1. Food Preservation

2. Conditions for Spoilage
Water pH
Physical structure
Oxygen
temperature

3. Microorganism Growth in Foods

4. Intrinsic Factors composition pH presence and availability of water
oxidation-reduction potential
altered by cooking
physical structure
presence of antimicrobial substances

5. Composition and pH putrefaction
proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds
pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food

6. Water availability
in general, lower water activity inhibits microbial growth
water activity lowered by:
drying
addition of salt or sugar
osmophilic microorganisms
prefer high osmotic pressure
xerophilic microorganisms
prefer low water activity

7. Physical structure
grinding and mixing increase surface area and distribute microbes
promotes microbial growth
outer skin of vegetables and fruits slows microbial growth

8. Antimicrobial substances
coumarins – fruits and vegetables
lysozyme – cow’s milk and eggs
aldehydic and phenolic compounds – herbs and spices
allicin – garlic
polyphenols – green and black teas

9. Extrinsic Factors temperature relative humidity atmosphere
lower temperatures retard microbial growth
relative humidity
higher levels promote microbial growth
atmosphere
oxygen promotes growth
modified atmosphere packaging (MAP)
use of shrink wrap and vacuum technologies to package food in controlled atmospheres

10. Microbial Growth and Food Spoilage
results from growth of microbes in food
alters food visibly and in other ways, rendering it unsuitable for consumption
involves predictable succession of microbes
different foods undergo different types of spoilage processes
toxins are sometimes produced
algal toxins may contaminate shellfish and finfish

12. Food Spoilage
Approximately 1/3rd of all food manufactured in world is lost to spoilage
Microbial content of foods (microbial load): qualitative (which bugs) and quantitative (how many bugs)
Shelf life
Non-perishable foods (pasta)
Semiperishable foods (bread)
Perishable foods (eggs)

13. General Principles Minimize contamination by:
Good management processes
Acceptable sanitary practices
Rapid movement of food through processing plant
Well-tested preservation procedures

14. Spoilage Meat Cutting board contamination Conveyor belts Temperature
Failure to distribute quickly
Fecal bacteria from intestines
Fish
Polluted waters
Transportation boxes

15. Spoilage Poultry and Eggs Human contact Penetration by bacteria
Milk and Dairy Products
Lactobacillus and Streptococcus species that survive pasturization (sour milk)
Breads
Spores and fungi that survive baking
Grains
Fungi produce toxins

16. Food-Borne Diseases two primary types food-borne infections
food intoxications

17. Preventing Foodborne Disease
Food infections (microbes are transferred to consumer)
Food poisoning (results from the toxin consumption)

19. Food-Borne Intoxications
ingestion of toxins in foods in which microbes have grown
include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning

20. Toxins ergotism aflatoxins fumonisins
toxic condition caused by growth of a fungus in grains
aflatoxins
carcinogens produced in fungus-infected grains and nut products
fumonisins
carcinogens produced in fungus-infected corn

22. Controlling Food Spoilage

23. Removal of Microorganisms
usually achieved by filtration
commonly used for water, beer, wine, juices, soft drinks, and other liquids

24. Low Temperature
refrigeration at 5°C retards but does not stop microbial growth
psychrophiles and psychrotrophs can still cause spoilage
growth at temperatures below -10°C has been observed

25. High Temperature
canning
pasteurization

26. Canning
food heated in special containers (retorts) to 115 °C for 25 to 100 minutes
kills spoilage microbes, but not necessarily all microbes in food

27. Spoilage of canned goods
spoilage prior to canning
underprocessing
leakage of contaminated water into cans during cooling process

28. Pasteurization
kills pathogens and substantially reduces number of spoilage organisms
different pasteurization procedures heat for different lengths of time
shorter heating times result in improved flavor

29. Water Availability

30. Chemical-Based Preservation
GRAS
chemical agents “generally recognized as safe”
pH of food impacts effectiveness of chemical preservative

32. Radiation ultraviolet (UV) radiation Gamma radiation
used for surfaces of food-handling equipment
does not penetrate foods
Gamma radiation
use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables

33. Detection of Food-Borne Pathogens
must be rapid and sensitive
methods include:
culture techniques – may be too slow
immunological techniques - very sensitive
molecular techniques
probes used to detect specific DNA or RNA
sensitive and specific

34. comparison of PCR and
growth for detection of
Salmonella

35. nucleic acid can be detected
even when plaque-forming
ability is lost

36. Surveillance for food-borne disease
PulseNet
established by Centers for Disease Control
uses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen
enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source

37. Surveillance… FoodNet
active surveillance network used to follow nine major food-borne diseases
enables public health officials to rapidly trace the course and cause of infection in days rather than weeks

38. Helpful Suggestions
Refrigerate quickly
Wash hands
Clean cutting boards
Leftovers
Avoid home-canned foods

39. Microbiology of Fermented Foods
major fermentations used are lactic, propionic, and ethanolic fermentations

40. Fermentation
Any partial breakdown of carbohydrates taking place in the absence of oxygen.

43. Meat and Fish sausages hams bologna salami
izushi – fish, rice and vegetables
katsuobushi – tuna

44. Wine White vs. Red: juice or juice and skin
Yeasts: Ferment when no oxygen around.
Saccharomyces species
Dry
Sweet
Sparkling
Fortified

45. Production of Breads
involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions
maximizes CO2 production, which leavens bread
other microbes used to make special breads (e.g., sourdough bread)
can be spoiled by Bacillus species that produce ropiness

46. Other Fermented Foods silages
fermented grass, corn, and other fresh animal feeds

47. Microorganisms as Foods and Food Amendments
variety of bacteria, yeasts, and other fungi are used as animal and human food sources
probiotics
microbial dietary adjuvants
microbes added to diet in order to provide health benefits beyond basic nutritive value