Stevan D. Popov

Bioethanol production from intermediate products of sugar beet processing with different types of Saccharomyces cerevisiae

The use of biofuels as an alternative to fossil fuels has expanded in the last few decades. The aim of this study was to examine the application of different strains and forms of Saccharomyces cerevisiae for raw, thin and thick juice fermentation in order to produce bioethanol. According to the obtained results the strain applied in the form of pressed blocks with 70 % w/w moisture, attained higher value of the specific growth rate and lower value of ethanol yield in comparison with strains applied in dried form. In all culture media attained efficiency of sugar utilization was at least from 98-99 % w/w. Maximum productivity was achieved around 30th hour of fermentation and amounted ≈1.8 g l¹ h¹ for all applied yeast strains. Therefore, optimal duration of the process in technical and economic terms should be considered.

Process model and economic analysis of ethanol production from sugar beet raw juice as part of the cleaner production concept.

The batch fermentation process of sugar beet processing intermediates by free yeast cells is the most widely used method in the Autonomous Province of Vojvodina for producing ethanol as fuel. In this study a process and cost model was developed for producing ethanol from raw juice. The model can be used to calculate capital investment costs, unit production costs and operating costs for a plant producing 44 million l of 99.6% pure ethanol annually. In the sensitivity analysis the influence of sugar beet and yeast price, as well as the influence of recycled biomass on process economics, ethanol production costs and project feasibility was examined. The results of this study clearly demonstrate that the raw material costs have a significant influence on the expenses for producing ethanol. Also, the optimal percentage of recycled biomass turned out to be in the range from 50% to 70%.

Investigation of kinetics of zinc biosorption by Saccharomyces cerevisiae cells

The highest amount of zinc (approximately 90%) is bound after 3 h of contact at low initial (total) concentrations of zinc in yeast broth, 2.0-16.0 g/l at 10-30 degrees C. The equilibrium between bound and free zinc ions is established after 6 h of contact time, independently on total zinc concentration in yeast milk. No bigger changes of content of zinc bound to yeast cells was determined at 10 degrees C and 30 degrees C. 40% of bound zinc in the equilibrium state is bound during the first 15 min of contact of zinc ions and yeast cells at all initial (total) zinc concentrations in yeast milk both at 10 degrees C and 30 degrees C. The KEKAM (Kolmogorov-Erofeev-Kozeeva-Avrami-Mampel) equation can be used for the description of kinetics of zinc biosorption by yeast cells, for the ranges of zinc concentration of 2.0-16.0 g/l at 30 degrees C (mean correlation coefficient 0.96) and 10.0-16.0 g/l at 10 degrees C (mean correlation coefficient 0.95).

The application of natural organic compounds in bakery industry

Investigations include the analysis of the impact of commercial products: complex additive (0.1, 0.3, and 0.5%), L-ascorbic acid (0.002, 0.004 and 0.012%), diacetyl ester of tartaric acid with monoglycerides (DATEM E472e, 0.1, 0.3, and 0.5%), α-amylase (0.002, 0.006 and 0.012%), xylanase (0.004, 0.012 and 0.024%), alcohol extract of rosemary, thyme or sage (0.5, 1.0 and 2.0%), as well as the combination of complex additive and rosemary, thyme and sage extract on rheological characteristics of dough. The study includes amylograph, farinograph and extensograph analysis of dough with and without additives (control sample). The volume of lost CO2 gas (mL) is the lowest in dough samples with an added combination of complex additive and thyme extract (0.05 and 0.5%) and rosemary extract (2.0%). In the samples with thyme extract (1.0%) added, the volume of lost gas is at a level of samples with added complex additive, DATEM, and L-ascorbic acid.

Sensory and Color Characteristics of Frozen Ready-Made Sauces

The paper presents the results of investigation of the replacement of imported emulsifiers, which are in use with plant protein products e.g. soybean isolate >> SUPRO 500 E << as well as the use of microbiologic preparation like brewery yeast in combination with maltodextrin, aiming to investigate the sensory and color characteristics of frozen ready-made sauces. Color characteristics of investigated samples were defined by photoelectric tristimulus colorimeter Minolta CR 300. Regarding the obtained values it can be concluded that no color change was estimated neither after preparation, nor after 180 days of frozen storage and microwave defrosting, depending on the composition of sauces and applied packaging. Freezing, storage, and microwave defrosting affect the change of certain sensory characteristics (layering and homogeneity), and this reffers to the second group of samples in the first place.