Influence of growing conditions on the technological performance of bread wheat (Triticum aestivum L.)

Abstract

Six bread wheat cultivars were grown in the same environment according to a conventional and an organic agricultural protocol. Hardness, moisture, test weight, protein and ash content and falling number were determined on kernels. Flour yield, particle size distribution and damaged starch were determined on flours together with farinograph and alveograph parameters. Loaves of bread were also baked following a straight dough standardised recipe. Results indicated that protein content was the quality parameter which was negatively influenced by organic farming. Hardness was also negatively influenced in four out of six cultivars, whereas the other technological parameters did not show the same trend for all the cultivars. The milling performance was similar between organic and conventional samples, whereas the differences in protein contents were clearly responsible for differences in rheological properties. As expected, volumes of the organic loaves of breads were significantly lower than those of the corresponding conventional ones.

Introduction

In Europe, consumers’ interest in ecologically or organically produced foods has grown steadily in recent years prompting increased use of organic agricultural systems. It is a popular belief that organic raw materials have lower levels of environmental contaminants and that they are in general healthier than the corresponding conventional products, the main difference between conventional and ecological farming being the use of fertilisers and pesticides (Woese et al., 1997; Haglund et al., 1998; Bourn & Prescott, 2002; Fillion & Arazi, 2002; Makatouni, 2002; Magkos et al., 2003). This, in part, explains why although organic products are often more expensive than their conventional counterparts, they nevertheless have good market appeal.

Cereal products such as bread and pasta are very popular in Italy where they are part of the daily diet. Bread wheat flour is used to manufacture a tremendous variety of bread and baked products (cakes, biscuits) both at the artisanal and at the industrial levels. Some of these products are traditional products and they were granted marks of origin by the European Union. So the growing interest in organic foods is inevitably involving also the cereal foods sector (Carcea et al., 2002).

As well as the concern for the environment, quality attributes of the final products are also important when consumers choose organic foods and producers in particular are anxious to know about the influence of organic farming on the technological performance of their produce, especially in those raw materials such as cereals which are subject to several levels of processing along their food chain.

Growing conditions of a crop may have a significant effect on plant growth and metabolism, and thus have a direct relationship on raw material quality for the food industry. The effects of climatic factors such as temperature and moisture and agronomic inputs (tillage, weeding, fertilisation, etc.) on the wheat crop growth and metabolism have been well researched and links between these factors and crop performance expressed by grain yield, and grain physical and technological quality have been well researched (Yamazaki et al., 1981; Altenbach et al., 2003; Kihlberg et al., 2003; Clarke et al., 2004).

In this paper, we report a single-year field experiment investigating the effect of growing under the same climatic and soil conditions, six soft wheat cultivars very popular in Italy for conventional agriculture under both an organic and a conventional protocol, in order to assess the influence of organic farming on the technological quality of grains for milling and baking.

Materials and methods

Samples of bread wheat (Triticum aestivum L.) were collected at harvest in June 2003 in the same environment in Northern Italy (Lombardia) where experimental plots of 10 m² were set up according to a randomised block experimental design with four repetitions. The samples belonged to six cultivars widely grown in Italy for bread baking, namely Colfiorito, Enesco, Eureka, Sagittario, Serio and Saliente which were chosen, apart from their popularity, on the basis that they represented grain material ranging from soft to hard, in relation to milling potentials. The samples were grown according to an organic and a conventional protocol, commonly adopted in the growing area. Details regarding the two cultivation techniques are given in Table 1.

Grains belonging to the same cultivar and coming from the four replicated plots were grouped together, mixed well and an aliquot of 2 kg was taken for all the subsequent analyses and tests. The grains were cleaned and their test weight was determined by a Shopper chondrometer equipped with a 250-mL cylinder. Kernel Hardness (Hardness Index) was measured with the SKCS apparatus (Perten Instruments, Huddinge, Sweden) according to Standard Method 55–31 (AACC, 2003). Whole meal flour was obtained by grinding the grain in a laboratory mill (MLI 204, Bühler, Uzwill, Switzerland) and was used for the determination of moisture, protein and ash according to Standard Methods No.110/1, 104/1 and 105/2, respectively (ICC, 2003). A separate flour was also obtained with the Falling Number laboratory mill (model 3100, Perten Instruments, Huddinge, Sweden) for the determination of the Falling Number according to Standard Method No. 107/1 (ICC, 2003).

Flours were obtained from each sample by tempering the grains for 36–48 h to 15.5–17.5% moisture depending on their hardness and milling them in an experimental mill (model MLU 202, Bühler, Uzwill, Switzerland) equipped with three breaks and three reduction rolls and six screens. Flour particle size distribution was determined with a sifter (Bühler) by using 100 g of flour and a 5-min sifting time. Damaged starch, alveograph and farinograph parameters were determined according, respectively, to Standard Methods No.164, 121 and 115/1 (ICC, 2003).

Three loaves of bread were produced for each sample belonging to the cultivars Sagittario, Serio and Saliente in a pilot bakery according to a straight-dough standardised recipe involving the use of flour (1000 g), water (variable according to Brabender Farinograph Absorption, standard ICC method 115/1), salt (15 g) and compressed yeast (40 g). Malt was added in variable amounts depending on the Falling Number value to bring it to 250 s. All the ingredients were mixed for 6 min in a spiral mixer. The dough was then left to proof in bulk for 30 min in a proofing cabinet at 30 °C, 80 r.h. The dough was mixed again for a few minutes before dividing into quantities of 250 g and placing in suitable pans which were left to proof as before. The baking temperature was 250 °C and total baking time was 20 min. Three hours after baking and cooling at room temperature, the bread volume was measured by the rapeseed displacement method.

Where applicable, data were statistically analysed by Anova and Duncan's multiple range test for significant differences.

Results and discussion

The bread wheat cultivars were grown in Northern Italy, in an area which is devoted to bread wheat farming, on two adjacent farms which were matched on the basis of proximity, soil type and type of enterprise to minimise climatic and soil differences. The conventional farmers used fungicide-coated seeds, herbicides and fertilisers, whereas the organic farmers had applied no fungicides or herbicides. Some details regarding the cultivation techniques are reported in Table 1, whereas the main quality data of grains for milling and baking are reported in Table 2.

Hardness values for the conventional samples were within the range expected for that particular cultivar and ranged between 79 and 48. The correspondent organic samples showed similar values for the cvs Colfiorito and Serio, whereas the cvs Enesco, Eureka and Sagittario showed significantly lower values, but the cv Saliente had a significantly higher value. Samson et al. (2005) in a study on endosperms obtained from four durum wheat cvs grown under different nitrogen fertilisation designs concluded that hardness seemed to be linked to genotype and insensitive to nitrogen supply. The results presented in Table 2 support this claim.

Moisture, test weight and Falling Number values failed to show any significant difference between the conventional and the organic samples. Falling number is negatively related to α-amylase activity, which is in turn dependent on the growing season. All the samples, both conventional and organic, had high FN values (above 385 s), indicating that no pre-germination had taken place and all the kernels were sound. Clarke et al. (2004) also investigated the effects of irrigation, nitrogen fertliser and grain size on FN, specific weight and blackpoint in winter wheat and demonstrated that there was no clear correlation between the growing conditions studied and the above reported quality parameters. A conclusion that is supported by our results. The values for test weights for both series of samples were within the range expected for the particular cultivars.

Ash exhibited significant differences between conventional and organic samples belonging to the same genotype; however, these differences were not in the same direction for all the samples, with Colfiorito, Enesco and Sagittario conventional samples having a higher ash content than the organic ones and Eureka, Serio and Saliente showing just the opposite trend. Several studies have reported on the influence of crop management practices on the ash or mineral concentration of wheat. Zebarth et al. (1992) determined the influence of the rate of N fertilisation on the ash concentration in the grain of soft white wheat and hard red winter wheat, grown under an intensive cereal management system in Canada. They concluded that total ash concentration decreased with increasing nitrogen rate in a curvilinear fashion for both wheats and that variation in grain mineral concentration as a result of N management was minor relative to variation in grain mineral concentration between local environments. More recently, Ryan et al. (2004), studying grain mineral concentrations of wheat grown under organic and conventional management, found that the organic grain had higher Zn and Cu concentrations and lower Mn and P concentrations than the conventional grain; however, the organic grain did not contain the greatly elevated concentrations of grain minerals predicted by some commentators. Srikumar & Öckerman (1991) and Jorhem & Slanina (2000) investigated on the effects of organic and inorganic fertilisation on the content of trace metals in wheat and other vegetables. Srikumar and Öckerman concluded that inorganic fertilisation when compared with organic manuring increased the contents of manganese, zinc and iron in wheat, but organic manuring increased the contents of copper and selenium in wheat. Jorhem & Slanina (2000) concluded that there is not a clearcut correlation between the content of Cd in foodstuffs of plant origin and the cultivation system. In our situation, we can conclude that the differences between conventional and organic samples, considering the relative homogeneity of soil and environment, are more related to the genotype than to the cultivation system.

Protein content was negatively affected by organic farming when compared with conventional farming for all the cultivars studied. Protein content ranged between 15.26 and 13.90 for the conventional samples and between 13.31 and 11.86 for the organic samples. Previous studies on organic flours had indicated that organically grown wheat produced flour with protein and gluten levels lower than conventionally produced wheat. This reduction in protein content resulted in low baking volumes in yeast bread and rolls (Haglund et al., 1998; Keehan et al., 2004). Several works have also been published on the influence of nitrogen fertilisation on wheat quality and the experiments were conducted with one or more cultivars grown in the same or different locations and with different fertilisation schemes (Scheromm et al., 1992; Conforti et al., 1993; Jia et al., 1996a,b; Pechanek et al., 1997; Wieser & Seilmeier, 1998; Wooding et al., 2000; Ames et al., 2003; Tea et al., 2004). They all agree that nitrogen supplies have a strong influence on the quantity and quality of wheat storage proteins which play an important role in the breadmaking process and this is valid across environments. In particular, Pechanek et al. (1997) and Wieser & Seilmeier (1998) demonstrated that the quantities of albumins and globulins were scarcely influenced by different nitrogen fertilisation, whereas those of gluten proteins (gliadins and glutenins) were strongly influenced. Moreover, Scheromm et al. (1992) reported that as a consequence of increased nitrogen supplies, the composition in glutenin subunits remained unchanged, whereas the total amount of high molecular weight aggregates evolved differently according to cultivar. In our situation, where we tried to standardise environmental and soil conditions, there is no doubt that proteins in kernels are negatively influenced by the organic husbandry.

The milling performance of conventional and organic samples expressed by flour yield, particle size distribution and damaged starch is reported in Table 3. Flour yield and particle size distribution were very homogeneous between conventional and organic samples belonging to the same cultivar and differences observed between cultivars are to be ascribed to the different genotypes. In addition, damaged starch did not show significant differences between samples belonging to the same cultivar but grown in different ways. However, the samples exhibited a range of values from about 5% to about 3% as a consequence of the differing hardness in the original kernels. So, organic farming did not show any significant difference on the milling performance of bread wheat samples.

The rheological properties of the doughs were also studied by means of the farinograph and the alveograph parameters. Differences were observed for all the cultivars between conventional and organic farming (Table 4). The fact that there was no significant difference in the damaged starch content of the conventional and the organic flours of the same cv, indicates that the differences in the rheological properties of the doughs were caused by the different protein (presumably gluten) contents of the original flours. In particular, organic flours absorbed less water and in most cases had shorter development times in the farinograph test, indicating weaker flours clearly as a consequence of less protein, whereas apart from one sample, they had lower W alveograph values and higher P/L values. A higher W value is an indication of a better performance at baking, whereas a higher P/L value is an indication of the dough being more tenacious and less extensible.

The differences observed in the rheological tests on the basis of which it was possible to predict a worst baking performance of the organic vs. the conventional flours were confirmed in the baking experiment where flours from three cultivars, selected on the basis of similar damaged starch values, were utilised for baking loaves of bread. Bread volumes were measured and in all three cultivars, the conventional samples gave significantly higher volumes (ranging between 326 and 340 mL) than the organic samples (ranging between 322 and 340 mL). Similar results have also been obtained by Haglund et al. (1998) and by Keehan et al. (2004). The link between protein content, rheological performance of the doughs, and hence the baking potential of the flours appears to be prominent. Thus, in the lower protein-containing flours associated with the organic farming systems, the protein network (gluten matrix) formed during dough production is weakened when compared with the flours produced from conventional agricultural practices.

Conclusion

Our study, in which six bread wheat cultivars, commonly grown in Italy for conventional agriculture, were grown according to an organic protocol under conditions aimed at minimizing the influence of soil and environment, clearly demonstrated that the quality parameter which is mostly affected in grains was protein content. As a consequence, doughs from organic flours had different rheological properties and loaves of bread baked from organic flours exhibited smaller volumes than the corresponding conventional samples, in agreement with observations carried out also by previous researchers. The milling performance was instead unaffected.

On the basis of these results, we conclude that it is not advisable to use cultivars bred for conventional farming in organic agriculture where manuring is the only fertilisation, but maybe cultivars specially bred for organic farming should be utilised. Alternatively, fertilisation techniques should be explored, aimed at improving nitrogen availability for wheat grown under organic agriculture if wheat grains have to meet common baking requirements.

Acknowledgments

This research was performed within a project on organic farming financed by the Italian Ministry of Agriculture and Forestry. The authors are grateful to Drs G. Boggini, M. Perenzin and P. Vaccino of the Experimental Cereal Institute of Sant'Angelo Lodigiano (LO), Italy, who provided the wheat samples. Thanks are also due to Mr L. Bartoli of INRAN for performing the milling of grain samples and to Mr F. Martiri for secretarial help.

References