Transcript + Vegetables

+
Vegetables
Dr.Fatimah Yousef
+
Vegetables
 Water
80-90%
 High
fiber
 High
starch
 Low
in fat
 Incomplete

protein
High in vitamins and minerals
Dr. Fatimah Yousef12013
+
Classification of vegetables
The part of the plant used as a vegetable often
serves as a common method of classification
 Roots ( carrot, beets)
 Bulbs (onion, garlic)
 Tubers ( potato, ginger roots)
 Stems (celery, asparagus)
 Leaves (spinach, lettuce)
 Seeds (beans, corns)
 Flowers (broccoli, cauliflower)
Dr. Fatimah Yousef12013
Dr. Fatimah Yousef12013
+
Composition of vegetables
 Structure
of plant cells
 Cell
wall
 parenchyma cells
 Plant
pigments
 Carotenoids
 Chlorophylls
 Flavonoids
 Photochemical
+
I-Cell wall:
 Cells
are the building blocks of both plants and animal
organisms.
 Each
vegetables cell gain its structural support by being
surrounded by a sturdy wall
 Contributing
to the strength of these cell wall are several
fibrous compounds which are indigestible by humans
(cellulose, pectic compounds, hemicellulose, lignin, and
gums.
 pectic
compounds and hemicellulose found within and
between cells giving firmness and elasticity to the tissues
Dr. Fatimah Yousef12013
+ Cell wall cont’d
 The
outer layer of the skin, peel or rind has a
higher proportion of
cellulose and
hemicellulose the surface cells of these
protective layers secrete a waxy cutin, a waterimpermeable coat that protects the plant
 lignin is another type of fiber but non
carbohydrate compounds .as vegetable mature,
their lignin concentrations increase.this is why
spinach stems and the inner cores of carrots,
asparagus spears, and broccoli become tougher
with age and do not soften when heated .
+
parenchyma cells
 The
most common type of cell in
vegetables and fruits
 Within
the jelly –like cytoplasm of these
cells are the compounds responsible for the
plant strach content, color, water volume,
and flavor compounds such as
(saccharides, salts, and organic acids)
several of these substances are stored in
plastids that accurse in three types :
leucoplasts, chloroplasts, and chromoplasts.
 The
understanding of the structure of a
+
II-Plant pigments
It fall into three major groups:
1-Carotenoids.
2-Chlorophylls.
3-
Flavonoids.
Dr. Fatimah Yousef12013
+
 1-Carotenoids:

A group of yellow to red pigments occurring widely
in plants.
Carotenoids are found in plastids and are fat soluble.

(Xanthophylls) account for most of the yellow color of fruits
and vegetables ex. Corn and pinapple

(carotene) Lend orange color to carrots and winter squashs.

(lycopene) which are deeper red provide the bright color of
tomatoes.
Dr. Fatimah Yousef12013
 2-Chlorophyll
+
 Chlorophylls
are found in plastids and are fat soluble.
 Green coloring matter of all plant materials, by the aid of
which plants manufacture foodstuffs from simple salts
and carbon dioxide with energy derived from sunlight, i.e.
photosynthesis.
 Chlorophyll turns bright green when it first starts
cooking due to loss of oxygen.
 Color is markedly affected by the acidity and alkalinity
of substances:
 Dull green at low pH
 Bright green at higher pH
 alkali also increased nutrient loss and created an
undesirable texture.
Dr. Fatimah Yousef12013
+
 Flavonoids
pigments include
1- anthocyanin ( red to blue) it is found in red cabbage,
egg plant, radish, and red potato.
2- Anthoxanthins (creamy to white) thy are the reason for the
cream or whit color of qualiflower, onions, potato
3- betalains (purplish-red)
 Flavonoids are water-soluble pigments
 markedly affected by the acidity and alkalinity of
substances:
 Red at low pH
 Blue at higher pH
Dr. Fatimah Yousef
 Flavonoid pigments ,water soluble, have a tendency
to 2013
be
1
Dr. Fatimah Yousef12013
+
Preparation of vegetables
 General
guidelines
Regardless of the cooking method or serving style
selected, some general principles governing the handling
and preparation of vegetables should be followed:
 1-Buying.
 2-Storage.
 3-Washing.
 4-coocking liquid
 5-timing.
Dr. Fatimah Yousef12013
+
Preparation of vegetables cont’d
1-selecting
 The most important consideration when selecting
vegetables is
 season of the year. Thus selecting an out-of
season affects the quality of the results meal.
 Color is a good indication of nutrient content:
Choose brighter colors for more nutrients.
 only the amount that will be used within a few
days.
+
Preparation of vegetables cont’d
1-selecting cont’d
 The amount to buy depends on the type of
vegetables, leafy ones contain more water than
others ex. Lettuce has more water than carrots
+
How to selecting some vegetables :
-Cabbage: The stem should be solid,
hard, and heavy in relation to the head.
The surface is usually smooth and free
from any signs of dehydration and the
leaves firmly attached to the stem.
-Carrots: The surfaces should be smooth,
firm and free from cracks and the tops
should be free from any sprouting green
shoots, which would indicate an older
carrot.
Dr. Fatimah Yousef12013
+
-Eggplant:
It should be smooth, firm and
glassy, with a deep purple almost black
color, it is also available in white.
-Sweet potatoes: Selected sweet potatoes
that have large, uniform shape, with no
signs of discoloration, wrinkling or drying.
-Artichoke: It should be heavy, compact,
plump and have bronze-tripped leaves.
-Peas: It should be fresh, tender and sweet.
Avoid those that are in an advanced stage
of maturity, which is signaled by grayish
specks, yellow streaks, a darker color
dryness and wrinkling.
Dr. Fatimah Yousef12013
+
Preparation of vegetables cont’d
2-Storage
 Storage
times for various vegetables are ultimately based
on their water content (vegetables with a high percentage
of water, such as lettuce have shorter storage times than
vegetables with less water content such as potatoes.
Dr. Fatimah Yousef12013
+
 Store
vegetables immediately at the appropriate
temperature, and do not leave them out of storage for any
length of time unless they are being prepared.
 Leftovers should be refrigerated immediately and used
within three days.
 Dry Storage: Proper storage does not automatically
imply refrigeration. For instance:
**Tomatoes (unripe).
**Tubers (potatoes).
**Dried legumes.
**Most bulbs (onions).
…Should never be stored in a refrigerator.
Dr. Fatimah Yousef12013
+Preparation of vegetables
 3-Washing
cont’d
: All vegetables must be thoroughly washed
(with a vegetable brush when appropriate) to remove soil,
microorganisms, pesticides and herbicides.
 Washing
should be quick, because most vegetables
absorb excess water when soaked.
 Many
roots vegetables, except beets and baked potatoes
are peeled of the outer layer that is normally washed .
Dr. Fatimah Yousef12013
+
 4-Cooking
liquid: As small an amount of liquid as
possible should be used.
 5-Timing:
The cooking time should be as short as
possible, most vegetables when heated too long will
undergo undesirable changes in quality. Vegetables
should be served promptly after cooking.
Dr. Fatimah Yousef12013
+ Preparation of vegetables cont’d
Changes
during heating
 heating,
vegetables let them undergo several changes :
 Texture
 Flavor
 Odor
 Color
 Nutrient retention.
 Understanding
these phenomena can help to retain as much
of their quality as possible during preparation.
Dr. Fatimah Yousef12013
+
Changes during heating:
1-Texture:
 High
temperature gelatinize starch ex., potatoes, decrease
bulk by softening cellulose, and cause a reduction in
turgor due to water loss. This is desirable when baking
potatoes or cooking legumes, it is not recommended for
most other vegetables they should be heated until barely
cooked.
Dr. Fatimah Yousef12013
+
 Acids:
or acidic foods ex., vinegar or tomatoes, should be
added toward the end of cooking time, because they
make vegetables more resistant to softening and by
precipitating vegetable pectins, increase required heating
time.
 Salts:
calcium salts added to vegetables make them
firmer as pickles and canned vegetables
 Alkaline:
such as baking soda break down cellulose and
produce a very mushy texture and decreases cooking
time)
Dr. Fatimah Yousef12013
+ 2- Flavor:
Vegetables obtain there flavor from an assortment
of volatile oils, organic acids, sulfer compounds,
minerals, salts, carbohydrates and polyphenolic
compounds To retain flavor compounds, vegetables
should be heated in as little water as possible and
for short a time .
Dr. Fatimah Yousef12013
+
3-Odor :
 Vegetables
get it's odor from the same compounds as
flavor.

There are some vegetables that it's odor appear with
heat such as cabbage, while in onion and garlic the
odor is reduce by cooking heat.
Dr. Fatimah Yousef12013
+
 Garlic,
onions are odorless until they are cut or bruised ,
thus allows an enzyme to contact with a particular
substrate to create a smelling-sulfur compound. The
sulfur compounds released causing tears to form in
the eyes or the nose to run.
 The
strong odor of cooked cabbage can be reduced by
shortening the heating time, adding a little vinegar to the
cooking water, and/or by removing the lid during cooking
to let volatile organic acids escape.
Dr. Fatimah Yousef12013
+
4- Color:
 Undesirable
color changes can be prevented in a number of
ways:

Red cabbage, rich in anthocyanins, is prevented from turning
blue if cooked with something acidic.

Cauliflower (cream white), rich in anthoxanthin, is prevented
from turning yellowish if cooked with something acidic.
Adding
baking soda to green vegetables makes them appear
greener, (this is not recommended due to the deleterious effect on
B vitamin and texture .
Dr. Fatimah Yousef12013
+
 enzymatic
browning, which may be observed in cut-up
potatoes that turn pinkish-brown when exposed to oxygen
(due to oxygen reacts with the natural iron content of the
potato) , thus can be prevented by soaking cut potatoes in
water with little lemon).
Dr. Fatimah Yousef12013
+
5- Nutrient retention:
 Careful
 It
preparation of vegetables conserves important nutrients.
is important to cook vegetables using little water as possible.
 It
is better to avoid immersing them in water and instead revert
to steaming or baking.
 Leave
the skin on whenever possible, cut them to large pieces
rather than smaller.
 Cook
just to the point of doneness and no further.
 Some
nutrients may actually increase during heating, ex.,
heating increases the amount of protein available from legumes
(due to destroying the protease inhibitors enzymes).
Dr. Fatimah Yousef12013
+
Legumes:
 “Members
of the plant family Leguminosae
characterized by growing in pods”.
that are
 The
single common identifying factor among all legumes is
that they grow as seeds within a pods.
 Vegetable
legumes include beans, peas, and lentils, which
serve as excellent sources of fiber, protein, iron, and
complex carbohydrates
Dr. Fatimah Yousef12013
+
Preparation of legumes
 Legumes
are best prepared by simmering rather than boiling.
 There
are three methods for preparing dried beans:
 Overnight soak: Beans are sorted and thoroughly rinsed
and then immersed in water amounting to three or four
times their quantity for approximately 10 hrs.
 Short soak: Sorted and rinsed beans are brought to a full
boil for 2 min., removed from the heat and allowed to soak
in the same hot water for one hours. They are then cook
(simmered ) as in the above method.
Dr. Fatimah Yousef12013
+
Preparation of legumes
 No
soak: Beans can be prepared without soaking, but they
take twice the amount of water and double the heating
time. They also lose their skins more easily. The no soak
methods is used for lentils because their smaller size results
in shorter cooking times.
 When cooking legumes , it is important not to add salt or
acid until they well cooked, because these substances
inhibit the softening of pectic compounds.
Dr. Fatimah Yousef12013
+
Preparation of vegetables cont’d
 Both
fat and water-soluble coloring pigments are contained
in fruits and vegetables and are affected by the:
 pH
 Heating
 The presence of metals
Dr. Fatimah Yousef12013