Fermented Foods

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Fermented Foods

• Foods that have been subjected to the action of
  micro-organisms 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.

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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.

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Table 1 History and origins of some fermented
foods
Food
Approximate year of introduction
Region
Mushrooms Soy sauce Wine Fermented
milk Cheese Beer Bread Fermented Meats Sourdough
bread Fish sauce Pickled vegetables Tea
4000 BC 3000 BC 3000 BC 3000 BC 2000 BC 2000
BC 1500 BC 1500 BC 1000 BC 1000 BC 1000 BC 200
BC
China China, Korea, Japan North Africa,
Europe Middle East Middle East North Africa,
China Egypt, Europe Middle East Europe Southeast
Asia, North Africa China, Europe China
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Fermented Foods

• The term biological ennoblement has been used
  to describe the nutritional benefits of fermented
  foods.
• Fermented foods comprise about one-third of the
  world wide consumption of food and 20- 40 (by
  weight) of individual diets.

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Table 2 Worldwide production of some fermented
foods
Quantity (t)
Beverage
Food
Quantity (hl)
1000 million 350 million
Cheese Yoghurt Mushrooms Fish sauce Dried
stockfish
15 million 3 million 1.5 million 300 000
250 000
Beer Wine
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Table 3 Individual consumption of some
fermented foods average per person per year
Annual consumption
Food
Country
Beer (I) Wine (I) Yoghurt (I) Kimchi
(kg) Tempeh (kg) Soy sauce (I) Cheese (kg) Miso
(kg)
Germany Italy, Portugal Argentina Finland Netherla
nds Korea Indonesia Japan UK Japan
130 90 70 40 25 22 18 10 10 7
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Table 4 Benefits of fermentation
Raw material
Fermented food
Benefit
Preservation
Milk (Most materials)
Yoghurt, cheese
Enhancement of safety
Vinegar Beer Wine Salami Gari, polviho azedo Soy
sauce
Acid production Acid and alcohol
production Production of bacteriocins Removal of
toxic components
Fruit Barley Grapes Meat Cassava Soybean
Enhancement of nutritional value
Bread Kimchi, sauerkraut Nata de coco Bifidus
milk, Yakult, Acidophilus yoghurt
Improved digestibility Retention of
micronutrients Increased fibre content Synthesis
of probiotic compounds
Wheat Leafy veges. Coconut Milk
Improvement of flavour
Coffee beans Grapes
Coffee Wine
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Cassava

• Fresh cassava contains cyanhydric acid (HCN) that
  should be eliminated from any product originating
  from cassava to render it fit for human
  consumption. Depending on the production method
  (particularly traditional methods) gari could
  contains up to 20 mg / kg of HCN - against 43 mg
  / kg for fresh peeled cassava.
• Gari is a fermented, gelled and dehydrated food
  produced from fresh cassava. It is a popular diet
  in Nigeria, Benin, Togo, Ghana and in other West
  Africa's countries. The consumption area even
  expands to Central Africa Gabon, Cameroon, Congo
  Brazzaville and Angola.
• Polvilho is a fine tapioca/manioc/cassava flour.
  it can be found at latino markets in california
  as "sour starch" (polvilho azedo) or "sweet
  starch" (polvilho doce)

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Nata de Coco

• A high fiber, zero fat Philippino dessert.
• A chewy, translucent, jelly-like food product
  produced by the bacterial fermentation of coconut
  milk.
• Commonly sweetened as a candy or dessert, and can
  accompany many things including pickles, drinks,
  ice cream, and fruit mixes.
• Highly regarded for its high dietary fiber, and
  its zero fat and cholesterol content.
• It is produced through a series of steps ranging
  from milk extraction, mixing, fermentation,
  separating, cleaning, cutting to packaging.

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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.

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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.

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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.

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Lactic Acid Bacteria

• All members of Pediococcus, Lactococcus,
  Streptococcus, Vagococcus, along with some
  lactobacilli are homofermenters.
• Carnobacterium, Oenococcus, Enterococcus,
  Lactosphaera, Weissells and Lecconostoc and some
  Lactobacilli are heterofermenters
• The heterolactics are more important than the
  homolactics in producing flavour and aroma
  components such as acetylaldehyde and diacetyl.

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Lactic Acid Bacteria - Growth

• The lactic acid bacteria are mesophiles
• they generally grow over a temperature range of
  about 10 to 40oC,
• an optimum between 25 and 35oC.
• Some can grow below 5 and as high as 45 oC.
• Most can grow in the pH range from 4 to 8.
  Though some as low as 3.2 and as high as 9.6.

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Starter Cultures

• Traditionally the fermenting organisms came from
  the natural microflora or a portion of the
  previous fermentation.
• In many cases the natural microflora is either
  inefficient, uncontrollable, and unpredictable,
  or is destroyed during preparation of the sample
  prior to fermentation (eg pasteurisation).
• A starter culture can provide particular
  characteristics in a more controlled and
  predictable fermentation.

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Starter Cultures

• Lactic starters always include bacteria that
  convert sugars to lactic acid, usually
• Lactococcus lactis subsp. lactis,
• Lactococcus lactis subsp. cremoris or
• Lactococccus lactis subsp. lactis biovar
  diacetylactis.
• Where flavour and aroma compounds such as
  diacetyl are desired the lactic acid starter will
  include heterofermentative organisms such as
• Leuconostoc citrovorum or
• Leuconostoc dextranicum.

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Starter Cultures

• The primary function of lactic starters is the
  production of lactic acid from sugars
• Other functions of starter cultures may include
  the following
• flavour, aroma, and alcohol production
• proteolytic and lipolytic activities
• inhibition of undesirable organisms

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A good starter CULTURE will

• Convert most of the sugars to lactic acid
• Increase the lactic acid concentration to 0.8 to
  1.2 (Titratable acidity)
• Drop the pH to between 4.3 to 4.5

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• Food scientists frequently use the ability of
  bacterial cells to grow and form colonies on
  solid media to
• isolate bacteria from foods,
• to determine what types and
• how many bacteria are present.
• Streak plates

A single bacterial colony
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The streak plate technique

• Bacteria are streakedover the surface of an
  agar plate so as to obtain single colonies.
• Obtaining single colonies is important as it
  enables
• the size,
• shape and
• colour of the individual colonies to be examined.
  
• It can also highlight the presence of
  contaminating micro-organisms

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The Streak Plate Technique
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When conditions are right bacteria can double in
number every 20 minutes
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Microscopic examination

• Can provide information on the size
• and shape of the bacteria
• Rods (1)
• Cocci (2)
• Spiral (3)
• It cannot provide enough information
• to enable bacteria to be identified

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Microscopic views of stained bacteria
Lactobacillus spp.
Lactococcus spp.