THIN-LAYER DRYING KINETICS OF FISH IN A HYBRID SOLAR-CHARCOAL DRYER

Introduction Fish is a very important source of animal protein. It is of high nutritive value in the diet of Nigerians (Akande, 1997). It also contains many vitamins and minerals which are also available in meal due to the cheapness of the product, these essential nutrients are available to many people (Babiker et al., 2016). Since fish flesh deteriorates rapidly as soon as it dies (Fellow and Hamptum, 1992), it must be processed as soon as it is harvested. Spoilage is caused by bacterial action and deterioration is quickened by the high temperatures. Preservation is a very essential unit operation for fish farmers and processors due to the easily perishable characters. Drying refers to any process involving removal of water from a material (fish product) mainly by evaporation. Salting, smoking, application of pressure and use of absorbent pads are other methods of dehydration (Eye, 2001). Fish preservation by drying is aimed at extending it’s shelve life or safe storage period by reducing microbiological activity (Shitanda and Wanjala, 2006). Preservation by drying is affected by lowering the water pressure of fish sample to a level where microbial activities are reduced considerably. Despite the health and environmental concerns arising from the use of smoke for preservation of fish and other food materials (Guan et al., 2013), the use of smoke (in traditional fish processing) from smoldering hard wood or hardwood charcoal in most developing countries has been found quite effective in preservation of fish products. This is because of its bacteriostatic, ABSTRACT This paper presented an empirical thin-layer model describing the drying kinetics of titus and sardine fish samples using an indirect passive hybrid solar-charcoal smoke dryer. The experiment was designed using a Complete Randomized Design (CRD) with two treatments (Titus and Sardine fish species), three levels of thicknesses (3, 5, and 7mm fish fillets) replicated three times. The effect of fillet thickness on the moisture ratio of the two fish species showed that the smoking process of fish samples took place in the falling rate period. The experimental drying data of the fish fillets at varying thicknesses was fitted into seven different commonly used thin-layer models by curve fitting methods and all were compared according to three statistical parameters: R2, χ2, and RMSE. The Page model was found most suitable for describing the drying process of titus fish sample with R2, χ2, and RMSE values of 0.9985, 0.00121, and 0.012 respectively; whereas the Lewis model best suited the sardine samples with R2, χ2, and RMSE values as 0.9995, 0.00125, and 0.015 respectively. The models were validated using the experimental and predicted values of moisture ratios (MR). The times required to reduce 50% initial moisture content (wet basis) of titus fish species (75.24%wb) were 90,120, and 160 minutes at fillet thicknesses of 3, 5, and 7mm respectively; whilst that of sardine (79.61%wb) was 60, 75, and 110 minutes of fillet thicknesses of 3, 5, and 7mm respectively. The maximum and minimum times required to smoke dry titus and sardine fish samples at varying fillet thicknesses were 41⁄2 to 7 hours and 4 to 61⁄2 hours respectively.