Study of moisture adsorption process in comfrey (symphytum officinale l.) roots ta 25 Celsius degree

Abstract

Sorption isotherms of comfrey (Symphytum officinale L.) root samples with different particle size were obtained at 25 °C. The shape of isotherm was similar to those of high-sugar-content foods and the particle size did not affect adsorption process in the aw range used in this study. Blahovec–Yanniotis model was considered to give the best fit over the whole range of aw tested. Various parameters describing the properties of sorbed water derived from GAB and Blahovec–Yanniotis models have been discussed. DSC method was used to measure the glass transition temperatures (Tg) of root samples in relation to water activity. The safe moisture content was determined in 13.39 g/100g in dried basis at 25 °C. Combining of the Tg line with sorption isotherm in one plot showed that 6 Červenka L. et al./Sci. Pap. Univ. Pardubice Ser. A 16 (2010) 5–18 the glass transition temperature concept overestimated the temperature stability for both root samples.