Research On The Key Bitter Compounds And Methods For Reducing Bitterness Of Toona Sinensis

Toona sinensis belongs to Toona of Meliaceae,which has a unique taste and has always enjoyed its laudatory name "vegetable on the tree".Toona sinensis has been planted in 18 provinces all over the country and has developed into a modern characteristic agriculture industry of the "Enriching Project".However,the bitterness of Toona sinensis affects consumers’ satisfaction and acceptability,which restricts the development of Toona sinensis industry.At present,the research on Toona sinensis mainly focuses on volatile compounds and biological activities,and there are few reports on its bitter compounds.Based on the above,this paper intends to analyze the bitterness and all kinds of potential bitter compounds of Toona sinensis,clarify the main types of bitter compounds,analyze the key bitter compounds,and explore the way of reducing bitterness.The main results are as follows:(1)The results of sensory evaluation of Toona sinensis from different producing areas and different picking periods showed that the bitterness intensity of Toona sinensis samples from different origin was different,and the overall trend was increasing from north to south,and the bitterness value of Yunnan Toon was the highest(4.80).The bitterness values of Ankang green Toon and Ankang red Toon generally showed an upward trend with the delay of picking.The correlation analysis between the bitter value of Toona sinensis and the contents of various potential bitter compounds showed that the contents of total phenols and total flavonoids in Toona sinensis from different origin and different picking periods were significantly positively correlated with the bitter value,and it was preliminarily judged that phenols and flavonoids were important compound types related to the bitter formation of Toona sinensis.(2)Based on the analysis of non-target metabonomics,2532 different metabolites were screened from Yunnan Toon,Chongqing Toon and Ningxia Toon.On the basis of all kinds of differential metabolites identified,52 kinds of bitter metabolites,including 12 kinds of amino acids,22 kinds of flavonoids,6 kinds of polyphenols,8 kinds of alkaloids and 4 kinds of saponins,were screened out by relying on the public database of bitter compounds and related references.Further,taking bitterness value as the dependent variable,11 key differential metabolites were screened by partial least square regression analysis,among which 7 were flavonoids,namely scutellarein,kaempferol,isoquercitrin,luteolin,morin,quercetin and astragalin.The quantity,relative abundance and differences between groups of bitter compounds were analyzed,and it was found that flavonoids were the main potential bitter compounds of Toona sinensis.(3)According to the guidance of sensory evaluation,the bitter compounds in Yunnan Toon were effectively separated by ethanol extraction,ethyl acetate extraction and column chromatography,and the flavonoids with high purity were obtained.The two components FIV-13 and F-IV-14 with the highest bitterness activity in the ethyl acetate extraction component were analyzed by UPLC-MS/MS,and a total of 24 flavonoids bitter compounds were identified.These bitter compounds include five key flavonoid metabolites(kaempferol,isoquercitrin,luteolin,quercetin and astragalin)which have been screened by non-target metabolomics analysis and contributed greatly to the bitter difference of Toona sinensis.(4)The bitterness of Toona sinensis was reduced by blanching,ultrasonication,salt immersion and blanching after salt immersion.The results showed that both blanching after salt immersion and blanching could significantly reduce the bitterness of Toona sinensis.Quantitative analysis of 9 kinds of flavonoids bitter compounds in Toona sinensis without and with different bitter reducing treatments showed that isoquercitrin,astragaloside,quercetin,kaempferol and luteolin were all high in content and were positively correlated with the bitter value,which verified that these five kinds of flavonoids were the key bitter compounds in Toona sinensis.Comprehensively comparing the changes in color,bitterness value,bitter compounds and volatile components,blanching treatment has a better bitterness reduction effect.To sum up,Toona sinensis contains many kinds of bitter compounds,such as amino acids,polyphenols,flavonoids,alkaloids,saponins,etc.Flavonoids are an important type of bitter compounds,and 24 kinds of bitter compounds were isolated and identified.Combined with metabonomics and quantitative analysis,it is clear that kaempferol,isoquercitrin,luteolin,quercetin and astragaloside are the key bitter compounds in Toona sinensis.Blanching treatment is a better method to reduce the bitterness of Toona sinensis.The research results provide a basis for controlling the bitterness of Toona sinensis and improving the quality of Toona sinensis products.