Other food preservation and processing methods and assessment of risks

What is the water activity in food?

Proportion of available water in food for micro organisms needs

What factors affect microbial growth in food?

How does adding salt affect microbial growth and survival in food?

Reduces water activity in food

What is the name for organisms that can grow in dry food?

Xerophilic

What is salt and curing and how does it work?

• Add 2-6% salt, Nitrite <150ppm max

• Salt reduced the water activity

• Gives red/pink colour when cooked

List examples of food additives

• Polyphosphates ( increase the ability of meat proteins to bind water. Enable incorporation of additional water, up to 30%)

• Antioxidants (Ascorbic acid)

• Food colours

• Preservatives

• Sweeteners (saccharin, acesulfame K, aspartame)

• Flavour enhancers (Na glutamate)

• Emulsifiers

What do polyphosphates do?

Increase the ability of meat proteins to bind water

What are the different types of curing?

• Dry curing

• Curing by injection

Define fermentation

• Phase of intensive growth and metabolism of lactic acid bacteria accompanied with rapid fall of pH

or

• Any partial breakdown of carbohydrates taking place in the absence of oxygen

What is the difference between natural fermentation and fermentation with starter cultures

Natural fermentation : gram negative flora replaced by gram positive

Fermentation with starter cultures: course essentially same but faster- add a culture

What factors lead to fermentation?

• Salt and drying: decrease a_w

• pH

• Antagonism

• Possibly pasteurised afterwards

What is smoking?

• A result of aerobic or anaerobic pyrolysis of woods, their polysaccharides: cellulose, hemi-cellulose and lignin

• Intensive exothermic nature

• Can be cold (30), warm (40-60) and hot (70-80)

What are the different ways of smoking?

Can be hardwood smoke or liquid (injected)

What is the maximum temperature of smoking and why?

• Not higher than 300°C

  • High temperatures can lead to inc. in carcinogens (Polycyclic aromatic hydrocarbons (PAHs))

What are the methods of drying?

• Keeping product suspended in air

• Lyphophilization (freeze drying)- frozen then low pressure and temp then removes ice by sublimation

What are the three groups of drying?

Based on final a_w values:

• High moisture products: 0.9-1.0

• Intermediate moisture products: 0.6-0.9 can be stored without refrigeration

• Low moisture products: <0.6 that are self stable

What are the heat treatments available?

• Pasteurisation in water or steam at temps <100°C

  • Various sausages, canned hams, hot-smoked meats

• Boiling in water at 100°C, product centre reaches 80-90°

  • Liver paté, black pudding, sausage etc.

• Commercial sterilisation at >100°C in pressurised steam autclaves

  • Canned mats sealed, botulinum treated can be stored for years

Example of an acid tolerant food borne pathogen

E. coli O157

What are the different divisions of the descriptive risk assesment in meat products?

• Uncooked

  • Fermented sausages

  • Dry, raw meats

• Cooked

  • Cooked, uncured meats

  • Cooked, cured meats

Which food borne pathogen produces spores?

Clostridium perfingens

Bacillus

What are the potential hazards associated with fermented (dry, raw) sausages?

From raw meat and/or contaminated equipment during batter preparation

• Foodborne bacteria (Listeria monocytogenes, Staphylococcus aureus)

• Toxins (enterotoxin S. aureus, aflatoxins on the surface)

• Parasites (Trichinella)

• Biogenic amines (tyramine)

What are the potential hazards associated with dry, raw meats?

• Growth and toxin production of botulinum due to low-quality raw meat, insufficient curing at higher temps.

What hazards are associated with undercooked uncured meats?

E. coli O157, Listeria monocytogenes, Salmonella and parasites (Trichinella)

• The risks greater with burgers, pathogens distributed throughout the product due to mincing (survival)

What temperature is required for inactivation of most aerobic mesophilic bacteria?

72°C for 2 minutes

What hazards are associated with lightly cooked (pasteurized) uncured meats?

• Clostridium perfingens, vegetative bacteria killes, but spores survive and germinate during refrigeration

• Heat stable S. aureus wont be inactivated

• Salmonella and L. monocytogenes post cooking cross- contamination

• Meat should be consumed shortly after cooking, stored at >63°C or rapidly cooled <4°C

What are the hazards associated with self-stable uncured sterilised cans?

• Botulinum cooked cans

  • Contamination with bacterial spores due to insufficient heat treatments

  • Main hazard clostridium botulinum

  • Faulty cans- cooling water can be sucked through

What are the main hazards associated with pasteurised cured meats?

• Listeria monocytogenes and S. aureus (halotolerant), % of salt and nitrites insufficient to prevent growth

• L. monocytogenes – psychrotroph, growth during refrigeration

• S. aureus – for growth and enterotoxin production higher temperature and the presence of oxygen required

• Possible recontamination – all other foodborne pathogens

• Gammon usually not cooked, so naturally present microbiota

What are the hazards with pasteurised cured sausages?

• Listeria monocytogenes – halotolerant, % of salt and nitrites insufficient to preventgrowth

• Possible recontamination during slicing and packing (S. aureus too)

What is mechanically separated meat?

• Paste-like meat product produced by forcing pureed or ground pork, turkey or chickenn under high pressure thorugh a sieve to separate bone from edible meat tissue

• MSM from all ruminants banned for human consumption