YIELDING AND QUALITY OF GARLIC LEAVES. PART II. PRIMARY METABOLITES

Jan Dyduch, Agnieszka Najda
Department of Vegetable Crops and Medicinal Plants, University of Life Sciences in Lublin, Poland

ABSTRACT

Studies carried out in 2006–2009 dealt with the evaluation of primary metabolites content in winter cultivated garlic leaves (local ecotype "R") depending on reproductive material used (cloves and air bulbils) as well as cultivation locality (high unheated foil tunnel, field). The content of dry matter, (13.08–17.76%), total sugars (4.56–6.60%), L-ascorbic acid (16.21–19.66 mg·100 g^-1), chlorophyll (1.012–1.601 mg·kg^-1) and crude fiber (1.35–2.18%) in leaves was determined.

Key words: garlic, Allium sativum, growing method, primary metabolites content in the leaves.

INTRODUCTION

Plant metabolites are compounds of differentiated properties and chemical structure which are formed in live plant organisms as a result of metabolic changes. Due to different ways of formation and the biochemical and physiological functions performed in an organism, so-called primary and secondary are distinguished. Primary metabolites perform the basic physiological functions in plants. They constitute the principal energetic and structural material of cells; they can also fulfill the function of spare materials. They include saccharides (carbohydrates), fats, proteins as well as enzymes, chlorophyll and vitamins [16,41,50]. Secondary metabolites as a side effect of secondary metabolism are derived from the compounds produced as a result of primary metabolism.

In recent years, the literature of the subject has shown an increased interest in foliate vegetables, which belong to biologically most valuable ones. Studies on the chemical composition and the content of primary metabolites (sugars, proteins, fats, vitamins, crude fiber) in those plants concern such vegetables as garden parsley [19,20], celery and celeriac [7,38,40], chard [22], corn salad [23,37], other foliate vegetables [14,51] and the chive of onion, shallot and garlic [3,4,6,10,11,13,25,27,28,35,36,42,43,44,45,46,47]. They are a very precious source of mineral salts and energetic, structural and biological compounds.

Dietary and medicinal properties of garlic were already known in ancient times and contemporary photochemical studies fully confirmed the multidirectional effect of compounds occurring in this plant [12,15,18,25,26,33,39,48,49]. The most popular manner of utilizing garlic is to use the heads and cloves of garlic, which are valuable in respect of their chemical composition, both for fresh consumption and in the form of additives to food, pickled products, etc. It is also used in pharmaceutical industry. The cultivation includes both the ecotypes that produce and do not produce generative shoots and which are planted in autumn or spring [5,6,8,9,17,30,31,32]. Seasonal consumption of garlic can be partly leveled off by the cultivation of this plant for leaf crop in the spring-summer period, both from field cultivations and from accelerated cultivations in rooms. Both Polish and foreign studies conducted so far point to the possibility of obtaining satisfactory and profitable yields of garlic leaves with valuable chemical composition [3,4,7,8,9,28,29,34,35,52].

The purpose of the present paper was to estimate the chemical composition of garlic leaves (primary metabolites) depending on the kind of the reproductive material (cloves, air bulbils) and the applied method of cultivation (field, unheated foil tunnel).

MATERIAL AND METHODS

Winter cultivated garlic (local ecotype "R") grown from clove setting and inflorescence bulbils in a field and a high foil tunnel for early harvest of leaves was the subject of the present study. The agrotechnical experiment was carried out in 2006–2009 at The Experimental Farm Felin (University of Life Sciences in Lublin). The soil under garlic cultivation was prepared in accordance with common agrotechnical recommendations. Celery was grown as a forecrop for garlic during the entire experiment. Garlic cloves (from 2.0 to 2.5 g each) and air bulbils (6–10 mm in diameter), after being treated with mordant Funaben T, were planted in autumn (the end of October) of 2006, 2007, and 2008 into plots of 1.6 m² area each (0.8 × 2.0 m), at 20 × 5 cm spacing (40 plants per row = 100 plants∙m^-2) in four replications. Garlic was harvested just before generative shoots production, i.e. on 17 May 2007, 19 May 2008, and 16 May 2009 in a foil tunnel, as well as on 1 June 2007, 6 June 2008, and 2 June 2009 in field production. The content of dry matter, total sugars, vitamin C, chlorophyll and crude fiber was determined directly after the garlic leaves harvest [1,2,21].

Garlic grown in a foil tunnel was harvested by 14 to 18 days earlier as compared with that grown in the field, regardless of the type of the reproductive material.
The measurement results were subjected to statistical processing using variance analysis and Tukey's confidence intervals at the significance level of p = 0.05.

RESULTS

Dry weight (Table 1) was within the range from 13.08% to 17.76%. It was significantly higher when the cloves were planted in a foil tunnel and it also depended on the year of studies.

L-ascorbic acid (Table 1) was within the range from 16.21 mg·100 g^-1 to 19.66 mg·100 g^-1 of fresh weight. It was significantly the highest in the combination where garlic cloves were planted directly in the field. The content of that substance was significantly related to the year of studies.

Chlorophyll (Table 2). Its content in garlic leaves ranged from 1.012 mg·kg^-1 to 1.601 mg·kg^-1 and was significantly related to the years and experimental factors. It was significantly the highest in the combination where plants obtained from cloves grew in the field.

Total sugars (Table 3). Their content in leaves ranged from 4.56% to 6.60%. It was significantly the highest in the combination where garlic cloves were planted in a foil tunnel. The content of sugars was significantly modified by atmospheric conditions in particular years of studies.

Crude fiber (Table 3) was established at the amount from 1.35% to 2.18%. Plants grown from cloves in field cultivation produced significantly the most of it in field cultivation. The content of crude fiber was also significantly modified in particular years.

DISCUSSION

Considering the biological value, garlic leaves can be compared to foliate vegetables. The green parts of plants are most abundant in nutrients and biological elements. Garlic leaves are characterized by a high content of dry weight and in this respect they are comparable to such vegetables as Brussels sprouts, kale, white cabbage, German turnip, savoy cabbage, parsley leaves. They are also rich in L-ascorbic acid. They contain it in the quantities comparable to such vegetables as parsnip, common turnip, lettuce, lentil and soybean sprouts and early potatoes. The content of chlorophyll has always been comparable with the amount occurring in the leaves of parsley, celery, dill and spinach [7,19,20,24,38,40].

Garlic leaves contain a similar amount of total sugars to that of chard, rutabaga, urad, kale, cauliflower, savoy cabbage, white and red cabbage, red pepper, leek and celeriac [22,24].

Considering the content of crude fiber, garlic leaves were comparable to potato, asparagus, celery, lettuce, tomato, Chinese cabbage, pumpkin, zucchini, onion and beet [7,24,38,40].

The manner of utilizing garlic leaves is similar to that of the leaves of other bulbous vegetables such as onion, chive, welsh onion or shallot. There are also similarities in their chemical composition as they contain considerable quantities of mineral salts, chlorophyll sugars, carotenoids of L-ascorbic acid and dietary fiber [10,29,34,35,46,47].

CONCLUSION

1. Garlic leaves are a valuable foliate vegetable abundant in such elements as total sugars (4.56–6.60%), chlorophyll (1.012–1.601 mg·kg^-1), L-ascorbic acid (16.21–19.66 mg·100 g^-1) and crude fiber (1.35–2.18%).

2. The supply of this vegetable in the market in spring can be an excellent supplement of scarce garlic cloves.

3. Garlic leaves can come both from accelerated and field cultivations.

4. Plants from an unheated foil tunnel could be picked up in the period between the 16 and 19 May, which is about 2 weeks earlier than those from field cultivation.

5. Leaves that are more valuable as regards the content of primary metabolites are obtained from field cultivations from autumn planting of cloves.

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Accepted for print: 14.04.2011

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