Marie-Françoise Samson

Impact of durum wheat milling on deoxynivalenol distribution in the outcoming fractions

The milling behaviour of two naturally infected samples of durum wheat grain with contrasting levels of mycotoxins was studied. Although the two samples showed a similar milling behaviour, an increase of ∼20% in deoxynivalenol (DON) levels was found in semolina from the sample containing the higher level of mycotoxin. However, even if the highest concentration of DON was found in fractions originating from the grain outer layers, the mycotoxin contamination in semolina and flours were not related to the amount of two compounds (ash or phytic acid) used to monitor these external tissues. The presence of the trichothecene-producing fungi in the inner-most semolina fraction was also shown using specific DNA primers and PCR amplification. Comparison of DON concentrations in the feed stock and corresponding output at each milling step or grinding of semolina fractions followed by sizing showed that concentration of mycotoxin occurs in the finest particles at the first processing steps. Therefore, DON contamination of milling fractions is not simply due to the presence of peripheral grain tissues.

Wheat yield and quality as influenced by reduced tillage in organic farming

Organic farmers are interested in soil conservation by reduced tillage, techniques well known in conventional agriculture to protect soil quality and limit labor time and energy costs. However, organic farming and reduced tillage can modify weeds, soil structure, and thus soil nitrogen (N) mineralization which strongly influences wheat yield and quality. The main objectives of this study were to analyze how reduced tillage applied to organic wheat influenced (1) grain yield, protein concentration, and weed infestation; (2) deoxynivalenol (DON) contamination on grain; (3) technological quality parameters such as dry gluten, zeleny index, falling number, and gluten index; (4) protein composition (F1, F2, F3, F4, and F5 fractions, and UPP, gliadin/glutenin ratio); and (5) baking test. For this purpose, we analyzed five site-years of data from winter wheat crops where mouldboard ploughing and reduced tillage were compared in three experimental trials (two in France and one in Switzerland). Main results concern wheat yields: the effect of reduced tillage on wheat yield was influenced by several factors such as weed competition. No significant increase in mycotoxin content (DON) due to reduced tillage was detected. Contamination with DON was always below the European threshold for human consumption. The technological quality parameters were less affected by the tillage treatments than grain yield: protein content, gluten index, zeleny index, and falling number showed on average no significant difference between treatments although the protein composition was slightly different. The main results of this study are that the effect of reduced tillage on grain yield depends very much on soil type, weather conditions, and time after conversion, whereas there is only minor impact on wheat quality. This is in contrast to the hypothesis that reduced tillage under organic farming will cause problems in baking quality.

Relationship between endosperm cells redox homeostasis and glutenin polymers assembly in developing durum wheat grain.

Assembly of glutenin polymers was examined for two contrasted durum wheat cultivars in connection with changes in the redox status of the endosperm cells that accompanied grain development. The evolutions of the redox state of ascorbate and glutathione, as well as the activities of antioxidant enzymes were measured. Changes in the size distribution profile and redox state of storage proteins were evaluated, with particular emphasis on protein-bound glutathione (PSSG). At the beginning of grain filling phase, the size distribution profile of proteins included an extra peak shoulder at about 40,000 g mol(-1). The shoulder was assimilated to free glutenin subunits as it disappeared concomitantly with the upturn in glutenin polymers accumulation. Irrespective of cultivars, small SDS-soluble polymers accumulated first, followed by larger and insoluble ones, attesting for a progressive polymerization. During the grain filling phase, catalase (EC 1.11.1.6) activity dropped, reaching a very low level at physiological maturity. During the same period, superoxide dismutase (EC 1.15.1.1) and glutathione reductase (EC 1.6.4.2) activities increased steadily while the equilibrium constant between GSSG and PSSG shifted from 10(-2) to unity. These results demonstrated that grain filling was accompanied by a continuous decrease in cellular redox potential. In this context, formation of protein-bound glutathione would represent a protective mechanism against irreversible thiol oxidation. Storage protein S-glutathionylation instead of limiting glutenin polymer assembly as it has been proposed might be a required intermediate step for glutenin subunits pairing.

Management Effects on Quality of Organically Grown Winter Wheat

The potential for improving wheat grain quality by management strategies involving crop rotation, catch crops, and organic manure was tested in organic long-term experiments in Denmark and Austria. Growing grass clover in a four-year rotation resulted in a higher wheat yield increase that could not be achieved by including leguminous catch crops in the rotation. Yield was also higher with a pre-crop of pea than of lucerne. The average protein concentration was 132 g kg−1 for grains from the Austrian experiments while the Danish grains held 85 g kg−1. Protein was generally much less affected by the experimental conditions than grain yield. None of the tested management parameters affected grain protein concentrations in the Danish experiment. In the Austrian trial, a significant pre-crop × treatment interaction reflected a positive effect of the animal manure treatment on protein and dry gluten in wheat following pre-crop pea. Danish grains generally contained more soluble polymers of less interest for the baking process than the Austrian ones. The study emphasizes the challenges in improving the quality of organically grown wheat beyond what is predetermined by environmental growth conditions and cultivar. However, baking quality appeared better than could be expected from the quality parameters determined.

Rheological behaviour, structural and physicochemical characteristics of vitreous and piebald durum wheat endosperm

ABSTRACT The vitreous structure of the kernel is an important quality trait for durum wheat end-uses. Endosperm floury parts within the endosperm lower the semolina milling value by decreasing the semolina to flour yield ratio. Moreover cooking quality is also affected as protein content of semolina decreases with yellow of the berry. A large study was undertaken on durum wheat to relate more precisely textural, structural and physiochemical characteristics of endosperm. Four durum wheat cultivars were grown at 4 locations with various levels of nitrogen input. From each harvest homogenous vitreous and mealy kernels were selected and their endosperms were analysed at different structural levels: macroscopic, microscopic and molecular. Vitreous and floury endosperms exhibited differences at all 3 levels considered. Rheological tests (indentation and compression) showed large differences in mechanical properties (Young modulus, rupture energy) and endosperm microstructure characterized by microscopic observation (MEB) revealed variable density and microporosity. Contrasted protein content and protein composition (gliadin/glutenin ratio) were observed depending on endosperm texture. Results are discussed in order to relate semolina yield with the rheological properties of vitreous and piebald endosperm.