42
be applied is −10 °C. The freezing of seafood is the process for lowering the temperature to below freezing point. At these temperatures, most of the water in the
material is converted into ice. The freezing point depends on the concentration of
different substances dissolved in the tissue fluid. The dissolved and colloidal substances in the water of the product reduce the freezing point below 0 °C
(Gokoglu 2002).
The freezing of seafood occurs theoretically in three stages. The first stage is the
time until the product temperature is just below 0 °C. The second stage is the passing time until approximately 75% of the water is frozen, during which time the
temperature does not drop, it remains at almost −1 °C. This stage is called thermal
stop period. This period should last 2 h at most. In the third stage, when the freezing
is continued, the product temperature decreases rapidly, and the remaining water is
frozen (Gokoglu 2002).
To produce good quality frozen products, fast freezing is essential. Thus, since
small ice crystals are formed in the cell, the cell is not overly damaged and as a
result the intermixing of the intracellular fluid is prevented. In addition, with rapid
freezing, water is transformed into ice crystals where it is located, and the cell water
is prevented from passing through the intercellular space. By creating small ice
crystals in intercellular spaces, the physical structure of the cell is protected. The
critical point, between −0.5/−5 °C, is rapidly passed. Since the temperatures at
which the activities of microorganisms are completely stopped are reached rapidly,
the possibility of microbiological deterioration during freezing is eliminated
(Gokoglu 2002; Gokoglu and Yerlikaya 2015).
Freezing Methods
Freezing of food is carried out using different freezing systems. A single freezing
system cannot meet all freezing needs due to a wide range in kinds of food products
and process properties. Product type, easy cleaning capability, hygienic design,
desired product quality and reliable and economical operation are available among
the selection criteria for freezing method. Plate contact, immersion, air blast,
fluidized- bed, and cryogenic freezing are common freezing methods in food industry (Rahman and Velez-Ruiz 2007).
Plate Freezing
The basis of this method is that the packaged products placed between the two
cooled plates are frozen by contact with the plate. The product to be frozen by this
method must be have a regular shape or in blocks. It is not possible to freeze a packaged but amorphous mass with this method. It is very important that the package is
in full contact with the plate on a smooth surface. Accordingly, packages of uniform
shape and the same thickness can be placed side by side on the plate and a fast freezing in two directions can be achieved when sitting on the other plate from the top.
This type of freezers is mostly used for packaged products (Gokoglu 2002).
2 Crustacean Shellfish
be applied is −10 °C. The freezing of seafood is the process for lowering the temperature to below freezing point. At these temperatures, most of the water in the
material is converted into ice. The freezing point depends on the concentration of
different substances dissolved in the tissue fluid. The dissolved and colloidal substances in the water of the product reduce the freezing point below 0 °C
(Gokoglu 2002).
The freezing of seafood occurs theoretically in three stages. The first stage is the
time until the product temperature is just below 0 °C. The second stage is the passing time until approximately 75% of the water is frozen, during which time the
temperature does not drop, it remains at almost −1 °C. This stage is called thermal
stop period. This period should last 2 h at most. In the third stage, when the freezing
is continued, the product temperature decreases rapidly, and the remaining water is
frozen (Gokoglu 2002).
To produce good quality frozen products, fast freezing is essential. Thus, since
small ice crystals are formed in the cell, the cell is not overly damaged and as a
result the intermixing of the intracellular fluid is prevented. In addition, with rapid
freezing, water is transformed into ice crystals where it is located, and the cell water
is prevented from passing through the intercellular space. By creating small ice
crystals in intercellular spaces, the physical structure of the cell is protected. The
critical point, between −0.5/−5 °C, is rapidly passed. Since the temperatures at
which the activities of microorganisms are completely stopped are reached rapidly,
the possibility of microbiological deterioration during freezing is eliminated
(Gokoglu 2002; Gokoglu and Yerlikaya 2015).
Freezing Methods
Freezing of food is carried out using different freezing systems. A single freezing
system cannot meet all freezing needs due to a wide range in kinds of food products
and process properties. Product type, easy cleaning capability, hygienic design,
desired product quality and reliable and economical operation are available among
the selection criteria for freezing method. Plate contact, immersion, air blast,
fluidized- bed, and cryogenic freezing are common freezing methods in food industry (Rahman and Velez-Ruiz 2007).
Plate Freezing
The basis of this method is that the packaged products placed between the two
cooled plates are frozen by contact with the plate. The product to be frozen by this
method must be have a regular shape or in blocks. It is not possible to freeze a packaged but amorphous mass with this method. It is very important that the package is
in full contact with the plate on a smooth surface. Accordingly, packages of uniform
shape and the same thickness can be placed side by side on the plate and a fast freezing in two directions can be achieved when sitting on the other plate from the top.
This type of freezers is mostly used for packaged products (Gokoglu 2002).
2 Crustacean Shellfish