Abstract
Post-harvest losses in developing Countries have contributed to the unavailability of foodstuffs. Estimation of these losses is generally cited to be of the order of 4% but under very adverse conditions, it is estimated as high as 100%. A significantpercentage of these losses are related to improper and or untimely preservation of foodstuffs such as fish, meat. Fish being an important component of the diet for people throughout the World, has high protein and nutritional value. It supplies 6% of global protein and may be classed as either white, oily, or shell fish. In most developing countries where there is high rate of malnutrition, fish provides nutritious food which is often cheaper than meat and therefore available to a larger number of people. Fish being an extremely perishable food which in most cases becomes inedible within twelve hours at tropical temperature, spoilage therefore begins as soon as the fish dies and processing should therefore be done quickly to prevent the growth of spoilage bacteria. Fish is a low acidfood and is therefore very susceptible to the growth of food poisoning bacteria hence another reason why it should be processed quickly. Basically the moisture content of fish stands around 80%; if this is reduced to around 25% bacteria cannot survive and autolytic activity will be greatly reduced. Further moisture content of 15% or less mould and bacteria will cease to grow; well dried fish if stored under the right conditions can be kept for several months. The use of appropriate methods of preservation creates the possibility of having greater increase in the amount of fish available for human consumption. The purpose of preservation is to reduce the moisture content of the fishy because micro-organisms that are responsible for spoilage and wastage cannot survive without moisture. Some of the preservation methods/ techniques include the following; cooking (boiling or frying), salting, smoking and drying collectively known as curing (lowering the moisture content) and fermentation (lowering the pH). However, it should be noted that the scope of this research project paper is basically aimed on drying as a means of fish preservation via a multipurpose solar powered fish drying mechanism devise. Drying is a dual process of heat and mass transfer of moisture from the interior of the product to the surrounding air. Drying involves the abstraction of moisture from the product by heating and the passage of air mass around it to carry away the released vapour. The basic essence of drying is to reduce the moisture content of the product to a level that preventsdeterioration within a certain period of time normally regarded as the “safe period” There are basically two common methods of drying fish namely; open air/sun drying and smoking. Open air/sun drying is probably the oldest method used for preserving fish and other foodstuffs primarily used in developing countries because it is the simplest and cheapest method of conserving fishes. This traditional method involves spreading of products on the ground or on rack in the open air/sun drying or on local three stone stove for smoking. Some disadvantages ofopen air/sun drying and smoking are; exposure of the fish to rain and dust, uncontrolled drying;exposure to direct sunlight which is undesirable for some foods; infestation by insect; attacks by animals etc. The use of solar powered drying mechanisms has not gained popularity in developing countries and reasons can be attributed to; poor problem definition which makes the developed dryers technically inadequate and economically unviable; inappropriate understanding of dryers designs due to the choice of construction materials; inadequate understanding of the operations of solar powered dryers and lack of design procedures. Herein, a forced convection solar powered fish dryer is designed, constructed andcharacterized to yield a better means of drying fish. The designed solar powered dryer would incorporate a heat storage unit which would variably compliment the drying rate of the product during off sunshine hours. As envisaged the device would be characterized during rainy and dry seasons, however results, calculations and analysis clearly indicate the influence of seasonal variation on the performance of the device. Average hourly variation of the dryer and ambient temperatures measured on selected days of different months of measurement during the two seasons, clearly indicated that temperatures were significantly enhanced by the device. This was due to the high ability of the designed solar collector to trap large amount of long waves. Average daily moisture loss from the drying fish was notably high, especially during dry season which was due to the high dryer temperatures and decrease in atmospheric humidity.
