Organic olericulture differs from conventional agriculture due to the absence of pesticide, synthetic fertilizers, genetically modified organisms, some food additives and ionizing radiation, producing vegetables with a different chemical composition and with different amounts of bioactive compounds. The objective of this study was to quantify, in organic vegetables consumed in Brazil, the amount of total phenolic compounds using Folin-Ciocalteu reagent and the antioxidant activity through DPPH method. Among the analyzed vegetables, the effectiveness in the antioxidant capacity was obtained in decreasing order, by the broccoli (69.35), kale (63.20), cabbage (35.72) and carrot (20.39), expressed in % of DPPH consumption after 30 minutes of reaction. The amount of total phenolic compounds (mg GAE/ml of fluid extract-FE) present in the kale (0.606), broccoli (0.511), cabbage (0.214) and carrots (0.124) demonstrates a positive correlation between phenolic amounts and the antioxidant activity of the vegetables analyzed.
Food of plant origin, especially vegetables, is the source of vitamins, minerals, fibers, carbohydrates and bioactive compounds, such as polyphenols, a group of phytochemicals acknowledged as the most plentiful in our diet [
World Health Organization (WHO) asserts that, with scientific evidence level, an increase in fruits, vegetables and whole cereals intake has significant positive effects on the overall health of people, more specifically, on preventing non-communicable diseases [
Organic vegetables production aims the encouragement of a rational use of the soil, water and air, reducing to minimum levels of the employment of non-renewable resources. Its purpose is to offer healthy food items, free from intentional contaminants that can generate risks for the environment or for the farmer’s or consumer’s health. It differs from the conventional agriculture for its non-usage of agrochemicals, synthetic fertilizers, genetically modified organisms, some food additives and ionizing radiation [
The objective of this study was to quantify, in organic vegetables consumed in Brazil, the amount of total phenolic compounds using Folin-Ciocalteu reagent and the antioxidant activity through DPPH method. The study presents the contents of phenolic compounds and the antioxidant capacity of organic carrot (Daucus carota L.), broccoli (Brassica oleracea var. Italica), kale (Brassica oleracea var. Acephala) and cabbage (Brassica oleracea var. Capitata) produced in Petropolis, a small mountainous city in the state of Rio de Janeiro―Brazil.
The samples were randomly harvested in farms, from 2011 to 2013, in crop growing farms, at the beginning, center and end regions of the beds, totalizing five harvests and three batches for each vegetable in each harvest. The vegetables samples were transported in refrigerated vehicles (5˚C) to the laboratory where they went through a process of selection, hygienic cleaning, manual peeling and grinding in a food processor so they could be used in preparing the extracts.
The DPPH method is based on the capture of the purple colored DPPH radical (2,2-diphenyl-1-picrylhydrazyl), which absorbs at 517 nm. By the action of an antioxidant or a radical species, the DPPH• is reduced creating 2,2- diphenyl-1-picrylhydrazyl, of a yellow color, and consequent absorption disappearance, so it can be monitored by the decrease of absorbance. Based on the results obtained it is possible to obtain the free radical antioxidant or scavenging activity percentage and/or the DPPH remaining percentage in the reaction environment [
The DPPH method was performed according to the process described by Rufino et al. [
The phenolic compounds standard curve was constructed with gallic acid (Sigma-Aldrich, Germany). The stock solution was prepared with 100 mg of gallic acid diluted with methanol at 80% in a 10 ml volumetric flask. A 1 ml aliquot was removed from the stock solution and it was diluted with methanol at 80% in a 100 ml volumetric flask, establishing the sample solution. Aliquots of 0.05 at 1.2 µg/ml were removed from that sample solution and they were mixed with 1600 µL to 2600 µL Folin Ciocalteu reagent (Sigma-Aldrich, Germany) and with 1280 µL of Na2CO3 at 20%. The homogenization was carried on, leaving the solutions at rest at room temperature for 2 hours, and then the concentrations were measured. The results were expressed in µg of gallic acid/mL. All the analysis were performed in triplicates.
An amount of 20 g of each sample was diluted in methanol in a 100 ml volumetric flask to obtain the vegetables extracts. The content was agitated for one hour, on a non-heated stirrer plate with the help of a bar magnet. Right after that it was vacuum filtered with a sintered funnel number 3, adapted according to the Swain and Hillis [
The absorbency was determined using a Spectrophotometer Model Nova 2000 UV equipment, with a 685 nm wave length (γ), after being cooled at the absence of light [
All the analytical determinations were performed in triplicates, with estimation of the averages and standard deviations. The DPPH data obtained were submitted to variance analysis and Tukey test (p < 0.05), using the GraphPad PRISM 6 statistic program. To determine the relationship between the total amount of phenolic and the antioxidant activity of the vegetable extracts the correlation coefficient was calculated and a regression analysis was performed using the same statistic program.
The antioxidant activity of the organic vegetables analyzed is presented on
Among the vegetables analyzed, the effectiveness in the antioxidant capacity was obtained in decreasing order, by the broccoli (69.35), kale (63.20), cabbage (35.72) and carrot (20.39) expressed in % of consumption of DPPH after 30 minutes of reaction. However, there was no significant difference (p < 0.05) between the extracts of organic broccoli and kale in the different reaction times. The broccoli and kale extracts presented a higher efficiency in the free radical scavenging while the cabbage and the carrot showed inhibition percentages lower than 40%, which demonstrates a weak capacity of scavenging DPPH radical.
Melo et al. [
Vegetables | Phenolic totals mg GAE/ml | DPPH % consumed | ||
---|---|---|---|---|
15 min | 30 min | 60 min | ||
Broccoli | 0.511 ± 0.011 | 65.69 ± 4.49a | 69.35 ± 5.29a | 72.11 ± 8.26a |
Cabbage | 0.214 ± 0.003 | 33.68 ± 1.51c | 35.72 ± 3.39c | 37.20 ± 5.64c |
Kale | 0.606 ± 0.014 | 60.31 ± 3.25ab | 63.21 ± 3.85ab | 66.53 ± 4.49ab |
Carrot | 0.124 ± 0.021 | 19.46 ± 0.62d | 20.39 ± 1.13d | 20.92 ± 1.29d |
Average ± three determination standard deviation. Averages followed by the same letter in a column don’t differ statistically according to the Tukey test (p < 0.05).
methanolic extracts of butter lettuce, white onion and string bean showed moderate action (60% - 70% inhibition), while the red onion, chayote, cucumber, cabbage and carrot showed the weakest capacity in scavenging the DPPH radical. Similar behavior was observed in this study with the organic vegetables.
In a study presented by Faller and Fialho [
The antioxidant action of the bioactive compounds depends on its chemical structure and food concentration, among other factors [
The amount of total phenolic compounds found in the organic vegetables studied were: 0.606 mg GAE/ml FE in the kale; 0.511 mg GAE/ml FE in the broccoli; 0.214 mg GAE/ml FE in the cabbage; and 0.124 mg GAE/ml FE in the carrot. A positive correlation was observed between the phenolic amounts and the antioxidant activity in the vegetables studied after, 15, 30 and 60 minutes (Figures 1-3).
Broccoli, cabbage and kale are vegetables from the Brassicaceae family, better known as crucifers. The protective action of the crucifer vegetables has been associated to the presence of antioxidant vitamins including ascorbic acid, α-tocopherol, β-carotene, however a great part of these vegetables’ antioxidant activity comes from phenolic compounds [
Singh et al. [
Huber and Rodriguez-Amaya [
The antioxidant capacity obtained by the DPPH method showed greater expression on the organic broccoli and kale and lower expression on the organic cabbage and carrot; however they all showed a positive correlation with the polyphenols amounts, also greater in kale and broccoli. In view of what was exposed, added to the results obtained, it is possible to assert that the organic vegetables evaluated can contribute to the dietary input of antioxidant compounds. However, phenol profile could be done in the future research because it was not studied in this paper.
The authors are thankful to FAPERJ (Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro) for the financial support.