Abstract:
The development and evaluation of Mixed Mode Passive Solar Stockfish Dryer was conducted. The dryer comprised solar air heater (solar collector) and heat storage materials for sensible heat storage to discharge heat during the intermittent solar radiation period. The collector and the storage medium were insulated using sawdust. The drying chamber is integrated with three racks of wire mesh trays and a suction device to aid the convective air flow to avoid reversible reaction during the discharge of accumulated moisture. The heat storage medium was found to attain a temperature range of 29oC – 53oC with a corresponding ambient temperature range of 24oC – 34oC. The solar dryer was evaluated with fresh cod at initial moisture content of 79%. Three sets of the fresh cod classified as: Moringa treated, salted and unsalted were used for the performance evaluation. The results showed that the initial moisture content of 79% with respect to Moringa treatment, salt treatment, unsalted were reduced to 16.03%, 13.33%, 15.01% respectively under solar dryer while 19.55%, 13.46%, 14.64% respectively under ambient condition in six days. There was slight difference in moisture drop as a result of cloudy and humidity situations at the time of test. Further laboratory test showed that bacteria and fungi counts for Moringatreatment under solar dryer was Bacillus at 1.09 x 105count without fungi development while for open sun drying Coliform and Bacilllus were found at 1.1 x 104 and 5.0 x 103 respectively. For salt treatment under dryer, Staphylococcus and Mould were found at 2.9 x 104 and 1.0 x 103 respectively while Coliform and Staphylococcus were found under open sun drying at 1.2 x 103 and 1.48 x 104 counts. The unsalted cod had under solar dryer, Bacillus, Staphylococcus, Mould and Coliform at 9.68 x 105, 5.9 x 104, 1.0 x 103 and 3.0 x 103 counts respectively while for open sun drying, Bacillus and Staphylococcus at 2.35 x 105 and 1.58 x 105 respectively. For health wise the bacteria count range of 103 – 105 was below the consumable limit of103 – 105≤107. The bacteria counts were higher in solar dryer compared to open drying because of the ultraviolet rays were absent in solar dryer due to its low passage through the dryer glazing materials but present in ambient drying. Its direct influence on the stock fish under open drying was bactericidal and therefore had high efficacy in destroying some of the bacteria.
