Effect of wheat gluten proteins on bioethanol yield from grain
Introduction
Bioethanol is one of the modern biomass-based transportation biofuel used worldwide. The use in vehicles usually takes place at either a low blend of 5% or 10%, or at a high blend of 85% [1], [2], [3], [4]. Biofuels are expected to be the most feasible alternative to fossil fuel, and possibly an answer to the emerging global energy shortage [5]. The use of biofuels and other renewable fuels for transport is supported by a large number of world countries, including the European Union [6], [7], [8].
Bioethanol is a form of renewable energy that can be produced from energy crops and lignocelluloses biomass from agricultural residues, wood, fast-growing trees, etc. [6], [9], [10]. Bioethanol production from starch is a traditional first-generation conversion technology. Starch is a high yield feedstock for bioethanol production. During ethanol production starch is hydrolysed to glucose. Glucose is fermented by certain species of yeast (e.g., Saccharomyces cerevisiae) to produce ethanol and carbon dioxide. Ethanol is separated by distillation [3], [4], [9]. The technology of ethanol production from fermented cereal grains has been known since about the 10th century [11].
Cereal grains containing less grain protein and high starch are favoured by distillers because they increase the bioethanol conversion [12]. Hence, the nitrogen regime of an ethanol grain crop is adjusted to favour starch accumulation instead of protein synthesis, as is done in food or feed-crop production [13]. In the Czech Republic, the high bread-making quality wheat grains are not favoured because of high protein content [14], [15] and the presence of gluten proteins, especially high molecular weight glutenin subunits and low molecular weight glutenin subunits. Raw material with high amylase activity of grain (low falling number) is desirable because high amylase activity of grain reduces the necessary amount of added amylase. In addition to basic parameters, content of admixtures and impurities is recommended for evaluation [15]. One of the most suitable cereals for bioethanol production is triticale [16], [17] – the first successful man-made cereal produced by crossing wheat and rye. Triticale grain is generally lower in starch content [18], [19], [20] but triticale grain is less sensitive to changes in fermentation conditions during the process and gives good bioethanol yields. The increased activity of amylolytic and proteolytic enzymes reduces a necessary amount of supplied enzyme preparations, which improves the economics of ethanol production [15], [21].
The aim of the research presented in this paper was to study the direct effect of wheat gluten proteins (high molecular weight glutenin subunits, low molecular weight glutenin subunit and gliadin) on ethanol yield from triticale grain. The hypothesis that the presence of wheat gluten proteins has no effect on bioethanol yield was tested on special lines of triticale cv. Presto. Two lines with introduced selected segments of wheat chromosome 1D, encoding high molecular weight glutenin subunits, low molecular weight glutenin subunit and gliadin, into the triticale chromosome 1R were examined [22], [23], [24], [25]. Direct effect of high molecular weight glutenin subunits on bioethanol yield was examined on triticale Presto 1R.1D5+10-2. Direct effect of high and low molecular weight glutenin subunits and gliadin on bioethanol yield was examined on triticale Presto Valdy.
Section snippets
Material
The direct effect of wheat gluten proteins on bioethanol yield was studied on triticale grain. The experiments involved triticale Presto 1R.1D5+10-2 and Presto Valdy. Samples were derived from cv. Presto and two lines of samples were studied:
- (a)
Presto 1R.1D5+10-2 – A rye chromosome of triticale Presto 1R.1D5+10-2 carries the segment of wheat chromosome 1D (allele Glu-D1d) encoding wheat high molecular weight glutenin subunits (HMW-GS) 5 + 10 [26]. In short – more wheat glutenins are present in grain
Results
Based on published results, the effect of wheat gluten proteins on investigated parameters was expected to be more significant. At the same time, it has to be pointed out that the lines analysed in the present work were only two (Presto 1R.1D5+10-2 and Presto Valdy) and they do not afford to make definitive assumptions, but it can be noticed that only specific weight and protein content were significantly affected by the presence of wheat glutenin proteins. Strong depression in grain yields
Discussion
The presence of gliadin showed more significant effect on investigated parameters than the presence of high and low molecular weight glutenin subunits. Even if the presence of glutenin subunits did not significantly decrease the investigated parameters and both triticale lines showed better ethanol yields than those expected, based on their starch and protein contents [12], [33], strong depression in grain yields caused by the presence of gliadin and glutenin decreased the energy balance of
Conclusions
Even if the samples analysed in this study were only two (Presto 1R.1D5+10-2 and Presto Valdy) and they do not afford to make definitive assumptions, it can be concluded that in analysed cases the presence of gliadin had more significant deteriorating effect on investigated parameters than the presence of glutenin. Despite the presence of glutenin subunits did not significantly decrease the investigated parameters (specific weight, Hagberg falling number and starch content met the requirements
Acknowledgements
The research was supported by the Ministry of Education, Youth and Sports of the Czech Republic (Projects Nos. MSM2532885901 and 1M0570).
The authors thank Mr. Petr Martinek from the Agricultural Research Institute Kroměříž, Ltd., Czech Republic, for planting the triticale, Mrs. Jarmila Janíková and Mr. Jonathan Blowers for language help.
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