2. Fish is a highly perishable
commodity
The spoilage process starts
immediately after the death of fish.
In tropical conditions, fish spoils
rapidly, within a few hours of landing,
if not properly cooled. Spoilage
therefore is the indicative of post
harvest change.
The main components of fish are
water, protein and fat. The spoilage
of fish is a complicated process
brought about by actions of
enzymes, bacteria and chemical
constituents.
The process involves three
stages:1.Rigor mortis 2.Autolysis 3.
Bacterial invasion and putrefaction
INTRODUCTION
3. The major cause of food spoilage is microbial growth
and metabolism resulting in the formation of amines,
sulfides, alcohols, aldehydes, ketones, and organic
acids with unpleasant and unacceptable off-flavours
4. The spoilage process of fish is complex
interactions between bacteria, the raw
material itself and environmental factors .
the main bacterial spoilers which have been
referred to as the specific spoilage
organisms (SSO).
the specific spoilage organism (SSO)
concept has contributed significantly to
understanding of seafood spoilage.
The SSOs are typically present in low
numbers and constitute only a very small
fraction of the microflora on newly
processed seafood.
…..cont
SSO-specific spoilage
organism
5. Fresh and minimally processed fish and seafood spoil due to the
action of a microorganisms, the so-called specific spoilage
organisms (SSOs) that have the ability to dominate and produce
metabolites.
The metabolic products of SSOs are various volatile compounds
that mainly come from the assimilation of nonprotein-
nitrogen(NPN) of fish flesh.
SSO has contributing to the unpleasant smell and off flavours of
spoiled fish.
SSOs' metabolic potential and activity and the estimation of the
growth and population level provide us with tools for rapid evaluation
of fish freshness/spoilage status and remaining shelf life.
6. Examples of specific spoilage
organisms of seafood products
Product Specific spoilage organism
Iced marine fish Shewanella putrefaciens
Iced freshwater fish Pseudomonas spp.
CO2-packed chilled fish Photobacterium
phosphoreum
8. • Shewanella putrefaciens has been named after
James M Shewan who worked on fish spoilage over
several decades . Mesophilic, halotolerant strains are
now recognized as Shewanella algae and the
psychrotolerant group has been split into Shewanella
putrefaciens and Shewanella baltica .
9. Shewanella putrefaciens
Gram negative pleomorphic bacterium.
isolated from marine environments, as well as from
anaerobic sandstone in the Morrison formation.
S. putrefaciens is also a facultative anaerobe with the
ability to reduce iron and manganese metabolically.
It is one of the organisms associated with the odor
of rottingfish,whichproduces trimethylamine (hence
the species name putrefaciens, from putrid).
10. •In both solid and liquid media, S.putrefaciens is
recognizable by its bright pink color colonies.
• On blood agar plates, the colonies are typically
convex and large, with a brown pigment, and
cause “greening” of the agar around the
colonies.
11. Shewanella baltica
Scientific classification
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteob
bacteria
Order: Alteromonadale
es
Family: Shewanellaceae
Genus: Shewanella
Species: S. baltica
Binomial name
Shewanella baltica
Shewanella baltica
12. Shewanella baltica (baltica of
the Baltic Sea)
aerobic and anaerobic marine bacterium.
S. baltica are H2S-producing bacterial isolated from
marine fish (mainly cod, plaice, and flounder) caught
from the Baltic Sea.
In aerobic conditions, S. baltica absorbed significant
quantities of Fe(III) from its medium, then reducing it to
Fe (II) in anaerobic conditions.
Under anaerobic conditions, S. baltica also oxidizes
organic matter from the reduction of nitrate and sulfur
compounds.
Shewanella baltica can grow at 4°C, but not at 37°C.
Due to its temperate nature, S. baltica has been found
to play a major role in the spoilage of aerobically
stored fish in ice.
13. Photobacterium phosphoreum
Photobacterium phosphoreum
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacter
ia
Order: Vibrionales
Family: Vibrionaceae
Genus: Photobacterium
Species: P. phosphoreum
Binomial name
Photobacterium phosphoreum
14. Photobacterium phosphoreum or Vibrio
phosphoreum .
Gram-negative bioluminescent bacterium living in symbiosis with
marine organisms.
It can emit bluish-green light (490 nm) due to a chemical
between FMN, luciferin and molecular oxygen catalysed by an
called luciferase.
can grow in anaerobic conditions,
Bioluminescence of Photobacterium phosphoreum is caused by an
oxidation reaction. Reduced flavin mononucleotide (FMNH2), and
chain fatty acids are oxidized by molecular oxygen to flavin
mononucleotide (FMN) and a corresponding fatty acid
…….cont
15. It is believed that the spoilage of packed fish, such as
salmon and cod, caused by P. phosphoreum due to the
bacterium’s ability to produce AHL’s (N-acylated homoserine
lactones), which are communication molecules regulating
bioluminescence.
AHL’s were only found in nonbioluminescent strains of P.
phosphoreum.
P. phosphoreum is able to remain viable on the external
surfaces of migrating salmon by living under the protection
of the fish’s slime.
The reduction of TMAO to TMA also contributes to the
spoiled result of the fish’s exposure to P. phosphoreum.
16. SPOILAGE OF FRESH FISH
• Spoilage of fresh and lightly preserved fish products is caused
by microbial action.
• . Shewanella putrefaciens and Pseudomonas spp. are the
specific spoilage bacteria of iced fresh fish
• . Modified atmosphere stored marine fish from temperate
waters are spoiled by the CO2 resistant Photobacterium
phosphoreum.
• Fish products with high salt contents may spoil due to growth
of halophilic bacteria (salted fish) or growth of anaerobic
bacteria and yeasts (barrel salted fish)..
17. • In dead fresh fish, enzymes can bring about the destruction
of cells via autolytic changes.
• Both S. putrefaciens and Pseudomonas spp. can produce
hypoxanthine from inosine or inosine monophosphate
which come from the autolytic changes in dead fish and use
them as biosynthetic materials to grow.
• For fresh chilled fish stored in air, Pseudomonas
spp. typically produce biogenic amines, ketones, aldehydes,
ketones, aldehydes, esters, sulfur compounds.
• S. putrefaciens typically produce TMA, H2S, acetic acid, and
acetic acid, and other sulfur compounds.
18. • the environment of a fresh fish provides an
abundance of biosynthetic materials that the
spoilage organisms such as Shewanella
putrefaciens and Pseudomonas spp. can readily
use to survive and proliferate.
• The products of metabolic processes of these
microbes include biological compounds that signal
spoilage and render the fish unsuitable for human
consumption.
19. SPOILAGE OF PROCESSED FISH
• The spoilage activity of lightly preserved fish and fish
products may develop due to the inhibitory strength of
the processing and storage conditions.
• The microorganisms living off the food products have
evolved and managed to endure the physical and
chemical processing techniques, including CO2 and
vacuum packing, salting, heating or pasteurization, and
addition of preservatives.
• Numerous studies have identified several SSOs
including Photobacterium phosphoreum and lactic acid
bacteria (Lactobacillus and Carnobacterium) which are
largely responsible for spoilage of lightly preserved
products
