9. Food microbiology Flashcards
(40 cards)
-which type of microorgs are most often involved in foods? (3)
- describe the characteristics of the main one ish (gram WHAT, aero or anaerobic?, shape? –> 2 types of fermentation
- what 2 things are produced: why?
- lactic acid bacteria, variety of yeasts (ie saccharomyces stains) and molds (ie aspergillus stains)
- lactic acid bacteria: gram-positive, aerotolerant, rods or cocci
1) HOMOfermentative: fermentation yields primarily/ONLY lactic acid (pickles, sauerkraut).
2) HETERO fermentative: fermentation yields lactic acid AND a variety of flavorful compounds (waste product for bacteria) (fermented sausages such as salami, fermented milk products). - Lactic acid reduces food spoilage (by decreasing pH) and improves storage qualities (brings the pH down).
- Flavor compounds produced by different organisms give each product its distinctive
taste.
- does milk naturally contain lactic acid? what is usually done to make milk products?
- how to make yogurt? which bacterias? explain 3 steps ish
- how to make cheeses? which bacterias? 2 main steps
- yes! but usually pasteurized to remove potential pathogens (to have a more controlled product) –> desired microorgs are then added back to give the final product
YOGURT
- cultures of streptococcus thermophilus and lactobacillus bulgaris are added + incubated at 42°C
1) streptococci produces some acids (ie lactic acid) and favors growth of lactobacillus which produce most of the acid
2) acid denatures casein (by decrease pH) –> which results in thickening of milk
3) other microorgs are sometimes added (BL, bifidobacterium animalis)
CHEESE:
- hundreds of microorgs may be involved. raw milk cheese may contain pathogens
1) Curdling: lactic acid bacteria precipitate the proteins –> curd
2) Ripening: lactic acid bacteria ± other organisms –> flavor
what are the steps of cheese production? 7 steps
1) most milk will be pasteurized + standardized + filtered OR traditional cheese making –> raw milk
2) Starter cultures of lactic acid bacteria are added –> ferment lactose and produce lactic acid: promotes development of curd (precipitated proteins, fat and other suspended material) and whey (supernatant).
3) Usually, an enzyme, rennin, is added to the culture. Rennin cleaves casein which results in curd formation. (Rennin or lactic acid bacteria work, one or the other or both)
4) Whey is drained off: starting material for other processes, or discarded (high BOD, must be treated like sewage)
5) Curd is then heated (T° depending on final product): more whey is expelled, and the curd becomes more solid
6) Salt may be added: flavor, promotes extraction of water, inhibits growth of spoilage organisms.
7) Packaging (fresh cheese like cottage and cream cheese), or other processes: pressing, brining, ripening.
what is done with the whey produced during cheese making?
used to be thrown in the sewage but now: try to make it more sustainable and use it for other purposes: ie added to chips to make it cheese flavored
CHEESE RIPENING:
- ripening leads to changes in (3) –> these changes are due to what? (2 ish)
- explain process for cheddar, swiss (which bacteria) and gouda
- for how long is the ripening?
- the longer the ripening, the higher (2)
- oka: which bacteria?
- changes in texture, consistency, and flavor –> Due to the presence of specific microorganisms added
with starter culture or spread on the surface of the pressed curd + Some of the ripening is due to lactic acid bacteria, rennin or other enzymes present.
CHEDDAR, SWISS, GOUDA
- Wrapped (cheddar in paper, gouda in wax)
- Cheddar: ripening involves the lactic acid bacteria only (might get crunchy parts in your cheese –> crystals of lactic acid)
- Swiss cheese: propionibacteria produce propionic acid and acetic acid (flavor), and CO2 (bubbles).
- 3-12 months (or longer)
- The longer the ripening the higher the acidity and sharpness.
- Oka: pressed curd is brined, and surface is washed frequently. Growth of Geotrichum
CHEESE - ripening:
- blue and roquefort: what bacteria? explain. how long?
- why blue?
- camembert, brie: wrapped? what microorgs? what conditions for ripening? how long? why is the cheese soft?
BLUE/ROQUEFORT:
- Ripening is mainly due to the mold
Penicillium roquefortii.
- Spores from the mold are mixed with the milk (or the curd)
- Small holes are drilled in the curd before inoculating with bacteria + wrapping.
- 3-6 months.
- The mold grows in the holes (hyphii network) and produces spores (blue) + also produces proteases: affects texture of cheese
CAMEMBERT/BRIE:
- Unwrapped
- Mixture of mold (Penicillium) and bacteria (Brevibacterium) that are spread on the surface of the curd.
- Ripened in curing room (high humidity)
- 1-5 months.
- Proteases secreted by the microorganisms is responsible for softening of the cheese (break down protein so bacteria can have protein)
– Good sanitary practices are required so that the cheese does not get contaminated
*tends to smell like ammonia
WINE:
- difference between red and white wine?
- main steps?
- what is must?
- what can be added to wine? what does it do?
- which 2 main microorgs (bacteria, yeast or mold?) –> 2 good characteristics
- red: not filtered, everything is fermented including stalks, skin, etc. VS WHITE: only ferment juice (no stalks or skin)
- pressing + fermentation + aging + bottling
- MUST = crushed grapes
- metabisulfite (Na2S2O5) –> can be added to kill wild yeasts –> wild yeasts = hard to control + cannot tolerate high levels of alcohol
- commercial yeasts: S. cerevisiae and S. ellipsoideus:
resistant to Na2S2O5 + tolerate 12- 14% alcohol.
WINE:
- what may be added to final product (2)
- dry vs sweet wine?
- Sugar and organic acids may be added depending on the final product.
- DRY WINE: all the sugar is fermented (ie all becomes ethanol) –> use commercial yeast OR choose low sugar starting product
- SWEET WINE: some sugar is left or
added after fermentation –> not all is converted to ethanol
BEER:
- what is the main grain for making beer?
- can grains be digested by yeasts? solution?
- explain the steps to make beer: 9 steps ish
- Barley
- Grains contain starch that CANNOT be digested by yeasts –> Grains (BARLEY!) are allowed to germinate, producing amylase
1) MALTING: grains germinate (spray some water + right temp) to produce amylase
2) The grains are then dried (+ sometimes roasted) and crushed –> makes MALT
3) MASHING: Malt is then soaked in warm water (65°C) for 1-2h –> amylase degrades starch into fermentable sugars (glucose and maltose)
4) The mash is then filtered –> produces WORT
5) Hops is added to the wort. Wort is boiled for 1-2 hours (near sterilization, but not completely, some spores remain)
6) Commercial beer: filtered.
7) Cooled to 20°C
8) Yeast is added
9) Polishing: filtration, carbonation, pasteurization, etc.
- why is hops added to beer? (3 ish) added in which step?
- which microorgs (yeasts, mold, bacteria) are added to beer? 2 types + fermented at which temperature (important!) + top or bottom + produces what?
- how to make light beers?
- Hops gives flavor and bitterness. It also has antimicrobial properties and prevents lactic acid bacteria from growing in the final product
- added to wort before it’s boiled for near sterilization and before yeast is added
YEASTS!
- LAGER: Saccharomyces carlsbergensis (bottom yeasts, 6-12 °C) –> takes months to produce: only ethanol is produced
- ALE: Saccharomyces cerevisisae (top yeasts (so much CO2 produced that it floats on top of beer, carried up by CO2 during fermentation, 14- 23 °C) –> ethanol + flavors!
- Light beers: yeasts manipulated genetically so they can use all the sugars in the wort (just like dry wine!)
DISTILLED ALCOHOLIC BEVERAGES
- similar to _______ making process BUT what is different? (2)
- give examples + starting material (5)
- then what is done?
- aged types –> what is done?
- what can be added?
to beer making BUT hops is NOT added + different grains are used
- Vodka: wheat, rye or potatoes
- Gin: grains or starchy product + juniper oil and other flavor ingredients
- Rum: sugar cane (molasses)
- Brandy/Cognac: wine
- Whiskies: malt brews (like beers but ferment mash without boiling it)
- basically extract alcohol + other flavour compounds –> then alcohol is distilled
- Aged: diluted with water.
- Flavor ingredients are added (ie steep with herb/flowers/plants)
whiskey:
- what type of beverage?
- use what starting material (2)
- process?
- distilled alcoholic beverages
- malt brew (scotch) (from mashing barley, extract –> wort –> ferment) or other cereals (corn in the US)
- wort is NOT boiled –> mixed fermentation of added yeasts and resident lactic acid bacteria
what are the factors affecting flavor of distilled alcoholic bevs?
- Water
- Resident lactic acid bacteria/ microbes that fall in the beverage
- Source and cultivar of the barley
- Shape of the still (big thing where the distillation happens ish, can be metal, type of fuel…)
- Ageing in wood cask (ie burned wood = Jack Daniels)
VINEGAR
- what process?
- metabolism of the microbes?
- which microbe used in all commercial application?
- very efficient BUT what can happen and how to prevent?
- explain process ish similar to what process?
- ethanol oxidized to acetaldehyde –> oxidized to acetic acid (vinegar)
- strict aerobes! this is NOT fermentation –> both steps of oxidation allows to make proton motive force –> gives ATP (how the bacteria makes energy!)
- acetobacter
- VERY efficient but in absence of ethanol, will oxidize acetic acid to CO2 and H2O = bad (bc you don’t have vinegar anymore) –> so some ethanol must remain to prevent this + need O2!
- bit like trickling system for water purification: alcoholic juice trickles down beechwood shavings (enough space btw them to have enough O2) –> air is pump into it –> acetic acid collects in collecting chamber –> product removal
FOOD SPOILAGE
- def
- in North America: ___-___% of foods are not suitable for consumption bc of spoilage, up to ___% in developing countries
- which types of microorgs can cause spoilage?
- factors affecting spoilage (8)
- any change in the appearance, smell, taste that makes it unacceptable to the consumer. MAY still be safe to eat, not necessarily a health hazard.
- 10-20% in NA, up to 50% in developing countries (poor infrastructure, transport…)
- molds, yeasts, bacteria.
1) Types of microorganisms involved.
2) Extent of growth of the microorganisms.
3) Moisture content of the food.
4) Temperature.
5) pH.
6) Availability of oxygen.
7) Chemical composition and physical state.
8) Surfaces VS insides, grinding distributes the surface contaminant (ie if you cut it, you bring outside stuff on the inside)
- why does moisture content affect food spoilage?
- what is measured to assess moisture content?
- how to reduce this measurement?
- what are the ranges for fresh food, most spoilage microorgs can grow at most bacteria/yeast unable to grow, S. aureus can grow
explain/define which foods these can spoil. at which Aw?
XEROPHILES
OSMOPHILES
HALOPHILES
- bc all microorgs need water!
- water activity! (measurement of vapour pressure) –> availability of water to microorganisms! ie low Aw = water stays in food = less available for microorgs
- solutes dissolved in water reduces availability of water to microorgs (vapor pressure decreases)
(don’t need to know exactly)
- fresh food: aw > 0.95 (ie cucumber)
- most spoilage microorgs can grow to an aw as low as 0.9
- a < 0.9: most bacteria/yeasts unable to grow. many molds can grow
- a < 0.8: only specialized organisms can grow:
XEROPHILES: dry environment, low osmolarity (breakfast cereal, grains)
OSMOPHILES: high osmolarity, high sugar (ie jams (0.75))
HALOPHILES: high salinity, dry sausage, prosciutto (0.86)
TEMPERATURE:
- what is the danger zone? consequence?
- most pathogens do NOT grow at ____°C except (3) –> these are _________
- does cold kill the microbes?
danger zone: 4°C to 60°C –> microbes can grow! SO Hot foods should be kept above 60°C (steam table) + Cold food should be kept below 4.5°C.
- Most pathogens don’t grow at 4.5°C, except: Yersinia enterocolitica, Listeria monocytogenes (associated with cold cuts), Clostridium botulinum –> Psychrotrophs (able to grow at low T°)
- cold does NOT kill microbes! –> Microorganisms can survive for extended periods of time at 4°C, if the temperature is then allowed to increase, microorganisms can resume growth
pH
- most foods are either ________ or _________
BACTERIA
- many grow at pH as low as ____
- lactic acid bacteria at pH _____
- very few bacteria able to grow below pH _____
MOLDS and YEASTS
- many can grow at pH ___ and lower
- main spoilage organisms in _______ foods (below pH of ___) ie?
- neutral or acidic (not many alkaline foods)
BACTERIA: - many at 5
- lactic acid bacteria at pH 4
- very few below 4
MOLDS and YEASTS:
- pH 4 and lower
- in acidic foods (below pH 4.5) ie orange juice, tomatoes, rhubarb, peaches, vinegar
- what are the benefits of excluding O2 from food packaging? (ie vacuum packaging, canning, modified atmosphere) (2)
- useful for a really long time?
- what can happen?
*O2 required for molds and many aerobic bacteria and yeasts
1) prevent growth of aerobic microbes
2) reduces oxidation of product (can cause color and flavor changes)
- good for a few months, but then O2 can diffuse through plastic
- Some yeasts and many bacteria can grow under anaerobic conditions (ie do fermentation); can cause swelling of the package (CO2
production) –> if you see air inside vacuum packaging = red flag
CHEMICAL COMPOSITION
- _________ available determine types of organisms that grow
- ________ produced and secreted will determine the type of foods that microorgs can use
- meat: high in (2) require (2) –> what microbes?
- vegetables: high in (3)
- fruits: high in (2)
- f&v require (3) –> what microbes?
- nutrients
- enzymes!
MEAT - high in protein and fat
- requires proteases and lipases
- proteolytic and lipolytic microorganisms: bacteria and molds.
VEGTABLES
- high in starch, cellulose, pectin;
FRUITS:
- high in sugars and pectin.
F&V:
- Require saccharase, cellulase, pectinase
- saccharolytic, cellulolytic and pectinolytic microorganisms (bacteria, yeasts (more for starchy, fruits, veg), molds)
- are a lot of fresh foods contaminated with pathogens? explain
- what permits growth of pathogens to a level sufficient to cause illness?
IMPORTANT: what are 2 types of food “diseases” ish + explain their differences
*Many diseases can be transmitted by means of foods. Any food that is handled, processed or stored improperly may be a public health hazard.
- yes! Many fresh foods are contaminated with pathogens, but the initial population is usually too low to cause illness in a healthy individual. Ex.: raw milk.
- subsequent abuse of the food (e.g. storage at warm temperature) permits the growth of pathogens to a level sufficient to cause illness.
1) Food POISONING/INTOXICATION:
- caused by microbial toxins in food (ie microbes grow on food, and produce toxins, and you consume toxins)
- Symptoms appear quickly
- you DONT have infection –> doesn’t last long
2) Food INFECTION:
- organisms are ingested with the food and multiply in the host –> microbes grow inside you!
- Symptoms take longer to develop (ie 48h)
- Illness may be due to tissue invasion, production of toxins or both.
- what are the most common food-borne pathogens in canada? lots of deaths?
NOROVIRUS:
- leading cause of food-borne illnesses and hospitalizations!
- super contagious: 1M illnesses
- but not many deaths (21)
LISTERIA: leading cause of DEATHS related to food-borne illness
- 178 illnesses, 35 deaths
SALMONELLA:
- 88 000 illnesses, 17 deaths
E. COLI O157:
- 12 800 illnesses, 8 deaths
CAMPYLOBACTER:
- 145 000 illnesses, 5 deaths
- low death, not uper contagious
what are the top 10 causes of food-borne diseases?
- Leaving cooked foods at room temperature and/or storing foods in large containers in fridges
- Lapse of 12 h or more between preparation and consumption
- Colonized/infected persons handling food
- Inadequate reheating
- Improper hot holding (should be at 60°C)
- Contaminated raw food/ingredients (ie you don’t wash your veggies)
- Foods from unsafe sources (ie poorly stored/processed)
- Improper cleaning of equipment
- Cross contamination – raw to cooked (ie same cutting board for raw chicken and salad)
- Inadequate cooking
BOTULISM:
- causes food poisoning, intoxication or infection?
- which bacteria produces WHAT
- ___% mortality –> causes what symptoms? (5 ish)
- lasts how long?
- what metabolism? produces endospores?
- what are risk factors (3)
- does heating food destroy toxin? spore?
food intoxication/poisoning! (bc you consume the toxin!)
- Clostridium botulinum –> produces AB-type neurotoxin
- 10% mortality –> causes flaccid paralysis, respiratory or cardiac failure + difficulty swallowing, double vision, breathing difficulty, paralysis
- lasts 1-2 days.
- Anaerobe! produces endospores
RISK FACTORS:
- Home canning, insufficient heat to kill the spores.
- Processed foods that are not reheated (non-acid canned vegetables, sliced meats)
- Spores germinate, growth, toxin is produced
- Toxin is destroyed by heating (80°C, 10 min) –> properly cooked foods are sage to eat; it destroys toxin but not the organisms/endospores
*honey contains lot of spores –> don’t give to infants: don’t have enough microbiota to kill the spores = kills the baby
