77
the other hand, the samples stored on ice for 1 day could remain in good condition
for 50 weeks, 7 days for 21 weeks, and 14 days for 8 weeks (George 1973).
The quality changes of leg meat and body meat of Jonah crabs, which were frozen in −23 °C in an air blast freezer after being cooked in steam for 8 min and then
cooled in ice water, were examined and it was reported that earlier quality changes
were observed in leg meat (Rebach et al. 1990). The maximum storage time of snow
crab (Chionoecetes japonicus) at −20 °C was determined as 2 weeks (Jun et al.
2017). In a study conducted by Yerlikaya and Gokoglu (2004), it was determined
that the whole blue crab (Callinectes sapidus) packaged in polyethylene bags and
stored at −18 °C had a shelf life of 10 months.
While freezing increasing the shelf life of crabs one hand, on the other hand can
accelerate the onset of melanosis. The freeze-thaw process is reported to increase
melanosis by lysis of tissue cells. This leads to the rapid development of melanosis
of PO enzymes that maintain functional integrity during the freeze-thaw process,
together with appropriate substrate and oxygen. The fact that raw-frozen and
cooked-frozen snow crabs (Chionoecetes opilio) exhibit significantly higher drip
loss during storage compared to those that have not undergone freezing is indicated
as a clear indication of the mechanical damage to cellular tissue membranes due to
the freeze-thaw process (Lian et al. 2018).
Changes During Freezing and Frozen Storage
Changes in Proteins
Reactive sulphide group is generally reduced during frozen storage (Jiang et al.
1988). The reduction in the sulfhydryl group consists either of oxidation of sulfhydryl, disulphur changes, or the formation of hydrogen and hydrophobic bonds that
mask the reactive sulfhydryl structure of actomyocin molecules (Benjakul and
Bauer 2000). The sulfhydryl group content of hard- and soft-shell mud crab (Scylla
serrata) was found to be reduced during 12 weeks of frozen storage (Benjakul and
Sutthipan 2009).
An increase in the hydrophobicity of the proteins can be observed during frozen
storage. This increase is due to the opening of proteins and the release of hydrophobic aliphatic and aromatic amino acids. As a matter of fact, Benjakul and Sutthipan
(2009) found an increase in surface hydrophobicity of the samples during 6–8
weeks of frozen storage of mud crab (Scylla serrata).
Protein solubility is widely used as an indicator of structural changes in proteins.
Protein solubility is indicative of protein denaturation. When the protein is denatured, the hydrophobic amino acids in the protein molecules will be exposed to the
surface, and then the apolar groups will tend to interact with another to form protein
aggregates that cause a decrease in solubility (Chan et al. 2011). A decrease in protein solubility was detected during the frozen storage of the mud crab (Benjakul and
Sutthipan 2009).
2.2 Crabs
the other hand, the samples stored on ice for 1 day could remain in good condition
for 50 weeks, 7 days for 21 weeks, and 14 days for 8 weeks (George 1973).
The quality changes of leg meat and body meat of Jonah crabs, which were frozen in −23 °C in an air blast freezer after being cooked in steam for 8 min and then
cooled in ice water, were examined and it was reported that earlier quality changes
were observed in leg meat (Rebach et al. 1990). The maximum storage time of snow
crab (Chionoecetes japonicus) at −20 °C was determined as 2 weeks (Jun et al.
2017). In a study conducted by Yerlikaya and Gokoglu (2004), it was determined
that the whole blue crab (Callinectes sapidus) packaged in polyethylene bags and
stored at −18 °C had a shelf life of 10 months.
While freezing increasing the shelf life of crabs one hand, on the other hand can
accelerate the onset of melanosis. The freeze-thaw process is reported to increase
melanosis by lysis of tissue cells. This leads to the rapid development of melanosis
of PO enzymes that maintain functional integrity during the freeze-thaw process,
together with appropriate substrate and oxygen. The fact that raw-frozen and
cooked-frozen snow crabs (Chionoecetes opilio) exhibit significantly higher drip
loss during storage compared to those that have not undergone freezing is indicated
as a clear indication of the mechanical damage to cellular tissue membranes due to
the freeze-thaw process (Lian et al. 2018).
Changes During Freezing and Frozen Storage
Changes in Proteins
Reactive sulphide group is generally reduced during frozen storage (Jiang et al.
1988). The reduction in the sulfhydryl group consists either of oxidation of sulfhydryl, disulphur changes, or the formation of hydrogen and hydrophobic bonds that
mask the reactive sulfhydryl structure of actomyocin molecules (Benjakul and
Bauer 2000). The sulfhydryl group content of hard- and soft-shell mud crab (Scylla
serrata) was found to be reduced during 12 weeks of frozen storage (Benjakul and
Sutthipan 2009).
An increase in the hydrophobicity of the proteins can be observed during frozen
storage. This increase is due to the opening of proteins and the release of hydrophobic aliphatic and aromatic amino acids. As a matter of fact, Benjakul and Sutthipan
(2009) found an increase in surface hydrophobicity of the samples during 6–8
weeks of frozen storage of mud crab (Scylla serrata).
Protein solubility is widely used as an indicator of structural changes in proteins.
Protein solubility is indicative of protein denaturation. When the protein is denatured, the hydrophobic amino acids in the protein molecules will be exposed to the
surface, and then the apolar groups will tend to interact with another to form protein
aggregates that cause a decrease in solubility (Chan et al. 2011). A decrease in protein solubility was detected during the frozen storage of the mud crab (Benjakul and
Sutthipan 2009).
2.2 Crabs