Diffusion into food

Gas permeation Generally oxygen (O ) diffusion into food, or carbon dioxide (COj) diffusion out of the packaging (Tawfik et al., 1998 Hemandez-Munoz et al., 1999). 

During the process, the solute diffuses into the intercellular space and, depending on the characteristics of the solute, it may pass through the membrane and enter the intracellular space. Differences in chemical potentials of water and solutes in the system result in fluxes of several components of the material and solution water drain and solute uptake are the two main simultaneous flows. Together with the changes in chemical composition of the food material, structural changes such as shrinkage, porosity reduction, and cell collapse take place and influence mass transfer behavior in the tissue. 

At the end of the process of losing electrons, the carbon atoms in our carbon-based foods end up as carbon dioxide, CO2. This diffuses into the blood, is carried back to the lungs, and then exhaled. At the end of the process of accepting electrons, molecular oxygen is converted into water. This can be exhaled or eliminated through the kidneys or as sweat. 

The Sarcina lutea test is the official US Food and Drug Administration (FDA) test for detecting penicillin residues in milk and dairy products (41). In this test, milk samples are placed in stainless steel cylinders on an agar plate seeded with Sarcina lutea ATCC 9341. As milk diffuses into the agar, inhibitors prevent the growth of the organism, causing a zone the width of which is a measure of the antibiotic concentration. The test is sensitive to about 0.006 g/ ml penicillin G, and confirmation of positive results can be performed by the addition of penicillinase. 

Other Dyes. Other dye classes listed in the Colour Index include dyes lor leather, solvents, paper, and food. Leather dyes arc those acid, direct, mordant, and basic dyes that show substamivily for leather, good diffusion into it. and acceptable fastness. They are essentially applied in an analogous... 

Carbon-14 atoms produced in the upper atmosphere combine with oxygen to yield 14CC>2, which slowly diffuses into the lower atmosphere, where it mixes with ordinary 12CC>2 and is taken up by plants during photosynthesis. When these plants are eaten, carbon-14 enters the food chain and is ultimately distributed evenly throughout all living organisms. 

The exact expression for the differential equation (7-12) that takes into consideration the diffusion in food and finite values for VP and VL is extremely complicated. The extensive calculation required for the exact expression does not justify its use when one compares the accuracy achievable in practice with the errors or deviations resulting from the use of the approximate formula (Reid et al. 1980). 

It is also possible to have the reverse process whereby a substance condenses out of the atmosphere on the package surface, e.g. water, with subsequent diffusion into P. If the packaging surface (or also that of the food) is dry, i.e. the surface has a lower water partial pressure than that in the gas phase G, then water can be absorbed. 

One can assume that styrene migration out of PS into food is slowed down or braked by the diffusion of styrene in the plastic material (P). Eq. (14-4) the simplified expression for the estimating the concentration, cF.i (mg kg-1),of the styrene in the food (F) at time t can be used ... 

The process of mixing of gas particles is called diffusion molecules move from an area of high concentration (such as liquid oil in a dish) to an area of low concentration such as the air in the room. We smell food as it is heated up and cooked due to molecules of gas forming, escaping and diffusing into the air. Diffusion also takes place in liquids as molecules of one substance intermingle and spread out among those of another. Diffusion is important for movement of substances in the body. 

Another approach to obtain migration data particularly for some plastic materials is the use of modelling. Today this approach is only suitable for certain materials but is accepted by the EU Commission. Diffusion within, and migration from, food contact materials are predictable processes that can be described by mathematical equations. Mass transfer from a plastic material, for instance, into food simulants obeys Tick s laws of diffusion in most cases. Physico-mathematical diffusion models have been established, verified and validated for migration from many plastics into food simulants and are accepted in the USA and in the EU. 

For Dp Dp and /fpp < 1 we obtain eqn 8.24. If the diffusion coefficients in the packaging and in the food are approximately equal, the partition coefficient, /fpp determines transport through the system. The packaging determines the rate of the whole process. If the migrant dissolves much better in the food than in the packaging, that means /fpp < 1 and the food determines the rate of the whole process. But if the migrant dissolves much better in the packaging than in the food, A pp 1. If Dp < Dp the mass transport is determined by the diffusion coefficient in the food. Dp and the partition coefficient, A"pp. This leads to the build up of a concentration profile in the foodstuff. An exact analytical solution of the differential equation that takes into consideration the diffusion in food and finite values for Vp and Vp is not available and in consequence the application of numerical methods is necessary. 

Migration Diffusion- and/or partitioning-controlled mass transfer from a packaging material or article into food or a food simulant. Classically, migration is experimentally determined by standardised tests using food simulants. Due to the scientific progress in this field, migration can also be mathematically modelled and conservatively predicted. 

GC-MS can be used for determination of A-trifluoroacetyl derivatives of PAA. In cases when various analytes are present in the sample, MS detection in the scan mode instead of the SIM mode allows further identification by display of the full MS. A study was carried out of water spiked with aniline (la), toluene-2,4-diamine (2e), toluene-2,6-diamine (2f), 4,4/-diaminodiphenylmethane (5a), 4,4/-oxydianiline (6a), 3,3 -dimethylbenzidine (7d), 1,5-diaminonaphthalene and 1,3-phenylenediamine (lk), which underwent SPAD to the corresponding trifluoroacetamides (Section III.B.l). The LOD were in the 0.1 to 0.4 ftgL-1 range, with RSD from 4 to 17%. The method was used for testing the diffusion of PAA into food (simulated by water) which was in contact with laminated flexible food packaging materials. Detectable extracted levels were found for 2e, 2f and 5a68. 

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