Analysis on the pericarp browning and related enzyme activities in different pomegranate cultivars

FENG Lijuan; YIN Yanlei; YANG Xuemei; FU Ying; LI Yingpeng

doi:10.13925/j.cnki.gsxb.20160271

Abstract：[Objective] Fruit browning of pomegranate is a physiological disease,which influences its commercial value.Polyphenol oxidase (PPO),peroxidase (POD) and phenylalanine ammonialyase (PAL) are the regulatory enzymes of fruit browning.Phenolic compounds are the substrate of enzymic browning.There are abundant germplasm resources of pomegranate in China.The difference in browning and related factors among different pomegranate cultivars has not been reported.The purpose of the study was to explore the differences in percarp browning and its correlations to related enzyme activities,total phenolic contents and antioxidant capacity in different pomegranate cultivars at mature stage.[Methods] Twenty dominant pomegranate cultivars were used as the experimental materials in the study.The browning degree of the pericarp was determined by colorimetric analysis with absorption at 410 nm.The activities of PPO,POD and PAL were determined with ultraviolet spectrophotometry,which measured the optical absorption at wavelengths of 410 nm,470 nm and 290 nm,respectively.The Folin-Ciocalteu method was used for total phenol content determination,which involved measurement of optical absorption at a wavelength of 750 nm.The DPPH radial scavenging activity was determined colorimetrically at 517 nm.Data were generated from triplicate experiments and analyzed using one-way ANOVA and Duncan's multiple comparison tests.The software used for statistical analysis was SPSS 19.0.[Results] The browning degree,total phenolic contents and DPPH radial scavenging activity of the twenty pomegranate cultivars were in the ranges of 0.278-0.369 mg· g-1,108.3-123.7 mg· g-1 and 73.6％-82.4％,respectively.The browning degree,total phenolic contents and DPPH radial scavenging activity were all highest in ‘Shuijingtian’ pericarp,which was 0.369,123.7 mg· g-1 and 82.4％,respectively.Except for ‘ Heyinhuapi’,‘ Taihanghong’,‘ Mantianhong’,‘ Huaibeifenpi’ and ‘ Huaibeimanaozi’,the difference in browning degree between ‘ Shuijingtian’ and the remaining fourteen cultivars was significant (P ＜ 0.05).The difference in total phenolic content was not significant between ‘ Shuijingtian’ and ‘ Heyinhuapi’,‘ Mantianhong’,‘ Huaibeifenpi’ or ‘Huaibeimanaozi’,but was significant between ‘Shuijingtain’ and the other fifteen cultivars (P ＜ 0.05).There was significant difference in the DPPH radial scavenging activity among different pomegranate cultivars (P ＜ 0.05).The activities of PPO and POD were highest in ‘Shuijingtian’,which were 297.4 U· min-1· g-1 and 147.6 U· min-1· g-1,respectively,and lowest in ‘Taishanjinhong’,which were 215.3 U· min-1· g-1 and 126.321 U· min-1· g-1,respectively.The PAL activity was in the range of 157.2-182.6 U·min-1· g-1 and was highest in ‘Taihanghong’ and lowest in ‘Taishanjinhong’.The PAL activity of ‘ Taihanghong’ was about 1.16 times that of ‘ Taishanjinhong’.The PPO activity in ‘ Shuijingtian’ and ‘ Taishanjinhong’ had significant difference from that of the other cultivars (P ＜ 0.05).The POD activity in ‘Shuijingtian’ and PAL activity in ‘Taihanghong’ had significant difference from those in all the other cultivars (P ＜ 0.05) except for ‘Mantianhong’ and ‘Heyinhuapi’.There was significant difference (P ＜0.05) in POD and PAL activities between ‘Taishanjinhong’ and all the other cultivars but ‘Yanzhihong’.Correlation analysis indicated that pericarp browning degree was significantly and positively correlated with the activities of PPO,POD and PAL,total phenolic content and DPPH radial scavenging activity.The correlation coefficient of browning degree and PPO activity was 0.920,which was higher than those between browning degree and PPO activity (r=0.896) and POD activity (r=0.881).POD activity had significant positive correlations with PAL activity,total phenolic content and DPPH radial scavenging activity,with a correlation coefficient of 0.809,0.912 and 0.868,respectively.PAL activity had significant positive correlations with total phenols content and DPPH radial scavenging activity,and their correlation coefficients were 0.837 and 0.718,respectively.There was a significant positive correlation between total phenolic content and DPPH radial scavenging activity,with a correlation coefficient of 0.939.The eigenvalue of the first principal components was 5.423,with cumulative variability of 90.4％.Basically,the first principal components could reflect the original index information.The first principal components included browning degree,activity of PPO and POD,total phenolic content and DPPH radial scavenging activity of pomegranate pericarp.The greater the score value of the first principal components,the greater the values of browning degree,activities of PPO and POD,total phenols content and DPPH radial scavenging activity.The distributions of browning degree and PPO activity were overlapping.The second principal components mainly included PAL activity.The score of the first principal components and the overall score were both highest in ‘Shuijingtian’ and lowest in ‘Taishanjinhong’.[Conclusion] There were differences in pericarp browning,its related enzyme activities,total phenolic contents and DPPH radial scavenging activity among different pomegranate cultivars at maturation stage,and they displayed significant correlations.PPO was the dominant enzyme related to pericarp browning in pomegranate.The activities of POD and PAL were significantly and positively correlated to pericarp browning.The phenolic compound content in pomegranate pericarp was closely related with its antioxidant capacity.‘Taishanjinhong’ ‘Yanzhihong’ and ‘ Linxuanerhao’ were resistant to browning and worth exploitation and utilization.