47
During storage of frozen shrimps, lipid oxidation, protein denaturation, sublimation and recrystallization of ice crystals may occur. This causes undesirable taste
and odour formation, drip loss, water loss, weight loss, dehydration, and toughening
(Londahl 1997). Glazing process is applied between 6 and 12%. Ice percentage over
>20% to be added to the product in coating is considered as over-coating which is
accepted as fraud. It has been reported for shrimps that glazing as thick as 25–45%
was defined as excessive glazing. For this reason, the amount of ice in glazed product should be inspected (Manso et al. 2013). The amount of glaze applied depends
on the different factors such as product temperature, water temperature used for
glazing, product size, glazing time, and product shape (Gonçalves et al. 2009).
Several researches were conducted to determine the effects of these factors on glaze
uptake of frozen shrimps. In one of these studies, effects of initial temperature of
frozen shrimp and glazing time on glaze uptake were studied. In that study, different
glaze percentages and their effects on physical and chemical changes of frozen
shrimp during storage were also investigated. It was found that glazing time and
shrimp temperature showed significant effect on glazing uptake. The increase of
glazing time caused an increase in glazing uptake. Glazing time of 15 and 20 s
showed best protection. On the other hand, the most reasonable glazing percentages
were found as 15 and 20% in terms of the quality of final product (Gonçalves
et al. 2003).
Freezing of Shrimps/Prawns
On Board Freezing
The shelf life of shrimps is considerably increased as the storage temperature is
lowered. Fatima et al. (1988) examined the quality changes of ice-chilled (0 °C) and
partially frozen (−3 °C) shrimps and found that they kept their quality for 8 days on
ice and for 16 days in frozen storage. Tsironi et al. (2009) found that shrimps kept
at −12 °C and −15 °C were still acceptable in the eighth and eleventh months,
respectively. Shrimps, especially in catching in distant seas, need to be quickly frozen on ships to increase shelf life. Frozen shrimps may have a shelf life of 1 year or
more. Mechanical freezing equipment on vessels allows the shrimp to be frozen
immediately. This is the ideal system and the shrimp is always of first-class quality.
Freezing of shrimp at sea is not economical, needs expensive freezing equipment
and experienced staff. Shrimps can be frozen by dipping into a cold brine or a sugar
and salt solution by air flow or by plate freezers. It is reported that the freezing process with dipping and air flow methods has been successfully applied in the fishing
boats especially in North and Central America. Glazing is formed on the shrimp
when is frozen in sugar and salt solution, this makes shrimps easier to separate when
it thaws. Deep water shrimps can be frozen by immersing them into the brine at
−20 °C for 10–15 min. Very long immersion times can result in an undesirable
product formation due to excess salt intake. Shrimp can also be frozen in a vertical
plate freezer in 50 mm blocks. Shrimps are placed in a polyethylene bag and placed
2.1 Shrimps/Prawns
During storage of frozen shrimps, lipid oxidation, protein denaturation, sublimation and recrystallization of ice crystals may occur. This causes undesirable taste
and odour formation, drip loss, water loss, weight loss, dehydration, and toughening
(Londahl 1997). Glazing process is applied between 6 and 12%. Ice percentage over
>20% to be added to the product in coating is considered as over-coating which is
accepted as fraud. It has been reported for shrimps that glazing as thick as 25–45%
was defined as excessive glazing. For this reason, the amount of ice in glazed product should be inspected (Manso et al. 2013). The amount of glaze applied depends
on the different factors such as product temperature, water temperature used for
glazing, product size, glazing time, and product shape (Gonçalves et al. 2009).
Several researches were conducted to determine the effects of these factors on glaze
uptake of frozen shrimps. In one of these studies, effects of initial temperature of
frozen shrimp and glazing time on glaze uptake were studied. In that study, different
glaze percentages and their effects on physical and chemical changes of frozen
shrimp during storage were also investigated. It was found that glazing time and
shrimp temperature showed significant effect on glazing uptake. The increase of
glazing time caused an increase in glazing uptake. Glazing time of 15 and 20 s
showed best protection. On the other hand, the most reasonable glazing percentages
were found as 15 and 20% in terms of the quality of final product (Gonçalves
et al. 2003).
Freezing of Shrimps/Prawns
On Board Freezing
The shelf life of shrimps is considerably increased as the storage temperature is
lowered. Fatima et al. (1988) examined the quality changes of ice-chilled (0 °C) and
partially frozen (−3 °C) shrimps and found that they kept their quality for 8 days on
ice and for 16 days in frozen storage. Tsironi et al. (2009) found that shrimps kept
at −12 °C and −15 °C were still acceptable in the eighth and eleventh months,
respectively. Shrimps, especially in catching in distant seas, need to be quickly frozen on ships to increase shelf life. Frozen shrimps may have a shelf life of 1 year or
more. Mechanical freezing equipment on vessels allows the shrimp to be frozen
immediately. This is the ideal system and the shrimp is always of first-class quality.
Freezing of shrimp at sea is not economical, needs expensive freezing equipment
and experienced staff. Shrimps can be frozen by dipping into a cold brine or a sugar
and salt solution by air flow or by plate freezers. It is reported that the freezing process with dipping and air flow methods has been successfully applied in the fishing
boats especially in North and Central America. Glazing is formed on the shrimp
when is frozen in sugar and salt solution, this makes shrimps easier to separate when
it thaws. Deep water shrimps can be frozen by immersing them into the brine at
−20 °C for 10–15 min. Very long immersion times can result in an undesirable
product formation due to excess salt intake. Shrimp can also be frozen in a vertical
plate freezer in 50 mm blocks. Shrimps are placed in a polyethylene bag and placed
2.1 Shrimps/Prawns