The contents of total phenols and total flavonoids in T3 group were 1.42 and 1.36 times of those in CK,and increased by 21.34%and 19.22%(7 d),respectively,compared with those in T1 group.Correlation studies showed that the antioxidant capacity,tyrosinase activity and acetylcholinesterase inhibition rate of Tartary buckwheat sprouts were significantly positively correlated with the contents of total phenols and flavonoids in the sprouts(r=0.903?0.972,P<0.01).The effects of microwave and L-Phe treatment on the contents of four flavonoids and the PAL,CHI and FLS specific activities in.Tartary buckwheat were studied,and the dynamic relationship between the content of total flavonoids and the specific activities of three enzymes was discussed.The results showed that germination could significantly increase the contents of chlorogenic acid,vitexin and rutin in Tartary buckwheat,and the PAL,CHI and FLS specific activities increased.The contents of chlorogenic acid and rutin in the sprouts germinated for 7 d were 116.51 times and 2.85 times of those in the seeds,respectively.Microwave and L-Phe treatment could further promote the synthesis of chlorogenic acid,and the content of chlorogenic acid increased by 30.06%compared with CK(7 d).Correlation analysis showed that the content of total flavonoids in Tartary buckwheat sprout was significantly positively correlated with the specific activities of PAL,CHI and FLS(r=0.939?0.968,P<0.01).The effects of microwave and L-Phe treatment on the expressions of FtPAL,FtCHI and FtFLS,key enzymes of flavonoid synthesis in Tartary buckwheat sprout were studied.And the dynamic relationship between the content of total flavonoids in Tartary buckwheat sprout and the expression levels of these three enzymes were investigated.The results showed that with the prolonging of culture time,the expression levels of FtPAL,FtCHI and FtFLSl in Tartary buckwheat sprout increased firstly and then decreased,while the expression levels of FtFLS2 decreased gradually.Microwave and L-Phe treatment could increase the expression of FtPAL,FtCHI,FtFLS1 and FtFLS2.Compared with CK group,the expression of FtPAL,FtCHI,FtFLSl and FtFLS2.in T3 group were increased by 41.52%,20.45%,35.20%and 99.83%(5 d),respectively.The synthesis of total flavonoids was not simply positively correlated with the expression of the corresponding genes,and the synthesis of flavonoids lagged behind.The effects of microwave and L-Phe treatment on the content of flavonoids in Tartary buckwheat sprout were consistent with the expression levels of FtPAL,FtCHI and FtFLS,indicating that microwave and L-Phe treatment promoted the synthesis of flavonoids by promoting the expression of key enzyme genes in the synthesis of flavonoids in phenylpropane-metabolism.