Abstract
Purpose: To evaluate the effectiveness of Urtica dioica (Urticaceae) extract as a natural antioxidant and compare with the most commonly used synthetic antioxidants, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT).Methods: Three different U. dioica extracts, viz, chloroform, methanol (80 %) and water extracts, were prepared. The antioxidant activity of the extracts were evaluated by 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging and soybean oil models. Varying concentrations of the extracts (200, 500 and 800 ppm), BHA and BHT (100 and 200 ppm) were separately added to soybean oil and stored in the oven (60±1 °C) for 25 days. Peroxide and thiobarbituric acid (TBA) values were measured at various heating periods for the oil samples. Total phenolic and flavonoid contents of the extracts were determined using Folin–Ciocalteu and aluminium chloride methods, respectively, while the aerial parts of the plant were also phytochemically screened.Results: Analysis of the chemical composition of U. dioica aerial parts showed they contain crude proteins (21.78 %±0.11), crude lipids (1.66 %±0.03), total soluble carbohydrates (37.19 %±0.21), crude fibers (19.62 %±0.14) and ash (19.75 %±0.17). The aqueous extract contained the highest level of total phenolic contents (7.89 ±0.38, mg g-1 of powder) while the choroform extract contained the highest level of flavonoid contents (15.40 ±0.53 mg g-1 powder). The half-maximal concentration (IC50) values for chloroform, methanol (80 %) and aqueous extracts in respect of DPPH radical scavenging activity were 77.53±0.99, 199.71±1.02 and 159.88±1.57 μg ml-1, respectively. Mixing soybean oil with 200 - 800 ppm of extract decreased oil oxidation and formation rate of TBA reacting substances at a level that is almost equivalent to the synthetic antioxidant, BHT, at a concentration of 200 ppm.Conclusion: These findings demonstrate that mixing soybean oil with U. dioica extract can improve the quality of the oil during frying process.Keywords: Antioxidant activity; Soybean oil; DPPH; Peroxide value; Thiobarbituric acid value; Urtica dioica
Highlights
Urtica dioica L. (U. dioica) or nettle is a plant belonging to the family of Urticaceae
The aim of the present study was to investigate the antioxidant activity of chloroform, methanol (80 %) and aqueous extracts of U. dioica aerial parts using diphenyl-2-picryl hydrazyl (DPPH) free radical scavenging and soybean oil models
There are two stages of oil oxidation, i.e., the first stage is the formation of hydroperoxides and the second one is the decomposition of hydroperoxides to produce secondary oxidation products which could be react with thiobarbituric acid (TBA) reagent to produce colored compounds which absorb usually at 530 nm [20]
Summary
Urtica dioica L. (U. dioica) or nettle is a plant belonging to the family of Urticaceae. (U. dioica) or nettle is a plant belonging to the family of Urticaceae. The small, green, dioecious flowers occur as racemes in the axils of the upper leaves [1]. It is widely used in folk medicine in many countries. The aerial parts of the plant are recognized as a natural remedy for hypertension [1] and it possesses many therapeutic effects such as antiviral [5], analgesic [6], and hypolipidemic [7]
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