Murat Ozdemir

Active Food Packaging Technologies

Active packaging technologies offer new opportunities for the food industry, in the preservation of foods. Important active packaging systems currently known to date, including oxygen scavengers, carbon dioxide emitters/absorbers, moisture absorbers, ethylene absorbers, ethanol emitters, flavor releasing/absorbing systems, time-temperature indicators, and antimicrobial containing films, are reviewed. The principle of operation of each active system is briefly explained. Recent technological advances in active packaging are discussed, and food related applications are presented. The effects of active packaging systems on food quality and safety are cited.

Freeze-Drying of Pharmaceutical Products: Research and Development Needs

Significance of pharmaceutical formulation (choosing of correct excipients in optimal quantities), effects of glass transition temperature, importance of theoretical modeling of the process, benefits of optimal control, and the advantages of remote monitoring of the process are presented. Experimental and theoretical research and development needs for the freeze-drying of pharmaceutical products are proposed and discussed.

Application of gaseous ozone to control populations of Escherichia coli, Bacillus cereus and Bacillus cereus spores in dried figs

The effect of ozonation as a method to reduce Escherichia coli, Bacillus cereus and Bacillus cereus spores in dried figs was investigated. Dried figs were sprinkle inoculated with E. coli, B. cereus and B. cereus spores in sterile bags at a level of 10(7)microorganism g(-1), mixed and allowed to dry for 1h at 25 degrees C prior to ozonation. Inoculated samples were exposed to gaseous ozone in a chamber at 20 degrees C and 70% relative humidity. Ozone concentrations of 0.1, 0.5 and 1.0 ppm up to 360 min were used to inactivate E. coli and B. cereus while 1.0, 5.0, 7.0 and 9.0 ppm ozone concentrations for 360 min were used to treat B. cereus spores. E. coli and B. cereus counts were decreased by 3.5 log numbers at 1.0 ppm ozone concentration for 360 min ozone treatment. Up to 2 log reductions in the number of B. cereus spores were observed above 1.0 ppm ozone concentration at the end of 360 min of ozonation. No significant changes in color, pH and moisture content values of dried figs were observed after the ozonation treatments. No significant changes were found between sweetness, rancidity, flavor, appearance and overall palatability of ozonated and non-ozonated dried figs. Ozonation was found to be effective especially in reduction of vegetative cells in dried figs and a promising method for the decontamination of dried figs.

Optimal Control of the Primary Drying Stage of Freeze Drying of Solutions in Vials Using Variational Calculus

Abstract The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies.

Cross‐Linking of Starch with Reactive Extrusion and Expansion of Extrudates

Abstract Starch was extruded in a single‐screw extruder with sodium hydroxide and three levels of sodium trimetaphosphate (STMP) as 5, 10, and 15% after moisture content was adjusted to 40%. The amount of phosphorus that was incorporated into starch during extrusion, paste viscosity, water solubility index, and sectional expansion index (SEI) of extrudates were determined. A pasting viscosity of phosphorylated starch showed that starch was cross‐linked with phosphorus that was incorporated into starch. The cross‐linking of starch with STMP and increasing the levels of STMP from 5 to 15% reduced the water solubility index and SEI of extrudates.

Bactericidal Activity of Ozone against Escherichia coli in Whole and Ground Black Peppers

The effects of different ozone concentrations and ozonation times on the inactivation of Escherichia coli and on the organoleptic properties of whole and ground black peppers were determined. Black peppers were exposed to three different ozone concentrations (0.1, 0.5, and 1.0 ppm) for different periods (0 to 360 min) at 85% +/- 3% relative humidity (RH) and 25 +/- 0.5 degree C. An approximately 7-log CFU/g reduction of E. coli in whole black peppers was achieved by treating the samples with 0.1, 0.5, or 1.0 ppm of ozone for 360, 240, or 120 min, respectively. E. coli populations in ground black peppers were reduced from an initial count of about 7.5 log CFU/g to 1 log CFU/g after 360 min at 0.1- and 0.5-ppm ozone concentrations, whereas the same microbial reduction was obtained after 240 min at 1.0-ppm ozone concentration. An ozone concentration of 0.1 ppm for 360 min was found to be appropriate to inactivate E. coli in whole and ground black peppers without alteration of the organoleptic properties. No significant differences (P > or = 0.05) were present in the bitterness, flavor, odor, color, or overall acceptability values of the whole and ground black peppers treated with 0.1 ppm of ozone for up to 360 min.

Phosphorus binding to starch during extrusion in both single- and twin-screw extruders with and without a mixing element

The effect of a mixing element in single- and twin-screw extruders on the amount of phosphorus incorporated into starch was investigated for chemical modification of starch that has applications in the food and paper industries. Starch was mixed with sodium hydroxide and sodium trimetaphosphate and then the mixture was extruded. Screw speeds, which result in approximately the same residence time in both single- and twin-screw extruders with and without a mixing element, were determined. Screw speeds of 220 rpm in a single-screw extruder with a mixing element, 180 rpm in a single-screw extruder without a mixing element, and 160 rpm in a twin-screw extruder with and without a mixing element resulted in similar residence times. The presence of a mixing element did not have an effect on vessel dispersion number and flow pattern in the single-screw extruder but it affected vessel dispersion number and changed the flow pattern in the twin-screw extruder. The amount of phosphorus bound to starch did not increase with the mixing element in single- and twin-screw extruders for a constant mean residence time.

A Mathematical Model for Potassium Sorbate Diffusion Through Whey Protein Films

A mathematical model was constructed and solved to quantitatively describe the dynamic behavior of the potassium sorbate diffusion through whey protein films. The model results were compared with the experimental data of the potassium sorbate diffusion through whey protein films, and excellent agreements between the experimental data and the model results are observed. The experimental data for potassium sorbate diffusion through whey protein films were used for mathematical model of potassium sorbate diffusion through whey protein films and the determination of both potassium sorbate and solvent diffusion coefficients. The diffusivities of potassium sorbate at 25°C ranged from 4.12 to 9.34 × 10−11 m2/s, while that of the solvent was between 1.38 and 8.74 × 10−10 m2/s, depending on the film composition.

Mathematical modelling of temperature effect on growth kinetics of Pseudomonas spp. on sliced mushroom (Agaricus bisporus)

The growth data of Pseudomonas spp. on sliced mushrooms (Agaricus bisporus) stored between 4 and 28°C were obtained and fitted to three different primary models, known as the modified Gompertz, logistic and Baranyi models. The goodness of fit of these models was compared by considering the mean squared error (MSE) and the coefficient of determination for nonlinear regression (pseudo-R2). The Baranyi model yielded the lowest MSE and highest pseudo-R2 values. Therefore, the Baranyi model was selected as the best primary model. Maximum specific growth rate (rmax) and lag phase duration (λ) obtained from the Baranyi model were fitted to secondary models namely, the Ratkowsky and Arrhenius models. High pseudo-R2 and low MSE values indicated that the Arrhenius model has a high goodness of fit to determine the effect of temperature on rmax. Observed number of Pseudomonas spp. on sliced mushrooms from independent experiments was compared with the predicted number of Pseudomonas spp. with the models used by considering the Bf and Af values. The Bf and Af values were found to be 0.974 and 1.036, respectively. The correlation between the observed and predicted number of Pseudomonas spp. was high. Mushroom spoilage was simulated as a function of temperature with the models used. The models used for Pseudomonas spp. growth can provide a fast and cost-effective alternative to traditional microbiological techniques to determine the effect of storage temperature on product shelf-life. The models can be used to evaluate the growth behaviour of Pseudomonas spp. on sliced mushroom, set limits for the quantitative detection of the microbial spoilage and assess product shelf-life.

Computer vision system approach in colour measurements of foods: Part II. validation of methodology with real foods

The colour of food is one of the most important factors affecting consumers’ purchasing decision. Although there are many colour spaces, the most widely used colour space in the food industry is L*a*b* colour space. Conventionally, the colour of foods is analysed with a colorimeter that measures small and non-representative areas of the food and the measurements usually vary depending on the point where the measurement is taken. This leads to the development of alternative colour analysis techniques. In this work, a simple and alternative method to measure the colour of foods known as “computer vision system” is presented and justified. With the aid of the computer vision system, foods that are homogenous and uniform in colour and shape could be classified with regard to their colours in a fast, inexpensive and simple way. This system could also be used to distinguish the defectives from the non-defectives. Quality parameters of meat and dairy products could be monitored without any physical contact, which causes contamination during sampling.