INFLUENCE OF VARIETY AND CULTIVATION ON MINERAL ELEMENTS AND PROTEIN CONTENT OF ASPARAGUS (ASPARAGUS OFFICINALIS L.)

Abstract

The aim of this research work was to study the effect of variety and cultivation region on mineral elements and protein content of white asparagus spears (Asparagus officinalis L.). Therefore an extended field survey was conducted in the regions of Braunschweig (Lower Saxony) and Erfurt (Thuringia). Statistically significant differences between cultivation regions were found for Ca, Mg and sulphate. Additionally, spear samples of crop performance experiments with new varieties and genotypes in Lower Saxony and Schleswig-Holstein were analyzed. For nitrate and sulphate significant differences were found between varieties in Schleswig-Holstein. In Lower Saxony, genotypical differences were determined for nitrate, sulphate, Ca, S, Fe, Zn, Mn and Cu. INTRODUCTION White asparagus (Asparagus officinalis L.) is an important vegetable crop in Germany, with a production area of about 12,000 hectare (Anon, 2002). The selection of a variety is crucial for the successful commercial production, because asparagus is a perennial crop (Nichols and Fisher 1999). The economical profit depends on the variety and differences may be as high as three times in terms of total yield and even seven times in marketable yield (Nichols and Fisher, 1999). Variety and growth conditions will, however, not only affect crop productivity, but also spear quality (Poll, 1995; Paschold et al., 1996 and Mullen et al., 1999). Asparagus is a medicinal plant, which has a diuretic effect and is beneficial for humans with heart problems (Leung and Foster, 1996). The quality assessment of new varieties is an important part of any research program. Information on genotypical and regional differences in the content of primary and secondary compounds of asparagus is limited. It was the aim of this research work to study the influence of cultivation region and variety on quality parameters such as protein, nitrate, sulphate and the mineral composition of white asparagus in Germany. MATERIALS AND METHODS Experimental Design In 2000 an extended field survey was conducted in the regions of Braunschweig (52°19.0`N; 10°29.1`E) and Erfurt (51°01.4`N; 11°02`E). Spear samples were taken simultaneously on 15 May from 24 production fields in the area of Braunschweig and 27 samples were collected in the region of Erfurt. In 2001 spear samples of different asparagus varieties and genotypes (Ariane, Eposs, Gijnlim, Hannibal, Ramada, Ramos, Ramses, Rapid, Ravel, Stamm 12, Stamm 14, 17/24, 17/30 and 96012) were taken in crop performance trials on 11 May in Burgwedel (52° 37.4' N; 9° 50.2' E), Lower Saxony. At Wiemersdorf (53° 52.7' N; 10° 20.6' E) in Schleswig-Holstein samples from in total five varieties (Boonlim, Eposs, Gijnlim, Huchels Alpha and Thielim) were taken on 15 May. Both experiments were laid out in a completely randomized design with four repetitions in Burgwedel and three repetitions in Wiemersdorf. Proc. XXVI IHC – Future for Medicinal and Aromatic Plants Eds. L.E. Craker et al. Acta Hort. 629, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 314 Sample Preparation The spear samples were carefully cleaned with distilled water and cut to a length of 15 cm. Afterwards, the samples were dried at 80 °C until constancy of weight and fineground to a particle size < 0.12 mm employing an ultra-centrifugal mill (RETSCH ZM 1). Chemical Analysis The total nitrogen content was determined according to the Kjeldahl method. Nitrate and sulphate were extracted by de-ionized water and determined colorimetrically according to Kuecke and Schnug (1996) and Novozamsky et al. (1986), respectively. A dry ashing procedure was applied in order to determine the total content of K, Ca, P, Mg, Cu, Fe, Mn, and Zn: the dry sample material (0.5 g) was incinerated at 490 °C for 16 hours. After cooling to room temperature 10ml 2N HCl were added and afterwards the solution was completely evaporated on a hot plate. Then 10 ml 2N HCl were added and the solution quantitatively transferred into 50 ml volumetric flasks, made up to volume with de-ionized water and finally filtered (Schleicher & Schuell 593 1/2). For determination atomic absorption spectroscopy (AAS) was employed for Fe, Zn, Mn, and Cu, flame emission spectroscopy for K and Ca and colorimetry for P. S was determined by X-ray fluorescence spectroscopy according to Schnug and Haneklaus (1999). Statistical Analysis The analysis of variance using the General Linear Model (GLM) was performed by SPSS program version 10 (Anon, 1998).