Abstract
Water sorption isotherms are unique for individual food materials and can be used directly to predict shelf life and determine proper storage conditions. In this context, the aim of this study was to determine the moisture adsorption isotherms of amaranth flour at 15℃, 25℃ and 35℃ in a range of water activity from 0.1 to 0.9. Experimental data were modeled using five equations commonly applied in the foods field. The goodness of the fit for each isotherm model was evaluated through the coefficient of determination, the variance due to error and the confidence interval of the estimated parameters. All models can predict the adsorption isotherms of amaranth flour, but the GAB equation gives a better understanding of the observed sorption behavior. Estimated adsorption monolayer water contents ranged from 6.4 g to 7.2 g of water per 100 g of dry material. It was observed by a weak dependence of water activity with temperature. For ensuring microbiological stability, water content in amaranth flour should not be higher than 13 g of water per 100 g of dry material.
Highlights
Amaranth (Amaranthus caudatus) is a native plant in America, which has been domesticated, cultivated and used for over 6000 years [1]
Protein content found in amaranth grain is very similar to that of milk and is very close to the ideal protein balance proposed by FAO (Food and Agriculture Organization) for human consumption [4]
The results show that the Oswin, Henderson and Chung-Fost parameters do not vary significantly with temperature, whereas the Peleg and Guggenheim-Anderson-De Boer (GAB) equations show a temperature dependence of the amaranth flour isotherms
Summary
Amaranth (Amaranthus caudatus) is a native plant in America, which has been domesticated, cultivated and used for over 6000 years [1]. The quality of flour depends to a great extent upon its physical, chemical and microbiological stability This stability is mainly a consequence of the relationship between the equilibrium water content of the food material and its corresponding water activity at a given temperature [9]. The Guggenheim-Anderson-De Boer (GAB) equation has been recommended by the European Project Group COST 90 on Physical Properties of Food [12] as the fundamental equation for the characterization of water sorption in food materials [13,14,15,16] This equation is based on the adsorption theory after Brunauer-Emmet-Teller (BET) for the monolayer, which gives a physicochemical explanation of the parameters involved [17]. Five mathematical equations were chosen from the literature for describing the experimental sorption behavior
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