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In recent decade, there have been observed extreme variations in climatic conditions which in combination with inadequate agro techniques lead to decreased quality of mercantile wheat, actally flour. The application of improvers can optimise the quality of substandard wheat flour. This paper focuses to systematic analysis of individual and interaction effects of ascorbic acid and transglutaminase as dough strengthening improvers. The effects were investigated using the Response Surface Methodology. Transglutaminase had much higher linear effect on the rheological and fermentative properties of dough from substandard flour than L-ascorbic acid. Both transglutaminase and L-ascorbic acid additions had a significant linear effect on the increase of bread specific volume. Effects of transglutaminase and ascorbic acid are dependent on the applied concentrations and it is necessary to determine the optimal concentration in order to achieve the maximum quality of the dough and bread. Optimal levels of tested improvers were determined using appropriate statistical techniques which applied the desirability function. It was found that the combination of 30 mg/kg of transglutaminase and 75.8 mg/kg of L-ascorbic acid achieved positive synergistic effect on rheological and fermentative wheat dough properties, as well on textural properties and specific volume of bread made from substandard quality flour.

The pollution caused by the use of fossil fuels for the production of mechanical or electrical energy is one of the most important environmental issues nowa­days. In this respect, biofuels represent a viable source of energy. Bioethanol as a renewable energy source is derived from organic material of plant origin, so-called biomass, thus reducing environmental pollution. The aim of this study was to analyze the potential of bioethanol in meeting future energy demands in the Republic of Serbia. [Projekat Ministarstva nauke Republike SRbije, br. TR31002: The improvement of bioethanol production from sugar beet processing products]

In this paper the bioethanol production in batch culture by free Saccharomyces cerevisiae cells from thick juice as intermediate product of sugar beet processing was examined. The obtained results suggest that it is possible to decrease fermentation time for the cultivation medium based on thick juice with starting sugar content of 5-15 g kg-1. For the fermentation of cultivation medium based on thick juice with starting sugar content of 20 and 25 g kg-1 significant increase in ethanol content was attained during the whole fermentation process, resulting in 12.51 and 10.95 dm3 m-3 ethanol contents after 48 h, respectively. Other goals of this work were to investigate the possibilities for experimental results prediction using artificial neural networks (ANNs) and to find its optimal topology. A feed-forward back-propagation artificial neural network was used to test the hypothesis. As input variables fermentation time and starting sugar content were used. Neural networks had one output value, ethanol content, yeast cell number or sugar content. There was one hidden layer and the optimal number of neurons was found to be nine for all selected network outputs. In this study transfer function was tansig and the selected learning rule was Levenberg-Marquardt. Results suggest that artificial neural networks are good prediction tool for selected network outputs. It was found that experimental results are in very good agreement with computed ones. The coefficient of determination (the R-squared) was found to be 0.9997, 0.9997 and 0.9999 for ethanol content, yeast cell number and sugar content, respectively.

Methods that can provide adequate accuracy in the estimation of variables from incomplete information are desirable for the prediction of fermentation processes. A feed-forward back-propagation artificial neural network was used for modelling of thick juice fermentation. Fermentation time and starting sugar content were usedas input variables, i.e. nodes. Neural network had one output node (ethanol content, yeast cell number or sugar content). The hidden layer had nine neurons. Garson's algorithm and connection weights were used for interpreting neural network. The inadequacy of Garson's algorithm can be seen by comparing with the results of regression analysis, which indicates that the influence of the fermentation time is higher. A better agreement of the results was obtained using network connection weights, a method that can be used to determine the relative importance of input variables.

The present study examines xanthan production by Xanthomonas campestris under aerobic conditions on spent grains liquor based cultivation media containing four different amounts of maltose. All four experiments were performed simultaneously, so that all stages of the biotechnological process would be carried out under identical conditions. In addition to the cultivation parameters (pH value, contents of dissolved oxygen, reducing sugars and assimilable nitrogen, turbidity and trickling time), xanthan yield and sugar conversion percentage were also determined. Based on the results of the experiments maltose addition up to 5% to spent grains liquor does not hinder the cultivation course. On the other hand, the conversion of sugars into xanthan decreases with the increase of maltose content to 5% and a large amount of sugars lags in the cultivation broth.

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.

Cell immobilisation in alcoholic fermentation has been extensively studied during the past few decades because of its technical and economical advantages over those of free cell systems. A biocatalyst was prepared by immobilising a commercial Saccharomyces cerevisiae strain (baker yeast) on corn stem ground tissue for use in alcoholic fermentation. For this purpose, the yeast cells were submitted to the batch tests 'in situ' adsorption onto pieces of the corn stem ground tissue. Cells immobilisation was analysed by optical microscopy. It was determined that the addition of the corn stem ground tissue led to an increase of the pH value, total dissolved salts content, and sugar content in fermentation medium. The addition of 5 and 10g of the corn stem ground tissue per liter of medium, increased ethanol yield, decreased amount of residual sugar and the cells immobilisation was effective. Corn stem is one of the abundant, available, inexpensive, stable, reusable, nontoxic celulosic biomaterial with high porosity, which facilitates the transmission of substrates and products between carrier and medium. The prepared immobilised biocatalyst showed higher fermentation activity than free cells. The results indicate that corn stem might be an interesting support for yeast cell immobilisation, and also a cheap alternative recourse of mineral components with possibility of application for improving ethanol productivities.

The need to freeze dough is increasing in bakery production. Frozen dough can be stored for a long time without quality change. The capacity of bakery production can be increased in this way, and in the same time, the night shifts can be decreased. Yeast cells can be damaged by freezing process resulting in poor technological quality of dough after defrostation (longer fermentation of dough). The influence of frozen storage time of dough on survival percentage of Saccharomyces cerevisiae was investigated. Dough samples were taken after 1, 7, 14 and 28 days of frozen storage at -20°C. After defrosting, at room temperature, samples were taken from the surface and the middle part of dough (under aseptic conditions), and the percentage of living S. cerevisiae cells was determined. During frozen storage of dough, the number of living S. cerevisiae decreased. After 28 days of frozen storage, the percentage of live cells on the surface and inside the dough was 53,1% and 54,95%, respectively. The addition of k-carragenan to dough increased the percentage of living cells in the middle part of dough up to 64,63%. Pure cultures, isolated from survived S. cerevisia cells in frozen dough by agar plates method (Koch's method), were multiplied in optimal liquid medium for yeasts. The content of cytochromes in S. cerevisiae cells was determined by spectrophotometric method. The obtained results showed that the content of cytochromes in survived S. cerevisiae cells was not affected by dough freezing process. Growth rate and fermentative activity (Einchor's method) were determined in multiplied cells.

Processing parameters of Kantata wheat variety indicate that it is not suitable for bread making. Therefore, an investigation was carried out to evaluate the suitability of the variety for ethanol production. Wheat was cultivated at the following sites: Kovin, Zrenjanin, Pančevo and Vrbas. Ethanol yields depend on the location on which the samples were grown and on the temperature during thermal and enzymatic preparation of flour samples. Wheat sample cultivated on the Vrbas site gave the highest ethanol yield.

Dough samples with different content of amylases were investigated immediately after mixing and after 7, 14 and 30 days of frozen storage. The obtained results show that the fermentation time is shorter, both in fresh and frozen samples, when amylase sample 1 was added, compared to dough without enzymes. The addition of amylase 2 to dough resulted in minimal decrease of "rising" time, both is frozen and fresh dough samples. The rising time of fresh samples was shorter when amylase 3 was added to dough. The specific fermentative activity of fresh dough samples is increasing by about 10% compared to the control sample, for all amounts of amylase 1 and 2 added to the do- ugh. The fermentative activity of yeast in frozen samples increased by 5-10%, after keeping of dough with the addition of amylase 1 for 14 days. The specific fermentative activity of fresh dough samples increased compared to the control, for all amounts of added amylase 3 to the dough. In frozen dough samples the fermentative activity of yeast decreased by 10% for all added amounts of amylase 3. Baked goods made of fresh and frozen dough, prepared with the addition of amylase 1, are better than the ones made of control dough sample, considering all evaluated parameters.

The highest amount of zinc (= 90%) is bound after 3 hrs of contact at low initial (total) concentrations of zinc in suspension of yeast, 10-100 mg/l at 10-30°C. The equilibrium between bound and free zinc ions is established after 6 hrs of contact time, independently on the total zinc concentration in yeast milk. No bigger changes of content of zinc bound to brewer's yeast cells was determined at temperatures 10°C and 30°C. 40% of bound zinc in the equilibrium state is bound during the first 15 min of contact of zinc ions and brewer's yeast cells at all initial (total) zinc concentrations in suspension of yeast both at 10°C and 30°C. The "KEKAM" equation can be used for the description of kinetics of zinc biosorption by waste brewer's yeast cells, for the ranges of zinc concentration 10-100 mg/l at 30°C (mean correlation coefficient 0,96) and 60,0-100 mg/l at 10°C (mean correlation coefficient 0,95).

The waste brewer's yeast S. cerevisiae (activated and non-activated) was compared with the commercial baker's yeast regarding the volume of developed gas in dough, volume and freshness stability of produced bread. The activation of waste brewer's yeast resulted in the increased volume of developed gas in dough by 100% compared to non-activated brewer's yeast, and the obtained bread is of more stable freshness compared to bread produced with baker's yeast. The activation of BY affects positively the quality of produced bread regarding bread volume. The volume of developed gas in dough prepared with the use of non-activated BY was not sufficient, therefore, it should not be used as fermentation agent, but only as an additive in bread production process for bread freshness preservation. Intense mixing of dough results in more compressible crumb 48 hrs after baking compared to high-speed mixing.