28
bottom. However, during processes such as peeling, packaging, washing, baking,
and freezing, there is a rapid increase in the burden of microorganism.
The shrimp-related bacterial flora is primarily included in the genera Flavobacter,
Achromobacter, Bacillus and Microccus. The dominance of each genus varies considerably during storage. While Gram-negative bacteria constituted 73% of the total
flora in fresh prawn (Macrobrachium rosenbergii) and dominant flora was
Enterobacteriaceae and Aeromonadaceae, after 19 days of iced storage, Gramnegative bacteria constituted more than 80% of the bacterial flora and also
Pseudomonas, Aromonas hydrophila, A. veronii boivar sobria and Shewanella
putrefaciens were identified as the dominant spoilage organisms (Lalitha and
Surendran 2006). Akintola and Bakare (2011) reported that the total number of
aerobic bacteria in freshly caught freshwater shrimps ranged from 3 to 5 log cfu/g
and that the isolates consisted mainly of Gram-negative bacteria and E. coli was
dominant (61%). Acinetobacter, Enterobacter, and Flavobacterium species were
reported as predominant spoilage microflora of fresh shrimp (Penaeus aztecus)
(Heinsz et al. 1988). Dominant spoilers in Litopenaeus vannamei have been reported
as Pseudomonas followed by Enterobacteriacea (Don et al. 2018). Tsironi et al.
(2009) found that 91% of the bacteria isolated from frozen shrimps were
Psychrobacter phenylpyruvicus. Jeyasekaran et al. (2006) reported that the bacterial
flora of fresh raw shrimp (Penaeus indicus) consisted of the genera Aeromonas,
Pseudomonas, Vibrio, Flavobacterium and Serratia, and 38% of the flora was
Aeromonas. Fatima et al. (1988) found that the shrimp (P. merguiensis) had a bacterial load of 10
9
cfu/g on the 20th day of iced storage. However, Jeyaweera and
Subasinghe (1988) observed a total viable count of 10
7
cfu/g in P. indicus on the
17th day of iced storage. Some researchers reported that Vibrio, Aeromonas,
Pseudomonas, Acinetobacter and Moraxella were the dominant bacterial genera
associated with the shrimp, Penaeus (Vanderzant et al. 1973; Cobb et al. 1976).
Çolakoğlu et al. (2006) found that the numbers of total aerobic bacteria and
Pseudomonas were 6.78 log cfu/g and 6, 95 Log cfu/g in shrimps (Parapenaeus
longirostris) stored at 7 °C ± 1 after 6 days.
Mechanism of Microbial Spoilage
After death, shrimps become contaminated with a wide variety of microorganisms.
These microorganisms multiply faster in the product and cause degradation. Amines,
biogenic amines, organic acids, sulphides, alcohols, aldehydes, and ketones are
formed by microbial growth and metabolism and produce unpleasant odours and
flavours. Bacteria convert the fish odour and flavour into sour, heavy, fruity, ammonia and faeces odours through their enzymes, (Quang 2005; Ghaly et al. 2010).
Apart from odour and flavour changes, bacteria are also responsible for the appearance and physical characteristics of meat.
Many degradation products are formed from seafood components via bacterial
activity. Levels of these products are used as objective degradation indicators in
seafood. Microorganisms and their enzymes catalyse autolytic and proteolytic
changes in muscle tissue of fish during storage. Peptides, amino acids, ammonia,
2 Crustacean Shellfish
bottom. However, during processes such as peeling, packaging, washing, baking,
and freezing, there is a rapid increase in the burden of microorganism.
The shrimp-related bacterial flora is primarily included in the genera Flavobacter,
Achromobacter, Bacillus and Microccus. The dominance of each genus varies considerably during storage. While Gram-negative bacteria constituted 73% of the total
flora in fresh prawn (Macrobrachium rosenbergii) and dominant flora was
Enterobacteriaceae and Aeromonadaceae, after 19 days of iced storage, Gramnegative bacteria constituted more than 80% of the bacterial flora and also
Pseudomonas, Aromonas hydrophila, A. veronii boivar sobria and Shewanella
putrefaciens were identified as the dominant spoilage organisms (Lalitha and
Surendran 2006). Akintola and Bakare (2011) reported that the total number of
aerobic bacteria in freshly caught freshwater shrimps ranged from 3 to 5 log cfu/g
and that the isolates consisted mainly of Gram-negative bacteria and E. coli was
dominant (61%). Acinetobacter, Enterobacter, and Flavobacterium species were
reported as predominant spoilage microflora of fresh shrimp (Penaeus aztecus)
(Heinsz et al. 1988). Dominant spoilers in Litopenaeus vannamei have been reported
as Pseudomonas followed by Enterobacteriacea (Don et al. 2018). Tsironi et al.
(2009) found that 91% of the bacteria isolated from frozen shrimps were
Psychrobacter phenylpyruvicus. Jeyasekaran et al. (2006) reported that the bacterial
flora of fresh raw shrimp (Penaeus indicus) consisted of the genera Aeromonas,
Pseudomonas, Vibrio, Flavobacterium and Serratia, and 38% of the flora was
Aeromonas. Fatima et al. (1988) found that the shrimp (P. merguiensis) had a bacterial load of 10
9
cfu/g on the 20th day of iced storage. However, Jeyaweera and
Subasinghe (1988) observed a total viable count of 10
7
cfu/g in P. indicus on the
17th day of iced storage. Some researchers reported that Vibrio, Aeromonas,
Pseudomonas, Acinetobacter and Moraxella were the dominant bacterial genera
associated with the shrimp, Penaeus (Vanderzant et al. 1973; Cobb et al. 1976).
Çolakoğlu et al. (2006) found that the numbers of total aerobic bacteria and
Pseudomonas were 6.78 log cfu/g and 6, 95 Log cfu/g in shrimps (Parapenaeus
longirostris) stored at 7 °C ± 1 after 6 days.
Mechanism of Microbial Spoilage
After death, shrimps become contaminated with a wide variety of microorganisms.
These microorganisms multiply faster in the product and cause degradation. Amines,
biogenic amines, organic acids, sulphides, alcohols, aldehydes, and ketones are
formed by microbial growth and metabolism and produce unpleasant odours and
flavours. Bacteria convert the fish odour and flavour into sour, heavy, fruity, ammonia and faeces odours through their enzymes, (Quang 2005; Ghaly et al. 2010).
Apart from odour and flavour changes, bacteria are also responsible for the appearance and physical characteristics of meat.
Many degradation products are formed from seafood components via bacterial
activity. Levels of these products are used as objective degradation indicators in
seafood. Microorganisms and their enzymes catalyse autolytic and proteolytic
changes in muscle tissue of fish during storage. Peptides, amino acids, ammonia,
2 Crustacean Shellfish