VEGETABLES AND FRUITS: OVERVIEW AND THEIR COMPOSITION

VEGETABLES AND FRUITS:

These are rich in phytochemicals, natural substances found in fruits and vegetables that give color, flavor, and smell. When eaten, they may help prevent heart disease, cancer, diabetes and high BP .Populations with higher amounts of fruits and vegetables in their diet have a lower risk. However, there is no evidence that phytochemical supplementation is as beneficial as eating the foods from which they are extracted. Fruits and vegetables are high in fiber, which helps prevent constipation, heart disease and some cancers. The fiber content is also filling, which increases satisfaction and curbs appetite.

Compositions of vegetables and fruit not only vary for a given kind in according to botanical variety, cultivation practices, and weather, but change with the degree of maturity prior to harvest, and the condition of ripeness, which is progressive after harvest and is further influenced by storage conditions. Nevertheless, some generalisations can be made.

Fruits and vegetables provide an abundant and cheap source of vitamins, minerals, and fibre. Their importance in the diet is largely determined by culture, for example, a religion such as Hinduism demands that its followers are vegetarian and their diet therefore contains a high proportion of fruit and vegetables. Other communities, however, only serve vegetables as accompaniments to main meals, and fruits as appetizers and desserts.

Most fresh vegetables and fruit are high in water content, low in protein, and low in fat. In these cases water contents will generally be greater than 70% and frequently greater than 85%. Commonly protein content will not be greater than 3.5% or fat content greater than 0.5 %. Exceptions exist in the case of dates and raisins which are substantially lower in moisture but cannot be considered fresh in the same sense as other fruit. Legumes such as peas and certain beans are higher in protein; a few vegetables such as sweet corn which are slightly higher in fat and avocados which are substantially higher in fat.

In addition to a great range of textures, much of the interest that fruits and vegetables add to our diets is due to their delightful and variable colours. The pigments and colour precursors of fruit and vegetables occur in the chloroplasts and other chromoplasts, and some dissolved in fat droplets or water within the cell protoplast and vacuoles.These pigments are classified into four major groups which include the chlorophylls, carotenoids, anthocyanins, and anthoanthins. Pigments belonging to the latter two groups also are referred to as flavonoids, and include the tannins.

The Chlorophylls

 These are contained mainly within the chloroplasts and have a primary role in the photosynthetic production of carbohydrates from carbon dioxide and water. The bright green colour of leaves and other parts of plants is largely due to the oilsoluble chlorophylls, which in nature are bound to protein molecules in highly organised complexes. When the plant cells are killed by ageing, processing, or cooking, the protein of these complexes is denatured and the chlorophyll may be released. Such chlorophyll is highly unstable and rapidly changes in colour to olive green and brown. This colour change is believed to be due to the conversion of chlorophyll to the compound pheophytin. Conversion to pheophytin is favoured by acid pH but does not occur readily under alkaline conditions. For this reason peas, beans, spinach, and other green vegetables which tend to lose their bright green colours on heating can be largely protected against such colour changes by the addition of sodium bicarbonate or other alkali to the cooking or canning water. However, this practice is not looked upon favourably nor used commercially because alkaline pH also has a softening effect on cellulose and vegetable texture and also destroys vitamin C and thiamin at cooking temperatures.

The Carotenoids

These are fat-soluble and range in colour from yellow through orange to red. They often occur along with the chlorophylls in the chloroplasts, but also are present in other chromoplasts and may occur free in fat droplets. Important carotenoids include the orange carotenes of carrot, maize, apricot, peach, citrus fruits, and squash; the red lycopene of tomato, watermelon, and apricot; the yellow-orange xanthophyll of maize, peach, paprika and squash; and the yellow-orange crocetin of the spice saffron. A major importance of some of the carotenoids is their relationship to vitamin A. A molecule of orange beta-carotene is converted into two molecules of colourless vitamin A in the animal body. Other carotenoids like alpha-carotene, gamma-carotene, and cryptoxanthin also are precursors of vitamin A, but because of minor differences in chemical structure one molecule of each of these yields only one molecule of vitamin A. In food processing the carotenoids are fairly resistant to heat, changes in pH, and water leaching since they are fat-soluble. However, they are very sensitive to oxidation, which results in both colour loss and destruction of vitamin A activity.

The Flavonoids

Pigments and colour precursors belonging to this class are water-soluble and commonly are present in the juices of fruit and vegetables. The flavonoids include the purple, blue, and red anthocyanins of grapes, berries, plump, eggplant, and cherry; the yellow anthoxanthins of light coloured fruit and vegetables such as apple, onion, potato, and cauliflower, and the colourless catechins and leucoanthocyanins which are food tannins and are found in apples, grapes, tea, and other plant tissues. These colourless tannin compounds are easily converted to brown pigments upon reaction with metal ions. Properties of the anthocyanins include a shifting of colours with pH. Thus many of the anthocyanins which are violet or blue in alkaline media become red upon addition of acid.

Some examples of phytochemicals found in fruits and vegetables are given on the table below.

FOOD	PHYTOCHEMICAL(S)
Allium vegetables (garlic,onions, chives, leek)	Allyl sulfides
Cruciferous vegetables (broccoli, cauliflower, cabbage, Brussels sprouts, kale, turnips, bok choy)	Indoles/glucosinolates Sulfaforaphane Isothiocyanates/thiocyanates Thiols
Solanaceous vegetables (tomatoes, peppers)	Lycopene
Umbelliferous vegetables (carrots, celery, cilantro, parsley, parsnips)	Carotenoids Phthalides Polyacetylenes
Citrus fruits (oranges, lemons, grapefruit) Glucarates	Monoterpenes (limonene) Carotenoids
Other fruits (grapes, berries, cherries, apples, cantaloupe, watermelon, pomegranate)	Ellagic acid Phenols Flavonoids (quercetin)
Beans, grains, seeds (soybeans, oats, barley, brown rice, whole wheat, flax seed) Protease inhibitors	Flavonoids (isoflavones) Phytic acid Saponins
Herbs, spices (ginger, mint, rosemary, thyme, oregano, sage, basil, tumeric, caraway, fennel)	Gingerols Flavonoids Monoterpenes (limonene)
Licorice root Green tea Polyphenols	Glycyrrhizin Catechins

FRUITS AND VEGETABLES COMPOSITION

With a few exceptions, the general  composition of fruits and vegetables are as follows::

—  High in water (≥ 85 %)

—  Exceptions: raisins and dates

—  Low in protein (≤ 3.5 %)

—  Exceptions: Legumes

—  

Low in fat (≤ 0.5 %)

—  Exceptions: sweet corn & avocardos

—  Rich in fibre

Fruit and vegetables have many similarities:

–      Their compositions,

–     Methods of cultivation and harvesting,

–     Storage properties and processing.

–     Many vegetables may be considered fruit in the true botanical sense.

CHEMICAL COMPOSITION OF FRUITS AND VEGETABLES:

1. Water

Fruits & vegetable cells contain water, which is usually present in more than 70%. It plays a vital role in

–      the evolution

–     reproduction cycle 

–     in physiological processes.

–     It has effects on the shelf life of fruits & veggies

 It is usually present as:

i. Free water: oozes out when fruit is cut

ii. Bound water or dilution water which is present in the cell and forms true solutions with mineral or organic substances;

Bound water exists as:

(i) Colloidal bound water

–     It is present in the membrane, cytoplasm and nucleus

–     It acts as a swelling agent  for these colloidal structure substances;

 (ii) Constitution water,

–     directly bound on the chemical component molecules

–      which is also removed with difficulty.

The chemical compositions of some fruits and vegetables are as shown below.

FRUITS Apple Grapefruit Apricot  Cabbage Banana Pear Pineapple Orange

(%) 84 91 86 93 74 84 87 96

VEGGIES Eggplant Brocolli Lettuce Peas (green) Peach   Peppers Potato Radish

(%) 92 91 96 79 88 92 95 79

 2.Minerals

Minerals compose about 4% of the human body. We cannot produce minerals within our bodies, so we must obtain them through our food. They ultimately come from the earth. Good soil is 45% minerals, yet our soils today are quite lacking due to synthetic fertilizers, mono-cropping and more.
They come from the earth and will eventually return to the earth.

There are 103 known minerals, at least 18 of these are necessary for good health. Mineral imbalance is epidemic. Osteoporosis is on the rise Osteoporosis isn’t even diagnosed until you’ve lost 30% of your bone mass....

Role of Minerals in the Body:

•      Minerals act as co-factors for enzyme reactions. Enzymes don’t work without minerals. All cells require enzymes to work & function.

•      They maintain the pH balance within the body.

•      Minerals actually facilitate the transfer of nutrients across cell membranes.

•      They maintain proper nerve conduction

•      Minerals help to contract and relax muscles.

•      They help to regulate our bodies tissue growth.

•      Minerals provide structural and functional support for the body

There are two categories of minerals essential within the body, macro-minerals & micro-minerals.

There is no one mineral deficiency, they all must be maintained in balance within the body.

Macro-minerals: Calcium, Phosphorous, Potassium, Magnesium, Sulfur , Sodium • Chloride Micro-minerals: (or Trace Minerals):Iron, Iodine, Manganese, Selenium, Boron, Chromium, Molybdenum

Calcium: Of all of these minerals found in the body, calcium is the main mineral, it comprises almost half of the mineral content in the body. Just 1% of the calcium in the body is actually in the blood, so blood tests are not accurate answers to just how much calcium our body truly has. The other 99% is stored in the bone. In order for calcium to be absorbed and utilized by the body there are several factors to consider. For example, if the overall systemic pH is off, it will be difficult to utilize the calcium you eat. Also, the hormonal function affects the ability to attain the calcium consumed. Other factors include whether or not an individual is adequately hydrated or if the digestion is impaired. Calcium also works in tandem with other minerals (particularly magnesium), vitamins and fatty acids. If an individual is  not eating a properly prepared, whole foods, nutrient dense diet, staying hydrated and improving the over all digestion, Calcium consumed will not be retained in the body. Most everyone gets adequate calcium in their diet, but are missing some or all of the above co-factors in their lives to make it of use to the body in the way it is intended.

Having appropriate calcium homeostasis plays a significant role in bone remodeling. Old bone tissue is continually being destroyed and broken down and new bone is continually being created. Osteoblasts are bone-forming cells that convert cartilage to bone. Osteocytes are our primary bone cells, and they maintain bone tissue. Osteoclasts are the bone-destroying cells that help with the function in resorption. Calcium is only made available for other tissues in the body when the bone is broken down during remodeling. Bone helps to buffer the pH level of the blood through the release of calcium from the bone. (Bone is a major buffer of calcium and calcium is a major buffer of blood pH.) When blood is too acidic it will pull calcium from the tissues. And when the blood gets too alkaline, calcium can separate out and get deposited into the wrong tissues, thereby causing problems if an if an excess occurs in those tissues. Calcium is also needed for every nerve impulse. In order for calcium to be absorbed it needs an acidic environment. If there is inadequate hydrochloric acid in the stomach the calcium consumed will not be utilised. Additionally, zinc is needed to help create the hydrochloric acid. Minerals are more difficult for the body to extract from the food. Absorption from the GI tract is the first step to getting the minerals into circulation, it can be a fairly complex process. If you see any aspect of undigested food in the stool, you can be sure you are not getting your minerals. Anyone with osteoporosis or osteopenia should check the pH of the stomach and check for adequate hydrochloric acid levels.

 3.Vitamins

These are organic materials which must be supplied to the human body in small amounts to facilitate various functions in the body. The two major groups include:

•      Fat -soluble

•      Water-soluble

Functions:

•      Facilitate the metabolism of carbohydrates, proteins and fats

•      However, their roles in maintaining health  may extend yet further.

•      Vit C: Antioxidant properties!!

•      Important in the prevention of CD

 3.1 Vitamin A or Retinol.

They are found only in animal materials such as meat and milk.  Plants contain no vitamin A but contain its precursor, beta-carotene.  Man can easily convert beta-carotene to vitamin A.

Beta-carotene is found in the orange & yellow vegetables

 Deficiency of vitamin A leads to:

–     night blindness,

–     failure of normal bone and tooth development in young kid

–     diseases of epithelial cells and membrane of the nose

–      throat and eyes diseases which decrease the body's resistance to infection.

 3.2 Vitamin C.

Vitamin C is the anti-scurvy vitamin. Lack of it causes  fragile capillary walls, easy bleeding of the gums, loosening of teeth and bone joint diseases. It is necessary for the normal formation of the collagen, which is an important constituent of skin and connective tissue.  

Like vitamin E, vitamin C favours Fe absorption

Deficiency of vitamin A leads to:

–     night blindness,

–     failure of normal bone and tooth development in young kid

–     diseases of epithelial cells and membrane of the nose

–      throat and eyes diseases which decrease the body's resistance to infection.

Vitamin C is  easily destroyed by oxidation especially at high temperatures. It is the vitamin most easily lost during processing and storage. Excellent sources of vitamin C are citrus fruits, tomatoes, cabbage and green peppers.

 4. Carbohydrates

They are the main component of fruits and represent more than 90% of their dry matter.

Functions:

–     They play a major role in biological systems & in foods.  

–     They may serve as structural components as in the case of cellulose;

–     Stored as energy reserves (starch)

–     Function as  essential components of ribose

–     Components of vitamins such as ribose and riboflavin.

Sugars such as glucose, fructose, maltose and sucrose all share these characteristics

 They supply energy for nutrition; they are readily fermented by microbes

On heating they darken/ caramelize; Some of them combine with proteins- browning reaction (refer to FT 100 notes on Browning reactions)

 Some properties of starches:

•      Provide a reserve energy source in plants ,supply energy

•      They occur in seeds and tubers as characteristic  starch granules

 Some properties of celluloses and hemicelluloses:

•      They are abundant in the plant kingdom and act primarily as supporting structures in the plant tissues;

•      They are insoluble in cold and hot water;

•      They are not digested by man

•      The fibre in food which produces necessary roughage is largely cellulose.

 Properties of pectins &carbohydrate gums.

•      Pectins are common in fruits and vegetables and are gum-like

•      They are found in and between cell walls and help hold the plant cells together;

•      In colloidal solution contribute to viscosity of the tomato paste;

•      They form gels when sugar and acid are added; The basis for jam & jelly manufacture.

 5. Fats

Fruits contain very low of fats (<0.5%). However, significant quantities are found :

–     in nuts (55%),

–     apricot kernel (40%),

–     grapes seeds (16%),

–      apple seeds (20%) and

–     tomato seeds (18%).

 6. N-containing substances

These substances are found in plants as different combinations including proteins, amino acids,  amides and amines. Vegetables contain between 1.0 and 5.5 % whereas fruit have less than 1% in most cases.  Among nitrogen containing substances the most important are proteins. Vegetable proteins have  a colloidal structure and, are less valuable than animal ones  because of their composition

Differentiate between: Essential and non-essential amino-acids!!!!

Food	CHO	Protein	Fat	Mineral	Water
Banana	24.0	1.3	0.4	0.8	73.5
Orange	11.3	0.9	0.2	0.5	87.1
Apple	15.0	0.3	0.4	0.3	84.0
Strawberries	8.3	0.8	0.5	0.5	89.9