Plants as Food
Introduction
New ideas on nutrition are incorporated
by the health conscious segment of
society and by advertisers looking for a
new marketing gimmick. Nevertheless,
the benefits of nutritional concepts such
as fiber, monounsaturated oils and lowcarbohydrates diets have made headlines
and influenced large lifestyle
changes in the American
population.
Introduction
These nutritional concepts promise better health
and most of them are dependent on a greater
consumption of plants in the human diet.
The world has over 50 000 edible plants. Just 15
crop plants provide 90 percent of the world's
food energy intake, and just three of them: rice,
maize and wheat, provide
60 percent of the world's
food energy intake*.
This chapter involves
on how plants can
satisfy these needs.
*FAO
Macro and micro nutrients
The function of the basic nutritional needs of
humans are to supply energy and raw materials for
all the various activities of the human body. These
nutritional needs can be classified as:
Water
Macronutrients: Carbohydrates, Lipids and
Proteins
Micronutrients (required in small amounts):
Minerals and Vitamins.
What is the world eating?
What sources
of food
provides these
nutritional
needs?
Energy requirements
Human energy requirements vary within a wide
range of 1200-3200 per day depending on:
Gender
Age
Activity level
The current energy recommendation for
Americans is an average of 2000 kilocalories/day
or 2200 kcal/day for man and 1600 kcal/day for
women.
Energy from Food
In the US food energy is measured in
kilocalories (commonly called just calories).
Carbohydrates provides 4 cal./gram while a
fats provides 9 cal./gram.
Only Carbohydrates and Fats are used as
sources of energy while proteins are used as
raw materials. (Proteins will only be used as a
source of energy (4 cal/gram) during
starvation).
A little bit of chemistry.
How do we build large molecules?
Most of the large molecules in living things
are macromolecules called polymers.
Polymers are long chains of smaller
molecular units called monomers.
A huge number of different polymers can be
made from a small number of monomers
Cells link monomers to form polymers by
dehydration synthesis
1
2
3
Short polymer
Unlinked monomer
Removal of
water molecule
1
2
3
Longer polymer
4
Polymers are broken down to monomers by
the reverse process, hydrolysis
1
2
3
4
Addition of
water molecule
1
2
3
Coating of
capture strand
Carbohydrates
CARBOHYDRATES
Carbohydrates are a class of molecules
They include sugars, starches and fiber.
Composed of the elements C, H and O
Major source of energy from our diet
Produced by photosynthesis in plants
Types of Carbohydrates
Monosaccharides
Single monomer
Disaccharides
Contain 2 monosaccharide units
Polysaccharides
Contain many monosaccharide units
Examples of Monosaccharides
Many monosaccharides form rings, as shown
here for glucose
Abbreviated
structure
Figure 3.4C
Energy
Glucose + Glucose
H2O
Maltose
Enzyme
Enzyme
Energy
H2O
Energy
H2O
Disaccharides Store Energy and Serve As Building Blocks
Glucose + Fructose
Energy
Enzyme
Enzyme
Sucrose
H2O
Energy
Glucose + Galactose
Energy
H2O
Enzyme
Enzyme
Lactose
H2O
What is sucrose?
Table Sugar!
What is lactose?
Lactose is the disaccharide
sugar found in milk!
What is lactose intolerance?
Lactose intolerance is a
condition that those who are
afflicted cannot digest milk.
This is the normal hydrolysis reaction
Energy
Glucose + Galactose
Energy
H2O
Enzyme
Enzyme
Lactose
H2O
A lactose intolerant person does not have the
enzyme that breaks down the lactose,
therefore lactose is indigestible and it causes
indigestion!
Polysaccharides
Polysaccharides are carbohydrates composed of
many monosaccharides. These large molecules
are polymers of hundreds or thousands of
monosaccharides linked by dehydration synthesis.
These are known as complex carbohydrates.
There are two types of polysaccharides
 Storage Polysaccharides: They store energy.
 Structural Polysaccharides: These are use for
building cell structures.
Starch (plants) and glycogen (animals) are
storage polysaccharides that store sugar for later
use.
Cellulose is a structural polysaccharide in plant
cell walls
Starch granules in
potato tuber cells
Glycogen granules
in muscle tissue
Cellulose
molecules
Glucose
monomer
STARCH
GLYCOGEN
CELLULOSE
Cellulose fibrils in
a plant cell wall
Starch
It is a storage polysaccharide. It is the storage form o
glucose in plants.
It occurs abundantly in seeds (grains), tubers,
taproots and some fruits.
The major starchy grain crops are: wheat, corn and
rice.
The major underground crops are potatoes, sweet
potato and cassava.
The major starchy fruits are the legumes (beans and
peas)
Cellulose (fiber)
There are many types of dietary fiber. Cellulose is one
of them. It is a structural polysaccharide found only in
plants and a major component of cell walls.
Humans do not have the enzymes to break cellulose
thus it passes through the digestive track as
roughage, largely unaltered. By adding bulk it helps
the digestive process.
Fruits, vegetables, seeds and whole grains supply
most of the fiber in the human diet. The major
starchy fruits are the legumes (beans and peas).
What Are Lipids?
These are a group of diverse molecules that are
grouped together because they share the
characteristic that do not mix with water.
They comprise Oils, Fats, Waxes, Phospholipids
and Steroids.
Lipids are classified into two groups
1. Lipids with fatty acids: Triglycerides
Phospholipids
2. Lipids without fatty acids: Steroids.
Triglycerides
Commonly known as fats oils and waxes.
Most plants contain unsaturated fats
which are made with unsaturared fatty
acids. Examples are olive oil, peanut oil
corn oil, soybean and canola oil.
Some plant oils such as coconut oil,
cocoa butter and palm oil contain
saturated fatty acids.
Functions of Lipids