Food Microbiology and Industry

what are the microorganisms most often involved in fermented food products

lactic acid bacteria and yeasts

lactic acid bacteria (LAB) characteristics

gram+

aerotolerants anaerobes

reduce food spoilage by bringing pH down

can give distinct flavours

homofermentative LAB

fermentation yields lactic acid

ex. pickles

heterofermentative LAB

fermentation yields lactic acid and flavourful compounds

ex. salami

yeast and mold examples

saccharomyces and aspergillus strains

used for anything with soy

milk products and fermentation

milk naturally has LA

certain microorganisms are added back to create the desired final product

what microorganisms are added to make yogurt

streptococcus thermophilus and lactobacillus bulgaris

they produce acids which denature the milk to make it thick

what microorganisms are added to cheese

“hundreds”

LAB precipitate proteins to make curd, and other organisms are added to “ripen” for flavour

cheese curdling and overview

whoops! see the slide

what does ripening cheese do

changes flavour, texture, etc

can be caused by LAB or other enzymes

(examples on slides)

soft cheese ripening

done in high humidity

proteases soften the cheese

how is wine fermented

must (crushed grapes) are combined with metabisulfites that kill wild yeasts

what is the difference between dry and sweet wine

dry wine has all the sugar fermented, whereas sweet has some sugar left

what are the stages of beer brewing

malting/mashing, boiling, fermentation

what is the malting and mashing stage

malting is when grains are allowed to germinate and make amylase

they are then crushed to make malt

malt is soaked (mashing) and the amylase degrades starch into fermentable sugars (glucose and maltose)

malt is filtered to make wort

what is the boiling stage

hops is added to wort and boiled until sterilized

hops gives flavour and prevents LAB growth in the final product

what is the fermentation stage

yeast is added

it is then “polished” - filtered, carbonated, pasteurization

what yeast is added for lager

Saccharomyces carlsbergensis

“bottom yeasts”

6-12C

what yeast is added to ale

Saccharomyces cerevisisae

top yeasts - carried up by CO2 during fermnetation

14-23C

what are light beers

yeasts are manipulated genetically so they can use all the sugars in the wort

how are distilled alcoholic beverages made

in a similar process to beer but without hops

different grains are used

distilled in pot stills

what are whiskies

malt brew or other cereals are used in the distilling process

wort is not boiled, mixed fermentation of added yeasts and resident LABs

what are the factors that determine flavours of whisky

amount of water

amount of resident LABs

source and cultivar of the barley

shape of the still

ageing in wood cask and type of cask

how is vinegar made

acetic acid bacteria oxidize ethanol to acetic acid

strict aerobes - NOT FERMENTATION

ethanol to acetaldehyde to acetic acid

what bacteria is used in vinegar

acetobactor

efficient - but will oxidize acetic acid to Co2 and H2O is there is no ethanol

what is food spoilage

any change in the appearance, smell, taste that makes it unacceptable for consumption

it is not necessarily a health hazard

caused by molds, yeasts, and bacteria

what factors affect spoilage

types of microorganisms

extent of growth of microorganism

moisture content

temperature

ph

oxygen availability

chemical composition and physical state of food

amount of exposed insides, distribution of any surface contaminants

how does moisture content influence food spoilage

all microorganisms need water

solutes dissolved in water reduce availability of water to the organism

spoilage microorganisms can grow in aw as low as 0.9

what is water activity aw

availability of water to microorganisms

when aw < 0.9

most bacteria and yeasts are unable to grow

many molds can still grow

when aw < 8.0

only specialized organisms can grow

• xerophiles (dry, low osmolarity)

• osmophiles (high osmo: high sugar)

  • halophiles (high salt)

what is an example of a microorganism that can grow in very low aw

staphylococcus aureus

grows at > 0.83 - its a halophile

how does temperature influence food spoilage

hot food kept > 60C

cold food kept < 4.5C

psychrophiles and psychrotrophs can grow at low temperatures

microorganisms can survive at low temperatures for a long time, and will resume growth when temperatures rise

what pathogens can grow at 4.5C

Yersina enterocolitica, Listeria monocytogenes, Clostridium botulinum

how does pH affect food spoilage

most food are neutral or acidic

bacteria can grow at pH 5 or higher, LAB can grow at 4

molds and yeasts can grow at 4 or lower - main cause of spoilage in acidic food

how does oxygen influence food spoilage

molds NEED, yeasts and bacteria are sometimes aerobic

by excluding oxygen, spoilage is prevented - oxygen can sometimes diffuse into the packaging

anaerobic yeasts and bacteria can grow (swollen packages)

how does chemical composition influence food spoilage

determines the available nutrients which impacts the types of organisms

meat chemical composition influence

high protein and fat

bacterias and molds spoil because they have proteases and lipases

vegetables and fruits chemical composition influence

veg: high starch, cellulose, pectin

fruit: sugars and pectin

bacteria, yeasts, mold spoil (saccharase, cellulase, pectinase)

what is food poisoning/intoxication

caused by microbial toxins in food

symptoms appear quickly

food infection

organisms are ingested with the food and multiply in the host

symptoms take longer to develop

can be caused by tissue invasion, toxin production, or both

top 10 causes of food-borne disease

see the slide! im not typing all that

what causes botulism

ingestion of AB neurotoxin produced by Clostridium botulinum

the anaerobe produces endospores

toxin is destroyed by heat (endospore/organism is still there)

what are the symptoms/etc of botulism

can cause mortality

paralysis

double vision, difficulty breathing

happens in 1-2 days

what is staphylococcal food poisoning

due to an enterotoxin produced by S aureus

heat stable!

it will transfer and grow, producing a toxin

1-6h onset

what si salmonella

infection of mammals, birds, reptiles

grows in the intestinal tract

colonizes of the intestinal epithelium

how is salmonella transmitted

can be transmitted to humans by animals, water, or other humans

how does salmonella grow and manage to invade

many organisms are needed - salmonella will grow on food before its eaten

destroys the intestinal epithelium

cooking will kill it

what is e.coli O157:H7

it is a fecal coliform but does not grow at 44.5C

is not detected by standard fecal coliform methods

it is a type of Enterohemorrhagic ecoli (EHEC)

what is an EHEC

a category of e. coli that has an extremely low effective dose

zoonose

can be killed by cooking

how do EHECs/O157:H7 work

it will attach to intestinal mucosa and produce an AB-type exotoxin (shiga-like) that stops protein synthesis

toxin released damaged tissues and causes bloody diarrhea (hemorrhagic colitis)

toxin will travel through blood stream and destroy kidney cells causing hemolytic uremic syndrome

can result in renal failure and death

what are the goals of food processing/preservation

prevent or delay decomposition (spoilage)

destroy or inhibit pathogen growth

prevent or delay self-decomposition by enzymes present in the food

what is the aim of refrigeration and freezing

to slow or inhibit the growth of microorganisms

lowers aw so that most microorganisms cannot grow

viable microorganisms will resume growth when temperature rises

who is alice evan

showed that raw milk could cause disease (1917)

lobbied for mandatory pasteurization of milk (1930)

what is the aim of pasteurization

reduce to the number of organisms to delay spoilage and eliminate pathogens

used for dairy, liquid egg, fruit juices

what are the 3 methods of pasteurization of milk

low temp, long time - leaves bad taste (further processed for cheese)

high temp, short time - used for drinking milk

ultrahigh temp - used for shelf stable milk, virtually sterile

LTLT and HTST are equally safe - time and temp is affected by fat, sugar, and protein content

what is the aim of canning

seals the food from outside world and heating of the container will kill most microorganisms, creates an anaerobic environment

low acidity foods need a higher temperature

includes the 12D process

what is the 12D process

a canning process in which the temperature and time of exposure must be sufficient enough to kill 10^12 spores of C botulinum

what is the aim of reducing water availability

prevents microorganisms from growing

by different types of drying or by reducing water availability by adding sugar

inhibits growth, but won’t kill

why does adding sugar reduce water availability

increases osmotic strength of the surrounding solution

what is the aim of irradiation

to reduce contamination of fresh product by pathogen and spoilage organisms

it is not carcinogenic

dosage can be adjusted

radappertization

radiation dosage that kills all microorganisms

radicidation

irradiation dosage that kills specific microorganisms

radurization

irradiation dosage that reduces overall contamination

what is the aim of chemical treatments

to control the growth of microorganisms (usually selected)

use of chemicals generally recognized as safe (GRAS)

can use bacteriophage preparation

what are GRAS examples

nitrite - prevents growth of C botulinum

sulfites - inhibits wild yeasts (wine)

nisin - bacteriocin produced by L lactis

what is bacteriophage preparation

an FDA cocktail of bacteriophages against listeria

what is industrial microbiology

use of organisms to produce useful compounds for different industries

what are primary metabolites in industrial microbiology

metabolites produces during the exponential growth phase

ex. alcohol

what are secondary metabolites in industrial microbiology

metabolites produced at the end of growth, near or at the stationary phase

ex. antibiotics

what is an industrial fermentor

vessel used for industrial growth of microorganisms

what is fermentation in industrial microbiology

any large-scale microbial process

can be aerobic or anerobic processes

NOT the same as fermentation in food products

what do fermentors control (industrial)

temperature, nutrient availability, pH, dissolved oxygen

what microorganisms will be selected for industrial fermentation processes

NOT wild-types

spontaneous mutants that overproduce desired metabolites

GMOs/cloned genes

what are spontaneous mutants used to produce

amino acids

what are GMOs used to produce

human insulin and enzymes