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3.1.3.4 Oyster Processing and Preservation
Chilling/Refrigerating of Oysters
Chilling is defined as a unit operation that reduces the temperature of a food to −1
to 8 °C to reduce biochemical and microbiological changes and to extent shelf life
(Songsaeng 2010).
Storage conditions, especially storage temperature, affect the quality of oysters.
Other factors such as type of product, microbial and enzymatic inactivation degree,
hygienic conditions, packaging are also effective on shelf life of chilled oyster.
Quality changes of shell-on white-scar oyster (Crassostrea belcheri) packed in air
and stored at ambient (30 + 2 °C) and chilled (4 + 2 °C) temperatures were compared with shell-on oysters packed in 2.5% brine and stored at ambient and chilled
temperatures. Lower changes in chemical and microbiological qualities were found
in chilled shell-on oysters when compared with those stored at ambient temperature.
Shell-on oyster packed in 2.5% brine showed a slower decrease in pH but increased
in total volatile basic nitrogen (TVB-N), total viable count (TVC) and psychrotrophic bacteria at a faster rate than those stored in air. According to microbiological
and sensory analyses results, it was found that oysters (shell-on) can be kept at
chilled temperature in air and in brine (4%) for 9 and 10 days respectively (Songsaeng
et al. 2010). It was reported that the total viable count (TVC) increased from
6.6 × 10
4
to 5.5 × 10
6
in 14 days at 4 °C in oyster (C. gigas), reaching 9.7 × 10
8
at
7 °C (Hu et al. 2008).
Oysters (Crassostrea gigas) shucked and wrapped in plastic bag were stored at
0, 5 and 10 °C. During the storage, the oysters were investigated for sensory, chemical, and microbiological quality. The shelf-life of oysters stored at 10 °C, 5 °C., and
0 °C was found to be 6–7 days, 10–11 days, and 17–18 days, respectively (Cao et al.
2009a, b).
Oysters (O. edulis) were stored at different temperatures (5, 7 and 15 °C) for
11 days and sensory changes were investigated. Oysters stored at 5 and 7 °C showed
changes on the seventh, and those stored at 15 °C on the fifth day (Hasanspahić 2011).
Effects of temperature and period of postharvest storage on the microbiological
quality and shelf life of raw mangrove oysters, Crassostrea brasiliana were investigated and it was reported that raw mangrove oysters remained in safe microbiological conditions for consumption up to 8 days after harvesting, regardless of
temperature. It was also stated that their shelf life may be extended to 15 days if they
are stored at temperatures not exceeding 15 °C (Montanhini and Neto 2015).
An on-board rapid chilling unit for small vessels was designed to control vibrio
during warmer months. Vibrio levels did not change significantly with icing application, while gaping increased (Thomas 2016). In another study, it was reported for
oysters (Crassostrea virginica) which were kept at 54.5 °C for 15 min after dipping
slurry ice (Thomas et al. 2016). Melody et al. (2008) reported significant gaping in
oysters (Crassostrea virginica) exposed to the iced after 7- and 14-days
post-harvest.
3 Molluscan Shellfish
3.1.3.4 Oyster Processing and Preservation
Chilling/Refrigerating of Oysters
Chilling is defined as a unit operation that reduces the temperature of a food to −1
to 8 °C to reduce biochemical and microbiological changes and to extent shelf life
(Songsaeng 2010).
Storage conditions, especially storage temperature, affect the quality of oysters.
Other factors such as type of product, microbial and enzymatic inactivation degree,
hygienic conditions, packaging are also effective on shelf life of chilled oyster.
Quality changes of shell-on white-scar oyster (Crassostrea belcheri) packed in air
and stored at ambient (30 + 2 °C) and chilled (4 + 2 °C) temperatures were compared with shell-on oysters packed in 2.5% brine and stored at ambient and chilled
temperatures. Lower changes in chemical and microbiological qualities were found
in chilled shell-on oysters when compared with those stored at ambient temperature.
Shell-on oyster packed in 2.5% brine showed a slower decrease in pH but increased
in total volatile basic nitrogen (TVB-N), total viable count (TVC) and psychrotrophic bacteria at a faster rate than those stored in air. According to microbiological
and sensory analyses results, it was found that oysters (shell-on) can be kept at
chilled temperature in air and in brine (4%) for 9 and 10 days respectively (Songsaeng
et al. 2010). It was reported that the total viable count (TVC) increased from
6.6 × 10
4
to 5.5 × 10
6
in 14 days at 4 °C in oyster (C. gigas), reaching 9.7 × 10
8
at
7 °C (Hu et al. 2008).
Oysters (Crassostrea gigas) shucked and wrapped in plastic bag were stored at
0, 5 and 10 °C. During the storage, the oysters were investigated for sensory, chemical, and microbiological quality. The shelf-life of oysters stored at 10 °C, 5 °C., and
0 °C was found to be 6–7 days, 10–11 days, and 17–18 days, respectively (Cao et al.
2009a, b).
Oysters (O. edulis) were stored at different temperatures (5, 7 and 15 °C) for
11 days and sensory changes were investigated. Oysters stored at 5 and 7 °C showed
changes on the seventh, and those stored at 15 °C on the fifth day (Hasanspahić 2011).
Effects of temperature and period of postharvest storage on the microbiological
quality and shelf life of raw mangrove oysters, Crassostrea brasiliana were investigated and it was reported that raw mangrove oysters remained in safe microbiological conditions for consumption up to 8 days after harvesting, regardless of
temperature. It was also stated that their shelf life may be extended to 15 days if they
are stored at temperatures not exceeding 15 °C (Montanhini and Neto 2015).
An on-board rapid chilling unit for small vessels was designed to control vibrio
during warmer months. Vibrio levels did not change significantly with icing application, while gaping increased (Thomas 2016). In another study, it was reported for
oysters (Crassostrea virginica) which were kept at 54.5 °C for 15 min after dipping
slurry ice (Thomas et al. 2016). Melody et al. (2008) reported significant gaping in
oysters (Crassostrea virginica) exposed to the iced after 7- and 14-days
post-harvest.
3 Molluscan Shellfish