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A balanced diet
Bread and Yeast
Nutrients in Bread
• Bread contains mainly carbohydrates.
• There is a small amount of protein and fat.
• In wholegrain breads there is also fiber.
• There are three types of carbohydrates:
– Sugars
– Starches
– Fibers
Grain
• Grains include foods like wheat, oats, barley,
and rice.
• Grain can be broken down into whole grain or
refined grain.
• A grain, let's take wheat for example, contains
three parts:
– bran
– germ
– endosperm
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Parts of Grain
Bread - making
• The bran is the outer hard shell of the grain. It is
the part of the grain that provides the most fiber
and most of the B vitamins and minerals.
• The germ is the next layer and is packed with
nutrients including essential fatty acids and
vitamin E.
• The endosperm is the soft part in the center of
the grain. It contains the starch. Whole grain
means that the entire grain kernel is in the food.
• Core ingredients: Flour, water and sugar are
mixed together to make bread dough.
• Yeast, baking powder, salt, herbs, and other
ingredients may also be added to the dough
mixture
• If the bread has a leavening agent in it (a
substance that will make the dough rise), the
dough is left to prove (given time to grow in size,
ie. rise)
• The bread is then baked in an oven at high
temperatures until cooked
Wholegrain vs refined grain
Yeast in bread
• If you eat a whole grain food, it contains the
bran, germ, and endosperm so you get all of
the nutrients that whole grains have to offer.
• Wholegrain is also called whole-meal
• If you eat a refined grain food, it contains only
the endosperm or the starchy part so you miss
out on a lot of vitamins and minerals.
• White flour or plain flour are both refined
•
Yeast is used to make ‘leavened bread’ (baking
powder is another ‘leavening’ substance)
• Leavened bread is bread that contains a
substance that will make the bread rise (grow
larger in size). For example whole-meal or white
loaf bread.
• Unleavened bread is bread that does not rise, for
example roti bread or cracker bread.
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pH in food production
pH = % hydrogen ions
• The pH of a substance is the measure of its acidity.
• pH is measured on a scale from 1 to 14.
• 0-6 pH is acidic, 7pH is neutral, 8-14pH is alkaline
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Energy for living
• There are two types of cellular respiration:
– aerobic, which requires oxygen and releases lots
of energy
– anaerobic, which does not require oxygen but it
releases much less energy per quantity of starting
material
• Aerobic respiration chemical equation:
Oxygen + glucose  water + carbon dioxide
(+ energy)
Yeast cells grow and reproduce in specific ranges of
pH and temperature, they prefer neutral
environments and 25-32C temperature range.
When you use yeast to make bread, the yeast cells
produce carbon dioxide gas (CO2) inside the bread
dough.
When CO2 dissolves into water it forms carbonic acid.
The yeast cells produce CO2 because they are using
the process of fermentation to make the energy they
need to grow, reproduce and stay alive.
Fermentation is a type of cellular respiration
(anaerobic)
No oxygen = pain!
• Sometimes organisms reach a point where the
body cannot provide enough oxygen to make
the energy that they need, eg. carry out heavy
exercise .
• At this point anaerobic respiration starts to
make energy. This backup system does not
need oxygen to work.
• In animals, as well as producing energy it also
produces something called lactic acid, which
then builds up in the muscles. Unfortunately,
lactic acid makes muscles ache.
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Anaerobic respiration
• Anaerobic respiration in humans may be
summarised by the word equation:
glucose  lactic acid (+ energy)
• In yeast, anaerobic respiration is the only way
they produce energy. Their anaerobic
respiration may be summarised by:
glucose  ethanol + carbon dioxide (+ energy)
• Another name for anaerobic respiration is
fermentation
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