MOISTURE ADSORPTION CHARACTERISTICS OF BLACK CURRANT (RIBES NIGRUM L.), BLACK ELDERBERRY (SAMBUCUS NIGRA L.) AND CHOKEBERRY (ARONIA MELANOCARPA, [MINCHX.] ELL.) SAMPLES AT DIFFERENT TEMPERATURES

Abstract

ABSTRACTAdsorption isotherms of black currant, black elderberry and chokeberry were obtained at 10, 25 and 40C. Generally, increasing temperature decreased adsorbed moisture particularly at 10C, whereas the adsorption was similar at 25 and 40C in the range of 0.10–0.75 water activity (Aw) for all the berry samples. All the berries sorbed more water at 40C than at 10 or 25C above 0.75 Aw. Of the six sorption models, Peleg's model gave the best fit. The net isosteric heats of adsorption were obtained using Clausius–Clapeyron equation showing that the adsorbed water is strongly bound to adsorbent at low moisture content. The glass transition temperature concept was also discussed. Based on the results of the study and the literature reviewed, the chilled storage has a favorable effect on the quality and shelf life of the dried berries.PRACTICAL APPLICATIONSThe knowledge of the moisture content and water activity (Aw) relationships of food products is very important. These can be estimated by determining moisture sorption isotherm that can be used for defining storage conditions and in making shelf life determination. The unsuitable storage conditions may lead to deterioration of the product caused both by native enzymes and by microorganisms activity (Ross 2001). The sorption data for the berries are restricted for those used in human diet (Khalloufi et al. 2000) but have never been published for berries predominantly used in medicine. The results of this study would be useful in assessment of proper storage condition to keep the quality of the product in a high level.