On the temporal stability of analyte recognition with an e-nose based on a metal oxide sensor array in practical applications

The paper deals with a functional instability of electronic nose (e-nose) units which significantly limits their real-life applications. Here we demonstrate how to approach this issue with example of an e-nose based on a metal oxide sensor array developed at the Karlsruhe Institute of Technology (Germany). We consider the instability of e-nose operation at different time scales ranging from minutes to many years. To test the e-nose we employ open-air and headspace sampling of analyte odors. The multivariate recognition algorithm to process the multisensor array signals is based on the linear discriminant analysis method. Accounting for the received results, we argue that the stability of device operation is mostly affected by accidental changes in the ambient air composition. To overcome instabilities, we introduce the add-training procedure which is found to successfully manage both the temporal changes of ambient and the drift of multisensor array properties, even long-term. The method can be easily implemented in practical applications of e-noses and improve prospects for device marketing

A Simplified Analytical Model for Thawing Time Calculation in Foods

A simplified analytical model for the thawing time prediction of simple-shaped foodstuffs was developed. It was assumed in the model that the solution to the unsteady state, unidirectional heat conduction equation with constant thermophysical properties was valid throughout the thawing operation. The latent heat effects were incorporated into effective diffusivity terms defined for the various phases of the thawing operation. The predictions of the model were compared to experimental and numerical data obtained on thawing of infinite slabs, infinite cylinders, and spheres. The level of agreement between the predictions of the present model, and the experimental and numerical data was quite satisfactory. Copyright © 1989, Wiley Blackwell. All rights reserve

A SIMPLIFIED ANALYTICAL MODEL FOR FREEZING TIME CALCULATION IN BRICK-SHAPED FOODS

A simplified analytical model for the freezing time prediction of brick-shaped foodstuffs was developed. It was assumed in the model that the solution to the unsteady, one-dimensional heat conduction equation with constant thermophysical properties was valid during cooling and freezing for each of the three directions of the brick-shaped food. Cooling and freezing times were calculated by superposition of the solutions of the unsteady, one-dimensional heat conduction equation with constant thermophysical properties for each direction. the latent heat effects were incorporated into an effective thermal diffusivity term. the predictions of the model were compared to the available experimental data on freezing of two- and three-dimensional bricks and to the experimental data obtained in this research for the freezing of ground beef and mashed potato bricks. Mean errors varying between -6.3% and 2.3%, and standard deviations from the mean being between 6.6% and 14.0% were obtained for the data sets considered. Copyright © 1989, Wiley Blackwell. All rights reserve

The effects of concentration on electrical conductivity of orange juice concentrates during ohmic heating

Ohmic heating is an alternative heating technique, using an electrical current passing through the food product. It can be specially used in pumpable food lines as an alternative heating unit. In this study, orange juice concentrates having 0.20-0.60 mass fraction soluble solids were ohmically heated by using five different voltage gradients (20-60 V/cm). The dependence of electrical conductivity on temperature, voltage gradient and concentration were measured. The ohmic heating system performance coefficients were calculated by using the energies given to the system and taken by the orange juice samples. The mathematical model results, taking system performance coefficients into account, were compared with experimental ones. The predictions of the mathematical model were found to be very accurate. © 2004 Springer-Verlag.2001/BIL/002 2001/MUH/03Acknowledgement This study was partially supported by Ege University Science-Technology Research and Application Center (EBILTEM) Project No: 2001/BIL/002, Ege University Scientific Projects Fund Project No: 2001/MUH/03, ETAP Agricultural and Food Products Packaging SA Turkey and Pinar Dairy Products SA Turkey. -

Determination of the optimum spray drying conditions of alpha-amylase and rennin solutions [alpha-amilaz ve peynir mayasinin (rennet) puskurtmeli kurutucuda optimum kurutma kosullarinin saptanmasi]

Optimum spray drying conditions of alpha-amylase and rennin solutions in a Mobile Minor Niro Atomizer was investigated for a feed rate of 40ml/min, the optimum inlet or outlet air temperature ranges were found to be 150-160 degreesC and 60-70 degreesC respectively. The moisture content of the enzyme powder obtained was 3-4%. The enzymatic activity of the dried product was found to depend on the retention time of the dried product in the product jar. To eliminate the undesired odor and moisture and to obtain a fluid product, Carboxy Methyl Cellulose and soluble starch, which have a coating effect were used. The use of these coating agents reduced the enzymatic activity loss, depending on the retention time in the product jar, to the level of 1%. (English summary

Electrical conductivity of apple and sourcherry juice concentrates during ohmic heating

Ohmic heating is based on the passage of electrical current through a food product that serves as an electrical resistance. In this study, apple and sourcherry concentrates having 20-60% soluble solids were ohmically heated by applying five different voltage gradients (20-60 V/cm). The electrical conductivity relations depending on temperature, voltage gradient and concentration were obtained. It was observed that the electrical conductivities of apple and sourcherry juices were significantly affected by temperature and concentration (P < 0.05). The ohmic heating system performance coefficients (SPCs) were defined by using the energies given to the system and taken up by the juice samples. The SPCs were in the range of 0.47-0.92. The unsteady-state heat conduction equation for negligible internal resistance was solved with an ohmic heating generation term by the finite difference technique. The mathematical model results considering system performance coefficients were compared with experimental ones. The predictions of the mathematical model using obtained electrical conductivity equations were found to be very accurate