Ispitivanje različitih hibrida kukuruza kao sirovine za proizvodnju bioetanola, skroba i hrane za životinje / Investigation of various maize hybrids for bioethanol, starch and animal feed production

Bioethanol is a biofuel that is mostly used as a replacement for fossil fuels worldwide. Trends of producing this alternative fuel are rising and maize is one of the best renewable raw materials for the production of fuel ethanol due to the high content of starch in the grain. Major by-product that arises from the fermentation process of corn is dried distillers’ grains with solubles (DDGS). Due to its high feeding value, high protein and other valuable nutrients it represents an excellent component for livestock feed mixtures. Corn grain wet milling process produces apart from corn starch, which is the main product of great importance to the food and other industries, valuable byproducts, which may also find their applications in human and animal nutrition. In the theoretical part of this dissertation a comprehensive overview of global trends in the production of bioethanol was made. State of the art technologies of corn grain processing used in the production of this alternative fuel and starch, as well as innovations that are being developed in order to improve the efficiency and costeffectiveness of these production processes were introduced. Hybrids created in the Maize Research Institute "Zemun Polje" represent unique starting material for research of the possibilities of bioethanol, starch and animal feed production. The aim of this study was to, starting from different physical properties and chemical composition of standard and specialty hybrids of different genetic background, determine how and in which level do the grain characteristics affect the yield and quality of the final products. The physical and chemical properties of grain corn hybrids were investigated. The optimization process of enzymatic hydrolysis and fermentation of whole grain flour obtained from the selected maize hybrids by using thermostable enzyme α-amylase Termamyl SC and glucoamylase SAN Extra L, as well as the production microorganism - yeast Saccharomyces cerevisiae var. ellipsoideus was conducted. Under optimal reaction conditions (ratio of corn flour and water 1:3, the concentration of α-amylase Termamyl SC 0.02% (v/w), glucoamylase SAN Extra L 0.12% (v/w) and inoculum concentration of Saccharomyces cerevisiae var. ellipsoideus 2% (v/v), fermentation temperature 30˚C) adequate fermentation time for the modified process of simultaneous saccharification and fermentation (SSF) was determined (36h) in order to obtain a higher yield of ethanol as well as electricity savings. Maximum ethanol yields that can be achieved by fermentation of certain hybrids were determined. Highest ethanol yield (94.5% of theoretical content) was obtained from whole grain flour of hybrid ZP 434 in the separate hydrolysis and fermentation process (SHF), and it was concluded that higher bioethanol yields can be achieved on standard hybrids in regard to the specialty hybrids. Statistical analysis based on calculated correlation coefficients examined a link between certain physical and chemical parameters and ethanol yield. It was concluded that bioethanol yield was influenced by different factors. Chemical composition and physical properties of the whole kernel as well as other process parameters influenced the overall bioethanol yield. According to chemical composition and digestibility analysis of dried distillers’ grains with solubles (DDGS), it was found that all samples meet the quality requirements of the components of animal feed and can be used in complete and concentrated feed mixtures. Technological characteristics of corn grain wet milling process of the selected hybrids, i.e. the yield and quality of starch, as well as by-products (bran, gluten, germ, steep water and process water). In addition, amylose and amylopectin content, i.e. amylose and amylopectin ratio of the starches yield isolated from different maize genotypes were determined. Based on calculations, energy values of ethanol that can be obtained from one kilogram of maize, or combustion energy, of whole grain, certain components of grain, corn cobs and DDGS, it was determined that these products are rich in energy which indicates their quality and potential use of maize as energy source. Based on the average costs of production per acre of corn grain, and total ethanol production costs, potential incomes from the sale of by-products of this fuel, evaluation the feasibility of bioethanol production compared to corn per hectare of arable land and per kilogram of maize in Serbia was conducted. It was found that profit from one liter of ethanol would be higher than from one kilogram of corn grain. However, because production of one liter of ethanol requires on average 2.5 kg of corn grain, according to calculations it can be concluded that production of corn grain per hectare of arable land would be more profitable in our country.