week 2

• What are the aims of the lecture on the microbiology of meat and fish?


  • Outline different microbiology in meat and fish
  • Demonstrate natural presence of bacteria
  • Show bacteria may lead to spoilage or disease
  • Overview of preservation methods
  • Identify sources of microbes in meat and fish
  • Differentiate between natural and contaminating bacteria
  • Outline microbial mechanisms of spoilage and disease
  • Describe differences in spoilage mechanisms between meat and fish
  • Understand preservation methods

  
• How many broiler chickens are consumed each year in the UK?


  982 million
• What is the approximate composition of meat?


  • Water: 75%
  • Protein: 19%
  • Fat: 2.5%
  • Carbohydrate: 1.2%
  • Inorganic compounds: 0.65%
• What is the water activity (aw) of meat?


  ~0.99
• What is the typical pH range of meat?


  1. 2 to 7 (~5.6)
• What are the key steps in the production of meat?

  1. Farm
  2. Transport
  3. Lairage
  4. Slaughter
  5. Dressing
  6. Chilling
  7. Cutting and boning
  8. Packaging
  9. Processing
• What are intrinsic bacteria in meat?


  Commensal bacteria naturally present in muscular tissues and blood vessels
• What are extrinsic bacteria in meat?


  Spoilage or pathogenic bacteria that contaminate meat during slaughter, processing, and storage
• What are the main sources of meat contamination?

  • Faeces
  • Hide contact
  • Spilling of body fluids
  • Aerosols and sprays
  • Contaminated hands or equipment
  • Abattoir workers
  • Inappropriate preservation methods

  
• What did the study find regarding bacteria in hams during the slaughter process?


  The highest percentage of total growth was observed in samples taken before scalding, dehairing, or evisceration

  
• What is the significance of Gram-negative bacteria in the study's findings?


  Low percentage of Gram-negatives was found, suggesting limited gut invasion during evisceration
• What are the differences between intrinsic and extrinsic bacteria?

  • Intrinsic bacteria: originate from the gut and reach tissues internally
  • Extrinsic bacteria: derived from the environment and occur only on the meat surface

  
• What factors contribute to the spoilage of meat under warm conditions?

  Growth of both intrinsic and extrinsic bacteria
• What are common meat spoilage bacteria?

  • Salmonella
  • E. coli
  • Lactic Acid Bacteria (LAB)
  • Staphylococcus
  • Shewanella
• What are the factors and changes associated with meat spoilage?


  • Carbohydrates: Glycogen and glucose
  • Protein: Collagen, actin, myosin, myoglobin
  • Lipids: Various fatty acids and compounds
  • Changes: Production of CO2, organic acids, aldehydes, ketones, and short-chain fatty acids

  
• What are the preservation methods for meat?


  • Raw fresh meat
  • Cured meats
  • Fermented meats
  • Aerobic chill storage
  • Vacuum packing
  • Modified atmosphere packing
  • Canning
  • Freezing
• What are some meat-borne pathogens?

  Salmonella species, E. coli O157:H7, C. jejuni, L. monocytogenes, C. botulinum
• What is the role of the FSA Meat Hygiene Service?


  • Provides verification, audit, and inspection in slaughterhouses
  • Ensures animal welfare at slaughter
  • Conducts meat inspection for human consumption
  • Performs HACCP analysis and emergency controls

  
• What percentage of UK households purchase seafood?


  Around 97%
• What types of seafood are included in the study material?

  • Fish (round, flat, fatty, freshwater/seawater)
  • Crustaceae (lobsters, crabs, shrimps, prawns)
  • Molluscs (mussels, oysters, clams)
• What is the microflora of fresh fish?


  • Skin: ~10^3 – 10^5 cfu/cm²
  • Gills: ~10^3 – 10^4 cfu/g
  • Intestines: ~10^3 – 10^9 cfu/g
  • Lower counts in clean, cold waters; higher in polluted waters
• How does spoilage of fresh fish differ from fresh meat?


  Fish spoilage begins immediately after death, has a higher pH, and uses protein/amino acids earlier
• What are the microbial spoilage processes in fish?


  1. Indole production from tryptophan
  2. Formation of ammonia from deamination of amino acids
  3. Formation of TMA from TMAO conversion
• What are the preservation methods for fish?


  • Raw fresh fish
  • Frozen products
  • Dried fish
  • Fermented fish
  • Smoked fish
  • Marinated fish
  • Canned fish
  • Cooked products
• What are some fish-borne diseases mentioned in the study material?

  Vibrio cholerae, Vibrio parahaemolyticus, Vibrio vulnificus, enteric viruses
• What are the particular problems associated with bivalve molluscs?


  • Concentrate pathogens and toxins
  • Grow in polluted waters
  • Frequently eaten raw or lightly cooked
  • Often consumed whole

  
• What are the categories for shellfish harvesting areas based on CFU/100g?


  • Category A: <230 E. coli, <300 Coliforms (direct consumption)
  • Category B: <4,600 E. coli, <6,000 Coliforms (must be treated)
  • Category C: <60,000 Coliforms (must be relaid)
  • Category D: >60,000 Coliforms (prohibited)
• What are the conclusions regarding bacteria in meat and fish?


  • Bacteria are naturally present in both
  • Predominant bacteria in meat: Gram-positive, facultative anaerobes (LAB)
  • Predominant bacteria in fish: Gram-negative aerobes
  • Natural bacteria involved in spoilage and fermentation
  • Most pathogens controlled by heating

  
• What further reading is suggested in the study material?

  • Gill. 1979. Intrinsic Bacteria in Meat.
  • Kosowska et al. 2017. Volatile compounds in meat.
  • Reith. 1926. Bacteria in muscular tissues.
  • Weinroth et al. 2019. Ground beef microbiome changes.