(4) Food Microbiology Flashcards
What are the two types of lactic acid bacteria used in food production and how do they differ?
Homofermentative: yields primarily lactic acid
Heterofermentative: yields lactic acid AND other flavorful compounds
What are the two most used microorganisms in food microbiology?
Lactic acid bacteria
Saccharomyces strands
How is yogurt produced, microbiologically speaking?
Lactic acid bacteria are incubated at 42°C and produce acid -> denatures casein -> thickens
What are the two basic roles of microorganisms when producing cheese?
Curdling: lactic acid bacteria and/or rennin precipitate proteins to make curd
Ripening: lactic acid bacteria w/ or w/o other organisms make flavor and texture change
How are the 5 different cheese ripened?
(lactic acid bacteria = LAB)
Cheddar = LAB
Swiss = LAB + propionibacteria
Oka = LAB + Geotrichum (surface)
Blue & Roquefort = Penicillium Roqueforti
Camambert & Brie = Penicilum + Brevibacterium (surface)
How is vinegar produced?
Not trough fermentation:
Acetobactor (strict aerobe) converts ethanol into acetic acid
In wine making, what is first added?
Metabisulfite -> to kill wild yeast present on grapes
How is red wine and white wine production different?
White wine: skin is removed
Red wine: skin is kept
How is dry wine and sweet wine production different?
Dry = no more sugar => all fermented Sweet = not all fermented or added after full fermentation
What are the 6 steps in beermaking?
Malting: germinate grains -> produce amylase; obtain MALT
Mashing: soak malt in warm water -> amylases transform starch in maltose + glucose; Mash is filtered to obtain WORT
Hops (antimicrobial activity + flavor) added to wort
Boiling of wort (get virtually sterile)
Fermentation:
- S. carlsbergensis {carlsB for Bottom} = bottom yeast = Lager {bottom is Lower -> Lager}
- S. cervisiae = top yeast = Ale
Polishing (filter, add flavorings…)
How are distilled beverages produced?
Malting, Mashing, Fermenting, Distillation, Aging and/or Add flavors
How is Scotch whiskies production different than other distilles beverages?
The wort is not boiled; mixed fermentation done by LAB + yeasts
How can Food Spoilage be defined?
Any change making product unacceptable to the consumer
What microorganism (3) spoil foods?
Bacteria, molds & yeasts
What 6 factors affect food spoilage and their characteristics?
- Moisture content (water activity; if a-w <0.9, most are -inhibited; if a-w <0.8, only specialized organisms survive)
- Temperature (hot > 60°C, cold <4.5°C; prevents further growth)
- pH (molds and yeast can survive below 4.5, bacteria cannot)
- Oxygen availability (required for molds)
- Chemical composition (proteins & fat not accessed by yeasts)
- Surface Vs. Inside
What are the 3 specialized organisms that can survive in low water activity?
Xerophiles (dry env.)
Osmophiles (high osmolarity {sugar})
Halophule (high salt)
How does food poisoning/intoxication differs from food infection?
Poisoning/intoxication = caused by toxins => symptoms appear quickly Infection = organisms ingested infect host => delayed symptoms
Describe two examples of food poisoning/intoxication
Botulism: botulinum toxin is heat-labile (80°C for 10 min), spores are not (dangerous only to infants)
Staphylococcus aureus: carried by humans -> food contamination -> exotoxin (Vs. endo) affecting intestinal cells = enterotoxin
Describe two examples of food infection
Salmonella enterica: infects and grows in intestinal cells. Killed by cooking
E. Coli O157:H7 produces AB-type (shiga-like toxin) once in intestinal cells. If toxin enters bloodstream, may damage kidney cells (hemolytic uremic syndrome). Killed by cooking
What are the 3 main goals of food preservation?
Prevent/delay decomposition by microorganisms
Destroy pathogens or inhibit their growth
Prevent/delay self decomposition by enzymes in food
What are 6 food preservation techniques?
- Refrigerating & Freezing: slows growth, freezing reduces water activity
- Pasteurization: reduce number of microorganisms
- Canning: 100°C for acidic; 121°C for low-acid
- Water availability:
a) drying
c) lyophilisation
c) addition of salt/sugar - Irradiation: protects food’s surface
- Chemicals: control growth microorganisms with Generally Recognized as Safe (GRAS)
What are 3 pasteurization methods for milk?
Long Time Low Temp: 30min, 62.8°C
High Temp Short Time: 15 sec, 71.2°C
Ultrahigh temperature: 2 sec, 141°C (virtually sterile)
In canning, what is the 12D process?
Norm by which if kill 10^12 botulinum spores, consider product sterile
What are 3 GRAS chemicals?
Nitrite -> C. botulinum
Sulfites -> wild yeast
Nisin (produced by lactococcus lactis {cheese})
What are primary metabolites?
Metabolites produced during exponential growth (alcohol)
What are secondary metabolites?
Metabolites produced near the stationary phase (end of growth) -> antibiotics
In industrial microbiology, what is considered fermentation?
Any microbiological process (aerobic or anaerobic)
What two types of organism variation can be used in industrial microbiology?
Spontaneous mutants: overproduce desired metabolites
Genetically modified organisms: cloned genes expressed in bacteria/yeasts
