THE USE OF BENTONITE AS A MOISTURE REGULATING SYSTEM 1 - STUDY ON SOME SORPTION PROPERTIES OF BENTONITES FOR THEIR POTENTIAL USE IN FOOD-TECHNOLOGY

Five bentonite samples were laboratory processed to improve their adso rbing properties by means of a treatment with sodium carbonate at thre e concentrations: 2%, 3% and 4% by weight. The effectiveness of ion ex change between sodium carbonate and bentonite was controlled through t he measure of the swelling volume of the bentonites. All the samples ( n = 15) were tested for their hygroscopic properties. Adsorption isoth erms were measured at 25 degrees C, using desiccators with silica gel, saturated salt solutions and bi-distilled water The data of weight in crease of bentonites were also expressed as a function of the time in order to obtain the adsorption kinetics. Through a mathematical equati on the specific mass capacity of each sample was calculated as a funct ion of the a(w) value. Moreover as an example, a comparison of isother ms of one bentonite with four different 'sample foods' was made. Resul ts have shown that the hygroscopic properties of bentonites are closel y related to their geographical origin and also that it is possible to modulate the use of bentonites as hygrostatic systems. Furthermore, f or most samples it has been calculated that the adsorbing velocity is about 25-32% higher than the corresponding desorbing velocity. (C) 199 7 Elsevier Science Limited.