The effect of climatic change on the rheological properties of winter wheat doughs

The rheological characteristics of doughs are determined by the amount and proportion of gliadin and glutenin proteins, and their significance lies in the fact that they affect both the processing ability of the dough and the quality of the end product. Probably the most significant factor in determining the baking quality of winter wheat is the variety, as it primarily accounts for the amount and quality of gluten proteins. However, other factors, such as cropping year, site, mineral fertilization also have considerable importance (Pepó et al., 2005, Győri and Sipos, 2006, Baric et al., 2007, Drezner et al., 2007). The variation in the quality parameters originated in the glutenin subunit composition, in particular, in the balance between the high and low molecular weight subunits (Gupta et al. 1992, Tóth et al., 2006). The extensigraph is widely used in the milling and baking industries as well as in applied basic research to classify and evaluate flours on the basis of the physical characteristics (especially the strength) of the dough. The Brabender extensigraph is one of the numerous empirical rheological equipment that measures the expansibility and the resistance to expansion of the dough after a determined period of resting time (Preston and Hoseney 1991). The analysis with the extensigraph can determine the expansibility and the resistance to expansion of the dough, on the basis of which the bread-making properties or the quality of the final product of a flour can be concluded (Bloksma 1990a,b; Hoseney 1994). Our objective in this investigation was to study the influence of weather conditions during the growing period on extensigraph properties of winter wheat doughs.


INTRODUCTION
The rheological characteristics of doughs are determined by the amount and proportion of gliadin and glutenin proteins, and their significance lies in the fact that they affect both the processing ability of the dough and the quality of the end product.
Probably the most significant factor in determining the baking quality of winter wheat is the variety, as it primarily accounts for the amount and quality of gluten proteins.However, other factors, such as cropping year, site, mineral fertilization also have considerable importance (Pepó et al., 2005, Győri and Sipos, 2006, Baric et al., 2007, Drezner et al., 2007).The variation in the quality parameters originated in the glutenin subunit composition, in particular, in the balance between the high and low molecular weight subunits (Gupta et al. 1992, Tóth et al., 2006).
The extensigraph is widely used in the milling and baking industries as well as in applied basic research to classify and evaluate flours on the basis of the physical characteristics (especially the strength) of the dough.The Brabender extensigraph is one of the numerous empirical rheological equipment that measures the expansibility and the resistance to expansion of the dough after a determined period of resting time (Preston and Hoseney 1991).The analysis with the extensigraph can determine the expansibility and the resistance to expansion of the dough, on the basis of which the bread-making properties or the quality of the final product of a flour can be concluded (Bloksma 1990a,b;Hoseney 1994).
Our objective in this investigation was to study the influence of weather conditions during the growing period on extensigraph properties of winter wheat doughs.

MATERIAL AND METHODS
Samples are from the Látókép Experimental Site of The University of Debrecen, Centre of Agricultural Sciences.It has calcareous chernozem soil with a 70-90 cm deep humic layer, the humus content 2,8-3 %.The groundwater level is between 6-8 m.This soil has medium level nitrogen and phosphorous and high level potassium supplies.The pH measured in KCl is 6.2.In the experiment we applied the following treatments: a control, 30 kg ha -1 nitrogen, 22.5 kg ha-1 P 2 O 5 and 26.5 kg ha -1 K 2 O and the double, threefold, fourfold and fivefold amount of these doses in four repetitions.Five winter wheat cultivars were investigated from 2006, 2007, and 2006 harvest years.In total, 216 flour samples were analyzed for extensigraph properties.Dough properties were determined by the Brabender Extensigraph according to Approved Method 54-10 (AACC International 2000) after a 135minute rest period.
The precipitation and temperature data of cropping years are from the Institute of Crop Sciences of the University of Debrecen.
Statistical analysis of the data was performed using SPSS 13.0 statistical software.One-way ANOVA was used to analyze data to ascertain whether the weather conditions significantly affected the rheological properties of dough.

RESULTS AND DISCUSSION
The weather conditions were very different during the studied cropping years.As the Figure 1 shows, the least precipitation fell in 2007, and the mean yearly rainfall was the highest in 2008.We can say that the quantity of precipitation in 2006 was average and equal to the average of the last 30 years period.We studied the distribution of precipitation of years.We found differences between the fell precipitations during the first two months (Figure 3.), which data is important to know the weather conditions of start phase of growing of winter wheat plants.In 2006 fell the smallest quantity rain in October and November in spite of the precipitation of this year was average (575 mm); the distribution of precipitation was disadvantageous.The highest precipitation level was measured during this months in 2008, and moderate precipitation was in 2007 (32 mm).The quantity of precipitation during the whole growing period is a better parameter than the mean yearly rainfall measurement.In contrast with the previous (Figure 3), the Figure 4 show that the most precipitation was in the 2006 growing period (399 mm).The rainfall during the growing period was relatively low in 2007 and it was above the 30 years average in 2008.The extensigraph properties of winter wheat cultivars were affected by weather conditions during the growing period.The area under the curve is one of the most important parameter among the studied rheological parameters.The winter wheat cultivars got the highest mean area values (81 BU) in 2007 (Table 2.).It is very interested because this year was the droughtiest and the mean yearly temperature was the highest.In 2006, we got the worst extensigraph values (Table 1.) in order to the most rain fell in growing period of this year.The extensibility and maximum resistance parameters of doughs were the highest in 2007.The different weather conditions of studied cropping years affected the cultivars in different way and extent.The changed weather conditions did not affected the rheological parameters of Öthalom than Lupus or Suba.These two last mentioned cultivars improved to a great extent responded to the changed weather conditions (Table 2. and Table 3.).

CONCLUSIONS
Based on our examinations, we have established that the extensigraph properties of dough are affected by the weather conditions of cropping year.
The cultivars got better extensigraph values when the weather during the cropping year was warmer and the quantity of precipitation was less than the 30 years average.We determined that not only the quantity of precipitation is important but the distribution of precipitation can affect the rheological parameters of winter wheat doughs.
We have observed that various cultivars very much distinctly react to the changing the temperature and precipitation.In generally, we experienced that the higher temperature and lower precipitation level improved the quality of winter wheat flour, but we do not have any information about the yield of wheat cultivars in these cropping years.
The data presented are for a set of cultivars grown at one location in three years, it could be very interesting to continue these examinations on further cropping years and different sites.

Figure 1 .:
Figure 1.: Precipitation in the studied years

Figure
Figure 2.: Average temperature in the studied years

Figure 3 .:
Figure 3.: Precipitation during the first two months (in October and November)

Figure 4 .:
Figure 4.: Precipitation during growing period (from October to July)