Varietal differences in antioxidant activity and phenolic composition of asparagus

Esra Cakir

The study was focused on two areas of inquiry. The first involved analyzing nine varieties of asparagus; 'Jersey Knight', 'Jersey Deluxe', 'Jersey Supreme', 'Jersey Giant', 'Guelph Millenium', 'UC 157', 'Purple Passion', 'Morehouse Select' and 'Syn4' for total phenolics (TPH), rutin content, and antioxidant activity using Folin-Ciocalteu procedure, colorimetric AlCl3 method, and the 1,1 diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assay, respectively. TPH of varieties ranged from 29.09 to 35.16 mg rutin equivalent/g dry weight basis (dwb) while rutin content varied from 12.09 to 16.09 mg/g dwb. TPH levels were well correlated with rutin content (R≥0.90, p<0.05). Rutin contributed approximately 45% of total phenolics. 'Guelph Millenium' contained the greatest TPH and rutin contents while Purple Passion had the least. DPPH scavenging activity of asparagus varieties ranged from 10.70 to 15.30 mg rutin/g dwb. Secondly, asparagus extracts were analyzed by reversed-phase high performance liquid chromatography (HPLC) equipped with a diode array detector to determine the content and profile of phenolics. Rutin was identified as the major phenolic compound, followed by chlorogenic acid, in all varieties. HPLC coupled to a radical scavenging method was applied in order to determine antiradical components in the asparagus extracts. The determination of antiradical activity was based on a decrease in the peaks correspondent to strong antioxidants, 60 min after the addition of DPPH. A green ('Guelph Millenium') and a purple ('Purple Passion') asparagus variety were analyzed to identify the variations in different colors of asparagus. Rutin was found to be the strongest radical scavenging component. After the addition of DPPH solution, the peaks corresponding to rutin and chlorogenic acid decreased by 93% and 72% of the initial peak intensity, respectively. Purple asparagus had a unique compound different than green asparagus varieties. This unknown compound did not possess any antiradical activity. Total anthocyanin contents of asparagus varieties were measured spectrophotometrically. 'Purple Passion' contained the largest total anthocyanin content (1.08 mg/g dwb) among the varieties tested. These results provide useful information about asparagus varieties having valuable potential health benefits.

Varietal differences in antioxidant activity and phenolic composition of asparagus

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