2.1 Drying Rate
Drying is a simple process to reduce moisture content from raw food products to prevent quality deterioration and to preserve it for long period of time [11]. Decreasing of the water activity will maintain
D DAVID PUBLISHING
Drying Characteristic of Anchovy Fish
88
food quality by reducing microbial growth and undesired chemical reaction [12]. It was found that the deterioration or spoilage of fish is particularly due to bacteria [13]. Generally, product moisture content must be reduced to about 5%-10% in order to incapacitate the microbial growth [14]. However, the dried fish has less rigorous requirement of moisture content. The maximum moisture content of dried fish can be 25% to avoid microbial growth, and 15% to avoid mushroom deterioration [15]. There are two periods of drying process. The first is constant rate period at which the moisture is removed at an even rate till the required critical moisture content Mc. The second is falling rate period at which the rate of moisture removal is decreased [16]. During first period, the wet surface of the product behaves as a free water surface and the period continues as long as water is supplied to the surface. During second period, the drying is characterized by subsurface evaporation throughout till the equilibrium moisture content ME is reached. Most of the drying actually takes place in the falling rate period and involves the movement of moisture in the material to the surface and continued with the removal of the moisture from the surface.