Contents determination of eight phenolic compounds in Perilla frutescens leaves of different cultivation years and harvesting periods

Abstract

A method was established for content determination of two kinds of phenolic acids, including rosmarinic acid)(RA) and caffeic acid(CA), and six kinds of flavonoids including scutellarein-7-O-diglucuronide(SDG), luteolin-7-O-diglucuronide(LDG), apigenin-7-O-diglucuronide(ADG), scutellarin-7-O-glucuronide(SG), luteolin-7-O-glucuronide(LG), and apigenin-7-O-glucuronide(AG) in Perilla frutescens leaves. The content of eight chemical components was measured based on ten P. frutescens germplasms of different chemotypes of volatile oil, different cultivated years, and different harvesting periods. The results showed that there was a great difference between the two kinds of constituents of different germplasms. The total content of the two phenolic acids was 2.24-34.44 mg·g~(-1), and the total content of the six flavonoids was 11.55-34.71 mg·g~(-1). Then according to content from most to least, the order of each component was RA(2.13-33.97 mg·g~(-1)), LDG(1.31-14.80 mg·g~(-1)), SG(1.97-8.45 mg·g~(-1)), ADG(2.68-7.60 mg·g~(-1)), SDG(1.16-5.87 mg·g~(-1)), LG(0.78-1.91 mg·g~(-1)), AG(0.56-1.00 mg·g~(-1)), and CA(0.11-0.68 mg·g~(-1)). The chemical contents of the 5 PA-type germplasms in 2017 were mostly higher than those in 2018 showing a large variation with the cultivation years. These contents of two kinds of phenolic acids of 9 germplasms fluctuated with the harvesting time. The content decreased before early flower spike(the 3~(rd) to 18~(th) in August) at first and began to increase in flowering and fruiting period(the 18~(th) in August to 2~(nd) in September). However, these contents had slowly decreasing trend after 2~(nd) in September till 17~(th) in the same month. Interestingly, the content raised again in the maturity of fruits. The variation tendency of contents in six kinds of flavonoids components was inconsistent in different germplasms with the variation of harvesting time. The content of flavonoids in part of germplasms was negatively correlated with the fluctuation of phenolic acids. There was no correlation between phenolic acids and chemical type of the volatile oil. This paper may provide a reference for the high-quality germplasm of P. frutescens cultivation.