| Anthocyanin,a natural water-soluble pigment in plant bodies,can be used as a natural colorant in addition to its high antioxidant properties.However,anthocyanins have low stability and are easily affected by temperature,p H,light and other factors during extraction,preparation,deep processing and storage to lose their biological activity and unique properties.In this study,different kinds of acyl donors were used to undergo enzymatic acylation with cyanidin-3-O-glucoside(Cy-3-gluc),thus improving the stability,and also further investigating the stability and antioxidant properties of the acylated products,providing some theoretical basis for the industrial application of anthocyanins to become possible.The main findings of the study are as follows:(1)Novozym 435 lipase was used as the enzyme catalyst,and methyl ferulate was selected as the acyl donor for the enzymatic acylation of anthocyanin in response surface optimization test.With the acylation rate as the final index,the analysis results showed that the optimal reaction conditions were tert-amyl alcohol as the solvent system,reaction time of 24 h,temperature of56℃,enzyme dosage of 10 mg/m L and molar ratio of methyl ferulate to anthocyanin of 105:1,and the acylation rate was 96.41±0.45% under these optimal acylation process conditions.(2)Six aromatic methyl esters and four aliphatic methyl esters were selected as acyl donors for the enzymatic acylation of 10 acylated anthocyanins.And the 10 acylated phl oroglucinides were identified using UV-visible spectroscopy and liquid mass spectrometry as cyanidin-3-O-(6’’-vanillyl)glucoside,cyanidin-3-O-(6’’-galloyl)glucoside,cyanidin-3-O-(6’’-c innamoyl)glucoside,cyanidin-3-O-(6’’-p-coumaroyl)glucoside,cyanidin-3-O-(6’’-caffeoyl)gluco side,cyanidin-3-O-(6’’-feruloyl)glucoside,cyanidin-3-O-(6’’-lauryl)glucoside,cyanidin-3-O-(6’’-myristoyl)glucoside,cyanidin-3-O-(6’’-oleoyl)glucoside,cyanidin-3-O-(6’’-linoleoyl)glucoside.(3)The absorption spectra and color characteristics of Cy-3-gluc,aromatic acyl anthocyanin and fatty acyl anthocyanin were compared at different p H values as well as thermal stability,light stability and color stability.The experimental results showed that aromatic acyl anthocyanins improved the stability of anthocyanins,among which cyanidin-3-O-(6-feruloyl)glucoside was the most stable,while among fatty acyl anthocyanins,only cyanidin-3-O-(6-lauryl)glucoside was more stable than Cy-3-gluc,and the other fatty acyl anthocyanins decreased in stability with the increase of fatty chains.The geometric conformational optimization at the 6-31G(d,p)group level by the B3 LYP method of density flooding theory(DFT)via Gaussian09 software revealed that the benzene ring of aromatic acyl groups formed π-π stacking with the parent nucleus of the anthocyanin,which in turn produced a strong spatial site barrier to prevent the attack of the anthocyanin by water molecules and some oxidizing substances.(4)Compare the antioxidant ability of Cy-3-gluc,aromatic acyl anthocyanin and fatty acyl anthocyanin.The antioxidant capacity of aromatic acyl anthocyanin was higher than that of the precursor anthocyanin,and some aliphatic acyl anthocyanins decreased the antioxidant capacity of the precursor anthocyanin,and the ABTS radical scavenging capacity was consistent with that of DPPH radical scavenging capacity.Energy level calculations were performed at the 6-31G(d,p)group level by Gaussian09 software through the B3 LYP method of DFT,and the antioxidant active sites were analyzed by Multiwfn calculations of HOMO and LUMO energy levels.The calculations showed that cyanidin-3-O-(6"-p-coumaroyl)glucoside,cyanidin-3-O-(6"-caffeoyl)glucoside,cyanidin-3-O-(6"-feruloyl)glucoside,cyanidin-3-O-(6"-oleoyl)glucoside,and cyanidin-3-O-(6"-linoleoyl)glucoside were involved in the antioxidant active site of the phenolic group of the acyl moiety The main active site of the antioxidant activity of the other anthocyanins is the phenolic hydroxyl group on the B-ring. |
PDF Full Text Request