Composition of meat:

• Most B vitamins in useful quantities

• Water activity (aw ): ~0.99

• Redox potential (Eh): mostly facultative anaerobic or anaerobic

• pH: 5.2 to 7 (~5.6)

• Slaughter procedures, hygiene interventions and the addition of hurdles is important for shelf life and safety

Production of meat

Farm→ transport→ Lairage→ slaughter→ dressing→ chilling→ cutting & boning → packaging or processing

• Maintains reserve of animals for processing so the abattoir can operate at a constant speed

• Dressing→ head, the legs below the knees, tail, skin and ,with the exception of kidneys, all the viscera are removed. Pigs de-haired, for poultry feathers are removed after scalding but the skin is left

Intrinsic bacteria

• Commensal bacteria naturally present in muscular tissues and blood vessels

Extrinsic bacteria

• Faeces

• Hide contact

• Spilling of body fluids

• Aerosols and sprays

• Contaminated hands or equipment

• Abattoir workers

• Inappropriate preservation methods

Spoilage or pathogenic bacteria that contaminate meat during slaughter, processing and storage

Common meat spoilage bacteria

Facultative anaerobes

• LAB → natural gut microflora (Lactobacillus, Enterococcus, Pediococcus)

• Staphylococcus (hide)

• Shewanella (poultry)

Aerobes

• Pseudomonas

• Acinetobacter

• Moraxella

• Micrococcus

• Fungi & yeasts also contaminate the meat surface

Meat spoilage

Carbohydrates

• glycogen & glucose easily taken up by some bacteria producing organic acids - giving off sour flavour

Protein

• collagen, actin, myosin, myoglobin (Short peptides, amino acids, amines)

• Gram -ve aerobes Pseudomonas →Production of extracellular polysaccharides (EPS): slime → bitter/ putrid

Lipids

• Aldehydes Ketones Short-chain fatty acids

• Fruity Sweet

Preservation of meat

• freezing

• Canning (clostridia)

• modified atmosphere packaging → LAB

• vacuum packing → LAB

• Aerobic chill storage → Pseudomonas, Listeria monocytogenes

• Fermented meats → LAB

• cured meats → LAB

Lactic Acid Bacteria (LAB)

• Lactobacillus

• Enterococcus

• Pediococcus

Fish consumption

• Seafood is a generic term to cover all commercial fish & shellfish

• Fish

  • Round white fish: cod, haddock, whiting

  • Flat white fish: plaice, halibut

  • Fatty fish: herring, mackerel

  • Freshwater/Seawater fish: trout, salmon

  • Sharks and rays: dogfish, skates

• Crustaceae → lobsters, crabs, shrimps, prawns

• Molluscs → mussels, oysters, clams

microflora of fresh fish

• Skin ~ 103 – 105 cfu/cm2

• Gills ~ 103 – 104 cfu/g

• Intestines ~ 103 – 109 cfu/g

• Lower counts on fish from clean, cold waters

• Higher counts on fish from tropical, sub-tropical and polluted waters

• But more psychrotrophs on fish from cold waters

• Most bacteria are Gram -ve

• Important genera→ Pseudomonas, Acinetobacter, Aeromonas, Shewanella, Vibrio, Flavobacterium & Cytophaga

Spoilage of fresh fish vs fresh meat

• Like meat fish is nutritious & thus perishable, so spoilage will begin immediately after death

• pH is higher, so pH is less restrictive to bacteria

• There is less carbohydrates as glycogen is used by fish during catching, so protein/AAs are used by bacteria earlier on → results in more putrid volatiles

• In cold water fish → higher proportion of psychrotrophs that multiply during chill storage, accounting for > 80% of the spoilage population

Microbial spoilage in fish

1. Indole production→ spoilage bacteria convert tryptophan into indole, which has an intense faecal odour

2. Formation of ammonia→ spoilage bacteria deaminate free AAs to release ammonia

   • Even worse in sharks & rays as they contain high levels of urea that can also be converted into ammonia

3. Formation of TMA→ spoilage bacteria convert trimethylamine N-oxide (TMAO) & odourless osmolyte - into the foul smelling Trimethylamine (TMA)

Preservation of fish

• Cooked products

• Canned fish→ Clostridia

• Vacuum packed

• Marinated fish

• Smoked fish

• Fermented fish - Baltic sea herring → Halanaerobium sp (High pH, high salt concentration, acetic acid, formic acid)

• Dried

• Frozen products - Anisakis

Fish borne disease

• Vibrio cholerae

• Vibrio parahaemolyticus

• Vibrio vulnificus

• Enteric viruses (Norovirus)

• Scombroid fish poisoning→ If fish such as mackerel, tuna, bonito are not chilled properly after being caught → bacteria begin to convert histidine into histamine

• Shellfish poisoning→ bivalve molluscs are filter feeders ∴ accumulate toxins produced by microscopic algae & cyanobacteria

Considerations of Bivalve molluscs

Particular problems:

• Filter feeders → conc. pathogens & toxins

• Grow in inshore & perhaps sewage-polluted waters

• Freq. eaten raw or lightly cooked

• Freq. consumed whole (w/ gut)

• Scallops are safer: offshore, less polluted waters, eviscerated and cooked

Conclusions:

• Bacteria are naturally present in meat & fish

• The predominant natural bacteria found in meat are Gram +ve, facultative anaerobes (LAB)

• The most abundant natural bacteria present in fish are Gram -ve aerobes

• Natural bacteria are involved in spoilage & fermentation (also disease)

• Spoilage bacteria & pathogens contaminate meat & fish

• Most pathogens are controlled by heating