| Jujube（Ziziphus jujuba Mill.）has been a tonic in China since ancient times.Blackened jujube is a new product of jujube which is blackened by high temperature and high humidity solid-state fermentation without any additives.In this experiment,7 kinds of jujube（Muzao,Tanzao,Ningyangdazao,Jinsixiaozao,Goutouzao,Huizao,Hetiandazao）were blackened for96 h at high temperature（70℃）and a high humidity（80%RH）.The nutritional composition and antioxidant capacity of jujube before and after the blackening process of different cultivars were compared to obtain the common pattern of jujube,and the physical and chemical indexes were analyzed by principal component analysis and cluster analysis to screen out the jujube cultivars suitable for blackening.Phenolic substances（green tea powder,tea polyphenols,EGCG,pomegranate peel ellagic acid）were used to act on the blackening process of jujube to solve the problem of increased 5-hydroxymethylfurfural（5-HMF）content and decreased cyclic adenosine monophosphate（c AMP）content after the blackening process,and to ensure that the antioxidant capacity of blackened jujube will not be reduced,which provides a theoretical basis for further development of blackened jujube in the future.The specific contents and results of the study are as follows:（1）Comparison of the content of active components in 7 kinds of jujube before and after the blackening process.The content of the total phenols,total flavonoids,polysaccharides,monosaccharides（mannose,ribose,rhamnose,glucuronic acid,galacturonic acid,glucose,galactose,xylose,arabinose,and fucose）,5-HMF,and c AMP were determined and analyzed by spectrophotometry and high-performance liquid chromatography（HPLC）before and after the blackening process of seven jujube fruits.The results showed that the total phenolic content of 7 kinds of jujube increased significantly after blackening（P<0.05）,the increased range was 19.50%-86.61%,blackened Hetiandazao increased the most;the content of 5-HMF increased rang from 0.13 to 1.88 mg/g DW;the content of c AMP was significantly decreased（P<0.05）,among them,the decrease of blackened Goutouzao was the lowest,only 3.53%;the contents of soluble solid and polysaccharides in 6 kinds of jujube were significantly increased（P<0.05）,and the increased range was 3.92%～29.69%,4.44%～81.94%,respectively,and blackened Hetiandazao decreased slightly.The contents of total flavonoids in 5 kinds of jujube were significantly increased,the increased range was 21.09%～100.36%,blackened Jinsixiaozao and blackened Goutouzao decreased slightly.Different jujube cultivars showed different changes in monosaccharide content after blackening,the content of 9monosaccharides increased after blackening of Jinsixiaozao,while the content of monosaccharides decreased in all 10 of blackened Huizao.（2）Comparison of antioxidant capacity of 7 kinds of jujubes before and after blackening.The antioxidant capacity of all 7 jujube was significantly enhanced after blackening（P<0.05）:the scavenging capacity of DPPH free radicals was enhanced by 18.77%～217.05%,and blackened Jinsixiaozao had the strongest scavenging capacity of 6.14 mg Vc/g DW;the scavenging ability of ABTS free radicals was enhanced by 13.86%～97.63%,and blackened Hetiandazao had the strongest scavenging ability of 32.24 mg Trolox/g DW;the total reducing capacity was enhanced by 33.33% to 169.49%,and blackened Goutouzao had the strongest total reducing capacity of 56.00 mg Trolox/g DW.（3）Principal component analysis of 7 kinds of blackened jujube.Principal component analysis was used to comprehensively evaluate and analyze 7 kinds of blackened jujube,and3 unrelated principal components were determined,with a cumulative contribution rate of90.56%,representing most of the information of the sample.The top two jujubes were blackened Jinsixiaozao and blackened Hetiandazao by the comprehensive evaluation function.（4）Cluster analysis of 7 kinds of jujube before and after the blackening process.Cluster analysis was used to study the similarity of jujube varieties.The results showed that the 14 kinds of jujube were divided into 5 categories: the first category was Jinsixiaozao,Tanzao,Goutouzao,Hetiandazao,Muzao and Huizao,all indicators were at the medium or lower level.Ningyangdazao had the highest c AMP content.The third type was blackened Jinsixiaozao,which had the highest content of monosaccharides.The fourth type was blackened Hetiandazao,Ningyangdazao,Tanzao and Muzao,and the contents of total phenols and polysaccharides were the highest.The fifth type was blackened Huizao and Goutouzao,and the total flavonoid content was the highest,and ABTS free radical scavenging and total reducing ability were the strongest.It can provide a theoretical basis for breeding different jujube varieties.（5）Determination of indexes in the blackening process of red jujube impregnated with phenolic substances.Jujubes were blackened after impregnation with phenolic substances,and the changes in total phenol,5-HMF,c AMP contents and antioxidant capacity from 0 to 84 h of blackening were followed and compared with the control group（not impregnated with phenolic substances）.The results showed that the total phenolic content and antioxidant capacity were higher than those of the blank control group.Among them,the EGCG group had the highest total phenolic content and the strongest antioxidant capacity,the total phenolic content of the blackened jujube was 24.59 times higher than the control group at the end of blackening（84 h）.The scavenging of DPPH radicals,scavenging of ABTS radicals and total reducing capacity were 25.33,4.51 and 3.58 times higher than those of the control group,respectively.The 5-HMF content of blackened jujube in the EGCG and tea polyphenol groups was always lower than the control group during the blackening process,it was 72.36% and36.47% lower than the control group at the end of blackening,respectively;the green tea powder,the EGCG and ellagic acid groups had the highest c AMP content of blackened jujube at the end of blackening,which was 0.50,0.70 and 0.87 times higher than the control group,respectively.Therefore,the comprehensive effect of the EGCG group was the best. |
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