47
Food Microbiology Lecture #9

Microbiology Bio 127 Food Microbiology

Embed Size (px)

Citation preview

Page 1: Microbiology Bio 127 Food Microbiology

Food Microbiology

Lecture #9

Page 2: Microbiology Bio 127 Food Microbiology

Conditions for Spoilage

•Water•pH •Physical structure•Oxygen•temperature

Page 3: Microbiology Bio 127 Food Microbiology

Microorganism Growth in Foods

Page 4: Microbiology Bio 127 Food Microbiology

Intrinsic Factors• composition

• pH

• presence and availability of water

• oxidation-reduction potential– altered by cooking

• physical structure

• presence of antimicrobial substances

Page 5: Microbiology Bio 127 Food Microbiology

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

Page 6: Microbiology Bio 127 Food Microbiology

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

Page 7: Microbiology Bio 127 Food Microbiology

Physical structure

• grinding and mixing increase surface area and distribute microbes– promotes microbial growth

• outer skin of vegetables and fruits slows microbial growth

Page 8: Microbiology Bio 127 Food Microbiology

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

Page 9: Microbiology Bio 127 Food Microbiology

Extrinsic Factors• temperature

– 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

Page 10: Microbiology Bio 127 Food Microbiology

Microbial Growth and Food Spoilage• 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

Page 11: Microbiology Bio 127 Food Microbiology
Page 12: Microbiology Bio 127 Food Microbiology

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)

Page 13: Microbiology Bio 127 Food Microbiology

General Principles

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

Page 14: Microbiology Bio 127 Food Microbiology

Spoilage•Meat

•Cutting board contamination•Conveyor belts•Temperature•Failure to distribute quickly•Fecal bacteria from intestines

•Fish•Polluted waters•Transportation boxes

Page 15: Microbiology Bio 127 Food Microbiology

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

Page 16: Microbiology Bio 127 Food Microbiology

Food-Borne Diseases

• two primary types– food-borne infections– food intoxications

Page 17: Microbiology Bio 127 Food Microbiology

Preventing Foodborne Disease

•Food infections (microbes are transferred to consumer)•Food poisoning (results from the toxin consumption)

Page 18: Microbiology Bio 127 Food Microbiology
Page 19: Microbiology Bio 127 Food Microbiology

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

Page 20: Microbiology Bio 127 Food Microbiology

Toxins• ergotism

– 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

Page 21: Microbiology Bio 127 Food Microbiology
Page 22: Microbiology Bio 127 Food Microbiology

Controlling Food Spoilage

Page 23: Microbiology Bio 127 Food Microbiology

Removal of Microorganisms

• usually achieved by filtration

• commonly used for water, beer, wine, juices, soft drinks, and other liquids

Page 24: Microbiology Bio 127 Food Microbiology

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

Page 25: Microbiology Bio 127 Food Microbiology

High Temperature

• canning

• pasteurization

Page 26: Microbiology Bio 127 Food Microbiology

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

Page 27: Microbiology Bio 127 Food Microbiology

Spoilage of canned goods

• spoilage prior to canning

• underprocessing• leakage of

contaminated water into cans during cooling process

Page 28: Microbiology Bio 127 Food Microbiology

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

Page 29: Microbiology Bio 127 Food Microbiology

Water Availability

Page 30: Microbiology Bio 127 Food Microbiology

Chemical-Based Preservation

• GRAS– chemical agents “generally recognized as safe”

• pH of food impacts effectiveness of chemical preservative

Page 31: Microbiology Bio 127 Food Microbiology
Page 32: Microbiology Bio 127 Food Microbiology

Radiation• ultraviolet (UV) 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

Page 33: Microbiology Bio 127 Food Microbiology

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

Page 34: Microbiology Bio 127 Food Microbiology

comparison of PCR andgrowth for detection of Salmonella

Page 35: Microbiology Bio 127 Food Microbiology

nucleic acid can be detectedeven when plaque-formingability is lost

Page 36: Microbiology Bio 127 Food Microbiology

Surveillance for food-bornedisease• 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

Page 37: Microbiology Bio 127 Food Microbiology

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

Page 38: Microbiology Bio 127 Food Microbiology

Helpful Suggestions

•Refrigerate quickly•Wash hands•Clean cutting boards•Leftovers•Avoid home-canned foods

Page 39: Microbiology Bio 127 Food Microbiology

Microbiology of Fermented Foods

• major fermentations used are lactic, propionic, and ethanolic fermentations

Page 40: Microbiology Bio 127 Food Microbiology

Fermentation

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

Page 41: Microbiology Bio 127 Food Microbiology
Page 42: Microbiology Bio 127 Food Microbiology
Page 43: Microbiology Bio 127 Food Microbiology

Meat and Fish

• sausages

• hams

• bologna

• salami

• izushi – fish, rice and vegetables

• katsuobushi – tuna

Page 44: Microbiology Bio 127 Food Microbiology

Wine

White vs. Red: juice or juice and skin

Yeasts: Ferment when no oxygen around.Saccharomyces species

DrySweetSparklingFortified

Page 45: Microbiology Bio 127 Food Microbiology

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

Page 46: Microbiology Bio 127 Food Microbiology

Other Fermented Foods

• silages– fermented grass, corn, and other fresh animal feeds

Page 47: Microbiology Bio 127 Food Microbiology

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