A.Yu. Sharikov, L.V. Rimareva, V.V. Ivanov, V.I. Stepanov, N.I. Ignatova, L.I. Skvortsova
Russian Research Institute of Food Biotechnology Russian Academy of Agricultural Sciences
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Summary. Main trends in development of ethanol biotechnology are fermentation of very high-gravity mashes and usage of grains which are difficult to process, e.g. rye, barley. Combination of these trends within the framework of traditional ethanol technologies is limited due sharp deterioration of rheological properties of very-high-gravity rye mashes. An alternative to traditional water-thermal treatment of grain in ethanol tecnology can be extrusion cooking as processing stage before liquefaction and saccharification. Influence of extrusion cooking on process of very-high-gravity rye mash obtaining and its fermentation was investigated. Possibility to obtain rye hydrolyzates with solubles concentration about 30% (wt/vol) and acceptable rheological properties was shown. Studies indicated, that there was a need to use hemicellulose enzymes in mashing process in common with α-amylase and protease. Dynamic viscosity of very-high-gravity hydrolizate from extruded rye decreased notedly and was only 0,5 Pa•s on the moment of 30 minutes of liquefaction process. Fermentation studies with use of ethanol-tolerance strain of Saccharomyces cerevisiae indicated, that ethanol concentration and its yield within 72 hours were 15,09% (vol/vol) and 64,7 dkl of ethanol from 1 ton of fermentable carbohydrates. Fermentation of 30% (wt/vol) mash from extruded rye yielded 1% (vol/vol) more ethanol and 2,25 dkl/ton more ethanol yield in contrast with fermentation of mash which was obtained using traditional cooking technology. Concentrations of alcoholic fermentation by-products were 2844 and 4664 mg/ethanol dm3 for fermented mashes from extruded and non-extruded rye respectively. Maximum differences fixed for isoamilol, 2-phenylethanol and isobutanol. Differences in concentration of volatile acids, esters and aldehydes were not significant. According to fermentation results, extrusion of rye on cooking stage was shown to improve biochemical parameters of further fermentation such as high ethanol concentration and its yield, low concentration of alcoholic fermentation by-products.
Keywords: ethanol production, rye, extrusion, bioconversion, very high gravity fermentation, enzyme, viscosity, ethanol yield, by-products of alcoholic fermentation.