The Isothermal Sorption Measurement and the Isosteric Heats Determinations for the South Algerian Date Varieties Ahmed Mediani 1,2* , Houcine Moungar 1 , Ahmed Amine Larbi 1 , Akil Loumani 1 , Wafa Braham Chaouch 1 , Abdelkrim Djaber 1 , Cherif Tigani 1 , Ali Benatiallah 2 1 Unité de Recherche en Energies Renouvelables en Milieu Saharien, URERMS, Centre de Développement des Energies Renouvelables, CDER, Adrar 01000, Algeria 2 Laboratoire d’Energie, Environnement et Système d’Information (LEESI), Faculté des Sciences et Technologies, Université d’Adrar, Algeria Corresponding Author Email: medianiusto@yahoo.fr https://doi.org/10.18280/i2m.180408 ABSTRACT Received: 18 April 2019 Accepted: 10 July 2019 The equilibrium water content of a product to be dried is essential during a forced convection solar drying and storage operation. These values are often taken from the so-called isothermal sorption curves. The isotherms determination is an essential step to know the distribution and the intensity of the water connections in the products. They make it possible to determine the products final water content to be reached in order to optimize the drying conditions and give valuable information on the hygroscopic equilibrium. As a result, this experimental study aims to determine the physicochemical components' and the desorption isotherms curves for deferent date type L’hmira, Bamakhlouf and Tegazza from the Touat region, in South-West Algeria, using the saturated salt solution method. The experiment is carried out for three temperature values 40 ° C, 50 ° C and 60 ° C, to study the influence of the temperature on the equilibrium curves of the product and finally to describe the isothermal moisture desorption for deferent date types for three temperatures using known models of GAB, SMITH, LANGMUIR and OSWIN. Keywords: sorption isotherm, solar drying, gravimetric method, isosteric heats, date varieties, GAB and SMITH models 1. INTRODUCTION Many agricultural products, consumed in large quantities are not always available during the seasons. Several solutions are proposed to overcome this handicap for example: greenhouse cultivation, freezing and the preservation by drying. The solar drying use is a simple, safe and adequate solution for a large number of agricultural products. The Southern Algerian regions are beginning to experience more or less rapid development. A large part of the agricultural production of these regions: tomato, dates, henna, mint. etc., lends itself perfectly to conservation by drying to ensure continuity in their availability and allow their transport as well as to reducing the produces cost. The dates are the historical food of great and high energy and commercial values. According to FAO statistical data in 2012, Algeria is the world's sixth largest date producer, with an estimated average annual production of 789357 tones, for more than 12 million date palms, particularly in TOUAT areas. Certain dates varieties have excess production, such as: Aghammou or L’L’hmira, which is destined for export to the African countries: Mali, Niger, and Chad. As well as, some local applications such as livestock or for industrialization (manufacture of soup, vinegar). Date varieties are generally drayed after harvest using traditional solar dryer. Agriculture use solar energy; free, non-polluting and excellently clean. Those methods are subjects of several researches. Sorption isotherms are of great importance in the food industry, especially in solar drying, storage and food preservation. Their knowledge tells us about the hygroscopic or hydric balance of the product under consideration, the isosteric heats, and the lifetime's duration. We do not know the product stability types. This equilibrium is characterized by these curves whose experimental determination requires a large number of measurements. They are also useful during a solar drying process. Indeed, it is from these sorption curves that we can determine the final product water content, so as to ensure the physicochemical and microbiological stability during the storage, in addition the product shelf life can be predicted [1-6]. studies on sorption isotherms are carried out by mathematical modeling, eight mathematical models (in the literature) empirical and semi-empirical based on more or less physical bases [7-10], describing the correlation of water content with balance with the water activity of the products. among these models: GAB [11], modified BET [12], Henderson-Thompson [13], modified Halsey [14], modified Oswin [15], Peleg [16]. GAB is the most widely used model for various foods [17-20]. The present Works focus firstly the experimental determination of the sorption curves forL’L’hmira, Bamakhlouf and Tegazza varieties, secondly we are interested in defining among the existing mathematical models, the most appropriate model for the studied product and finally, we are interested in modelling the isosteric heats for deferent dates. Instrumentation Mesure Métrologie Vol. 18, No. 4, August, 2019, pp. 389-396 Journal homepage: http://iieta.org/journals/i2m 389