Experimental study and modelling of the kinetics of drying of tropical fruits. Application to banana and to mango.

摘要

Up till now, there is very little information on the drying of tropical fruits, in particular of bananas and mangoes. Yet this method of conservation whereby only 60% loss of foodstuff is recorded after harvest, is the most economical to undeveloped and developing nations. Using the dynamic gravimetric method, the sorption and desorption isotherms at 40 and 50degreesC for bananas and 50degreesC for mangoes were experimentally determined. These curves were modelled following a semi-empirical correlation proposed by HENDERSON. The advantage of this correlation method is that it takes into account the influence of temperature. The insensitive effect of temperature ranges of about 10degreesC, as is the case with bananas, was highlighted. Hysteresis between the sorption and desorption, with a maximum amplitude of 4% for bananas and 5% for mangoes, was observed. Consequently, experimental results of drying by forced convection of products tested in thin slices (10 mm thickness for mangoes and thickness of less than 15 mm for bananas) were obtained, using well controlled aeraulic and thermal conditions of air duct (40, 50 and 60degreesC for the temperatures; 0.5, 1.0 and 2.0 m(-1) for flow rates). A characteristic curve of drying is built for each product, independently of the different aerothermic conditions. This simplified method makes it possible to simulate the experimental kinetics satisfactorily. One of the peculiarities of our work is to identify a critical moisture which is different from the initial moisture content.