Olgica S. Grujić

PROGRESS IN THE PRODUCTION OF BIOETHANOL ON STARCH-BASED FEEDSTOCKS*

Bioethanol produced from renewable biomass, such as sugar, starch, or lignocellulosic materials, is one of the alternative energy resources, which is both renewable and environmentally friendly. Although, the priority in global future ethanol production is put on lignocellulosic processing, which is considered as one of the most promising second-generation biofuel technologies, the utilization of lignocellulosic material for fuel ethanol is still under improvement. Sugar-based (molasses, sugar cane, sugar beet) and starch-based (corn, wheat, triticale, potato, rice, etc.) feedstock are still currently predominant at the industrial level and they are, so far, economically favorable compared to lingocelluloses. Currently, approx. 80 % of total world ethanol production is obtained from the fermentation of simple sugars by yeast. In Serbia, one of the most suitable and available agricultural raw material for the industrial ethanol production are cereals such as corn, wheat and triticale. In addition, surpluses of this feedstock are being produced in our country constantly. In this paper, a brief review of the state of the art in bioethanol production and biomass availability is given, pointing out the progress possibilities on starch-based production. The progress possibilities are discussed in the domain of feedstock choice and pretreatment, optimization of fermentation, process integration and utilization of the process byproducts.

The bioethanol production with the thin stillage recirculation.

In this paper, the bioethanol production with the thin stillage recirculation in mashing was investigated. The mashing was performed with recirculation of: 0, 10, 20 and 30 % of the thin stillage. The thin stillage recirculation was repeated six times. In the experiment without the thin stillage, the recirculation bioethanol yield (compared to the theoretical yield) was 97.96 %, which implicates that the experiment conditions were chosen and performed well. With the addition of the thin stillage, the bioethanol yield increased and was above 100 %. Higher bioethanol yield than 100 % can be explained by the fact that the thin stillage contains carbohydrates, amino acids and yeast cells degradation products. The bioethanol yield increased with the increased number of thin stillage recirculation cycles. Dry matter content in fermenting slurry increased with the increased thin stillage quantity and the number of the thin stillage recirculation cycles (8.04 % for the first and 9.40 % for the sixth cycle). Dry matter content in thin stillage increased with the increased thin stillage quantity and the number of thin stillage recirculation cycles. Based on the obtained results it can be concluded that thin stillage recirculation increased the bioethanol yield. The highest bioethanol yields were obtained with recirculation of 10% thin stillage.

CONVENTIONAL AND ALTERNATIVE PRINCIPLES FOR STABILIZATION OF PROTEIN AND POLYPHENOL FRACTIONS IN BEER

Beer haze is primarily formed through complexation of protein and polyphenolic beer ingredients. The problem of reducing susceptibility of beer haze formation can be done either by lowering protein and/or polyphenol levels, or by minimizing the molecular size of protein/polyphenols. In experimental part of this work the shelf life of unstabilized beer is being compared with beer stabilized with various standard products, such as PVPP and silica gel. Furthermore, the trials have been made to prove the functionality of a new product consisting of carrageenan and cross-linked PVPP. The method used to determine shelf life was haze forcing test (0/60°C). Extract, alcohol, bitterness, foam, haze, color and pH were also monitored. The test results showed expectedly that combined treatment of beer ensures the highest level of product stability. Through selective stripping of polyphenols and protein fractions it is possible to improve shelf life of beer to a significant extent.

The influence of technological parameters on malt quality produced from different triticale varieties.

The analysis of eight different triticale varieties, from selective experiments, crop 2007, from Rimski Sancevi (Serbia) location was performed. On the basis of results obtained from triticale and produced triticale malt analysis as well as during micromalting, technological quality of investigated triticale varieties was evaluated. The aim of the work was to determine if the gibberellic acid added during the germination phase had a positive influence on the degradation of triticale grain during micromalting. Based on the obtained results it was concluded that triticale variety has the most important influence on the quality of produced triticale malt.

Effect of yeast storage temperature and flour composition on fermentative activities of Baker's yeast.

Bakers yeast is a set of living cells of Saccharomyces cerevisiae. It contains around 70-72% of water, 42-45% of proteins, around 40% of carbohydrates, around 7.5% of lipids (based on dry matter), and vitamin B-complex. On the basis of yeast cell analysis it can be concluded that yeast is a complex biological system which changes in time. The intensity of the changes depends on temperature. Yeast sample was stored at 4°C i 24°C for 12 days. During storage at 4°C, the content of total carbohydrates decreased from 48.81% to 37.50% (dry matter), whereas carbohydrate loss ranged from 40.81% to 29.28% at 24°C. The content of trehalose was 12.33% in the yeast sample stored at 4°C and 0.24% at 24°C. Loss of fermentative activity was 81.76% in the sample stored at 24°C for 12 days. The composition of five samples of 1st category flour was investigated. It was found that flours containing more reducing sugars and maltose enable higher fermentation activities. The flours with higher ash content (in the range 0.5-0.94%) had higher contents of phytic acid. Higher ash and phytic contents in flour increased the yeast fermentative efficiency. In bakery industry, a range of ingredients has been applied to improve the products quality such as surface active substances (emulsifiers), enzymes, sugars and fats. In the paper, the effect of some ingredients added to dough (margarine, saccharose, sodium chloride and malted barley) on the yeast fermentative activity was studied. The mentioned ingredients were added to dough at different doses: 0.5, 1.0, 1.5 and 2.0%, flour basis. It was found that the investigated ingredients affected the fermentative activity of yeast and improved the bread quality.

THE INFLUENCE OF CARBOXYMETHYLCELLULOSE, XANTHAN AND GUAR-GUM ADDITION IN BREAD DOUGH BEFORE FREEZING ON METABOLISM AND VIABILITY OF Saccharomyces cerevisiae

Doughs were prepared with different concentrations of carboxymethylcellulose, xanthan, and guar-gum (0.1, 0.2 and 0.3% in doughs), freezed at -20°C and analyzed after 0, 7, 15 and 30 days. Pure Saccharomyces cerevisiae culture was isolated from dough and was cultivated under optimal conditions during 24 hrs to determine the following parameters: specific growth rate, fermentative activities and cytochromes contents in intact cells with the aim of determining the respiration intensity. During freezing of dough for 30 days, the percentage of living cells from dough surface was 53.11% and from the middle 54.95%. Carboxymethylcellulose in concentration of 0.3 and 0.5% increased number of survived cells on the surface to 70.64, and 70.28% and in the middle to 74.79, and 76.54%, respectively. Guar-gum increased number of survived cells only in concentration of 0.1% on the surface to 70.17% and in the middle of the dough to 75.26%. The mean specific growth rate decreased by approximately 10% during 30 days of storage at -20°C. Content of cytochromes in intact cells decreased in all samples during freezing.