ANTIOXIDANT CONTENT IN BLACK CURRANTS FROM ORGANIC AND CONVENTIONAL CULTIVATION

Renata Kazimierczak, Ewelina Hallmann, Anna Rusaczonek, Ewa Rembiałkowska
Department of Functional Food and Commodities, Faculty of Human Nutrition and Consumer Sciences, Warsaw University of Life Sciences, Poland

ABSTRACT

Black currant is one of the most frequently consumed fruit, eaten raw as well as after processing. Fruits are rich in vitamin C, anthocyanins and phenolic compounds. Having antioxidant properties, all of these compounds are very important for human health. There are some scientific data demonstrating that organic fruits and vegetables contain more compounds with antioxidant properties in comparison to conventional produce, but these studies are not sufficient. However in case of black currant no studies have been conducted yet. Therefore it was advisable to compare bioactive compound content in black currant from organic and conventional cultivation. Three black currant cultivars were chosen to the study: Ojebyn, Ben Lomond and Titania. All fruits came from certified organic farm and corresponding conventional farm. The following parameters were determined in fruits: dry matter, biologically active compounds, like flavonols, polyphenols, vitamin C and anthocyanins, as well as antioxidant activity. The obtained results showed that organic black currant had considerably higher levels of compounds with antioxidant properties and higher antioxidant potential compared to fruits produced using conventional methods. Therefore black currant could be recommended as valuable enrichment of healthy diet.

Key words: black currant, organic cultivation, conventional cultivation, vitamin C, anthocyanins, flavonols.

INTRODUCTION

Since a long period of time there have been a great interest in products high in bioactive compounds, which by several functions in human body have an impact on the improvement of health status. One of the most valuable species among fruits, consumed both in raw and processed state, is black currant. Its fruits are a great source of vitamin C and polyphenolic compounds (flavonoids), from which special attention should be given to anthocyanins distinguishing with high concentration. All of this compounds with antioxidant character have significant health-promoting value. Flavonoids as natural antioxidants play positive role in preventing cardiovascular diseases by effective neutralization of LDL oxidation [5]. Through inhibiting the activity of phosphodiesterase and cyclooxygenase even more effective than aspirin, they reduce aggregation of platelets, which have decisive significance in sclerosis prevention [22]. Together with vitamin C, flavonoids take part in forming diagonal bonds between polypeptide chains of collagen fibres, that results in strengthening the blood vessels. Moreover, by the ability to catch free radicals and neutralizing cell damage caused by free radicals, as well as dioxygen and peroxide molecules, flavonoids show anti-cancer activity. This indicate that plant antioxidants should be delivered in diet daily [9].

There is a considerable number of scientific data testifying that organic vegetables and fruits contain more compounds with antioxidant properties compared to produce coming from conventional farming, which decide about their higher biological value. Therefore it could be presumed that regular consumption of organic products is one of the ways to limit the risk of some diseases and improve the general body health status.

According to organic farming idea, the quality of product starts in soil, therefore the attention should be given to the influence of cultivation methods on nutritional value of farm products. As a result of mineral fertilization yields increase in conventional cultivation, but many publications [among others 12, 16, 23] proves that at the same time water content in plant cells become higher and dry matter content drops. With the increase of dry matter content, nutrient content is also higher, therefore it could be presumed that organic cultivation is the way of keeping and increasing nutritional value of fruits and vegetables. In conventional farming vitamin and mineral levels in food often decline as crop yields increase, this phenomenon is called the “dilution effect” [3].

Conducted studies showed that nitrogen application decreases levels of phenolic compounds protecting plants against plant diseases and above all being natural antioxidants in human nutrition [3].

Although number of studies were carried out by scientist in different countries, the knowledge on differences in concentration of biologically active compounds in foods, coming from organic and conventional farming, is still too small. Thus there is a great need to carry out further research on the content of those compounds and antioxidant activity of plant produce. On the basis of the studies conducted on various species of fruits and vegetables, the hypothesis was formulated that currants from organic cultivation have higher nutritional value compared to those grown using conventional methods.

The aim of this paper was to compare biologically active compounds which function as antioxidants, i.e. flavonoids, polyphenols, vitamin C and anthocyanins, as well as antioxidant activity in the selected black currant cultivars coming from organic and conventional production.

EXPERIMENTAL MATERIAL AND ANALYTICAL METHODS

The experiment was conducted in 2006 in the Chair of Organic Foodstuffs at Warsaw University of Life Sciences. Three black currant cultivars were chosen to the study: Ojebyn, Ben Lomond and Titania. Fruits of those cultivars came from 5- and 6-old shrubs from two farms: organic and conventional. Certified organic farm was located in Rososz village, Wąsewo commune, Ostrów county, whereas conventional in Czarna village, Czarna commune and Łańcut county. Fruits of each cultivar were harvested manually at the full ripeness.

In organic farm organic fertilization by postharvest remains from vegetable field cultivation in the amount of 150 dt·ha^-1 was used. Comprehensive balance of fertilizing amounted as follows: nitrogen /N/ 48 kg, phosphorus /P/ 5.2 kg, potassium /K/ 77.5 kg, calcium /Ca/ 31 kg and magnesium /Mg/ 17.2 kg on hectare of area [20]. In conventional farm mineral fertilizer azofoska in the amount of 735 kg/ha was applied, according to nutritional needs of currants. Balance of mineral nutrients were as follows: nitrogen /N/ 100 kg, phosphorus /P/ 21 kg, potassium /K/ 117 kg and magnesium /Mg/ 20 kg on hectare of area.

In organic farm there were no chemical treatment. In conventional farm Anthrachnose (Drepanopeziza ribis) and White Pine Blister Rust (Cronartium ribicola) controls were carried out using Dithane M-45 80 WP. Additionally control treatment against Dasineura tetensi based on Owadofos 540 EC was applied twice.

The following parameters were determined in fruits: dry matter by the scale methods (PN-91/R-87019), flavonol content by the Christ – Müller’s methods, total anthocyanins by the spectrophotometric method and vitamin C by the Tillman’s method according to PN-90A-75101/11 norm. In addition, antioxidant activity was determined by the spectrophotometric method using artificial radicals ABTS (results were presented as TAEC – µM of Trolox per 1 g of dry matter).

Results concerning each antioxidant compound were statistically analyzed using Statgraphics 4.1 programme applying Tukey’s test at the significance level α = 0.05.

RESULTS

Results concerning dry matter in the studied currant cultivars are presented on Fig. 1. The kind of cultivation had no significant impact on dry matter content in black currant. However fruits coming from organic cultivation had slightly higher levels of dry matter, it was 18.58 g 100 g^-1 f.m., while in currants from conventional cultivation 18.08 g 100 g^-1 f.m.

Currants from organic cultivation contained on average significantly more flavonols in comparison to conventional ones, and it was respectively 4.70 mg 100 g^-1 f.m. and 3.74 mg 100 g^-1 f.m. counted for quercetin (Fig. 2). Among studied cultivars the highest content of flavonols showed Ojebyn cultivar. In organic cultivation it was 5.97 mg 100 g^-1 f.m., whereas in conventional – 4.62 mg 100 g^-1 f.m of quercetin.

A significant impact of cultivation method on vitamin C content in currants was found. Fruits from organic cultivation contained on average 170 mg 100 g^-1 f.m. of this vitamin and 125.70 mg 100 g^-1 f.m. when came from conventional cultivation. At the same time it was observed that the highest in vitamin C was Titania cultivar, amounted 211.59 mg 100 g^-1 f.m. in fruits from organic cultivation and 140.64 mg 100 g^-1 f.m. of this vitamin in conventional cultivation (Fig. 3).

Fig. 1. Dry matter content in studied black currant cultivars from organic and conventional cultivation

Fig. 2. Flavonol content in studied black currant cultivars from organic and conventional cultivation

Fig. 3. Vitamin C content in studied black currant cultivars from organic and conventional cultivation

Fig. 4. Antocyanin content in studied black currant cultivars from organic and conventional cultivation

Fig. 5. The antioxidant activity of studied black currant cultivars from organic and conventional cultivation

Cultivation practices had significant impact on anthocyanin compound concentration in the studied black currant cultivars. In organic cultivation fruits contained on average 948.81 mg 100 g^-1 f.m. of anthocyanins, while in conventional – 731.93 mg 100 g^-1 f.m. Ben Lomond and Titania cultivars contained more anthocyanins when coming from organic cultivation, whereas in Ojebyn cultivar the opposite situation was observed – conventional fruits had higher anthocyanin content (Fig. 4).

Currants coming from organic cultivation had higher antioxidant activity in comparison to those produced by conventional method. Antioxidant activity of currants from organic cultivation was on average 55.24 µM of Trolox 100g^-1 f.m., whereas for conventional currants it amounted to 42.15 µM of Trolox 100g^-1 f.m. (Fig. 5). This difference was statistically significant.

DISSCUSION

Organic farming has elevated antioxidant levels in about 85% of the cases studied to date. On average levels are about 30% higher compared to food grown conventionally [3]. This is an important step in proving that organic food consumption is beneficial to health.

In the light of presented results, it could be observed that black currants from organic farming showed 25% higher flavonol content compared to conventional fruits, and the differences in vitamin C and anthocyanins levels were respectively 35 and 40% higher in organic fruits. Antioxidant activity of currants grown organically was higher by 31%.

Similar results concerning phenolic compounds in currant from organic cultivation were obtained by Nikkonen et al. [15]. According to those studies average quercetin content in fruits of studied cultivars was by 18.4% higher when coming from organic cultivation. Comparable results were obtained by Asami et al. [2] in freeze-dried marionberry, noting by 50% higher level of total phenols in organic marionberry. Also in studies carried out by team of Italian scientists, who compare antioxidant levels in organic and conventional peaches, obtained results showed about one-third higher concentration of polyphenolic compounds in organic peaches [2]. Levite et al. [13] who assessed polyphenol concentration in wine grapes, showed on average 32% higher content of resveratrol in fruits from organic production. However studies by Anttonen and Karjalainen [1] on flavonol content in organic and conventional currants did not confirm impact of farming system on phenolic compound levels. In other studies quoted by Benbrook [3], organic cultivation also did not increase concentration of phenolic compounds in strawberries.

In own studies that assessed relation between vitamin C content in fruits and farming system, much more higher content of vitamin C was observed in currants from organic cultivation. However it should be pointed out that currants came from geographically distant farms, which might have an impact on differences of the vitamin C content in fruits. Thus to assess this parameter explicitly fruits taken to the study should ripen in identical conditions. However there are many studies that acknowledge impact of organic farming methods on higher content of vitamin C in plants. The results of own research on potatoes, cabbage, tomatoes, pepper and onion [10, 11, 16, 17], produced upon organic and conventional system, showed that products coming from organic cultivation had higher content of vitamin C by 53.7% in case of potatoes, 15 percent in cabbages, 41.5 percent in tomatoes, 26.8% in peppers and 129.9% in onions. Higher content of vitamin C was also found in organic apples [17] and in pumace made from those apples [18], as well as in peaches [8]. However in other studies on green peas and carrot quoted by Bourne and Prescott [6], results were opposite or did not show any differences, which confirms the significant impact of many environmental factors on vitamin C levels in plants. Woese et al. [24] in their review comparing organic and conventional food concluded that substantially higher number of studies on fruits did not show any differences in vitamin C, sugar, organic acid and dry matter content between products from organic cultivation and conventional one. At the same time in more than half of studies conducted on vegetables, higher level of vitamin C was found in organic foods.

Anthocyanin content in the studied currant cultivars from both systems, obtained in own research, turned out to be substantially higher (948.81 100 g^-1 f.m. and 731.93 100 g^-1 f.m.) in comparison to that obtained by Meyer et al. [14] who indicated that fruits of the same cultivars contained on average about 236 100 g^-1 f.m. of anthocyanis. Also in the studies on six currant cultivars Wu et al. [25] noted lower levels of anthocyanins, amounted from 322.7 to 586.6 mg 100 g^-1 f.m. Higher content of anthocyanins in organic fruits versus conventional was confirmed by results of research conducted by Rembiałkowska et al. [17] on different apple cultivars, which showed by 70% higher levels of those compounds in case of organic production. Other studies carried out on blueberries by Blumberg et al. [4] also confirmed that relation. In own study the highest content of anthocyanins showed currants of Titania cultivar, obtaining about 1189 mg 100 g^-1 f.m. in organic cultivation and 778 mg 100 g^-1 f.m. in conventional one. Average content of anthocyanins in organic fruits was substantially higher than in conventional ones. Only fruits of Ojebyn cultivar showed the opposite relation. For Ben Lomond cultivar, similar results to those from own studies were obtained by Stewart et al. [21], whereas studies by Cacae and Mazza [7] showed that fruits of this cultivar indicated nearly two-times higher values, obtaining even 1500 mg 100 g^-1 f.m. of anthocyanins. Studies by Rubinskiene et al. [19] on changes during ripeness of black currants showed that the highest anthocyanin content was found in overripe fruits. In this research growth conditions were also analyzed. Fruits that ripened in the year of higher temperatures and lower rainfalls had higher levels of anthocyanins. Taking into consideration impact of the cultivation conditions, it is hard to explicitly stated that organic production system is a way to increase anthocyanin content in currants.

Scientist from the Scottish Crop Research Institute showed that vitamin C make for 50 percent of total antioxidant capacity in black currants, at the same time anthocyanins share was 20% and flavonoids about 5% [21]. In spite of this fact, substantially higher content of those compounds in organic currants from own study reflects their higher antioxidant activity. It was also confirmed in paper by Blumberg et al. [4], who found higher antioxidant activity of cranberries produced organically, however the difference was substantially lower than in own research.

Concluding it could be stated that obtained results concerning black currant are very similar to results of previous, own research and results of other authors as regards to higher content of bioactive compounds in crop plants from organic production compared to conventional production. However it have to be emphasized that presented in this paper results are one of the first that concerns black currants. Further studies in this scope are needed, since many factors have an impact on bioactive compound content except for production practices. Those factors must have been strictly standardized to make reliable assessment.

CONCLUSIONS

1. Currants from organic cultivation contained significantly more compounds with antioxidant properties (flavonols, vitamin C, anthocyjanins), they also showed higher antioxidant activity in comparison to currants grown upon conventional system.

2. Among currants from organic production the highest content of flavonol compounds showed Ojebyn cultivar in both kinds of cultivation.

3. The Titania cultivar had the highest levels of vitamin C and have the highest antioxidant activity among organic currant cultivars, whereas the highest levels of dry matter and anthocyanins were found in Ben Lomond cultivar.

4. Higher content of bioactive compounds in currants grown organically are important source of antioxidants in diet that may have an impact on health promotion of consumers.

REFERENCES

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25. Wu X., Gu L., Prior R.L., McKay S., 2004. Characterization of anthocyanins and proanthocyanins in some cultivars of Ribes, Aronia, and Sambucus and their antioxidant capacity. J. Agric. Food Chem. 52, 7846-7856

 

Accepted for print: 4.06.2008

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Renata Kazimierczak
Department of Functional Food and Commodities,
Faculty of Human Nutrition and Consumer Sciences,
Warsaw University of Life Sciences, Poland
Nowoursynowska 166, 02-787 Warsaw, Poland
phone: (+48 22) 59 37 039
email: renata_kazimierczak@sggw.pl

Ewelina Hallmann
Department of Functional Food and Commodities,
Faculty of Human Nutrition and Consumer Sciences,
Warsaw University of Life Sciences, Poland
Nowoursynowska 166, 02-787 Warsaw, Poland
phone: (+48 22) 59 37 037
email: ewelina_hallmann@sggw.pl

Anna Rusaczonek
Department of Functional Food and Commodities,
Faculty of Human Nutrition and Consumer Sciences,
Warsaw University of Life Sciences, Poland
Nowoursynowska 166, 02-787 Warsaw, Poland
email: anna_rusaczonek@sggw.pl

Ewa Rembiałkowska
Department of Functional Food and Commodities,
Faculty of Human Nutrition and Consumer Sciences,
Warsaw University of Life Sciences, Poland
Nowoursynowska 166, 02-787 Warsaw, Poland
phone: (+48 22) 59 37 038
email: ewa_rembialkowska@sggw.pl

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