Hygroscopic parameters of gelatin from fish processing waste
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We studied the hygroscopic properties of gelatin from waste-products after processing of common fresh-waterfish species form the Astrakhan region (skin, scales, bones, fins, and cartilage) as an object of drying. The analysis of the thermodynamics of internal mass transfer was carried out during the interaction of the substance of the specified product with water. The objects of study were concentrates obtained by convective-radiation drying of gelatin granules, previously foamed to a constant expansion ratio and cooled to the gelatinization temperature. The studies were carried out experimentally and analytically using the tensometric method by Van Bamelen. For the thermodynamic analysis of hygroscopic characteristics, classical Gibbs–Helmholtz equation was used. On the basis of empirical data, sorption isotherms were obtained –functional dependences of the level of water activity Aw on the equilibrium moisture content and temperature of the product. The isotherms of the concentrates of the studied gelatin are S-shaped, typical for colloidal capillary-porous bodies, which is due to the foam structure of the product. The curves can be conventionallysubdivided into three zones, corresponding to the moisture of monomolecular and polymolecular adsorption, structural, microcapillary, and microcapillary moisture. Based on the analysis of sorption isotherms for the product under study, the hygroscopic moisture content of gelatin was determined for its various temperatures: Wg1= 0.280 kg/kg for T = 283 K and Wg2= 0.301 kg/kg for T = 303 K. The specified moisture content is a threshold for the range of hygroscopic states and is important from the point of view of rationalization and modeling heat and mass transfer during material dehydration. As a result of calculations using sorption isotherms and the Gibbs–Helmholtz equation, the dependences of free, bound, and internal energy as well as the total specific thermal energy of water evaporation on moisture content and temperature of the product under study were derived. It has been established that the nature of these dependences for the studied samples of gelatin concentrates is generally consistent with the published data for a number of materials of a biopolymer nature. These dependencies can be used in the development of dehydration processes and in the design of drying equipment for the production of gelatin concentrates from fish waste.
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