51
the end of the process, the cans from the autoclave are cooled, drained, and placed
in boxes (Gokoglu 2002).
It has been reported that heating at 115 °C for 24 min affects the texture of
canned shrimp (Macbrobrachium rosenbergii) due to collagen denaturation
(Noomhorm and Vongsawasdi 1998). Processing at 124 °C caused the toughening
at the first stage and the softening at the later stages of heating in shrimp muscle (Ma
et al. 1983).
2.1.3.6 Drying of Shrimps/Prawns
Drying is one of the oldest food preservation methods. It means removing water
from the product. Drying is a general definition and the process of removing water
from the product by evaporation. The high moisture content of shrimps causes rapid
deterioration. If they are not exposed to cold storage, they start to deteriorate shortly
after being caught. However, cold storage is expensive and may not be present in
some areas where the electricity becomes difficult. In many parts of the world, drying continues to be one of the best options for pre-processing of seafood. It is one of
the oldest food preservation methods and can be applied to a wide range of food
products, including shrimps. The principle of drying is to reduce moisture to levels
that are too low to prevent microbial growth, and slow down enzymatic and other
biological reactions (Akonor et al. 2016).
Principal of Drying
In the drying process, removing of water takes place by evaporation of the water as
vapour from the surface and transferring of the water from the inner layers to the
surface layer. The removal of water from the surface layer depends on the drying
temperature, the humidity and velocity of the air, as well as the surface and pressure
to be exposed.
Initially drying is the removal of water from the surface and near the surface by
evaporation. This period is called “constant rate drying” period. In this period drying continues at a constant rate. The drying rate depends on the air velocity, humidity, temperature, the surface area of the product, the amount of heat transferred from
the air to the product per unit time, and other conditions. Since the evaporation takes
place on the surface, the water in the fish muscle must first be transferred to the
surface. This transfer is largely carried out by diffusion. This period is characterized
by a gradual decrease in the rate of drying and this period is called “falling rate drying” period (Doe and Olley 1990; Gokoglu 2002).
Diffusion is the most important mass transfer mechanism responsible for the
transport of water and vapour in the muscle. Diffusion results from the concentration and pressure differences caused by protein denaturation, aggregation, and muscle shrinkage between inner and the outer layers of the muscle. Capillary forces are
also thought to contribute to water migration within the fish muscle. The water
2.1 Shrimps/Prawns
the end of the process, the cans from the autoclave are cooled, drained, and placed
in boxes (Gokoglu 2002).
It has been reported that heating at 115 °C for 24 min affects the texture of
canned shrimp (Macbrobrachium rosenbergii) due to collagen denaturation
(Noomhorm and Vongsawasdi 1998). Processing at 124 °C caused the toughening
at the first stage and the softening at the later stages of heating in shrimp muscle (Ma
et al. 1983).
2.1.3.6 Drying of Shrimps/Prawns
Drying is one of the oldest food preservation methods. It means removing water
from the product. Drying is a general definition and the process of removing water
from the product by evaporation. The high moisture content of shrimps causes rapid
deterioration. If they are not exposed to cold storage, they start to deteriorate shortly
after being caught. However, cold storage is expensive and may not be present in
some areas where the electricity becomes difficult. In many parts of the world, drying continues to be one of the best options for pre-processing of seafood. It is one of
the oldest food preservation methods and can be applied to a wide range of food
products, including shrimps. The principle of drying is to reduce moisture to levels
that are too low to prevent microbial growth, and slow down enzymatic and other
biological reactions (Akonor et al. 2016).
Principal of Drying
In the drying process, removing of water takes place by evaporation of the water as
vapour from the surface and transferring of the water from the inner layers to the
surface layer. The removal of water from the surface layer depends on the drying
temperature, the humidity and velocity of the air, as well as the surface and pressure
to be exposed.
Initially drying is the removal of water from the surface and near the surface by
evaporation. This period is called “constant rate drying” period. In this period drying continues at a constant rate. The drying rate depends on the air velocity, humidity, temperature, the surface area of the product, the amount of heat transferred from
the air to the product per unit time, and other conditions. Since the evaporation takes
place on the surface, the water in the fish muscle must first be transferred to the
surface. This transfer is largely carried out by diffusion. This period is characterized
by a gradual decrease in the rate of drying and this period is called “falling rate drying” period (Doe and Olley 1990; Gokoglu 2002).
Diffusion is the most important mass transfer mechanism responsible for the
transport of water and vapour in the muscle. Diffusion results from the concentration and pressure differences caused by protein denaturation, aggregation, and muscle shrinkage between inner and the outer layers of the muscle. Capillary forces are
also thought to contribute to water migration within the fish muscle. The water
2.1 Shrimps/Prawns