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Silva Grobelnik Mlakar
Faculty of Agriculture and Life Sciences, University of Maribor
September, 2013
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The present thesis is based on a survey of literature on grain amaranth (i); an experiment aimed at defining allelopathic potential of grain amaranth (ii); pot experiments conducted to determine the effect of various soil and climatic conditions on percentage of live seed emergence (PLSE) and seedling weight of four amaranth species (iii); a pot experiment conducted to study the effect of drought – induced at different phenological stages – on growth, yield performance, and leaf gas exchange (iv); a four-year field experiment conducted to investigate the effects of sowing date and nitrogen fertilisation on yields, protein content and amino acid composition (v); and on experiments with various amaranth-containing composite flours conducted to evaluate the rheological properties of dough (vi), and baking performance and sensory characteristics of resulted breads (vii). The survey of literature summarizes grain amaranth importance, botany, nutritive value and properties of crop processed as food (i). The seeds of garden cress were germinated with aqueous extracts of pigweed () and grain amaranth prepared from fresh roots, stems, leaves, and inflorescence with seeds, used either undiluted or at varying concentrations (ii). Although all the extracts delayed germination, leaf extracts of both species and inflorescence extracts of grain amaranth proved the most potent. Compared to pigweed, grain amaranth, which is known for its phytotoxic activity, exerted an even stronger inhibitory effect. The results of pot experiments (iii) revealed that the 15 mm sowing depth gave the highest seedling weight on sand and the highest PLSE on loam. gave the highest PLSE whereas gave the lowest PLSE but the heaviest seedlings. PLSE was severely reduced on the loam where topsoil crusting occurred after a decrease in soil moisture content, but not on the silt loam even when dry conditions were maintained throughout the experiment. PLSE was above 80 % with temperatures > 21 °C. Light regime with 12 h illumination gave the highest PLSE. In the greenhouse pot experiment (iv) amaranth plants were exposed to different soil water regimes: constant adequate moisture (W1), drought throughout the growing period (W2), drought initiated at crop inflorescence formation (W3), drought until inflorescence formation (W4), and drought from the beginning of inflorescence formation to the beginning of flowering (W5). Water shortage during inflorescence formation (W3 and W5) appeared to be critical, but soil drying after sowing until the beginning of inflorescence formation (W4) showed a pronounced ability to restore net photosynthesis, and provoke and improve the assimilate allocation to the aboveground biomass, particularly grain. In the field experiment (v) two sowing dates, May and June, and three target levels of soil mineral nitrogen (Nmin) were tested. There was a lower grain yield, higher protein content in grain, and lower EAA in grain protein of plants sown in June. Nmin target value of 140 kg N ha–1 raised grain yield, protein concentration in grain, and maintained the content of EAA in protein. The composite flours were made by mixing 0, 10, 20, and 30 % (w/w) wholegrain amaranth flours with refined wheat, refined spelt, or wholegrain spelt as basic flours. By increasing the amaranth replacement ratio, the gelatinisation temperature, water absorption, development time, and stability increased, whereas the dough softening was only slight. The amaranth addition strengthened the dough (vi). Composite breads made with 10 % amaranth flour had higher (refined wheat and spelt) or unaltered (wholegrain spelt) volume and specific loaf volume than sole basic flours. Samples made from refined spelt flour and samples with 10 % amaranth addition were considered as good, with slight deviation in quality (vii). According to the information obtained in the scope of investigation, grain amaranth is recognised as a perspective crop suitable for production of highly nutritive food also under our conditions.