SCIENCE IN FOOD

1.  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.

2.  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.

3. 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

4.  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.

5. Table 2 Worldwide production of some fermented foods
Food Quantity (t) Beverage Quantity (hl)
Cheese
Yoghurt
Mushrooms
Fish sauce
Dried stockfish
15 million
3 million
1.5 million
300 000
250 000
Beer
Wine
1000 million
350 million

6. Table 3 Individual consumption of some fermented
foods: average per person per year
Food Country
Annual
consumption
Beer (I)
Wine (I)
Yoghurt (I)
Kimchi (kg)
Tempeh (kg)
Soy sauce (I)
Cheese (kg)
Miso (kg)
Germany
Italy, Portugal
Argentina
Finland
Netherlands
Korea
Indonesia
Japan
UK
Japan
130
90
70
40
25
22
18
10
10
7

7. Table 4 Benefits of fermentation
Benefit
Raw
material
Fermented
food
Preservation Milk
(Most materials)
Yoghurt, cheese
Enhancement of safety
Acid production
Acid and alcohol production
Production of bacteriocins
Removal of toxic components
Fruit
Barley
Grapes
Meat
Cassava
Soybean
Vinegar
Beer
Wine
Salami
Gari, polviho azedo
Soy sauce
Enhancement of nutritional value
Improved digestibility
Retention of micronutrients
Increased fibre content
Synthesis of probiotic compounds
Wheat
Leafy veges.
Coconut
Milk
Bread
Kimchi, sauerkraut
Nata de coco
Bifidus milk, Yakult,
Acidophilus yoghurt
Improvement of flavour Coffee beans
Grapes
Coffee
Wine

8.  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)

9.  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.

10.  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.

11.  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.

12.  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.

13.  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.

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

15.  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.

16.  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.

17.  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

18.  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

19. A single bacterial colony
 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

20.  Bacteria are “streaked”over 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

22. When conditions are right bacteria can double in number every
20 minutes

23.  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

24. Lactobacillus spp.
Lactococcus spp.