30
and prawns are rich in non-protein compounds such as free amino acids and trimethylamine oxide (TMAO) (Lopez-Caballero et al. 2002; Abu Bakar et al. 2008).
The acceptability limit of shrimp TMA was reported to be 5 mg/100 g (Cobb et al.
1973; Shamshad et al. 1990; Zeng et al. 2005; Okpala 2014a). However, some
researchers have suggested different limits for different shrimp species. It is suggested as 9–12 mg/100 g for Penaeus notialis (Dabade et al. 2015), as <3 for
Littepenaeus vannamei (Don et al. 2018). Initial TMA content was reported to be
2.5 mg/100 g for Penaeus notialis (Dabade 2015).
Volatile compounds from degradation indicators are produced by specific degradation organisms. Total volatile basic nitrogen (TVB-N), consisting of trimethylamine (TMA), ammonia (NH3) and dimethylamine (DMA), has been reported to be
the most widely used parameter for microbiological degradation of seafood (Chan
et al. 2006; Pacquit et al. 2007). Total volatile base nitrogen (TVB-N) is a combination of total amount of ammonia (NH3), dimethylamine (DMA) and trimethylamine
(TMA) and is used as a freshness index (Wu and Bechtel 2008). There is also an
increase in the amount of TVB along with the increase in TMA during seafood
spoilage. While some researchers (Connell 1995; Dalgaard 2000) reported the
acceptability limit value for TVB-N to be 30 mg/100 g in seafood products, some of
them reported to be 35 mg/100 g (Amegovu et al. 2012; Huss 1995; Shamshad et al.
1990). However, this value may not be suitable for fresh shrimps and TVB-N values
are generally higher in shrimps (Oehlenschläger 1997). The fact that the baseline
TVB values were reported to be high for the shrimp stored in various methods confirms this statement. The initial TVB value was reported as 20.57 mg/100 g (Azam
et al. 2013) and 17 mg/100 g (Abu Bakar et al. 2008) for freshwater shrimp
(Macrobranchium rosenbergii), as 29 mg/100 g for deep water pink shrimp
(Parapenaeus longirostris) and narwal shrimp (Parapandalus narval) (Condurso
et al. 2016), 33.5 mg/100 g for Northern shrimp (Pandalus borealis) (Qingzhu
2003), 18.29 mg/100 g for Penaeus japonicas (Gokoglu 2004), 15.24 mg/100 g for
cold water shrimp (Pandalus borealis) (Paul 2015).
Leitao and Rios (2000) reported that TVB increased in Macrobranchium rosenbergii at 5 °C and reached to maximum allowable level after 5 days. They also found
a positive correlation between TVB and total psychrotrophic bacteria counts. It was
reported that the same shrimp species reached to acceptable limit after 12 weeks
during frozen storage (Azam et al. 2013). TVBN and TMA values increased in
shrimp (Penaeus notialis) stored at 0, 7 and 28 °C throughout the storage (Dabade
2015) and in Pacific white shrimp (Litopenaeus vannamei) (Okpala et al. 2014),
Penaeus merguiensis (Fatima et al. 1988) during ice storage.
Tryptophan which is an amino acid is metabolised to indole by some microorganisms. These microorganisms, which are often gram-negative, are found in
shrimps and grow at relatively high temperatures (15–35 °C). To produce indole, a
bacterial enzyme called tryptophanase, which oxidizes the free amino acid tryptophan is required. Enterobacteriaceae provides a significant indole production. It is
reported that indole is used by the US Food and Drug Administration to confirm the
results of sensory analysis in shrimps. The acceptable indole level determined by
the FDA is <250 μg/kg. Deterioration can be differentiated with a strong odour
2 Crustacean Shellfish
and prawns are rich in non-protein compounds such as free amino acids and trimethylamine oxide (TMAO) (Lopez-Caballero et al. 2002; Abu Bakar et al. 2008).
The acceptability limit of shrimp TMA was reported to be 5 mg/100 g (Cobb et al.
1973; Shamshad et al. 1990; Zeng et al. 2005; Okpala 2014a). However, some
researchers have suggested different limits for different shrimp species. It is suggested as 9–12 mg/100 g for Penaeus notialis (Dabade et al. 2015), as <3 for
Littepenaeus vannamei (Don et al. 2018). Initial TMA content was reported to be
2.5 mg/100 g for Penaeus notialis (Dabade 2015).
Volatile compounds from degradation indicators are produced by specific degradation organisms. Total volatile basic nitrogen (TVB-N), consisting of trimethylamine (TMA), ammonia (NH3) and dimethylamine (DMA), has been reported to be
the most widely used parameter for microbiological degradation of seafood (Chan
et al. 2006; Pacquit et al. 2007). Total volatile base nitrogen (TVB-N) is a combination of total amount of ammonia (NH3), dimethylamine (DMA) and trimethylamine
(TMA) and is used as a freshness index (Wu and Bechtel 2008). There is also an
increase in the amount of TVB along with the increase in TMA during seafood
spoilage. While some researchers (Connell 1995; Dalgaard 2000) reported the
acceptability limit value for TVB-N to be 30 mg/100 g in seafood products, some of
them reported to be 35 mg/100 g (Amegovu et al. 2012; Huss 1995; Shamshad et al.
1990). However, this value may not be suitable for fresh shrimps and TVB-N values
are generally higher in shrimps (Oehlenschläger 1997). The fact that the baseline
TVB values were reported to be high for the shrimp stored in various methods confirms this statement. The initial TVB value was reported as 20.57 mg/100 g (Azam
et al. 2013) and 17 mg/100 g (Abu Bakar et al. 2008) for freshwater shrimp
(Macrobranchium rosenbergii), as 29 mg/100 g for deep water pink shrimp
(Parapenaeus longirostris) and narwal shrimp (Parapandalus narval) (Condurso
et al. 2016), 33.5 mg/100 g for Northern shrimp (Pandalus borealis) (Qingzhu
2003), 18.29 mg/100 g for Penaeus japonicas (Gokoglu 2004), 15.24 mg/100 g for
cold water shrimp (Pandalus borealis) (Paul 2015).
Leitao and Rios (2000) reported that TVB increased in Macrobranchium rosenbergii at 5 °C and reached to maximum allowable level after 5 days. They also found
a positive correlation between TVB and total psychrotrophic bacteria counts. It was
reported that the same shrimp species reached to acceptable limit after 12 weeks
during frozen storage (Azam et al. 2013). TVBN and TMA values increased in
shrimp (Penaeus notialis) stored at 0, 7 and 28 °C throughout the storage (Dabade
2015) and in Pacific white shrimp (Litopenaeus vannamei) (Okpala et al. 2014),
Penaeus merguiensis (Fatima et al. 1988) during ice storage.
Tryptophan which is an amino acid is metabolised to indole by some microorganisms. These microorganisms, which are often gram-negative, are found in
shrimps and grow at relatively high temperatures (15–35 °C). To produce indole, a
bacterial enzyme called tryptophanase, which oxidizes the free amino acid tryptophan is required. Enterobacteriaceae provides a significant indole production. It is
reported that indole is used by the US Food and Drug Administration to confirm the
results of sensory analysis in shrimps. The acceptable indole level determined by
the FDA is <250 μg/kg. Deterioration can be differentiated with a strong odour
2 Crustacean Shellfish