Organic wheat quality from a defined Italian field-trial




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16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11732

Organic wheat quality from a defined Italian field-trial

Kokornaczyk, M.1, Kahl, J.2, Roose, M.2, Busscher, N.2 & Ploeger, A.2

Key words: organic wheat, quality, lutein, total protein, biocrystallization

Abstract

Organic and conventional wheat grain (Triticum aestivum and Triticum durum) samples coming from a defined field trial in Italy were measured in 2005 and 2006 for their total protein content and the contents of lutein and zeaxanthin. Additionally the samples were analyzed by means of the biocrystallization method. The grain samples could be differentiated by the total protein content, which was higher in the conventional samples. The organic samples contained a higher lutein content in Triticum aestivum but lower in Triticum durum. Biocrystallization differentiated Triticum durum from Triticum aestivum and organic from conventional grown samples when visual evaluation was applied. Differentiation of farming systems was possible for biocrystallization evaluated with computerized texture analysis but not significant for all samples and years.

Introduction

The growth of the organic food market is causing a growing interest in investigations on products deriving from differently managed farming systems. In such comparison studies it is of particular importance to use a possibly wide range of analysis methods, because the quality differences due to the farming system can appear in crops in various forms – in the contents of singular compounds, as well as in the structural features, which can be analyzed on the whole product only. In our research we have united therefore common chemical methods and holistic methods of analysis, so as to receive complementary information about the given samples. The aim of our experiment was to differentiate the organically and conventionally grown grain samples. The samples derived from the Mediterranean Arable System COmparison Trial (MASCOT) in Italian Toscana, a long-term experiment started in 2001 and carried out at the Interdepartmental Centre for Agri-environmental Research “E. Avanzi” (CIRAA) of the University of Pisa. The choice of the applied analysis methods was based on the founds in the available literature. The content of carotenoids, which belong to the secondary plant metabolites, was found to differ in organic and conventional crops because of the different growth conditions, like exposure to pests and diseases (Roose, 2008). Many studies were conducted on the antioxidants contents present in different wheat varieties (Roose, 2008). But to our knowledge there is still limited literature on the contents of antioxidants in wheat samples deriving from differently managed farming systems. Studies indicate that holistic methods, such as biocrystallization, are especially suitable for authenticity tests of organic produce, hence a validation of the methods has been demanded.



Materials and methods

Samples: Organic and conventional Triticum aestivum L. (variety ‘Bolero’) and Triticum durum L. (variety ‘Claudio’) wheat samples in three field replicates (in total 12 samples per year), harvest 2005 and 2006, coming from the MASCOT-trial (Bàrberi et al., 2006) were analyzed by means of common chemical analysis for the content of total protein, secondary plant metabolites (lutein and zeaxathin), and by means of the biocrystallization method for the picture forming properties. The aim of the experiment was the differentiation of the coded wheat samples. The experiment was performed in the laboratories of the University of Pisa and the University of Kassel. The fertilizer rates for the conventional system were the following ones: for T. aestivum 156 N, 92 P2O5, and 30 K2O kg ha-1 and for T. durum 156 N, 92 P2O5, and 0 K2O kg ha-1 on mineral basis and for the organic system: 30 N, 30 P2O5, and 30 K2O kg ha-1 for both T. durum and T. aestivum. The fertilizer applied for the organic system was on organic basis, from dried manure; the amount of nitrogen available after clover was estimated 70 kg ha-1. Total protein: The total protein levels were determined using the procedure of Kjeldahl (EN ISO 3188, 1994). Factor 5.75 was applied to calculate protein content. The statistical analysis was the one way ANOVA for randomized blocks performed by use of the CoStat software (CoHort, 2006). Xanthophylls: Lutein and zeaxanthin were prepared as described in Roose (2008) by extraction with Methanol/THF followed by HPLC-separation and DAD-detection. Biocrystallization procedure: The sample material was crystallized in Italy and Germany in parallel. The experimental conditions at the University of Pisa are described in Mazzoncini (2005). The mixing ratio was 70mg substance based on 10% watery extract in combination with 90mg dihydrate CuCl2 per plate. The resulting pictures were scanned and analyzed by means of the Image J computer software for the gray level distribution (Reinking, 2007). The mean values of the gray level distribution were measured within 10 ROI’s (regions of interest) of circular shape, with the centers placed in the geometrical center of the picture, and diameters of different length. The diameter of ROI 10 was equal with the picture’s diameter, whereas the diameters of ROI 9 to 1 were equal with 90 to 10% of ROI’s 10 diameter. The visual evaluation of the patterns from harvest 2005 was carried out at the University of Kassel (Kahl, 2007). The sample preparation at the University of Kassel is described in Kahl (2007). For every sample run a wheat standard is applied (Kahl, 2007). Construction and function of the crystallization chambers used here are documented in Kahl (2007). To evaluate the patterns a texture analysis acia is used, where the variables of the second order are used (Kahl, 2007; in contrast to Image J). In addition to the texture analysis the patterns were visually evaluated in that all patterns from the samples prepared on one day and in one chamber were placed in parallel with increasing evaporation time (which was recorded by camera) on a light box and evaluated by trained people (Kahl, 2007).

Results and discussion

In both examined years the grains of both species differed significantly in their protein contents depending on the cultivation system (Table 1). The protein content of the organically grown grains was 2-3% lower then in conventionally grown grains. In year 2006 the protein contents of both varieties and cultivation systems were slightly higher, than in year 2005. The differences in lutein content were very small. For Triticum aestivum the lutein content of the organic grains was significantly higher in both years. For Triticum durum the lutein content was lower in the organic samples, but only for the samples of the year 2005.

In both years there was a significant higher content of zeaxanthin in the conventional varietys of T. durum, but no difference for T. aestivum.

Tab. 1: Protein content of the wheat samples from MASCOT-trial


Protein content [%]




Harvest 2005

Harvest 2006




Organic

Conventional

Organic

Conventional

T. aestivum

8,54

11,84

10,10

12,28

significance

***

***

T. durum

8,15

10,87

8,88

12,47

significance

***

***

* significance at α=0,05 based on one way ANOVA for randomized blocks.



Figure 1: Classification of the MASCOT wheat samples according to the farming system (organic: gray/conventional: black). The bars are showing the percentage of proper classified sample replicates per field replicate/block.

Figure 2: Mean values of the gray levels calculated by Image J for the biocrystallization patterns measured at Pisa/I from MASCOT Triticum aestivum wheat samples (ROI: Region of Interest) in 2006 (3 patterns per field replicate).

The variation of the lutein content in T. durum was higher for the conventional samples than for the organic. There was no consistent differentiation between the farming systems for both lutein and zeaxanthin. For T. aestivum 70% of the samples can be classified correctly, for T. durum 80% (Figure 1). When the biocrystallization patterns from the harvest 2005 were evaluated by applying an adapted triangular-test, the difference between org. and conv. samples was significant for both, T. aestivum and T. durum. With computerized texture analysis based on the gray level distribution (Image J) a significant differentiation was possible for all samples and years for ROI 8, 7 and 6 (Figure 2). With the texture analysis based on second order statistics, there was a significant difference between T. durum and T. aestivum but the difference between the farming systems was not significant over all samples and years. When the patterns of the biocrystallization at the University of Kassel were visually evaluated by trained people (descriptive test), the farming systems could be differentiated and correctly classified in both years for all samples.



Conclusions

The introduction of holistic methods into our comparison study on organic and conventional wheat samples showed that differences due to different farming systems can be found applying both: common and holistic methods of analyse. The organic and the conventional wheat samples from the MASCOT-trial could be differentiated by total protein measurements and visual evaluation of standardised biocrystallization patterns. The difference could also be described applying different computerized image analysis programs on the biocrystallization patterns, although the difference was not always significant. Evaluation of lutein contents resulted in correct classification of the samples of 70-80%. The variation between the field replicates was higher than between the farming systems and moreover there seemed to be an opposite effect comparing lutein contents of T. aestivum and T. durum. The biocrystallization needs further development and validation when texture analysis with Image J and visual descriptive tests are applied.



Acknowledgements

MK thanks to the Centre “E. Avanzi” CIRAA, Via Vecchia di Marina 6, 56122 San Piero a Grado PISA, Italy for the wheat samples.



References

Bàrberi, P., Mazzoncini, M. (2006): The MASCOT (Mediterranean Arable Systems COmparison Trial) long-term experiment (Pisa, Italy). In: Raupp, J., C. Pekrun, M. Oltmanns & U. Köpke (Ed.): Long-term Field Experiments in Organic Farming. Berlin: Dr. Köster Verlag.

CoHort (2006): CoHort Software. http://www.cohort.com/costat.html.

Kahl, J. (2007): Entwicklung, in-house Validierung und Anwendung des ganzheitlichen Verfahrens Biokristallisation für die Unterscheidung von Weizen-, Möhren- und Apfelproben aus unterschiedlichem Anbau und Verarbeitungsschritten. Habilitationsschrift, Universität Kassel.

Mazzoncini, M., Belloni, P., Medaglini, F., Antichi, D. (2005): Confronto tra la qualità del frumento convenzionale e biologico secondo metodi tradizionali ed innovativi.XXXVI Convegno Sia,Foggia 20-22/9/2005.

Reinking, L. (2007): Image J Basics. Biology 211, Laboratory Manual. http://rsb.info.nih.gov/ij.



Roose, M. (2008): Charakterisierung von Möhren und Weizen aus ökologischem und konventionellem Anbau anhand ihrer Carotinoid- und Polyphenolkonzentration. Dissertation, Universität Kassel.

1 University of Pisa, Dep. Agronomy and Agro-Ecosystem Management, Via del Borghetto 80, 56124 Pisa, Italy

2 University of Kassel, Dep. Organic Food Quality and Food Culture, Nordbahnhofstr. 1a, D-37213 Witzenhausen, Germany



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