Influence of the development stage on the content of phenolic compounds and antioxidant capacity of Chinese cabbage (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt)

Sadržaj fenolnih spojeva, kao i njihov antioksidacijski kapacitet, ovise o razvojnom stadiju biljke. Do sada su u dostupnoj literaturi informacije o sadržaju fenolnih spojeva i antioksidacijskom kapacitetu pekinškog kupusa (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt) zabilježene za odrasle biljke, no ne postoje usporedni podaci o kvalitativnom i kvantitativnom sadržaju fenolnih spojeva i antioksidacijskom kapacitetu različitih razvojnih stadija ove vrste. Stoga je u ovom radu ispitano pet različitih razvojnih stadija pekinškog kupusa; prvi stadij su činile mlade biljke s otvorenim kotiledonama, drugom stadiju pripadale su biljke s razvijenim dvjema kotiledonama i dva prava lista, trećem biljke s četiri lista, a biljke četvrtog i petog stadija imale su po šest, odnosno deset razvijenih listova. Spektrofotometrijski je određen sadržaj ukupnih fenola, flavonola i hidroksicimetnih kiselina, metodom tekućinske kromatografije visoke moći razlučivanja su identificirani i kvantificirani najzastupljeniji pojedinačni flavonoidi i fenolne kiseline, te je određen antioksidacijski kapacitet pet razvojnih stadija pekinškog kupusa metodama koje se temelje na redukciji radikala 2,2'-azinobis (3- etilbenzotiazolin-6-sulfonske kiseline) i 2,2-difenil-pikrilhidrazila, te metodom određivanja antioksidacijske jakosti redukcijom željeza. Rezultati su pokazali da se najraniji stadij (samo kotiledone) pekinškog kupusa na razini količine ukupnih fenola, flavonola, hidroksicimetnih kiselina i kvercetina, kao i antioksidacijskog kapaciteta statistički ne razlikuje (p≤0.05) od stadija sa šest ili deset listova. Ova tri stadija ujedno imaju i značajno veće vrijednosti spomenutih parametara u odnosu na stadij s kotiledonima i dva prava lista ili stadij s četiri lista.Phenolic compounds content so as their antioxidant capacity depend on plant development stage. In the present literature, informations on the phenolic compounds content and antioxidant capacity of Chinese cabbage have been reported for mature plants, but there are no comparative data on the qualitative and quantitative phenolic compounds content and antioxidant capacity of Chinese cabagge different development stages. Therefore, in this study, five different development stages of Chinese cabbage were investigated; the first stage consisted of plants with developed cotyledones, the second stage were plants with developed two cotyledones and two leaves, the third stage consisted of plants with four leaves, and the plants of the fourth and fifth stages had six or ten developed leaves. Content of total phenols, flavonols and hydroxycinnamic acids was measured spectrophotometrically, most abundant individual flavonoids and phenolic acids were identified and quantified using High-Performance Liquid Chromatography method, and antioxidant activity of five different stages of Chinese cabbage were determined using methods based on a reduction of radicals 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) and 2,2-diphenyl-1-picryl-hydrazyl, and Ferric reducing/Antioxidant power method. The results showed that the earliest stage (containing cotyledones only) of Chinese cabbage, at the level of total phenols, flavonols, hydroxycinnamic acids and quercetin as well as antioxidant capacity does not statistically differ (p≤0.05) from the stages with six or ten leaves. These three stages also have significantly higher values of the mentioned parameters compared to the stage with the cotyledons and two leaves or the stage with four leaves