Statistical Optimization of Xanthan Gum Production and Influence of Airflow Rates in Lab-scale Fermentor

The present study was undertaken to investigate and optimize the possibility of xanthan gum production by Xanthomonas campestris PTCC1473 in 500ml shake flasks on the second grade date palm. Using an experimental response surface methodology (RSM) coupled with a central composite design (CCD), three major independent variables (nitrogen source, phosphor source and agitation rate) were evaluated for their individual and interactive effects on biomass and xanthan gum production in submerged fermentation. The optimum conditions selected for gum production were 3.15 g.l-1 for nitrogen source, 5.03 g.l-1 for phosphor source, and 394.8 rpm for agitation rate. Reconfirmation test was conducted, and the experimental value obtained for xanthan production under optimum conditions was about 6.72±0.26 g.l-1, which was close to 6.51 g.l-1 as predicted by the model. A higher yield of biomass production was obtained at 13.74 g.l-1 for nitrogen source, 4.66 g.l-1 for phosphor source, and 387.42 rpm for agitation rate. In the next stage, scale-up from the shake flasks to the 1-L batch fermentors was carried. By using the optimum conditions for xanthan gum, the biomass and xanthan gum concentrations after 72h in three levels of air flow rate (0.5, 1 and 1.5 vvm) were obtained as 3.98, 5.31 and 6.04 g.l-1,and 11.32, 15.16 and 16.84 g.l-1, respectively. Overall, the second grade date palm seemed to exhibit promising properties that can open new pathways for the production of efficient and cost-effective xanthan gum

Statistical Optimization of Xanthan Gum Production and Influence of Airflow Rates in Lab-scale Fermentor

The present study was undertaken to investigate and optimize the possibility of xanthan gum production by Xanthomonas campestris PTCC1473 in 500ml shake flasks on the second grade date palm. Using an experimental response surface methodology (RSM) coupled with a central composite design (CCD), three major independent variables (nitrogen source, phosphor source and agitation rate) were evaluated for their individual and interactive effects on biomass and xanthan gum production in submerged fermentation. The optimum conditions selected for gum production were 3.15 g.l-1 for nitrogen source, 5.03 g.l-1 for phosphor source, and 394.8 rpm for agitation rate. Reconfirmation test was conducted, and the experimental value obtained for xanthan production under optimum conditions was about 6.72±0.26 g.l-1, which was close to 6.51 g.l-1 as predicted by the model. A higher yield of biomass production was obtained at 13.74 g.l-1 for nitrogen source, 4.66 g.l-1 for phosphor source, and 387.42 rpm for agitation rate. In the next stage, scale-up from the shake flasks to the 1-L batch fermentors was carried. By using the optimum conditions for xanthan gum, the biomass and xanthan gum concentrations after 72h in three levels of air flow rate (0.5, 1 and 1.5 vvm) were obtained as 3.98, 5.31 and 6.04 g.l-1,and 11.32, 15.16 and 16.84 g.l-1, respectively. Overall, the second grade date palm seemed to exhibit promising properties that can open new pathways for the production of efficient and cost-effective xanthan gum

Modelling of simultaneous effect of moisture and temperature on A. niger growth in solid-state fermentation

In the present work a two factorial design of experiments was applied to study the simultaneous effect of temperature and moisture on A. niger growth in the solid-state fermentation (SSF). The increase of water content to more than 55% at the temperatures 35 and 40degreesC decreases microorganism growth. The logistic model was used to calculate growth kinetic parameters at different levels of temperature and moisture in solid-state fermentation. Ratkowsky equation was used to express the effect of temperature on specific growth rate. Quadratic polynomials express relationship between moisture content and growth parameters (maximum biomass and maximum specific growth rate) of A. niger inoculated on steamed wheat bran. The highest value of mu(m) and X-m were 0.29 h(-1) and 0.22 g biomass g DW-1 at 35degreesC and 55%, respectively. (C) 2004 Elsevier B.V. All rights reserved

Design of ultrasonic probe and evaluation of ultrasonic waves on E.coli in Sour Cherry Juice

Introduction: The common method used for juice pasteurization is the thermal method since thermal methods contribute highly to inactivating microbes. However, applying high temperatures would lead to inefficient effects on nutrition and food value. Such effects may include vitamin loss, nutritional flavor loss, non-enzyme browning, and protein reshaping (Kuldiloke, 2002). In order to decrease the adverse effects of the thermal pasteurization method, other methods capable of inactivation of microorganisms can be applied. In doing so, non-thermal methods including pasteurization using high hydrostatic pressure processing (HPP), electrical fields, and ultrasound waves are of interest (Chen and Tseng, 1996). The reason for diminishing microbial count in the presence of ultrasonic waves could be due to the burst of very tiny bubbles developed by ultrasounds which expand quickly and burst in a short time. Due to this burst, special temperature and pressure conditions are developed which could initiate or intensify several physical and/or chemical reactions. The aim of this study is to evaluate the non-thermal ultrasonic method and its effective factors on the E.coli bacteria of sour cherry. Materials and methods: In order to supply uniform ultrasonic waves, a 1000 W electric generator (Model MPI, Switzerland) working at 20±1 kHz frequency was used. The aim of this study is to evaluate the non-thermal ultrasonic method and its effective factors on the E.coli bacteria of sour cherry. For this purpose, a certain amount of sour cherry fruit was purchased from local markets. First, the fruits were washed, cleaned and cored. The prepared fruits were then dewatered using an electric juicer. In order to separate pulp suspensions and tissue components, the extracted juice was poured into a centrifuge with the speed of 6000 rpm for 20 min. For complete separation of the remaining suspended particles, the transparent portion of the extract was passed through a Whatman filter paper using a vacuum pump (Mehmandoost et al., 2011). Afterwards, the samples were poured into a reactor with diameter and height of 80 and 50 mm, respectively. It is necessary to mention that the dimensions of the reactor were optimized during pretests. Probe design: One of the most common types of horns used for ultrasonic machining technologies is step type horn (Naď, 2010). For obtaining the governing equations on deformation along the step type horn in steady state conditions, Eq. (1) was used. In the solution of the mentioned differential equation, the answers are divided into two subsets and each of the answers is obtained considering the boundary conditions (Hosseinzadeh et al., 2013): (1) c^2.[(∂S/∂x)/(S(x)).(∂u(x,t))/∂x+(∂^2 u(x,t))/〖∂x〗^2 ]=(∂^2 u(x,t))/〖∂t〗^2 From Eq. (1), it can be concluded that: (2) u(x,t)=(A cos⁡〖ωx/c〗+B sin⁡〖ωx/c)(C cos⁡〖ωt+D sin⁡ωt 〗 〗) The boundary conditions for Eq. (2) are written as follows: (3) {■(a) (∂u(x))/∂x=0,x=0@b) (∂u(x))/∂x=0,x=l@c) u(0)=u_in )} One of the most important parts in probe design is preventing stress concentration in locations in which the area changes. To avoid this problem, the displacement in this section must be equal to zero (Hosseinzadeh et al., 2013). For obtaining the probe length, the displacement equation and the l1 parameter are used: σ=-E.u_in.ω/c.sin⁡〖(ω.x)/c〗 (4) In order to determine the maximum axial stress in step type probe, Eq. (3) and (4) are derived and set equal to zero. Therefore, the maximum stress will be equal to: σ_max=π.E.u_in/l (5) Optimization and Modeling using Response Surface Method: Response surface methodology (RSM) has an important application in the design, development and formulation of new products, as well as in the improvement of existing product designs. It defines the effect of the independent variables, alone or in combination, on processes. In addition, to analyzing the effects of the independent variables, this experimental methodology generates a mathematical model which describes the chemical or biochemical processes (Anjum et al., 1997, Halim et al., 2009). In order to obtain the optimum value, Eq. (1) will be used: (6) Y_i=β_0+∑▒〖β_i X_i+∑▒〖β_ij X_i X_j+〗〗 ∑▒〖β_ij X_i^2 〗+ε where, β0, βj, βij, βjj are regression coefficients for intercept, linear, interaction and quadratic coefficients, respectively, while Xi and Xj are coded independent variables and ε is the error. For this purpose, four factors of ultrasonic power (200 to 600 W), wave exposure time (5 to 15 min), probe diameter (20 to 40 mm), and probe penetration depth in sour cherry juice container (0 to 40 mm) were selected. First, the probes with the desired diameters were designed using the related formulas by using CAD-CAM. Results and Discussion: Surface Method (RSM) indicated that the quadratic model with 0.96 coefficient of friction, standard error of 1545.3, and coefficient of variation of 14% is the best model for estimating the number of E.coli bacteria among the different studied treatments. The results showed that with increasing probe diameter and probe depth, the destructive effects of ultrasonic wave increase. It was also revealed that as the probe diameter and penetration depth increase, the destructive effect of ultrasonic wave is initially increased and then follows by a decreasing trend. With the increasing power of ultrasonic, ultrasonic intensity increases and leads to reducing number of E.coli in sour cherry juice. The increase in time of treatment with ultrasonic causes a decrease in the number of E.coli in sour cherry juice. This is due to the fact that the increase of ultrasonic exposure time leads to the increase of sonic stream in reactor and results in higher contributions of ultrasonic waves to E.coli. Finally, the examined variables were optimized by RSM and the values of ultrasonic power, waves exposing time, probe diameter, and probe penetration depth were obtained as 600 W, 15 min, 35.31 mm, 20.83 mm, respectively. Considering the mentioned values, the amount of E.coli bacteria reduction was estimated to be 1.97 logarithmic period. Conclusions: 1. Increasing probe diameter and probe depth increasesthe destructive effect of ultrasonic wave. 2. The examined variables were optimized by RSM and the values of ultrasonic power, waves exposure time, probe diameter, and probe penetration depth were obtained as 600W, 15 min, 35.31 mm, 20.83 mm, respectively. Considering the optimum values, the amount of E.coli bacteria reduction was estimated to be 1.97 logarithmic period. 3. With the increasing power of ultrasonic waves, ultrasonic intensity increases and leads to a reduction of the number of E.coli in sour cherry juice. 4. The increase in time of treatment with ultrasonic causesa decrease in the number of E.coli in sour cherry juice

A two-phase kinetic model for fungal growth in solid-state cultivation

A new two-phase kinetic model including exponential and logistic models was applied to simulate the growth rate of fungi at various temperatures. The model parameters, expressed as a function of temperature, were determined from the oxygen consumption rate of Aspergillus niger during cultivation on wheat bran. The model can describe the whole growth curve including the lag phase and the cessation of growth in the latter stages of the cultivation with an adequate approximation. Furthermore, the model describes the growth rate of Aspergillus oryzae on wheat properly. Comparisons between the current, logistic and previous two-phase kinetic models indicate that the new model can predict growth rate of fungi more accurately