Effect of organic and conventional agronomic practices and variety of choice on nutritional quality, the contents of undesirable compounds and yield of cereals

Abstract

Cereal products are one of the most important sources of nutrients and energy in the human diet, and common wheat is the most consumed crop globally. Spelt wheat -one of the most ancient cereals- is increasing its share in the food markets because of its ability to grow under low inputs and consumers’ belief about its high quality. The demand for spelt wheat and other minor cereals is particularly high in the organic food market, much of which is driven by consumers’ expectations that organic farming practices could improve the content of beneficial nutrients and decrease the content of undesirable compounds such as pesticides. The aim of this thesis was to explore the effect of organic and conventional agronomic practices (fertilisation and irrigation) and variety choice on the nutritional quality and undesirable compounds (heavy metals, mycotoxins and pesticides) of grain/flour of different cereal species (mainly common wheat and spelt wheat). The objectives were to carry out (1) a meta-analysis of data on effects of organic and conventional agronomic practices on mycotoxin contamination in cereals and (2) a shopping basket study to collect flour from supermarkets in the UK and Germany over three years; and (3) to carry out a field experiment, where various spelt wheat genotypes were cultivated under different fertility treatment and irrigation regimes. The contents of nutritionally relevant compounds such as phenolic acids, flavonoids, protein, and macro- and micronutrients, as well as undesirable compounds such as heavy metals were measured in the shopping basket and field study. In addition, mycotoxins and pesticide residues were measured in the shopping basket study. The meta-analysis of mycotoxin content of cereal grains was based on 79 published studies and found that, historically, conventional cereals had consistently higher levels of Fusarium mycotoxin contamination and organic cereals had higher levels of OTA contamination. However, the contamination and prevalence of OTA in organic cereals has decreased in cereal grains/products in the last 15 years in Europe due to the improvement of post-harvest drying and storage management. Results of the shopping basket study found that antioxidant capacity, concentrations of phenolic phytochemicals and mineral micronutrients were significantly higher in organic and wholegrain flours compared with conventional and white common wheat and spelt wheat flour, repectively, while conventional wholemeal flour was contaminated with significantly higher pesticide residues than conventional white flour. These results suggest that switching to organic wholemeal flour allows for higher intakes of phenolic phytochemicals and mineral micro-nutrients. These have been associated with potential health benefits of consuming wholegrain foods to be achieved without simultaneously increasing dietary exposure to pesticides. No differences in mycotoxin contamination were found between conventional and organic II farming systems. Results of a controlled experiment in Crete indicated that, supplementary irrigation substantially improved grain yield of spelt but had no negative effects on mineral and phenolic phytochemical content, and sheep and chicken manure fertilisation resulted in similar yields as mineral fertilisation which emphasised the suitability of spelt for organic production in semi-arid conditions. No major impact of fertiliser type was seen, but a significant impact of spelt variety was found on concentrations of phenolic phytochemicals and some minerals. The main achievements and novelty of the project were  carrying out the most comprehensive meta-analysis to date of mycotoxin contamination in organic vs conventional cereals;  carrying out an extensive and comprehensive investigation of the nutritionally relevant compounds and the content of undesirable compounds found in organic vs conventional common wheat and spelt wheat flours available in supermarkets in the UK and Germany, predicting the potential health effects for consumers switching to organic from conventional cereals consumption, which enables 11%, 16% and 30 % more phenolics, Fe and Zn intake and at least 4 times lower pesticide intake respectively, and switching to spelt from common wheat enable 2 times higher Zn intake.  carrying out the first assessment of the yield and grain quality performance of different spelt varieties with different irrigation management and fertility management in a semi-arid region of the Mediterranean; when taking both yield and grain quality, the “organic” spelt variety ZOR was recommended together with sheep or chicken manure fertilisation and sustainable drip irrigation.