Andreja Goršek

Cultivating conditions effects on kefiran production by the mixed culture of lactic acid bacteria imbedded within kefir grains

The influence of fermentation temperature, agitation rate, and additions of carbon sources, nitrogen sources, vitamins and minerals on production of kefiran by kefir grains lactic acid bacteria was studied in a series of experiments. The main aim of the work was to increase the exopolysaccharide (EPS) production where customised milk was used as fermentation medium. It was proved that the controlling of culturing conditions and the modifying of fermentation medium conditions (i.e., carbon, nitrogen, mineral sources and vitamins) can dramatically enhance the production of the EPS. The temperature and agitation rate were critical for kefiran production during the 24 h cultivation of grains; our optimised conditions being 25°C and 80 rpm, respectively. In addition, when optimising the effects of additional nutrition, it was found that 5% (w/v) lactose, 0.1% (w/v) thiamine, and 0.1% (w/v) FeCl3 led to the maximal production of EPS. The results indicate that nutrients can be utilised to improve the production of EPS and that good kefir grains growth does not appear to be a determining factor for a high production yield of EPS.

Soy-based adhesives for wood-bonding – a review

Abstract Over recent years, the interest in bio-adhesives, including soy-based adhesives, has increased rapidly. Among natural renewable resources suitable for industrial use, soy is a reasonable choice due to its high production volume and the small use of soy meal-based products for human food consumption. Soy flour can be an ideal raw material for the manufacturing of wood adhesives due to its low cost, high protein content and easy processing. There are also more concentrated forms of soy proteins, i.e. concentrates and isolates, which are also suitable raw materials for adhesive production except that their prices are higher. Extensive research has been carried out on improving the cohesive properties, especially water resistance, of soy-based adhesives. However, there is insufficient experimental data available for understanding the influences of modification methods on the structure of soy proteins and therefore for understanding the influences of structural changes on the adhesion. In this paper, some experimental techniques are proposed to be used for analysing soy-based adhesives to enable better understanding of those factors and improve future development. This review of soy-based adhesives is made with the focus on soy proteins’ chemical composition, soy protein product types (raw materials for adhesive production), modification methods for improving the adhesive properties of soy-based adhesives, and commercial soy-based adhesives.

Quantitative Examination of Process Parameters during Kefir Grain Biomass Production

This article examines the propagation of kefir grains in fresh HTP whole fat cows’ milk, with some additions (glucose and bakers yeast). The objective of our work was an experimental determination of the various process parameters relative influence on the propagation and daily kefir grain increase mass, using the Taguchi method for experimental design. The effects of medium temperature, glucose mass concentration, bakers yeast mass concentration and the rotational frequency of the stirrer at four levels were studied. Orthogonal array layout of L16 was selected for the proposed experimental design. All experiments were performed in an automated laboratory reaction calorimeter RC1 (Mettler-Toledo) with the same milk (3.5 % fat). The gravimetric method was used to determine daily kefir grain mass increases. Relative contributions of the proposed influencing process parameters on the daily kefir grains increase mass were estimated by analysis of the variance (ANOVA). The highest increase (51.5 %) was found at the rotational frequency of the stirrer 90 (1/min), at glucose mass concentration 20 g/L, and at medium temperature 24 ◦C. Within the observed range of yeast mass concentration this process parameter was found to be insignificant compared to others. The rotational frequency of the stirrer has the highest relative influence on the daily kefir grains increase mass (37.3 %) while glucose mass concentration and medium temperature have lower ones, 18.8 % and 9.9 %, respectively. The remaining fraction represents error influence. The main reason for its relatively high value (34.0 %) is that kefir grains are bulky and awkward to handle. This fact confirms the importance of optimal kefir grains production management.

Ultrafiltration of oil-in-water emulsion by using ceramic membrane: Taguchi experimental design approach

In this study, a Taguchi experimental design methodology was used to determine the importance of process parameters influencing the ultrafiltration (UF) of oil-in-water emulsions. Four parameters including pH (5–11), oil concentration (φ) (0.5–3% (v/v)), temperature (T) (25–45°C) and trans-membrane pressure (TMP) (1–5 bar) were studied at three levels. The highest flux was used as optimization criterion. In order to reduce the number of experiments, a Taguchi method was applied. Analysis of variance (ANOVA) was used to determine the most significant parameters affecting the optimization criterion.Filtration experiments were performed in a cross-flow operation at a total recycle condition in a laboratory-scale plant. The ceramic UF membrane with a pore size of 50 nm was employed in a tubular module with an active area of 0,418 m2. We used water-soluble cutting oil mixed with water as a model oil-in-water emulsion. During the experiment, the drop size and zeta potential distributions were evaluated.The optimum conditions for UF providing the highest flux were found at TMP = 5 bar, pH = 7, and φ = 0.5 v/v%. The pH of emulsion had the highest impact on COD retention. The results of this study could be used as a guideline for operating UF systems with ceramic membranes at optimal conditions.

Testing the corrosion resistance of stainless steels during the fermentation of probiotic drink.

BACKGROUND Over recent years, food producers have devoted much attention to the production of safe foods. Simultaneously, using advanced process technologies, it has been necessary to carefully select materials for use in process equipment. Milk and its products are exposed to metal surfaces from the time they are processed, through the various stages of handling and manufacture, to the packaging of the finished products for market. The selection of suitable materials for daily use in the dairy industry cannot be governed solely by their price and mechanical properties but must also take into consideration their influence on the quality of milk products. RESULTS This paper presents the results of testing the corrosion resistance of three stainless steels during the fermentation of a specific probiotic drink, kefir. Experiments were conducted using preliminarily activated kefir grains as a starter culture. Corrosion resistance was studied using a gravimetric and two electrochemical methods. The two steels showing the best corrosion performance differed mainly in their Mo and Nb contents. CONCLUSION The results indicated that Nb played the most protective role against corrosion during kefir fermentation, since the steel containing Nb but no Mo showed the lowest corrosion rate.

Bonding of densified beech wood using adhesives based on thermally modified soy proteins

The bondability/glueability of aged and sanded thermo-hydro-mechanically (THM) densified beech wood (Fagus sylvatica L.) was tested and compared with undensified sanded beech wood as a control. THM and control specimens were bonded with five different soy protein isolate (SPI) based adhesives. Commercial SPI powder was thermally modified in the vacuum chamber at 50 or 100 °C and pH adjusted (to pH 10.0) dispersions in water prepared at 24, 50 or 90 °C. Wettability was determined with measuring the sessile drop contact angles of water. Effective penetrations (EPs) and tensile shear strengths of THM and control specimens were determined. THM and control wood had similar wettability. Although THM wood had lower moisture content than control wood, it absorbed the water more slowly than control wood. THM specimens showed lower EPs than control specimens when comparing individual adhesives due to increased density of THM wood. Adhesives prepared with SPI thermally modified at 50 °C showed statistically significantly lower tensile shear strength of bonded THM specimens than that of bonded control specimens. THM densification had no significant effect on the bonding strengths of adhesives prepared with non-modified SPI and SPI thermally modified at 100 °C.

Kinetic modeling of benzoic acid esterification using functionalized silica gel

ABSTRACT In our study, we synthesized two types of solid acid catalysts. Silica gel with a particle size of 0.063–0.2 mm was silanized first at reflux (S1) and second at room temperature (S3) using (3-mecaptopropyl)trimethoxysilane in toluene, and further oxidized with H2O2, and methanesulfonic acid. Characterization of the synthesized catalysts was performed using adsorption/desorption of nitrogen (BET), Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Both catalysts were used in esterification reactions of benzoic acid with methanol. All reactions were performed in a batch reactor at temperatures, ϑ = 55, 60, and 64.5°C, stirrer speed, fs = 400 min−1, and catalyst loading, m = 5, 10, and 15 g. The concentration of produced methylbenzoate was determined by HPLC. The study was supplemented with a kinetic study of the reaction. First-order kinetics was confirmed for this esterification reaction. Using catalyst S1, higher conversion was reached, while catalyst S3 is much more suitable for reuse.

OXIDATION OF MENTHOL: REACTION-RATE DETERMINATION BASED ON THERMODYNAMIC PROFILES

This study investigated the reaction kinetics of menthol oxidation. For this purpose the thermal profiles obtained from the measurements within the reaction calorimeter were used for the first time. In our case the reaction was performed under isothermal conditions using potassium dichromate as a catalyst. Due to the low solubility of menthol in water, acetone was added to the diluted sulfuric acid as a co-solvent. This caused the reaction medium to become more homogeneous and thus more appropriate for kinetic analyses without considering a mass transfer term.

Mathematical model of CO2 release during milk fermentation using natural kefir grains: Modeling CO2 release during milk fermentation

BACKGROUND Milk fermentation takes place in the presence of various micro-organisms, producing a variety of dairy products. The oldest of them is kefir, which is usually produced by the fermentation of milk with kefir grains. Carbon dioxide (CO2 ), as one of the process products, also contributes to the characteristic flavor of kefir. The amount of CO2 generated during fermentation depends on bioprocessing conditions and may change, which is not desirable at the industrial level. RESULTS In this study we developed a simplified mathematical model of CO2 release in the milk-fermentation process. An intuitive approach based on superposition and experimental analysis was used for the modeling. The chemical system studied was considered as a two-input (temperature, rotational frequency of the stirrer) one-output (CO2 concentration) dynamic system. CONCLUSION Based on an analysis of CO2 release transients in the case of non-simultaneous stepwise changed input quantities, two differential equations were defined that describe the influence of the two input quantities on the output quantity. The simulation results were verified by experiments. The proposed model can be used for a comprehensive analysis of the process that is being studied and for the design and synthesis of advanced control systems, which will ensure a controlled CO2 release at the industrial level.

Proteinska lepila na osnovi soje, krvi in kazeina nekoč in danes

V clanku je podan pregled razvoja proteinskih lepil na osnovi soje, krvi in kazeina. Clanek obravnava formulacije in tehnologije lepljenja teh proteinskih lepil iz obdobja 1930-1960 ter danasnje komercialne formulacije. V tem obdobju so bile namrec poraba ter tehnoloske izboljsave proteinskih lepil na vrhuncu. Pri obravnavi danasnjih formulacij in tehnologij lepljenja je poudarek na sojinih lepilih, saj se le-ta uporabljajo v industriji lepljenja dekorativnih vezanih, ivernih in vlaknenih plosc ter parketa. Kazein se danes uporablja le se v lepilih za protipožarna vrata, medtem ko se živalska kri v lepilih ne uporablja vec. Proteinska lepila iz obdobja 1930%1960 sicer ne ustrezajo zahtevam danasnjih standardov in se zato vec ne uporabljajo, so pa vse opisane tehnologije se vedno uporabne in se lahko ponovno uvedejo, ce bodo svetovni viri nafte usahnili.