Transcript Powerpoint slides - New Zealand Institute of Food Science

Fermented Foods

Foods that have been subjected to the action of microorganisms or enzymes, in order to bring about a
desirable change.

Numerous food products owe their production and
characteristics to the fermentative activities of
microorganisms.

Fermented foods originated many thousands of years
ago when presumably micro-organism contaminated
local foods.
Fermented Foods

Micro-organisms cause changes in the foods which:
 Help to preserve the food,
 Extend shelf-life considerably over that of the raw
materials from which they are made,
 Improve aroma and flavour characteristics,
 Increase its vitamin content or its digestibility compared
to the raw materials.
Table 1 Benefits of fermentation
Benefit
Preservation
Enhancement of safety
Acid production
Acid and alcohol production
Production of bacteriocins
Removal of toxic components
Enhancement of nutritional value
Improved digestibility
Retention of micronutrients
Increased fibre content
Synthesis of probiotic compounds
Improvement of flavour
Raw
material
Milk
(Most materials)
Fruit
Barley
Grapes
Meat
Cassava
Soybean
Wheat
Leafy veges.
Coconut
Milk
Coffee beans
Grapes
Fermented
food
Yoghurt, cheese
Vinegar
Beer
Wine
Salami
Gari, polviho azedo
Soy sauce
Bread
Kimchi, sauerkraut
Nata de coco
Bifidus milk, Yakult,
Acidophilus yoghurt
Coffee
Wine
Lactic Acid Bacteria

Major group of Fermentative organisms.

This group is comprised of 11 genera of gram-positive
bacteria:
 Carnobacterium, Oenococcus, Enterococcus,
Pediococcus, Lactococcus, Streptococcus,
Lactobacillus, Vagococcus, Lactosphaera, Weissells
and Lecconostoc

Related to this group are genera such as Aerococcus,
Microbacterium, and Propionbacterium.
Lactic Acid Bacteria

While this is a loosely defined group with no precise
boundaries all members share the property of producing lactic
acid from hexoses.

As fermenting organisms, they lack functional heme-linked
electron transport systems or cytochromes, they do not have
a functional Krebs cycle.

Energy is obtained by substrate-level phosphorylation while
oxidising carbohydrates.
Lactic Acid Bacteria

The lactic acid bacteria can be divided into two groups based
on the end products of glucose metabolism.

Those that produce lactic acid as the major or sole product of
glucose fermentation are designated homofermentative.

Those that produce equal amounts of lactic acid, ethanol and
CO2 are termed heterofermentative.

The homolactics are able to extract about twice as much
energy from a given quantity of glucose as the heterolactics.
Fermentation – Definition

Fermentation is the metabolic process in which
carbohydrates and related compounds are partially oxidised,
with the release of energy, in the absence of any external
electron acceptors.

The final electron acceptors are organic compounds
produced directly from the breakdown of the carbohydrates.

With fermentation, incomplete breakdown of the parent
compound occurs and only a small amount of energy is
released during the process.

The products of fermentation consist of some organic
compounds that are more reduced than others
Glycolysis and Fermentation

Glycolysis, also called the Embden-Meyerhof pathway, is
the metabolic pathway used to, begin to, break down
glucose. Used by:

most autotrophic and heterotrophic organisms,
 aerobes and anaerobes.

The name glycolysis literally means splitting (lysis) of sugar
(glyco-).

It does not require oxygen and can occur in its presence or
absence.
Glycolysis
ATP
Required at steps 1 and 3,
Released at steps 7 and 10.
Each glucose yields 2, three carbon
sugars.
There is a net yield of 2 ATP per glucose.
Sugar Catabolism

The metabolism of glucose, or another sugar by glycolysis is a
process carried out by nearly all cells. The end result of
glcolysis is pyruvic acid.

How pyruvic acid is subsequently catabolised depends on
whether it is broken down by:
 Aerobic
Metabolism (Respiration) or
 Anaerobic
Metabolism (Fermentation)
Aerobic Metabolism
Formation of Acetyl-CoA and
the Krebs cycle
Energetically far more efficient
than fermentation
In conjunction with the electron
transport chain where oxygen is
the terminal electron acceptor

Produces
34 ATP (plus 4 from
glcolysis) from each molecule of
glucose
Fermentation

Process by which pyruvic acid is metabolised in the absence of
oxygen

Result of the need to recycle the limited amount of NAD by
passing the electrons off to other molecules

Two of the most important and commonly occurring pathways
are:
 homolactic

acid fermentation and
alcoholic fermentation.
Homolactic Acid Fermentation

Reduced
NAD
H
+ H+
O O
H3C - C - C - OH
Pyruvic acid
Oxidised
NAD

OH O
H3C - C - C - OH

H
Lactic Acid

Does not capture energy in ATP
from the metabolism of pyruvic
acid, but removes electrons from
reduced NAD so that it can
continue to act as an electron
acceptor.
Alcoholic fermentation is a
similar process
Thus, they indirectly foster
energy capture by keeping
glycolysis going.
Fermenation can occur via many
other pathways