Diversity analysis of phenolic in wild myrobalan plums (Prunus cerasifera)

Abstract: 【Objective】The wild Myrobalan plum (Prunus cerasifera) is a type of little arbor or sheepberry which belongs to the Prunus genus.As an important species of the wild fruit forests in the Ili river valley of Xinjiang, the wild Myrobalan plum is a type of National and Autonomous Region’s key protective species.And just as its phenotypic diversity, strong stress resistance and high nutritional value, the fruits of the Myrobalan plum contain an abundance of organic acids, pectin, mineral elements, all essential amino acids, and are rich in polyphenol, making the wild myrobalan plum a good prospect for utilization and garden breeding.In this study, the diversity of the polyphenol content and composition in ripened fruits of the wild myrobalan plum (P. cerasifera) were studied to provide basic materials for sustainable utilization of wild plum resources and breeding of new cultivars, and to widen gene sources of plum breeding.【Methods】In this research, 13 elite and rare resources were chosen from the total collection and conservation of103 wild myrobalan plum (P. cerasifera) and‘Wanshuhongli’ (P. salicina) in Xingcheng of Liaoning, according to their fruit weight, rate of fruit determined by other pollen, habit, fruit color, soluble solids content and titratable acid content.The plums were collected during the fruit’s ripening stage.Since the plum’s quality shows variablility within different trees, fruit sampling occurred under the following conditions:middle vigor trees, any parts of the tree.The fruit mass, soluble solids content and titratable acid content were measured soon after harvest.The average fruit mass was determined by using an electronic balance, the soluble solids content by using a hand held saccharometer, and the titratable acid content by using the method of acid-base titration.For polyphenolic compounds analyses, the whole fruits were cut directly to liquid nitrogen and crushed by using a laboratory mill for homogeneous powder in liquid nitrogen, and then the samples were stored in a freezer (-70℃) until analysis.The total contents of polyphenol were determined using the Folin–Ciocalteau method, Gallic acid was used as a standard, and the total phenolic content was expressed as grams gallic acid per kilogram of fresh weight (mg·kg^-1) .The composition and content of the polyphenol extracts were analyzed using a High Performance Liquid Chromatography (HPLC) system equipped with a photodiode detector (PDA) .The separations of the polyphenols were carried out using a Ultimate®LP-C18 column (4.6 mm×250 mm, 5μm) at 40℃, flow rate of 0.8 mL·min^-1, and the samples (10μL) were injected.The mobile phase was composed of solvent A (2.0%formic acid) and solvent B (100%of acetonitrile) .The ultimate®LP-C18 gradient elution was used at, 0-35 min, 0-30%B;36-50 min, 30%-45%B;51-60 min, 0B.【Results】There were considerable variations in the polyphenol content which revealed rich diversity.The wild myrobalan plum 9 was the richest in the polyphenol content (5 802.33 mg·kg-1) , was followed by the wild myrobalan plum 2 (5 606.50 mg·kg^-1) , and the polyphenol content in‘Wanshuhongli’was the lowest (1 856.93 mg·kg^-1) .The total phenolic content 13 wild myrobalan plum germplasms ranged from 2 587.10 mg·kg^-1 to 5 825.00 mg·kg^-1, and the variation coefficient was 19.51%;the polyphenol content in the wild myrobalan plums was significantly higher than in‘Wanshuhongli’.The results showed that the wild myrobalan plum fruits were rich in polyphenols, a total of 11 polyphenols were identified including chlorogenic acid, catechin, procyanidin B₁, procyanidin B₂, epicatechin, procyanidin C, quercetin rutinoside, quercetin galactoside, quercetin glucoside, quercetin xyloside, and quercetin arabinopyranosyl, but procyanidin C and quercetin galactoside were not detected in the wild myrobalan plum 8.The procyanidin B1, catechin, chlorogenic acid, procyanidin B2, epicatechin and procyanidin C were the major phenolics present in the wild myrobalan plums, while quercetin rutinoside and quercetin arabinopyranosyl were the major phenolics present in‘Wanshuhongli’, there were significantly higher polyphenol content in wild myrobalan plum germplasms than those in‘Wanshuhongli’ (except quercetin rutinoside) , the polyphenol content of chlorogenic acid, catechin, procyanidin B1, procyanidin B2, epicatechin, procyanidin C, quercetin rutinoside, quercetin galactoside, quercetin glucoside, quercetin xyloside, quercetin arabinopyranosyl were 71.57, 144.65, 64.70, 235.97, 139.81, 51.29, 24.43, 4.42, 31.29, 13.04, 46.99 mg·kg^-1, respectively.The variation ranges were 20.77-169.18, 36.03-313.47, 14.54-113.50, 45.59-373.04, 39.13-310.61, 0.00-74.98, 9.37-40.72, 0.00-9.15, 4.95-68.89, 1.72-27.77, 9.73-95.37 mg·kg^-1, respectively.The variation coefficient ranges were from 30.56%to 108.01%which revealed rich genetic diversity.【Conclusion】There were extensive diversity in the polyphenol content and components in the 13 wild myrobalan plums (P.cerasifera) , and the 13germplasms presented significant differences, wild myrobalan plum 5, wild myrobalan plum 7, wild myrobalan plum 9, wild myrobalan plum 10 and wild myrobalan plum 12 represent good natural sources of procyanidin B₁, catechin, chlorogenic acid, procyanidin B₂, epicatechin, and procyanidin C, which have a large potential for further selection.