Friday, August 22, 2014

Nutritional value and handling of fruits and vegetables

 Fruit and vegetable consumption is one element of a healthy diet. Fruits and vegetables provide excellent sources of nutrients such as fibre, complex carbohydrates and numerous vitamins, minerals as well as non-nutritive phytochemicals. The nutrient content of fruits and vegetables also vary greatly in quality and quantity. The phytochemicals present in fruits and vegetables are diverse, such as ascorbic acid, carotenoids and phenolic compounds and they function as antioxidants, phytoestrogens and anti-inflammatory as well as chemoprotective agents. The World Health Organization (2003) estimated that a low vegetable and fruit intake accounts for 2.7 million deaths annually. Insufficient  intake of fruits and vegetables is estimated to cause around 14% gastrointestinal cancer deaths, about 11% of ischemic heart disease deaths  and about 9% of stroke deaths worldwide (WHO 2009). The World Health Organization acknowledges that the global intake of vegetables is less than 20-50% of the recommended amount.



Types of fruits and vegetables

Vegetables can be categorized into 3 general types such as green leafy and cruciferous, low-glycemic and starchy. On the other hand fruits are mainly divided into sweet, sub-acid and acid fruits. Vegetables are derived from various parts of plants that include leaves, stems, shoots, flowers, roots, rhizomes, tubers, bulbs, seeds, pods and even fruits. Vegetables are often used for dietary variety, colour and taste and can be obtained in a range of processed state including fresh, frozen, canned and dried. The quality factors of vegetables include colour, flavour, nutritional composition and health – functionality. The content of individual fruits and vegetables is affected by factors such as variety, soil, climatic conditions, agricultural methods, physiological stress and degree of ripeness, storage conditions and length of storage before consumption.
Most fresh fruits and vegetables are high in water, low in protein and low in fat. The water content ranges from 70-85%, commonly protein content is no greater than 3.5% and fat content no greater than 0.5%. Legumes such as peas and certain beans are higher in protein; a few vegetables such as sweet corn are slightly higher in fat; and avocados are substantially higher in fat. The majority of proteins occurring in fruits and vegetables play enzymatic roles. Proteins are found mainly in the cytoplasmic layers. The lipids of fruits and vegetables are largely confined to the cytoplasmic layers, in which they are especially associated with the surface membranes. The total amount of mineral components in fruits and vegetables is in the range of 0.1% (in sweet potatoes) up to about 4.4% (in Kohlrabi). The most abundant mineral constituent in fruits and vegetables is potassium.

Nutrient composition

The water content in various foods ranges from about 15% in grains, about 16 to 18% in butter, 20% in honey, 35% in bread, 75% in meat to about 90% in many fruits and vegetables. The amount of carbohydrates in foods ranges from about 1% in meats and fish, 4.5% in milk, 18% in potatoes, and 15 to 21% in sugar beets to about 70% in cereal grains. The proteins constitutes from about 1% of the weight of fruits, and 2% of potatoes, 12% of eggs, 12 to 22% of wheat grains, about 20% of meat to 25 to 40% of various beans. Lipids makes up from less than 1% of the weight of fruits, vegetables and lean fish muscle, 3.5% of milk, 6% of beef meat and 32% of egg yolk to 85% of butter.


Dietary recommendations

The World Cancer Society and the American Institute for Cancer Research suggest that mouth, stomach and colorectal cancers are less likely with high intakes of non-starchy foods like leafy green, broccoli and cabbage. The American Cancer Society advising at least five servings of fruits and vegetables per day for good health. The Harvard School of Public Health recommending nine servings of vegetables and fruits each day. The U.S. Department of Agriculture recommends filling half of one’s plate with fruits and vegetables at each meal. The USDA 2000 Dietary Guidelines (USDA, 2000) encourages people to: (1) enjoy five a day, i.e., eat at least 2 servings of fruits and at least 3 servings of vegetables each day.(2) choose fresh, frozen, dried or canned forms of a variety of colors and kinds, and (3) choose dark green leafy vegetables, orange fruits and vegetables  and cooked dry beans and peas often.The Dietary Guidelines for Americans 2010 has  recommended  that  every individual  should  make one-half of his/her plate with fruits and vegetables. The Expert Committee of the Indian Council of Medical Research has recommended that every individual should consume at least 300g of vegetables and 100g of fruits per day.

5 A DAY message

The '5 A DAY' message highlights the health benefits of consuming five 80 grams portions of fruits and vegetables every day. ‘5 A DAY’ is based on advice from the World Health Organization which recommends eating a minimum of 400g (80 x 5g) of fruits and vegetables a day to lower the risk of serious health problems such heart disease, stroke, type 2 diabetes and obesity.

Health benefits of fruits and vegetables

Hydrating effects –Drinking fruit and vegetable juices can contribute to the hydration of body  fluids and supply sugars and minerals e.g., water melon, celery, cucumber and lettuce.
Diuretic effects – Diuretics improve the rate of urination. The presence of potassium and magnesium help to accelerate the frequency of urination e.g., lemon, lime, cucumber, rose apples, peach and water melon.
Alkaline forming effects – Potassium, magnesium, calcium, copper, zinc and iron are alkaline minerals that are found in most fruits and vegetables. Citrus fruits, soybeans, carrots, lettuce, water cress and spinach are some examples of fruits and vegetables with alkalizing properties.
Mineralizing effects – Fruits and vegetables are a good source of mineral nutrients such as potassium, magnesium and calcium. E.g., bok choy, amaranth leaves, French beans, Brussels sprouts, dates, avocado and passion fruit.
Laxative effects –The dietary fibres in fruits and vegetables maintain healthy bowel function. High fibre fruits and vegetables act as natural laxatives e.g., psyllium, wheat bran, bananas, berries, apples, prunes, raisins, pineapple, and cabbage.
Tonic effects – Fruits and vegetables have curative properties which are useful in the treatment of certain diseases. Vegetables rich in potassium may help to maintain blood pressure e.g., sweet potatoes, white potatoes, white beans, tomato, soybeans, spinach and lentils. Fruits like apple, date and mango have a direct effect on the central nervous system.

Precautions for storing and cooking vegetables

Fresh fruits and vegetables are contaminated by pesticides, herbicides and fertilizers. Wash and scrub all fruits and vegetables thoroughly under running tap water before using them. Rinsing and rubbing is quite effective at removing tiny pathogens and surface deposits of pesticides. Do not use any chemicals for washing because fruits and vegetables are porous and they absorb the chemicals. Peel fruits and vegetables if possible and wash them before peeling. Trim only the inedible parts of the vegetable and cut the vegetables just before cooking. Washing, peeling and cooking fruits and vegetables reduces pesticide levels and eliminates the waxes.  Drying fruits and vegetables with a paper towel provides another measure of safety.
Do not buy or use produce that is moldy, badly bruised, shriveled or slimy. Discord the outer leaves of leafy vegetables because pesticides residues tend to accumulate there. Store fruits and vegetables in a cool dark place and use them as soon as possible after purchasing. Refrigerated fruits and vegetables should be kept in bags or containers, to minimize the chance of cross contamination between other foods and surfaces. Do not store fruits and greens together because fruits give off ethylene gas, which causes greens to decay. Frozen vegetables are often as healthy as fresh vegetables. Keep your fruits and vegetables separate from raw meats, poultry and sea-food. Store newly bought ones separate from old ones.
Dry and shelf –stable foods include flours, rice, and sugars should be stored in jars or containers in a cool, dry and well ventilated area. The food storage area should be regularly swept out and cleaned and any spit food should be cleaned up immediately. Onions should be stored away from other food in a cool, dry and well-ventilated area.
Water soluble vitamins are destroyed by cooking and are lost over time. Minerals and vitamins leach out into cooking water. Use minimum amount of water for cooking and avoid overcooking. Cover the pot when cooking vegetables to keep in steam and reduce cooking time.  Use vegetable water in stocks or gravies. Avoid frying vegetables. This will lead to loss of all valuable vitamins. Dulling of the greens can be minimized by keeping cooking times short. Do not use sodium bicarbonate, when cooking vegetables. Cook frozen vegetables without prior thawing and for as little time as possible. Eat food as soon as possible after cooking and avoid reheating.
Try to vary the intake of your vegetables. Because different pesticides are used on different crops, eating a variety of fruits and vegetables help ensure too much of any one pesticide. The best way to eat fruits and vegetables is without additional fat or sugar. Storage and cooking can lead to overall losses of up to half of the original nutrient content prior to consumption.
Choose cooking methods that minimize losses of vitamins and minerals. Since vegetables are very fragile,cook them as lightly as possible. Vegetables taste, keep their color and retain their nutrients better, when not overcooked. The best method is to steam the vegetables lightly and eat them while they are still crunchy.Fruits and vegetables should be eaten as far as possible in their natural state.


7 comments:

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