71
2.2.3 Quality Changes and Spoilage of Crab Meat
Seafood spoilage is faster than other muscular foods. This can be attributed mainly
to the fact that seafood contains more water than other muscular foods in the edible
portion. High water activity and a loose connection between protein fibres provide
a rich environment for microbial growth in seafood. This causes faster microbial
spoilage in seafood than other muscle foods. Nitrogenous compounds found in
shellfish cause spoilage metabolites.
The chemical degradation of crab meat is like that of other shellfish products, but
it is reported to be different from that of fish meat. The free amino acid content of
the crab meat is reported to be high and crab meat contains non-protein nitrogenous
compounds. These nitrogenous compounds are converted to metabolites such as
ammonia and biogenic amines (Sarnoski 2007). Enzymatic processes such as deamination of free amino acids, degradation of nucleotides, and oxidation of amines
cause the increase in ammonia level in the tissue (Gill 1990).
Decomposition of macromolecules into small molecular compounds, constitutes
good nutrient source for microorganisms and increases microbial growth and spoilage in crab. Growth of microorganisms is a main cause of shelf-life reduction.
Sanitation during the processing of the crab will make a significant contribution to
keeping the microbial load low. In a study in which 46 crab processing plants were
examined, it was reported that crabs processed under good sanitation conditions had
better bacteriological results than those processed under poor sanitation conditions
and that microbial quality products could be obtained if the processors applied sanitation rules (Phillips and Peeler 1972). Manual processing of crabs can lead to
cross-contamination of spoilage bacteria and pathogenic bacteria, as well as residues remained on the machine during machine operations may contaminate the next
product to be processed.
Microbial flora of crabs is affected by environmental factors. The microbial flora
reflects the environment in which it was harvested. In addition, the microbial flora
of the crab has been affected by factors such as the region, season, water temperature and water quality. In a previous study, in all tissue of two crab species examined
in terms of microbial population, gram negative bacteria, Alicaligenes faecalis,
Pseudomonas aeruginosa, Moraxella lacunata, and Aeromonas salmonicida were
determined to be predominant. Moreover, in the same study, Pseudomonas aeruginosa in shell tissue, Bacillus cereus in gill tissue, Alcaligenes faecalis in muscle
tissue and E. coli in hepatopancreas were determined in more levels (Mahalaxmi
et al. 2013). In another study, it was reported that the dominant aerobic microorganisms isolated from fresh crab meat were Acinetobacter, Carnobacterium piscicola,
Exiguo bacterium and Pseudomonas which were both Gram positive and Gramnegative organisms. Aeromonas, Arthrobacter, Bacillus, Brevibacillus,
Brevibacterium, Chryseobacterium, Marcococcus, Providencia, and Staphylococcus
were reported to be less dominant (Suklim et al. 2008).
2.2 Crabs
2.2.3 Quality Changes and Spoilage of Crab Meat
Seafood spoilage is faster than other muscular foods. This can be attributed mainly
to the fact that seafood contains more water than other muscular foods in the edible
portion. High water activity and a loose connection between protein fibres provide
a rich environment for microbial growth in seafood. This causes faster microbial
spoilage in seafood than other muscle foods. Nitrogenous compounds found in
shellfish cause spoilage metabolites.
The chemical degradation of crab meat is like that of other shellfish products, but
it is reported to be different from that of fish meat. The free amino acid content of
the crab meat is reported to be high and crab meat contains non-protein nitrogenous
compounds. These nitrogenous compounds are converted to metabolites such as
ammonia and biogenic amines (Sarnoski 2007). Enzymatic processes such as deamination of free amino acids, degradation of nucleotides, and oxidation of amines
cause the increase in ammonia level in the tissue (Gill 1990).
Decomposition of macromolecules into small molecular compounds, constitutes
good nutrient source for microorganisms and increases microbial growth and spoilage in crab. Growth of microorganisms is a main cause of shelf-life reduction.
Sanitation during the processing of the crab will make a significant contribution to
keeping the microbial load low. In a study in which 46 crab processing plants were
examined, it was reported that crabs processed under good sanitation conditions had
better bacteriological results than those processed under poor sanitation conditions
and that microbial quality products could be obtained if the processors applied sanitation rules (Phillips and Peeler 1972). Manual processing of crabs can lead to
cross-contamination of spoilage bacteria and pathogenic bacteria, as well as residues remained on the machine during machine operations may contaminate the next
product to be processed.
Microbial flora of crabs is affected by environmental factors. The microbial flora
reflects the environment in which it was harvested. In addition, the microbial flora
of the crab has been affected by factors such as the region, season, water temperature and water quality. In a previous study, in all tissue of two crab species examined
in terms of microbial population, gram negative bacteria, Alicaligenes faecalis,
Pseudomonas aeruginosa, Moraxella lacunata, and Aeromonas salmonicida were
determined to be predominant. Moreover, in the same study, Pseudomonas aeruginosa in shell tissue, Bacillus cereus in gill tissue, Alcaligenes faecalis in muscle
tissue and E. coli in hepatopancreas were determined in more levels (Mahalaxmi
et al. 2013). In another study, it was reported that the dominant aerobic microorganisms isolated from fresh crab meat were Acinetobacter, Carnobacterium piscicola,
Exiguo bacterium and Pseudomonas which were both Gram positive and Gramnegative organisms. Aeromonas, Arthrobacter, Bacillus, Brevibacillus,
Brevibacterium, Chryseobacterium, Marcococcus, Providencia, and Staphylococcus
were reported to be less dominant (Suklim et al. 2008).
2.2 Crabs