Chapter 16: Micro of Food and Water

Food spoilage

can reduce the amount of food we have

available for consuming

food preservation

methods can make food last longer without

spoiling.

• Use of microbes to modify food can produce new varieties

(cheese, yogurt, vinegar, etc.).

Microbes can contaminate food and water, causing

human disease

perishable foods

Easily support microbe growth

• Green salad items, fresh meat

semi-perishable foods

Don’t spoil as quickly

• Nuts, potatoes

non-perishable food

Remain edible for long periods

• Flour, sugar, dried beans

Intrinsic food properties

Water availability

Osmolarity

Nutrient content

Antimicrobial constituents

Biological structures such as rinds or shells

pH and buffering capacity

extrinsic food properties

temperature

humidity

presence and concentration of gases

Good food spoilage

milk to yogurt, cheese, butter, etc.

food preservation : drying out

Reduction of water activity can be achieved by drying food out or by

adding solutes (sugar/salt).

food preservation: temperature

Cooling or heating can be

used (pasteurization).

o Usually cheap and highly

effective.

o May be combined with

pressure to eliminate

endospores (canning)

lth pasteurization time for milk

63 degrees celsius for 30 min

htst pasteurization time for milk

72 degrees celsius for 15 secs

UHT

138 to 150 degrees celsius for 2 secs

food preservation: increasing acidity

Increasing the acidity in

foods can prevent

spoilage.

o Pickling places foods in

vinegar or allows

fermentation to

naturally drop the pH

over time.

o Many microbes cannot

grow or will die in a low-

pH environment.

natural antimicrobial preservatives

Bacteriocins (nisin) - peptide toxins

• Lactic acid

• Acetic acid (vinegar

artificial preservatives

Sodium benzoate

• Proprionate

• Sorbates

• Sulfur dioxide

• Nitrites

food preservation: Irradiation

Non-ionizing radiation (UV): Surface level only, not strong

• Ionizing radiation (gamma/X-rays): Stronger, more penetrating

modified atmosphere packaging

Vacuum packing takes oxygen out of the package.

• Many microbes need oxygen to survive and multiply.

o Sometimes, packaging is also flooded with CO2 to achieve the same

effect.

o Red meat may be packed in a high-oxygen environment to reduce

growth of harmful anaerobic microbes and keep the meat a

desirable red color.

hurdle technology

Using multiple levels of antimicrobial control in food.

o The levels often work synergistically, giving better overall

protection than a single method alone

starter cultures

microbes are added to

food to begin the fermentation process.

• The process is monitored and controlled for a desirable outcome of

flavors and textures

lactic acid bacteria

cheese and yogurt production

can be used for cheese but

also for sauerkraut,

salami, and sausage

Mold fermentation

Miso = Fermented soybean paste

• Tempeh = Fermented soybean

• Soy sauce

• Sake

Vinegar manufacturing

fermentation of ethanol

by acetic acid bacteria into acetic acid

foodborne intoxication

Food contaminated with microbes

foodborne infection

actual microbes in food

What percentage of Earth’s water is freshwater

only 3%

Goals for treating wastewater (sewage) include

Reducing total organic carbon (TOC)

o Removal or inactivation of harmful microbes in

wastewater

o Reduction of inorganic compounds (especially

ammonium, nitrogen, and phosphorus levels) to prevent

eutrophication of natural waters

pre-treatment

Physical removal of large objects

Primary treatment

Physical removal of sediments and

grease that form primary sludge

Secondary treatment

Uses trickling filter/activated

sludge unit to form complex biofilms that break down

organic compounds over time

Tertiary treatment

Not always used; filtration method

Disinfection

Chlorination, UV light exposure, or

ozonation

flocs

Clumps of biomass of adsorbed material and biofilm microbes