STUDIES ON MOISTURE SORPTION ISOTHERMOF DAIRY WHITENER
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Date
2014
Authors
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Publisher
Chhattisgarh Kamdhenu Vishwavidyalaya, Durg (C.G.)
Abstract
The state of water in the product plays a crucial role in the preservation of biological materials in both raw and processed conditions. Water activity is considered as one of the most important parameter in food preservation and processing. The active part of water could be much more important to the stability of food than the total amount of water present. Water activity is thus active part of moisture content in the product correlated well with the deterioration of food stability due to the growth of microorganism. To completely understanding the water relations in a product it requires moisture sorption isotherms which describe the relationship between water activity and moisture content at a constant temperature.
Isotherm curves can be obtained in one of the two ways: adsorption and desorption. Sorption isotherms, which describe water activity at a given temperature at different equilibrium moisture contents, are therefore, of special interest in the design of preservation processes such as drying, freeze-drying, mixing, packaging and storage, etc. Water activity data required for the prediction of food stability and shelf- life.
The moisture sorption characteristics of dairy whitener were determined by using static gravimetric method at 30, 40 and 50oC over the range of relative humidity11.1 to 92.2%. The isotherms obtained were of Type-II (sigmoid) shape. All isotherms shows that EMC, at given relative humidity decreases with increase in temperature. GAB, Caurie, Oswin, Modified Mizrahi and Halsey models were applied to the experimental isotherm data of dairy whitener. Out of all five models tested, GAB model selected as the best fitted equation which was having least RMS% value. Constants and model parameters were derived from the GAB equation.Net isosteric heat was determined from sorption data using the Clausius- Clapeyron equation. The isosteric heat of adsorption for dairy whitener ranged from 15.798 kJ/mol at 5% moisture content (d.b.) to 1.414 kJ/mol at 30 % moisture content (d.b.). Correspondingly the heat of desorption ranged from 18.977 to 2.219 kJ/mol for same range of moisture content. Monolayer moisture content of dairy whitener decreases with increase in temperature from 3.355 at 30°C to 2.199 glI00g solids at 50°C for adsorption and 4.773 at 30°C to 4.328 glI00g solids at 50°C for desorption.
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Keywords
food, preservation and processing, Water activity