The role of sulphur on the content of total polyphenols and antioxidant activity in onion (Allium cepa L.)

Judita Bystrická,Alena Vollmannová,Ján Tomáš,Matyáš Orsák,Petra Kavalcová

doi:10.5219/401

Abstract

Sulphur is one of the most important elements in plants. Sulphur also positive influences on growth functions (nitrogen metabolism, enzyme activity and protein and oil synthesis), yield and quality bulbs of onion. In this experiment was watched the progress of making the total polyphenols content in different levels of fertilizer sulphur in onion during vegetation. In the work we watched also the influence of sulphur fertilization on the antioxidant activity. Sulphur was added in amounts 7.3 mg.kg-1 S, 11 mg.kg-1 S and 14,6 mg.kg-1 S. Samples of fresh onion we collected at the beginning, in the middle and in the end of vegetation period and we prepared an extract: 50 g cut onion extracted by 100 ml 80% ethanol according sixteen hours. These extracts were used for experiment. The content of total polyphenols was estimated by using Folin-Ciocalteau reagent. The absorbance was measured at 765 nm of wave length against blank. Antioxidant activity was measured using a compound DPPH˙ (2.2-diphenyl-1-picrylhydrazyl) at 515.6 nm in the spectrophotometer. Our values of total polyphenolic content during vegetation period were in range from 508.16 ±27.59 mg.kg-1 to 638.2 ±12.84 mg.kg-1. The highest content of total polyphenolics was recorded at the end of the vegetation period (638.32 ±12.84 mg.kg-1) in III. sampling (incorporation of sulphur in quantity of 14.6 mg S.kg-1soil). This increase was statistically significant (P-value = 2.10-3). The lowest content of total polyphenols was measured in the middle of vegetation period (415.41 ±13.32 mg.kg-1) in II. sampling (incorporation of sulphur in quantity of 11 mg S.kg-1soil). Another indicator that has been evaluated and compared was the influence of sulphur fertilization on the antioxidant activity. The highest values of antioxidant activity were recorded at the end of vegetation period in all variants. The lowest value of antioxidant activity (25.41 ±7.67%) was measured in three sampling in II.variant.

Highlights

Onions (Allium cepa L.) is widely used as most important crop among the vegetables and spices in the Slovak Republic
Sulphur fertilization has a marked effect on the quality of the onion bulbs
Our values of total polyphenolic content during vegetation period were in range from 508.16 ±27.59 mg.kg-1 to 638.2 ±12.84 mg.kg-1

Summary

Introduction

Onions (Allium cepa L.) is widely used as most important crop among the vegetables and spices in the Slovak Republic. Onions are consumed in different ways, they are consumed uncooked, but is often cooked before eating. Onions have bioactive compounds including polyphenols and sulphur compounds that are antioxidants and positively affect human health. The consumers preference is for the higher pungent (high sulphur content) onion bulbs Gambo et al (2009). Many studies have suggested (Pellegrini et al, 2009; Pérez-Gregorio et al, 2010; Geetha et al, 2011) that biologically active phytosubstances such as phenolic acids, flavonoids, quercetin exhibit anti-inflamatory, antiviral, and vasodilating effect and i tis effective in prevention of cancer and heart diseases. Onion composition is variable and its derived from environmental and genetic factors. Nutrients play a significant role in improving productivity and quality of crops (Al-Fraihat, 2009)

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