Bioactive compounds in the aboveground part of hemiephemeroid onions (Allium L.)

Abstract

Background. Representatives of the genus Allium L. are valuable food and medicinal plants that have long been used for nutrition and human health. Modern research has proved their high biological activity. Earlier, we investigated the aboveground organs of a number of wild onion species in the consumer ripeness phase. Higher content of secondary metabolites has been observed in the hemiephemeroid species A. aflatunense B. Fedtsch., A. microdictyon Prokh., and A. rosenbachianum Regel. The aim of this work was to determine the content of bioactive compounds in the green biomass of Allium species during flowering.Materials and methods. We studied the freshly harvested raw materials – leaves and flower scapes. Dry matter content was measured by drying 1 g of raw material at 100–105°C to constant weight. The amounts of phenolic compounds, pectic substances, total sugars and carotenoids were assessed spectrophotometrically using the SF-56 (Russia) and SF Agilent 8453 (USA) instruments, and ascorbic acid was measured by the titrimetric method. The result was taken as an average of three measurements for each indicator calculated on absolute dry weight of raw material (except ascorbic acid).Results and conclusions. The green biomass of Allium species was found to contain 8,2–16,2% of dry matter; 4,5–12,0% of phenolics (catechins, flavonols and tannins); 6,9–32,4% of total sugars; 9,5–12,6% of pectic compounds (pectins and protopectins); 20,8–102,5 mg% of carotenoids, and 38,0–197,7 mg% of ascorbic acid (wet weight). A significant range of variation in the content of secondary metabolites was due to the species’ characteristics and weather conditions of the growing season. A. microdictyon had a higher content of dry matter, flavonols and tannins, whereas A. aflatunense and A. rosenbachianum were rich in ascorbic acid and sugars. The findings testify to the prospects of using Allium spp. as a source of bioactive compounds.

Keywords

• onions
• green biomass
• flowering
• phenolics
• sugars
• vitamins
• pectic compounds