What are fermented
foods?
Foods or food
ingredients that rely on microbial growth as part of their processing or
production
Food Fermentation
•
Metabolic activities
occur during fermentation that:
–
Extend shelf life by
producing acids
–
Change flavor and
texture by producing certain compounds such as alcohol
–
Improve the nutritive
value of the product by:
•
Microorganisms can synthesize vitamins
•
Breakdown indigestible materials to release nutrients, i.e., bound
nutrients
Fermented Foods
•
Foods fermented by
yeast
–
Maltà Beer
–
Fruit (grapes) Ã Wine
–
Rice à Saki
–
Bread dough à Bread
•
Foods fermented by
mold
–
Soybeans à Soy sauce
–
Cheese à Swiss cheese
•
Foods fermented by
bacteria
–
Cucumbers à Dill pickles
–
Cabbage à Sauerkraut
–
Cream à Sour cream
–
Milk à Yogurt
Food Fermentations –
Definitions
•
Anaerobic breakdown
of an organic substrate by an enzyme system in which the final hydrogen
acceptor is an organic compound
•
Biological processes
that occur in the dark and that do not involve respiratory chains with oxygen
or nitrate as electron acceptors
Food Fermentations –
Biochemistry
Sugars … Acids …
Alcohols, Aldehydes
Proteins … Amino
acids … Alcohols, Aldehydes
Lipids … Free fatty
acids … Ketones
Respiration vs.
fermentation
Refer to how cells
generate energy from carbohydrates
RESPIRATION:
•
Glycolysis + TCA (Kreb’s) Cycle + Electron
Transport
•
O2 is final electron acceptor
•
Glucose is completely oxidized to CO2
“Fermentation” is
used broadly – describe where the use of the word comes from.
ATP=main chemical
energy in a cell.
•
Some organisms (facultative anaerobes), including
yeast and many bacteria, can survive using either fermentation or respiration.
•
For facultative
anaerobes,
pyruvate is a fork in the
metabolic road that leads
to two alternative routes.
Respiration vs.
fermentation
FERMENTATION:
•
An organic compound is the final electron
acceptor
•
Glucose is converted to one or more 1-3 carbon compounds
In this class, we
will deal mostly with m/o that are generating energy by fermentation.
Why would a cell
ferment vs. respire (since less energy is produced)? Can’t respire, can, but no oxygen present.
Produces less energy
than respiration, but no oxygen required.
From food standpoint,
byproducts are important.
•
During lactic acid fermentation, pyruvate is
reduced directly by NADH to form lactate (ionized form of lactic acid).
–
Lactic acid
fermentation by some fungi and bacteria is used to make cheese and yogurt.
•
In alcohol fermentation, pyruvate is
converted to ethanol in two steps.
–
First, pyruvate is
converted to a two-carbon compound, acetaldehyde by the removal of CO2.
–
Second, acetaldehyde
is reduced by NADH to ethanol.
–
Alcohol fermentation
by yeast is used in
brewing and
winemaking.
•
Carbohydrates, fats,
and proteins can all be catabolized through the same pathways.
Respiration vs.
fermentation
Some cells can
respire and ferment sugars for energy.
The cell will do one or the other depending on the conditions.
Example: Saccharomyces cerevisiae
(baker’s, ale and wine yeast).
Some cells can only
respire or only ferment sugars for energy.
Example: Lactic acid bacteria produce energy by fermentation.
In this class, we
will deal mostly with m/o that are generating energy by fermentation.
Why would a cell
ferment vs. respire (since less energy is produced)? Can’t respire, can, but no oxygen present.
Produces less energy
than respiration, but no oxygen required.
From food standpoint,
byproducts are important.
Typical fermentation process
•
substrate disappears
as cell mass increases
•
sugar, then other
small molecules, then polymers used
•
primary metabolic
products (acids) accumulate during growth
•
pH drops if acids
produced
•
growth and product
formation stop as substrate is depleted
•
microbial succession
depends on substrate and acid levels
Food Fermentations
In food
fermentations, we exploit microorganisms’ metabolism for food production and
preservation.
Where do the
microorganisms come from to initiate the food fermentation?
Two ways to initiate
a food fermentation….
...traditional &
controlled fermentations
Fermentative energy
pathways that we are expoiting
Controlled vs.
Natural Fermentation
•
Natural fermentation
–
Create conditions to
inhibit undesirable fermentation yet allow desirable fermentation
–
Examples:
•
Vegetable
fermentations
–
Vegetables + salt
Controlled vs. Natural
Fermentation
•
Controlled
fermentation
–
Deliberately add
microorganisms to ensure desired fermentation
•
Example: fermented
dairy products
–
Lactose … Lactic acid
–
Starter culture
»
Lactics or Lactic
starter or Lactic acid bacteria (LAB)
Traditional
Fermentation
Disadvantage: Process and product are unpredictable depending on source of raw
material, season, cleanliness of facility, etc.
Advantage:
Some flavors unique to a region or product may only be attained this
way.
Relies on m/o
naturally found in the raw material.
Have been going on
for thousands of years. Long before we
knew what bacteria and fungi are.
Conditions adjusted
so that desirable microorganisms grow.
Controlled
Fermentation
Advantage: – uniformity, efficient, more
control of process and product
Disadvantage: Isolating the right strain(s)
to inoculate is not always easy. Complexity
of flavors may decrease.
Large numbers of
desirable m/o’s are added to the raw material.
This is a starter
culture.
It helps if raw
material is sterile or has reduced natural microflora, so that the added m/o’s
dominate quickly.
Conditions adjusted so
that desirable (starter culture) m/o’s grow.
Controlled
Fermentations: Starter cultures
Two main starter
culture types are used to inoculate the raw material:
1.
Pure microbial cultures prepared
specifically for a particular food fermentation. (More details on these later.)
2.
“Backslop” method = Using some of the
product from a previous successful fermentation to inoculate the next batch of
raw material.
Controlled
Fermentation: pure cultures
Provides most control
First used in the
1890s.
Controlled
Fermentation: “backslop” method
Can pass on
undesirable organisms too.
Balance of live
organisms may change in final product.
Can pass on
undesirable organisms too.
Balance of live
organisms may change in final product.
Used in the old
days. Not common now on an industrial
scale because of the risk of contamination.
Summary
•
Why we ferment foods
•
Microbial energy
metabolism: respiration vs.
fermentation
•
Traditional
fermentations – indigenous microflora
•
Controlled
fermentations – starter culture added
Food products
from milk:
cheese, yogurt, sour
cream, buttermilk
lactic acid bacteria
(lactobacilli, streptococci)
meats:
fermented sausages,
hams, fish (Asia)
lactic acid bacteria
(lactobacilli, pediococci), molds
beverages:
•
beer (yeasts make ethanol)
•
wines (ethanol
fermentation from grapes, other fruits)
•
vinegar (ethanol
oxidized to acetic acid)
•
breads:
•
sourdough (yeast +
lactobacilli)
•
crackers, raised
breads (yeasts)
single cell protein:
how cheaply and
efficiently can cells be grown?
waste materials as
substrate (bacteria, yeast, molds)
sunlight and CO2
(algae)
uses in animal feeds
(frequently) or human foods
prefer protein to
whole cells
high nucleic acids
--> kidney stones,
Organic acids
•
Primary Metabolites
•
Organic acids are.
(primary products of metabolism).
•
During the log phase of growth the products
produced are essential to the growth of the cells.
•
Secondary metabolites:
(Secondary products of metabolism)
•
During the stationary
phase some microbial cultures
synthesize compounds
which are not produced during
the trophophase* and
do not appear to have any
obvious function in
cell metabolism.(idiophase*)
Publisher
Gery
Purnomo Aji Sutrisno
FPIK Universitas Brawijaya Angakatan 2015
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