Studies of the water relations of dehydrated foods in relation to the diffusion of soluble constituents

Mohamed, Babiker Beshir (1965) Studies of the water relations of dehydrated foods in relation to the diffusion of soluble constituents. MSc(R) thesis, University of Glasgow.

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The primary object of this work was to study the water-relations of a range of dehydrated foods, in an attempt to define moisture levels which prevent solute diffusion and to examine the effect of molecular size of the solute on the diffusion process. The work entailed preparation of sorption isotherms for a number of dehydrated foods and examination of diffusion in similar materials stored in equilibrium with different relative humidities, using a carton 14- labelled solute and the technique of autoradiography. Results of the sorption experiments show that sorption isotherms for potato, haricot bean, green bean, pea, meat and onion are of the sigmoid type, and that the B.E.T. equation is applicable to these materials. Carrot, tomato, apple and date gave isotherms of the Brunauer type III. Results of the diffusion experiments show that a relationship exists between the calculated monolayer values for a number of the materials showing isotherms of the sigmoid type, and the moisture levels limiting for solute diffusion. This appears to be the case, for example, with onion, pea, meat and green bean, in which diffusion was detected at moisture contents little higher than the corresponding monolayer values. However, in green bean, some migration of the tracer was found to occur at moisture contents actually lower than the monolayer value. The results for the materials showing isotherms of the Brunauer type III were entirely negative at the moisture levels tested, except in the case of date, in which a positive result was obtained at a moisture content as low as 4.24 g. water per 100 g. dry solids. Results of the experiments carried out to study the effect of molecular size of the solute on diffusion have yielded evidence that it is not only the condition of the water in the material which determines the limiting moisture content at which diffusion can occur, but that the latter may vary with the molecular size of the solute, A further series of experiments was carried out to study the effect of treating materials with liquid glucose, prior to drying, on the rate of drying and on the hydration characteristics of the dried products, The final distribution of the liquid glucose in the dried materials and the effect of this treatment on solute diffusion was also examined. In addition, the effect of the treatment on tine culinary quality of the dried products was considered, using a tasting panel. Results of the drying curves show that the necessary drying period is not extended| that this treatment has the effect of reducing the initial moisture content and that the rate of drying is greater in the untreated materials during the first 4 hours of drying. Those of the hydration curves and the sorption isotherms show that the water-holding capacity of the treated materials is lower than that of the corresponding untreated materials. Results of the diffusion experiments suggest that the liquid glucose is present as a dry surface film which prevents contact between the solute and the surface of the tissue. Results of the tasting tests agree that the treatment results in an improved texture in apple and in a more satisfactory colour in onion.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Additional Information: Adviser: J Hawthorn
Keywords: Food science
Date of Award: 1965
Depositing User: Enlighten Team
Unique ID: glathesis:1965-72601
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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