The authors determined the location of the critical point for conduction heated food, involving simplified heat-treatment process. Infinite and finite cylinders have been investigated. Analytical method was applied to compute symmetrical temperatures. The spatial co-ordinates of the critical point were found by searching for the minimum of equivalent time (F-value), as microbial survival is the greatest in the critical point. The introduction of a z-value related dimensionless temperature enabled to extend similarity conditions for F-values. The locations of the critical points of species or attributes with diverse z-values differed in the same process. The most important factor influencing the critical point’s location was the difference between heating and initial food temperatures divided by the z-value. When this difference was sufficiently great, the critical point approached the geometric centre, but reached it only for the infinite cylinder. Decreasing difference shifted it towards the surface either along the axis, or in the median plane.
Authors:Gy. Pátkai, I. Körmendy, and A. Körmendy-Domján
Fibre-rich fruit juices are playing an increasing role in healthy nutrition, and consumers are regarding them, especially citrus juices of 100% fruit content, as reliable sources of vitamin C. Nevertheless relatively few scientific data are available on vitamin C retention during the heat treatment of aseptically packed fruit juices made from fruit concentrates. Authors investigated this problem within the scope of OTKA T 014965 research project (Körmendy et al., 1998, 1999a, 1999b; Pátkai, 1998).
Instead of separate case studies on different types of fruit juices and technologies, authors analysed the vitamin C content of model solutions with similar composition to real citrus juices as a function of temperature and duration of heat treatment and that of initial oxygen and ascorbic acid concentration. Based on the measured data, they elaborated kinetic relations and determined the reaction rate constants of vitamin C decomposition under the experimental conditions. By means of the calculated kinetic relations and reaction rate constants one can estimate the losses of vitamin C in the case of known parameters of the heat treatment, packaging material, oxygen and vitamin C concentration within the investigated domain. Results may promote technology and product development in the field of citrus fruit juices.
Authors:E. Nagy, I. Éliás, L. Körmendy, and J. Czeglédi-Jankó
Development of rapid methods is often needed for the in-line process control of the proximate composition (e.g. fat or moisture content) of meat in the meat processing plants. This paper reports on the continuous wave nuclear magnetic resonance (CW-NMR) technique applied for determining fat content in fresh meat. The interfering moisture content in meat was removed by microwave drying and the dried residue was transferred quantitatively into the NMR-tubes. The total analysis time was about 35 min. Experiments were performed with pork (with a fat content from 1.7% to 21%), beef (with a fat content from 1.0% to 16.1%), lard (rendered pork fat) and tallow (rendered beef fat) samples and with their combinations: lard-tallow, lard-lean pork, tallow-lean beef and lard-tallow-lean beef-lean pork. The regression (prediction) equations (NMR-signal vs. fat content determined with the Soxhlet reference method) of pork and beef did not differ significantly. However, there was a noticeable difference between the regression lines of pure lard and pure tallow. Moreover, the latter ones differed from the regression equations of pork, beef and of the various meat-fat combinations. The variability of the fatty acid composition of the fat also seems to influence the stability of the calibration curves, because the sensitivity of the CW-NMR signal to the fatty acid composition interferes with the quantitative determination of fat content in meat.
Authors:L. Körmendy, E. Zukál, I. Csapó, and N. Török
The aim of this study was a survey of relationships used for calculating ‘meat content’ with respect to the QUID regulation (Commission Directive
, 2001). The recommended equations are presented in a concise form. The advantages of a possible introduction of the meat equivalent concept are also treated [assessment of lean content of the meat ingredient(s)]. A non-negligible condition for applying the QUID equations is, in principle, the equality of the fat-free protein concentrations of the various tissue types in the raw meat materials. This needs an adjustment of the protein concentrations of the recipes to a reference value (PFFref), which can be achieved by effective or virtual addition of water to the formulation or ‘removal’ of water from it. The influence of moisture loss during meat processing on QUID is also discussed. The results of various calculation methods are presented with examples.