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1.
Analysis of growth models for batch kefir grain biomass production in RC1 reaction system
Marko Tramšek, Andreja Goršek, 2008, original scientific article

Abstract: This work describes the statistical analysis of three mathematical models, modified for describing the kefir grain biomass growth curve. Experimental data of time-dependent kefir grain mass increase were used. The propagation was performed in RC1 batch reaction system under optimal bioprocess parameters (temperature, rotational frequency of stirrer, glucose mass concentration) using traditional cultivation in fresh, high-temperature, pasteurized whole fat cow's milk. We compared values of biological parameters obtained by applying the nonlinear regression of experimental data in logistic, Gompertz and Richards models. The most statistically appropriate model was determined using the seven statistical indicators. We established that the kefir grain biomass growth curve during batch propagation under optimal bioprocess conditions can be most successfully described using the Gompertz growth model.
Keywords: chemical processing, milk products, kefir grain growth, process parameters, design of experiments, modeling, mathematical models, Gompertz growth model, RC1
Published: 31.05.2012; Views: 1889; Downloads: 73
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2.
Kefir grains production - An approach for volume optimization of two stage bioreactor system
Andreja Goršek, Marko Tramšek, 2008, original scientific article

Abstract: The main objective of the present study was to design a continuous two-stage bioreactor system for kefir grains production. Based on the experimental data of time-depended kefir grain mass increase and average pH profile during kefir grains batch propagation, parameters of predictive growth and exponential pH models were initially estimated. Afterwards, the non-linear programming (NLP) optimization problem for estimating the optimal volumes of two unequal in series connected continuously stirred tank bioreactors (CSTB) has been developed. The NLP problem is based on criterion of minimal total holding time (MTHT), kefir grain mass balances in CSTB and parameters of the growth and pH models. The results showed that novel kefir grains production plant with two-stage continuous operation, at capacity, qm,KG,pr=3 kgh-1 and conversion, Xo,2=0.980, would primarily require investment in two CSTB with V1=5.93 m3 and V2=5.62 m3, respectively. Technological and economical authorization for a two-stage continuous bioreactor system was mainly confirmed with a more than five times lower total bioreactor volume compared to one-stage plant.
Keywords: chemical processing, bioprocesses, milk products, kefir grains production, bioreactor design, modeling, optimization
Published: 31.05.2012; Views: 1965; Downloads: 81
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3.
Quantitative examination of process parameters during kefir grain biomass production
Andreja Goršek, Marko Tramšek, 2007, short scientific article

Abstract: 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 mediumtemperature 24 °C. Within the observed range of yeast mass concentrationthis 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.
Keywords: chemical processing, milk products, kefir, kefir grain growth, process parameters, design of experiments, Taguchi method, RC1
Published: 31.05.2012; Views: 1694; Downloads: 33
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4.
Multi-criteria and econometric evaluation of dairy products
Karmen Pažek, Jernej Turk, Sebjan Hari, Črtomir Rozman, Jernej Prišenk, 2014, original scientific article

Abstract: This study examined the multi-criteria assessment of four dairy products: "Pomursko mlejko" (Pomurje milk), "Lejko mleko" (light milk), "Fyto mleko" (Fyto milk) and "Posneto mleko v prahu" (dried milk). The research was executed by using a multi-criteria methodology, DEX, which was complemented by an econometric analysis for light milk to estimate the trends in production and consumption before analyzed dairy products were implemented on the market. DEXi computer program results indicated that all analyzed milk products were 'above average'. The econometric model was applied to examine changes in the demand for low-fat milk (light milk). Empirical results showed significant consumer response to the increase in the prices of low-fat milk demonstrating income elasticity (1,15 unit).
Keywords: multi-attribute decision theory, DEXi, econometric analysis, milk products
Published: 10.07.2017; Views: 435; Downloads: 60
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