Physical properties of proteins

Nearly half of the dry weight of a typical animal cell is protein. Structural components of the cell, antibodies, and many of the hormones are proteins but as much as 90% of cellular proteins are the enzymes upon which fundamental cellular function depends. They may be as many as 1000 different enzymes in a single cell.

The protein molecule is a polymer of amino acids joined in peptide linkages. Although the molecular weight is usually high, there is a vast range in both structure and complexity of protein molecules. Hemoglobin for example, has a molecular weight of about 64,500; myosin, a muscle protein is estimated to have a molecular weight of about 489,000.

It is not uncommon for peptide structures of fairly low molecular weight (less than 10,000 and containing less than 100 amino acids) to be designated polypeptides rather than proteins. On the average, about 20 different amino acids occur in most proteins, the amino acids present, their position in the molecule, and the spatial arrangement of the molecule all determine the proteins and characteristics of the proteins. In turn the function of a protein depends, in large measure, on its structure.

Other physical properties of proteins
*Dissociation
*Denaturation: denaturation refers to the changes in the properties of a protein. In other words, it is the loss of biologic activity. In many instances the process of denaturation is followed by coagulation— a process where denatured protein molecules tend to form largeaggregates and to precipitate from solution.
*Optical Activity
*Solubility, Hydration and Swelling Power
*Foam Formation and Foam Stabilization
*Emulsifying Effect
*Colour and taste: Proteins are colorless and usually tasteless. These are homogeneous and crystalline
*Shape and size: the proteins range in shape from simple crystalloid spherical structuresto long fibrillar structures.
Physical properties of proteins

Optical activity of carbohydrates

In 1811, Arago discovered that the “plane of polarization” of linearly polarized light was rotate when a beam of light propagated through quartz in a direction parallel to its optic axis. This property of quartz is called optical activity.

One of very important characteristic of sugars is their ability to rotate rays of polarized light. Carbohydrates contain several similarly substitute asymmetric carbon atoms and are therefore all optically active. This property is referred to as optical rotation and such compounds are said to be optically active.

A compound is optically active if its mirror image is not superimposable upon the original. In the application of this test, it must be realized that the atoms in a molecule are in constant motion with respect to each other.

The optical activity can be determined by optical rotation (OR), optical rotary dispersion (ORD) and circular dichroism (CD).
Optical activity of carbohydrates

Nutritional characteristics and health benefits of grapefruit

Good quality grapefruit has a turgid, smooth, glossy, and blemish-free peel. The fruit should be firm and the flesh should have reached an adequate total soluble sugar (TSS) – to-acidity ratio and have low bitterness. Grapefruit is low in calories which make it great for dieting. An 8 oz serving of grapefruit juice contains about 90 kcal.

Practically all grapefruit in the United States is grown in Florida, California, Arizona, and Texas. Basic Nutritional Facts:
• Grapefruit is a low-calorie food.
• An excellent source of vitamin C. Vitamin C is an important antioxidant and critical for production of collagen.
• A good source of inositol - a member of the vitamin B complex
• It is a common breakfast fruit, salad fruit, or juice fruit.

The grapefruit is known for its sour to semi-sour flavor. It contains grapefruit mercaptan, a sulphur, which in turn contain sterpene, influencing its flavor.

The major bioactive groups in grapefruit include flavonoids, carotenoids, limonoids, furanocoumarins, and organic acids.

White grapefruit has been reported to be slightly richer in flavonoids than pink and red ones. Pink grapefruit is rich in vitamin A, and acts as a natural antioxidant.

Red and pink grapefruits contain generous amounts of lycopene (1,419 μg per 100 g fresh weight), B-carotene (686 μg per 100 g fresh weight), vitamin A (1,150 IU per 100 g fresh weight), and flavanones, mainly naringin, which give the tangy or bitter taste to the fruit.

Grapefruit is an excellent cleanser for the digestive and urinary systems and the peel has many therapeutic properties.
Nutritional characteristics and health benefits of grapefruit

Characteristics of good nutritional status

Nutritional status is the state of human body as a result of the foods consumed and their use by the body. Nutritional status can be good, fair or poor. 

Good nutritional status refers to the intake of well-balanced diet, which supplies all the essential nutrients to meet the body’s requirements. Such a person may be said to be received optimum nutrition.

The characteristics of good nutritional status are an alert, good natured personality, with normal weight for height, well developed and firm muscles, reddish pink color of eyelids and membranes of mouth, good layer of subcutaneous fat, good appetite and excellent general health. Shiny hairs, smooth skin, clear eyes, and alert expression and firm flesh on well developed structure also reflect good nutritional status.

General good health is evident by stamina for work, regular meal times, sound regular sleep, normal elimination and resistance to disease.

A person with poor nutritional status cannot work as hard; low productivity means low income, and so a personals ability to make a living and obtain food for the family is less than it would be with good nutritional status.
Characteristics of good nutritional status

Characteristics of fats in general

*Fats are comprised of fatty acids bound, in bundles of three, to glycerol. There are about 20 different fatty acids that may be connected to glycerol in natural fats.

*Fatty acids are either saturated, monounsaturated or polyunsaturated. Those whose structures have the maximum number of hydrogen atoms are called saturated and those which are lacking hydrogen atoms at certain points in the structure are classified as unsaturated.

A saturated fatty acid

*Fats contains mixtures of all three types of fatty acids; the balance of the mix determines whether the fat is generally saturated (hard) or polyunsaturated (soft).

An unsaturated fatty acid

 *The amount of unsaturated fatty acids in a fat affects the temperature at which the fat melts. The more unsaturated a fat, the more liquid it is at room temperature.

*Fats are smooth, greasy substance that are insoluble in water. It is mainly a fuel source for the animal or plant in which it is found or for the animal that eats it.

*In digestion, bile acids act as detergents to solubilize fats to aids digestion. *In transport, the fatty material is surrounded by a coat of protein plus phospholipid. The full particle is a lipoprotein.

*The liver can convert carbohydrate to fat, which is exported from the liver as a lipoprotein. The lipoprotein complex responsible for transporting lipids from the small intestine is in the form of chylomicrons. It is the chylomicrons that responsible for the ‘milky’ appearance of blood plasma that occurs after a meal rich in fat has been eaten.

*Certain polyunsaturated fatty acids are nutritionally essentially because:
1. They are the precursors of the vitality important regulators of metabolism, the prostaglandins
2. The body cannot make them from either carbohydrate or existing dietary fatty acids.
Characteristics of fats in general

General characteristics of fat soluble vitamins

The fat soluble vitamins A, D, E and K are found in the fats and oils of food. Unlike water soluble counterparts, these vitamins are absorbed like dietary fat, with the assistance of bile acids.

Unlike water soluble vitamins, fat soluble vitamins are circulated away from small intestine in the lymph via chylomicrons before eventually entering the blood either as components of lipoproteins or bound to transport proteins.

Once absorbed, these vitamins are stored in the lover and fatty tissues until the body needs them.

The risk of toxicity from vitamin A and D is greater that that of vitamin E and K. A toxic affect from vitamin D can be seen when one consumes only ten times the body’s need. In contrast, consuming just three times the body’s need for vitamin A can lead to toxicity.

Fat soluble vitamins play diverse roles in the body. Vitamins A and D act somewhat like hormones, directing cells it convert one substance to another to store this or to release that.

Fat soluble vitamins typically found in fatty portions of foods, and they easily destroyed by heat and light.
General characteristics of fat soluble vitamins