Food Hygiene: Principles and Microorganisms

• Food Hygiene involves ensuring the safety of food from production to consumption.
• Food can be contaminated at any point during slaughtering, harvesting, processing, storage, distribution, transportation, and preparation.

Why food is a good vehicle for pathogens

• Food contains nutrients.
• Food handling from farm to table can increase levels of contamination.
• Food-borne pathogens don't discriminate based on the scale of production or management practices.

The Five Key Principles of Food Hygiene (WHO)

• Prevent pathogens contaminating food spread from people, pets, and pests .
• Separate raw and cooked foods to prevent contamination.
• Cook foods for the appropriate amount of time and at the appropriate temperature to kill pathogens.
• Store food at the correct temperature.
• Use safe water and raw materials.

Microorganisms in Food - Molds

• Molds are multicellular fungi that form filamentous growth known as mycelium, composed of filaments known as hyphae.
• They may grow submerged or on the surface of food.
• Fuzzy or cottony appearance characterizes mold growth.
• Molds grow at temperatures from 20-30°F, but many will grow near 0°C.
• Mold growth in meat occurs in humid atmospheres nearly freezing.
• Molds grow better in an acid environment, pH 6 is near optimum.

Molds In Meat

• Black spot caused by Cladosporium herbarum which is a growth of 1/4-1/2 inch dark in color caused by the dark threads of fungus.
• White spot is caused by Sporotrichum carnis seen as small, flat, woolly spots.
• Sporotrichum carnis develops at -8°C and grows profusely above 0°C.
• Thamnidium elegans and S.carnis is found on meat in chilling storage causing “whiskers” and “white spot".
• Whiskers are due to Thamnidium and Mucor (M. mucedo); it grows over one inch beyond the surface of the meat, and grows well at 0°C.
• Bluish green molds are due to the genus Penicillium, frequently seen on cheese, unsound fruit and meat with superficial growth and occur slightly higher than 0°C
• Brown to black rots in fruits, wheat, and meat are caused by Alternaria.

Microorganisms in Food - Yeasts

• Yeasts are unicellular fungi and do not form mycelium.
• They are slightly bigger than bacteria.
• They reproduce asexually by budding.
• Yeasts grow best at room temperature and are inhibited above 37°C.
• Yeasts are easily killed by heat during cleaning.

Microorganisms in Food - Viruses

• Viruses are ultramicroscopic filterable agents.
• Viruses are composed of protein surrounding a nucleic acid core, either DNA or RNA.
• Viruses are strictly parasitic within living cells.
• Viruses have specificity for certain hosts and even on specific cells.
• Viruses do not reproduce in food, unlike bacteria.
• Viruses contaminate food through poor personal hygiene of food handlers or contaminated water.

Common Foodborne Viruses & Characteristics

• Norovirus/Caliciviridae: Genome is ss RNA, causes gastroenteritis, source is from human stool/vomit, the transmission is fecal-oral with foods like berry fruit, deli meat, and shellfish, and the risk level is high.
• Hepatovirus A/Picornaviridae: Genome is ss RNA, causes Hepatitis A, source is human stool, the transmission is fecal-oral/person-to-person with foods like deli meat, raw beef, water, shellfish, and fruit, the risk level is high.
• Orthohepevirus: Genome is ss RNA, causes Hepatitis E, source is Pig Liver, transmission is environmental through Pork, and is low to moderately risky.
• Enteric viruses have a fecal-oral route of transmission.
• Enteric viruses causes viral gastroenteritis, and are common in water and foods like shellfish.
• Enteric viruses has a rapid recovery rate with only a few particles needed to infect.
• Enteric viruses is stable, acid-resistant, and inactivated by cooking temperature.

Detecting Viruses

• Detecting viruses has limitations.
• Viruses do not grow in culture media.
• Viruses are very small in size.
• Use Immunoassay or Viral genome analysis to detect viruses.

Microorganisms in Food - Bacteria

• Bacteria are single-celled with a size ranging from 0.5 – 5 microns.

• They reproduce by binary fission.

• The generation time is from 20 minutes to 24 hours.

• Bacteria’s growth pattern has different phases: Lag, Log, Stationary and Death.

• Lag phase represents a period of adjustment.

• Log phase is logarithmic or exponential.

• Stationary phase represents the number of viable bacteria remains constant.

• Death rate represents the death rate exceeding the rate of multiplication.

• Preservation methods aim at lengthening the lag phase.

• Methods hinder the growth of bacteria during the log phase by subjecting them to unfavorable conditions.

• The small size of bacteria allows it to transfer easily from hands, rodents, insects, birds, dust particles and air.

• Presence is not obvious until huge numbers are present.

• FACTORS of bacteria include Food / Nutrients, Acidity / Alkalinity, Temperature, Time, Oxygen / Gaseous environment, Moisture, and Initial number also have an impact.

Food

• If food has sufficient nutrients available that promote the growth of microorganisms.
• Protein-rich foods, such as meat, milk, eggs and fish are most susceptible.
• In order to grow and function normally, microorganisms require water, a source of energy, a source of nitrogen, vitamins, growth factors and minerals.

Acidity / Alkalinity

• Optimum growth of bacteria is usually near pH 7 (6.6-7.5)
• Some bacteria grows at about pH 4.
• Below pH 6, growth slows down, thus pickling of food at low pH is a common method of preservation.
• Most potentially hazardous food has a pH level between 4.6 and 7.0.
• pH of food is also important in the calculation of heat treatment in the canning industry.
• Low acid receives higher heat treatment than acid foods.
• Bacteria will not grow well at a pH below 4.6.

Temperature

• Temperature has the greatest effect on the rate of growth of bacteria.
• Foodborne pathogens grow best in temperatures between 4°C to 60°C, noted as the temperature danger zone (TDZ).
• According to the 2005 FDA Food Code, the danger zone is defined as 41°F - 135°F (5°C - 57°C).
• Groups of bacteria has temperature requirements.
• Thermophiles, Mesophiles, Psychrophiles & Psychrotrophs

Bacteria Temperature Requirements

• Thermophiles: minimum temp for growth 37-40, Optimum temp 45-75 & Maximum temp of growth 60-80; examples: Bacillus, Clostridium botulinum, Clostridium thermosacharolyticum
• Mesophiles: minimum temp for growth 8-15, Optimum temp 20-45 & Maximum temp of growth 40-50; examples: Salmonella, Staphylococcus, Shigella, Escherichia coli
• Psychrophiles: minimum temp for growth -5 to +5, Optimum temp 10-15 & Maximum temp of growth 20; examples: Moraxella, Thamnidium elegans, Vibrio
• Psychrotrophs: minimum temp for growth -5 to +5, Optimum temp 10-37 & Maximum temp of growth 20-50; examples: Listeria monocytogenes, Yersinia enterocolitica, Lactobacillus Pseudomonas
• Growth of mesophiles is rapid at body temperatures of freshly dressed carcass but does not happen below 8°C.
• Below 8°C which is the temperature range of chilled foods, psychrophiles and psychrotrophs are the important group.
• Optimum growth rate for the psychrotrophic bacteria occurs at a temperature higher than the minimum temp.
• If bacterial growth is to be avoided for flesh type foods, they must be quickly cooled and maintained at low temp during storage, processing, packaging and transport
• Cook Pork, Veal, and Lamb to 71°C (160°F).
• Cook Ground Meat to 71°C (160°F).
• Cook Whole chicken/turkey to 82°C (180°F).
• Cook Chicken/turkey stuffing (inside temp.) to 74°C (165°F).
• Cook Chicken/turkey pieces to 77°C (170°F).
• Cook Ground Poultry to 74°C (165°F).
• Cook Beef steaks/roasts to 63°C (145°F) for medium rare, 71°C (160°F) for medium, or 77°C (170°F) for well done.

Time

• Food should be removed from "the danger zone" within two hours.
• Most guidelines state two hours, while a few indicate four hours is still safe.

Oxygen

• They are classified into the following by their response to oxygen:
• Aerobic prefers to grow in an atmosphere containing oxygen.
  • Examples: Pseudomonas, Moraxella, Acitenobacter, Flavobacterium
• Anaerobic- Needs no oxygen for growth.
  • Ex: Clostridium
• Facultative anaerobe prefers an atmosphere devoid of oxygen but can grow at a reduced rate with oxygen.
  • Examples: Salmonella, E. coli, Shigella, Listeria, Vibrio, Yersinia, Staphylococcus, Streptococcus
• Microaerophilic prefers a reduced oxygen concentration but not necessarily an absence thereof.
  • Campylobacter jejuni

Moisture

• Water activity (a) – the term that is now used in the context of water relationships between food and spoilage organism; measures the available water.
• Measured on a scale of 0-1.0
• Food-borne pathogens grow best in foods that have aw between 1.0 and 0.85.
• As a decreases, more and more species of bacteria are unable to grow
• Most potentially hazardous food has water activity values of 0.97-0.99 which is ideal for bacterial growth
• Decreasing water activity can be done through freezing, surface drying, or adding sugar/salt.

Initial Numbers

• If the initial count of bacteria is low, lag phase is longer.
• Extent of initial contamination influences the storage life of food; the more bacteria present, the shorter the storage life.