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A simple set-up to measure translational diffusion of components in low moisture systems is described. The tracer technique was tested on the diffusion of t4C-labeled tripalmitin and palmitic acid in a model system containing paraffin oil, microcrystalline cellulose and gum arabic. Different methods to evaluate the apparent diffusion coefficients from the experimental diffusion curve were compared. Good results were obtained using a curve-fitting procedure based on the sum of least squares. The technique appears to be suitable for measuring diffusion coefficients up to .10e9 cm2/sec. The procedure offers the possibility to quantify the mobility of chemical components in dried foodstuffs in order to elucidate the mechanisms and kinetics of reactions occurring during storage.

The diffusional behavior of tripalmitin (TP) in a low moisture model system composed of microcrystalline cellulose and gum arabic was found to be very dependent on the water activity (a,), the temperature and the presence of paraffin oil (PO). The complex mechanism of mobilization of food components in dry systems, particularly that of TP in our system, has been discussed in detail. Such knowledge is especially important in relation to the reactions that occur in foodstuffs during dehydration and subsequent storage. As a typical example, the results on TP diffusion indicate that the restriction of enzymatic activity in dry systems may not solely be due to the diffusional limitations of the reactants.

A coherent view on the distribution of triglycerides in a multicomponent multiphase food model system is set forward. Upon freeze-drying only a minor part of triolein and nearly no tripalmitin is encapsulated within the matrix. The level of encapsulated triolein decreases when the system is stored at higher aw's. There is an absolute increase but a relative decrease in the level of encapsulated triolein with increasing initial triolein concentration. Free triglycerides are present as small, thin aggregates on the surface of the freeze-dried matrix or floating on the water film of the hydrated matrix. It is shown that by simple hexane extractiori it is possible to distinguish between free and encapsulated lipid. Only free lipid diffuses. Lipid encapsulation and volatiles retention are compared.

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