Tuesday, May 4, 2010

food science - water and minerals

Minerals
Mineral elements are inorganic substances found in body tissues and fluids. They occur in foods as salts e.g. sodium chloride, calcium phosphate, and ferrous sulfate. They constitute 4% of our body weight.
Unlike carbohydrates, fats, and proteins they do not furnish energy. They have many functions in our body such as tissue building, regulation of body fluids, and other functions. Like vitamins, they are required in small quantities and are vital to the body. They should be supplied daily as they are excreted through the kidney, the bowel and the skin.
Minerals are present in our body as:
a) Components of organic compounds, e.g. hemoglobin contains iron and thyroxin contains iodine.
b) In organic compound, e.g. calcium phosphate in the bones.
c) As free ions in every cell in the body and
d) In all body fluids
Sodium is the main electrolyte in the extracellular fluid, and potassium is the main electrolyte in the intracellular fluid.
The mineral elements are not destroyed by heat, oxidation, acid or alkali. Since they are soluble in water some loss occurs due to leaching when cooking water is discarded.
Minerals are inorganic elements require by the body in varying amounts to carry out various body functions. They remain largely as ash when plants and animal tissues are ignited.
Minerals may be classified into three groups:
Major minerals or macrominerals: Seven minerals are required in large amounts of over 100mg/day, e.g. calcium, phosphorus, sodium, chlorine, potassium, magnesium, and sulphur.
Minor minerals: These are required in small quantities, less than 100 mg/day, e.g. iron and manganese.
Trace elements: A few micrograms to a few milligrams are required per day e.g. iodine, fluoride, zinc, and molybdenum.
GENERAL FUNCTIONS OF MINERALS
1. Minerals form the structural components of bones, teeth, soft tissues, blood, and muscles, e.g. calcium, phosphorous, and magnesium in bones.
2. They regulate activity of nerves with regard to stimuli and contraction of muscles, e.g. calcium.
3. Maintain acid-base balance of body fluids, e.g. sodium and chlorine.
4. They control water balance by means of osmotic pressure and permeability of cell membranes, e.g. sodium and potassium.
5. They are constituents of vitamins, e.g. thiamine contains sulphur and cyanocobalamine contains cobalt.
6. They form part of molecules of hormones and enzymes, e.g. iodine in thyroxin and zinc in insulin.
7. They activate enzymes, e.g. calcium activates enzyme lipase.
8. They regulate cellular oxidation, e.g. iron and manganese.
9. Necessary for clotting of blood, e.g. calcium.
Calcium
The adult body contains 1.2 kg of calcium of which 99% is present in bones and teeth. It is the most abundant mineral in the body. The bones provide:
1. Rigid frame work for the body
2. Reserves of calcium and releases calcium on demand.
The remaining 1% is distributed in the extracellular and intracellular fluids and has the following functions:
1. Calcium acts as a catalyst in clotting the blood.
2. It increases the permeability of cell membranes thus helping in absorption.
3. It regulates contraction and relaxation of muscles including the heart beat.
4. It activated the number of enzymes such as pancreatic lipase and acts as a co-factor.
Factors affecting calcium absorption The amount of calcium absorbed by the humans depends on the body’s need. Approximately 40% of calcium ingested is absorbed.
1. Phosphate and phytic acid is present in cereals and form insoluble calcium salts if present in excess.
2. An alkaline intestinal pH (above 7) reduces absorption by forming insoluble salts.
3. Excess fibers decreases absorption of calcium.
4. Oxalic acid in green leafy vegetables forms insoluble calcium oxalate, which is excreted.
5. Faulty absorption of fats and fatty acids form insoluble calcium salts, which are excreted
6. Lactose increases calcium absorption.
7. High protein intake increases absorption.
8. Caffeine increases urinary calcium salts and high sodium also.
9. Strenuous exercise increases the loss.
The parathyroids regulate the calcium level in blood and calcium metabolism in bone. The calcium to phosphorus ratio should always be 1:1
Sources Various sources of calcium are:
1. Milk and milk products excluding butter, ghee, and cream.
2. Ragi, green leafy vegetables especially drumstick leaves, cabbage, curry leaves, carrot and cauliflower tops and amaranth.
3. Small dried fish, nuts, and oilseeds such as gingelly seeds.
4. Betel leaf with slaked lime is a rich source of calcium.
Deficiency A severe deficiency of calcium leads to rickets in children and osteomalacia and osteoporosis in adults (refer chapter 17, vitamin D deficiency for symptoms of rickets and osteomalacia).
Osteoporosis In osteoporosis the bones become porous because of bone mineral loss. This causes compression of the vertebrate that result in loss of height, back and hip pain, and increased susceptibility to fractures. It is seen in post menopausal women and can be controlled by weight bearing exercises such as walking, calcium supplements and hormone therapy.
Tetany A decrease in serum calcium levels gives rise to a condition called tetany. The symptoms of tetany are severe intermittent spasms of the muscles of hands and feet accompanied by muscular pain. Twitching of facial muscles occurs.
Phosphorus
Phosphorus comprises 1% of total body weight. It occurs along with calcium in human nutrition and also has many other functions in the body.
1. Building bones and teeth along with calcium and magnesium.
2. DNA and RNA, nucleic acids needed for genetic coding contain phosphorus.
3. As phospholipids, they regulate the absorption and transport of fats.
4. Adenosine triphosphate (ATP) and adenosine diphosphate (ADP) are necessary for storing and releasing energy according to body needs.
5. As part of enzymes needed for the metabolism of carbohydrates, fats, and proteins.
Sources Phosphorus is widely distributed in foods. Milk and meat are rich in phosphorous. Whole grain cereals, legumes, nuts, carrots, and fish are also rich resources of phosphorus.
Deficiency Phosphorous deficiency is rare since a diet that contains adequate protein and calcium will be rich in phosphorus. Deficiency symptoms are similar to calcium deficiency.
Iron
The human body 3-5 g of iron of which 70% is in the circulating hemoglobin.
Functions:
1. Essential for carrying O2 to the lungs where O2 is released and CO2 is picked up to be exhaled by hemoglobin in the red blood cells.
2. It is an essential part of several oxidative enzymes.
3. It helps in specific brain functions such as good attention span and capacity to learn and memorize.
4. It facilitates the complete oxidation of carbohydrates, proteins, and fats within the cell and release of energy for performing physical energy.
Diet improves iron in two forms:
1. Haeme iron i.e. iron associated to the protein, globin, to form hemoglobin. Haeme iron is found in flesh food only.
2. Non-haeme iron is the form present in all plant sources plus 60% of animal sources.
Haeme iron is present in small quantities in food. About 40% iron in flesh food is haeme iron, while 60% is non-haeme iron. It is rapidly absorbed and transported. About 23% is absorbed.
Non-haeme iron is the larger portion of iron in food. It is tightly bound to organic molecules in the form of ferric iron (Fe+++). In the acidic medium of the stomach, it is dissociated and reduced to its more soluble ferrous form (Fe++). The absorption rate of non-haeme iron is slow and approximately 8% is absorbed.
Vitamin C from the diet and hydrochloric acid in gastric juice help in converting ferric iron to ferrous iron.
Factors affecting iron absorption: The following factors enhance absorption:
Body need In periods of extra demand or in a deficiency, more iron is absorbed.
Acidic Medium Gastric acidity and ascorbic acid in the meal favour absorption.
Form of iron Haeme iron and ferrous iron are better absorbed.
Complete proteins Complete proteins such as meat favour absorption.
The following factors decrease absorption:
1. Ferric iron or non-haeme iron in the absence of proteins and ascorbic acid are poorly absorbed.
2. Achlorhydria or lack of hydrochloric acid in gastric juice and use of antacids with meal interfere with absorption.
3. Tea and coffee with meals.
4. Excessive intake of phytates and oxalates interferes with absorption.
5. Malabsorption due to intestinal disorders.
Iron is required for replacements of daily losses through excretion in urine, sweat, hair, and worn out cells. It is also needed for replacement of blood losses and an expanding blood volume in all stages of growth.
Sources Various sources of iron are:
1. Liver, organs meats, shellfish, lean meat, egg yolk are all good sources of iron.
2. Green leafy vegetables, whole grain, and enriched cereals, legumes and jaggery (50g will meet the requirement.
3. Garden cress seeds and niger seeds are excellent sources.
4. Peaches, apricots, manukas and figs
5. Use of iron cooking utensils contributes significantly to the iron content of the diet.
Non-haeme iron is present in plant food such as green vegetables, and cereals. 40% of iron in meat, poultry, and fish is haeme iron and 60% is non-haeme iron.
Deficiency Iron deficiency or anaemia is very common in the vulnerable age groups in all developing countries. Haemoglobin level may be as low as 5-9g. Normal haemoglobin levels for females are 11.5%-14.5% and for males 12.5%-16.5%.
Symptoms General fatigue, breathlessness on exertion, giddiness, and pallor of skin (paleness), oadema of ankles and spoon shaped nails are the common symptoms of iron deficiency.
Iron deficiency causes microcytic and hypochromic anaemia. Red blood cell’s appear pale and smaller in size. Iron deficiency may also be seen if excessive blood loss occurs or because of faulty absorption, intestinal disease, or parasites especially hookworm and roundworm infestations.
Iodine
Most of the iodine in adult body is found in the thyroid gland. The only known function of iodine is as a constituent of thyroxin. The thyroid hormone regulates the rate of oxidation within the cells. The iodine absorbed is incorporated into the amino acid tyrosine to form the hormone thyroxin.
Iodine + Tyrosine  Thyroxin
If intake of iodine is inadequate, the stores of thyroxin are gradually depleted and the thyroid gland enlarges in an attempt to produce the necessary thyroxin.
Sources Seafood contains maximum iodine and fruits contain the least. Wide variations are seen because food content of iodine depends upon the soil where they are grown. To provide sufficient iodine, salt is being iodized. Salt is a universally used dietary item. It is cheap and addiction of iodine does not affect its flavour. It is added in form of sodium or potassium iodide in the proportion of 1mg for every 10g of salt.
Deficiency Deficiency occurs when the iodine content of the soil is so low that insufficient iodine is obtained through food, e.g., the soil the Kangra valley in Himalayan region is deficient in iodine. Deficiency of iodine results in goitre.
Symptoms
1. Enlargement of thyroid gland.
2. Cretinism in children (stunted growth). Cretinism is characterized by a low basal metabolism rate (BMR), flabby and weak muscles, dry skin. Skeletal development stops and mental retardation is seen.
Goitrogens – are substances in food known to interfere with the use of thyroxin and can produce goitre. They are present in the red skin of peanuts and in vegetables such as cabbage and cauliflower, turnips and mustard.
Fluorine
Fluorine is the normal constituent of the body, found mainly in bones and teeth. Small amounts of fluorine brings about striking reductions in the tooth decay probably because the tooth enamel is made more resistant to the action of acids produced by bacteria in the mouth.
Sources Milk, eggs, and fish are important sources. Fluoridation of water to ensure a concentration of 1 ppm is a safe and economical way to reduce the incidence of dental caries.
Deficiency A deficiency results in dental caries and is seen in areas where drinking water contains less than 0.5 ppm of fluorine. Adding fluorine at a level of 1 ppm reduces the incidence of dental caries by 50%. Food as well as water contains varying amounts of fluorine.
Fluorosis Fluorosis or mottling of teeth occurs in parts of the world where drinking water contains excessive amounts of fluorine, i.e., 3-5 ppm. Teeth lose their lustrous appearance. Enamel becomes dull and unglazed and chalky white patches are seen. Sometimes enamel is pitted giving the tooth surface a corroded appearance. Skeletal Fluorosis may also be seen. There is hypercalcification of the bones. Mottled areas may get yellow brown stains or discolored.
Sodium Sodium chloride or common salt is a daily ingredient in our diet. The adult body contains 180g of sodium most of which is present in the extracellular fluid of the body.
The functions of sodium are as follows:
1. Maintaining fluid balance and normal osmotic pressure between intracellular and extracellular compartments.
2. It maintains normal irritability of nerves and helps in muscles contraction.
3. Regulates the alkalinity and acidity of body fluids along with the mineral chloride.
4. Regulates cell permeability or passage of substances into and out of the cell.
Sources Milk, egg white, meat, poultry, green leafy vegetables, Bengal gram dal, beetroot, and knolkhol are good sources.
The sodium from additives should also be included in the sodium content of a meal.
Deficiency A deficiency is seen in people engaged in heavy physical activities such as farm and mine workers and in athletes. It may also occur in cases of severe vomiting or diarrhoea. It results in weakness, giddiness, nausea, and muscles cramps. It can be treated by adding salt to water and lime juice and if this is not retained, intravenous saline could be given.
Excess An excessive intake of sodium should be avoided as it predisposes a person to hypertension. Salt is 40% sodium, which means that a teaspoon full of salt provides 2g or 2000mg of sodium. Sodium is present is food and as well as in many ingredient added to food such as sodium bicarbonate, monosodium glutamate, sodium benzoate, sodium propionate, and sodium nitrate. These need to be curtailed on a low sodium diet.
Potassium
It is present as the major electrolyte in all body cells.
Functions:
1. As a component of all living cells in the intracellular fluid it helps in regulating the water balance along with the sodium.
2. It regulates the acid-base balance like sodium.
3. It helps in transmitting nerve impulses and contraction of muscle tissues.
Sources Fruits, vegetables, pulses, nuts, flesh food, and whole grain are rich in potassium.
Deficiency Deficiency of potassium is unlikely in normal circumstances but may occur in severe malnutrition, chronic alcoholism, surgery and prolonged infection.
Magnesium
About 60% is found along with calcium and phosphorous in the bones and teeth. The remaining 40% is present in the tissues and the body fluids and performs the following functions:
1. It is present mainly in the intracellular fluid and helps in maintaining fluid balance along with sodium, potassium, and calcium.
2. It helps in transmission of nerve impulses, muscles contraction and regulation of the heart beat.
3. It acts as a co-factor in many metabolic reactions.
Sources Milk, cheese, fish, meat, whole grains, pulses, and nuts.
Deficiency Deficiency of magnesium is uncommon. It may not occur in malnutrition and alcoholism. Symptoms of deficiency are similar to tetany and include muscle tremors, spasms, and convulsions.





WATER

Water is so familiar and so large a constituent of the body that its fundamental importance in both structure and functioning of all tissues tends to be overlooked.

Water is the most essential constituent of our body. It accounts for 55%-70% of out total body weight. The total body fluid is distributed among two major compartments.

1. The extracellular fluid or water present outside the cells in the intestinal spaces and blood plasma.
2. The intracellular fluid or the water present inside the cells

Considering an average of 60% of body weight is contributed by water, an adult weighing 70kg has a total body water of 42 liters of which 28 is intracellular and 14 is extracellular. Water present in the body has electrolytes dissolved in it. Thus when the body looses water, it looses electrolytes as well.

Sodium is the principal electrolyte of the extracellular fluid while potassium is predominant in the intracellular spaces. The normal concentration of ions in the intracellular and extracellular fluids needs to be maintained at all times. This concentration of ions is preserved by a balance between the intake of water and the output or loss of body water.

FUNCTIONS

1. Water quenches thirst and is the most refreshing and cooling of all liquids
2. It is a structural component of all cells. In the bone, water is tightly bound, but in most tissues, a constant interchange takes place between the body compartments of water.
3. It it the medium in which all chemical reactions take place
4. It is an essential component of all body fluids such as blood, lymph, bile etc
5. It acts as a lubricant and helps food to be swallowed and digested food to pass through the gastro intestinal tract.
6. It is essential to maintain the turgidity of cells
7. It acts as a solvent for the products of digestion and helps in transporting these products to different tissues.
8. It regulates the body temperature by taking up and distributing heat produced in cells when metabolic reactions take place.
9. It helps in excreting waste products of metabolic reactions

DAILY INTAKE OF WATER

Apart from the water we drink during the day to relieve thrist between and during meals, there are three major sources of water.

Beverages and liquid foods: Hot and cold beverages such as tea, coffee etc. are largely made up of water. They are an important source of water and nutrients.

Water content of solid foods: Another important source of water is fruits, vegetables etc. Solid food contain varying percentages of water
The water consumed from beverages and solid food amounts to 2,100 ml/day approx.

Metabolic water: It is synthesized in the body as a result of oxidation of fat, proteins, carbohydrates adding to about 200 ml/day.
Oxidation of 100 g fat ► 107 ml water
100 g protein ► 41 ml water
100 g carbohydrate ► 56 ml water

The intake of fluid varies among different people and also varies according to the climate, habits and physical activity on a day to day basis.

DAILY LOSS OF BODY WATER

Insensible water loss: It is the loss of water we are not consciously aware of even though it occurs continuously in all living beings. It includes

(a) Continuous loss of fluid by evaporation frm the skin, which occurs independently of sweating and
(b) Insensible water loss though the respiratory tract, which is about 300-400 ml/day

Water loss through sweat: The extent of water loss through perspiration or sweat largely depends on physical activity and environmental temperature.

Water loss in urine: This is the most important mechanism by which the body maintains a balance between fluid intake and output as well as electrolyte homeostasis. Urine volume can be as low as 0.5 liters/day to as high as 20 liters/day. The rate of filtrations of water in the normal kidney is about 125ml/minute or approx. 180 liters a day for an adult. About 99% of the water filtered is reabsorbed into the blood while 500-2,000 ml is excreted as urine.

Water loss in faeces: Only a small amount of water is normally lost in faeces, The saliva, gastrointestinal secretion and bile may together add to 8 liters or more fluid per day. If there is diarrhea or vomiting, fluid losses may be large and cause dehydration.








WATER BALANCE

Deficiency of Water

Excessive loss of water could take place due to diarrhoea, vomiting, fever, excessive perspiration etc. It can result in dehydration. Dehydration can be classified as

Mild<5% fluid loss
Moderate 5-15% fluid loss
Severe 15-20% fluid loss

A dehydrated person feels thirsty, has a dry mouth, sunken and dry eyes and may feel restless, irritable, lethargic or unconscious in severe cases. The skin when pinched does not go back quickly. A dehydrated person is usually managed by Oral Rehydration Therapy (ORT). The WHO recommends Oral Rehydration Salts (ORS) that are to be dissolved to 1 litre of water.

ORS are most prescribed in cases of diarrhoea. Glucose present in ORS, ORT also includes any of the following.

1. Sugar and salt solution
40g sucrose + 4g NaCl in 1 litre of water
2. Rice water with salt
50g rice + 4 g salt in 1 litre of water
3. Dilute salted lassi
4. Plain water, lemon water, coconut water, thin soups or dal water may also be given along with ORT

If vomiting is severe, intravenous fluids such as normal saline and dextrose need to be given. When the body looses fluids, it looses both water and electrolytes, hence ORS or Dextrose Normal Saline (DNS) is given. Dehydration cannot be treated by giving pure water only

Retention of Water

Oedema is the retention of salt and water in the interstitial fluid giving rise to swelling of the skin. A pit of depression is formed when pressure is applied with the finger to the swollen skin and this is how oedema is distinguished from swelling. Water and salt may need to be restricted.

Daily Requirement

A minimum of sic to eight glasses of water is recommended to enable the body to perform optimally and keep one active and refreshed throughout the day. It should be consumed at regular intervals so that the body is always well hydrated this quantity is independent of other fluids consumed. .

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