No.10 Food Tests
Carbohydrates (Sugars and Starches)
Reducing Sugars.
The reducing sugars include all monosaccharides, Such as glucose and fructose, and some disaccharides, such as maltose. Use 0.1 – 1% sugar solutions.
Test for reducing sugar:
Benedicts test: Add 2 cm3 of a solution of the reducing sugar to a test tube. Add an equal volume of benedicts solution. Shake and bring gently to the boil, shaking continuously to minimise spitting.
Observation: The initial blue coloration of the mixture turns green, then yellowish and may finally form a brick red precipitate.
Basis of test: Benedicts solution contains copper sulphate. Reducing sugars reduce soluble blue copper sulphate containing copper (II) ions (Cu2+) to insoluble red - brown copper oxide containing copper (I). The latter is seen as a precipitate.
Non- Reducing sugars.
Non reducing sugars, the most common non reducing sugars is sucrose, a disacchriade. If reducing sugars have been shown to be absent (negative result in a above test) a brick red precipitate in the test below indicates the presence of a non reducing sugar. If reducing sugars have been shown to be present, a heavier precipitate will be observed in the following test than with the reducing test if non reducing sugar is also present.
Tests for non reducing sugar:
Add 2 cm3 of sucrose solution to a test tube. Add 1 cm3 dilute Hydrochloric acid. Boil for 1 minute. Carefully neutralise with sodium hydrogencarbonate (Check with pH paper) Care is required because effervescence occurs. Carry out benedicts test.
Observation:
As benedicts test.
Basis of test:
Disaccharide can be hydrolysed to it’s monosaccharade constituents by boiling with dilute hydrochloric acid. Sucrose is hydrolysed to glucose and fructose, both of which are reducing sugars and give the reducing sugar result with the benedicts test.
Test for starch:
Iodine/potassium iodide test.
Add 2cm3 of 1%starch solution to a test tube. Add a few drops of iodine potassium solution. Alternatively add the latter to the solid for of starch.
Observation:
A blue-black colouration.
Basis of test:
A polyiodide complex is formed with starch.
Test for a lipid:
Emulsion test:
Add 2cm3 fat or oil to a test tube containing 2cm3 of absolute ethanol. Dissolve the lipid by shaking vigorously. Add an equal amount of cold water.
Observation:
A cloudy white suspension.
Basis of test:
Lipids are immiscible with water. Adding water to a solution of the lipid in alcohol results in emulsion of tiny droplets in the water which reflect light and give a white , opalescent appearance.
Test for a protein:
Biuret test:
Add 2cm3 protein solution to a test tube. Add an equal volume of 5% potassium hydroxide solution and mix. Add 2 drops of 1% copper sulphate solution and mix. No heating is required.
Observation:
A mauve or purple colour develops slowly.
Basis of test:
A test for peptide bonds. In the presence of dilute copper sulphate in alkaline solution, nitrogen atoms in the peptide chain for a purple complex with copper(II) ions (Cu2+). Buiret is a compound derived from urea which also contains the –COHN- group and gives positive results.
EXTRA: TO THE SAME ABOVE
Test for Starch
1) 2cm³ of sample add 3 drops of Iodine solution
2) Positive result: colour change from orange/brown to blue/black
3) BECAUSE... starch is a polymer of alpha glucose and the chain coils up into an amylose helix AND the hole in the middle of the helix is the same size as iodine and forms a starch-iodine solution causing a structural change.
Test for Reducing Sugars
1) Benedict's Test: sample and Benedict's solution -> heated in hot water bath of 90°C
2) Positive result: blue to red
3) Semi-quantitive test that detects different amounts but not exact volume
4) BECAUSE... solution contains copper sulphate and reducing sugars (e.g glucose) has an exposed reducing group which reduces the Cu²⁺ ions into Cu⁺ forming a red precipitate
Test for Non-Reducing Sugar
1) Hydrolyse sample into monosaccharide units
2) Test with Benedict's regent -> no change -> add 2cm² of food sample to equal parts HCl -> heat in boiling water bath for 5 mins -> slowly add sodium hydrogen carbonate solution until neutralised -> re-test with Benedict's regent
Test for Protein
1) BIURET TEST
2) add equal volumes of sample, sodium hydroxide and then 5 drops of copper sulphate (biuret) -> colour change from blue to purple to pink
3) alkali (NaOH) hydrolyses proteininto fragments AND proteins contain amine groups (NH₂) which reacts with the Cu²⁺ ions to cause colour change
Test for Fat
1) add 2cm³ of sample to equal parts of ethanol -> shake vigorously using bung -> add 2cm³ cold water
2) POSITIVE RESULT will show a cloudy white suspension BECAUSE lipids present dissolve in the ethanol and when water is added, lipid-ethanol mixture disperses in the water to produce cloudy white colloid.
Main Human Diseases Associated With Aging
Definition of Degenerative Diseases
1. What are degenerative diseases?
Degenerative diseases are common non-infectious diseases whose incidences increase with age.
Risk Factors Explained
More Bite-Sized Q&As Below
2. What are risk factors for diseases?
Risk factors for a disease are everything that contributes to an increased risk of the disease appearing. For example, for most cardiovascular diseases, tobacco smoking and diabetes mellitus are both important risk factors; for some cancers having a genetic cause, a positive family history is a risk factor, etc.
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The Main Human Degenerative Diseases
3. What are the main human degenerative diseases?
The main human degenerative diseases are divided into three groups: cardiovascular diseases, neoplastic diseases and degenerative diseases of the nervous system. The main cardiovascular diseases are hypertension, cardiopathies, including coronary disease and myocardial infarction, and cerebrovascular accidents (CVAs, or strokes). Neoplasms are benign tumors and cancers. The main degenerative diseases of the nervous system are Alzheimer's disease and Parkinson's disease.
High Blood Pressure
4. What is hypertension?
Hypertension is a disease in which arterial blood pressure is abnormally high, during systole or during diastole.
Hypertension, or high blood pressure, is a condition that must be diagnosed and treated, since it produces irreversible injuries to arteries and, later, it causes other severe diseases in organs such as the heart, brain, kidneys, retina, etc.
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5. What are the main risk factors for hypertension?
The main risks factors for hypertension are tobacco smoking, stress, obesity, a sedentary lifestyle and alcoholism.
6. What is the relationship between the maximum and the minimum blood pressure during the phenomena of systole and diastole?
The maximum blood pressure is the pressure on the wall of arteries during systole, that is, when the heart is pumping blood to arterial vessels. The minimum blood pressure is the pressure on the wall of arteries during diastole, that is, when the heart ventricles are relaxing and filling with blood.
Heart Diseases
7. What are the main degenerative diseases of the heart?
The main degenerative diseases of the heart are heart failure, arrhythmias, valvular heart diseases, coronary insufficiency and myocardial infarction.
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8. What is coronary disease?
Coronary disease, or coronary insufficiency, is a disease in which there is total or partial obstruction of one or more of the arteries that irrigate the heart musculature; that is, obstruction of the coronary arteries. The disease is formed by the slow and gradual formation of atheroma plaques inside coronary arteries. The fatty plaques grow and block the flow of blood, a process known as atherosclerosis (not to be confused with arteriosclerosis, which is the hardening of the arteries generally caused by chronic high blood pressure).
The main risk factors for coronary disease are tobacco smoking, diabetes mellitus, hypertension, hypercholesterolemia (a high level of bad cholesterol and low level of good cholesterol), stress, alcoholism and a sedentary lifestyle.
Coronary disease may manifest into one of two ways, angina pectoris or myocardial infarction. If the arterial obstruction is not complete and extensive, the patient often feels chest pain (angina pectoris), mainly when performing physical exercise or in any situation when the heart needs more oxygen. If the obstruction of one or more coronary arteries is complete or blood cannot irrigate some regions of the heart muscle (myocardium), infarction occurs and the muscle cells of the affected area die.
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9. What is myocardial infarction (a heart attack)?
Myocardial infarction, or heart attack, is the condition in which an area of heart tissue or the entire heart muscle dies by hypoxia due to lack of blood irrigation. Myocardial infarction is a severe disease since the heart can fail depending on the extent of its damage, becoming unable to pump blood to the lungs or to the body, or even ceasing to beat (causing death).
The main cause of myocardial infarction is coronary obstruction, the blockage of the arteries that carry arterial blood to the heart muscle. Other events such as hemodynamic shock (circulation stoppage due to large hemorrhages, for example) can also cause myocardial infarction.
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10. What is coronary bypass graft?
A coronary artery bypass graft is a type of surgical myocardial revascularization; or rather, a way to provide blood to a myocardium whose blood supply is impaired or blocked due to coronary disease. In this surgical treatment of coronary disease, one or more blood vessel grafts taken from other parts of the body are used to join the obstructed artery (in a region after the obstruction) with the aorta or another healthy coronary artery, thus reestablishing blood flow to the myocardium. Often, the blood vessel grafts are done with part of the saphenous vein in the leg or of mammary artery in the chest, or even the radial artery in the forearm.
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Cerebrovascular Accidents
11. What are cerebrovascular accidents?
A cerebrovascular accident (CVA), also known as a stroke, is the generic name given to infarction (tissue and cellular death by hypoxia) of areas of the brain due to vascular obstruction or hemorrhages. CVAs are divided into ischemic and hemorrhagic. In ischemic CVAs, the blockage of arteries that carry blood to the brain occurs; its cause is generally atherosclerosis (atheroma formation) of these vessels. In hemorrhagic CVAs, one or more blood vessels in the brain ruptures and leaks blood, increasing intracranial pressure and therefore interrupting blood flow in some areas of the brain. The severity of the stroke depends on the function performed by the affected area of the brain, for example, motor functions, visual functions, vegetative functions, etc., and on the size of the involved area.
The main risk factors for cerebrovascular accidents are hypertension, hypercholesterolemia, tobacco smoking and old age.
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Neoplasia, Tumors and Cancer
12. What is neoplasia?
Neoplasia is any abnormal and uncontrolled proliferation of cells of in an organism. Neoplasias can be benign or malignant. Benign neoplasias are when cell proliferation is limited to a given site of the body and the neoplastic cells do not spread to other close or distant regions through circulation. Malignant neoplasias are when neoplastic cells disseminate over a distance to other sites and organs of the body, a process called metastasis, where they continue to proliferate. Malignant neoplasias injure tissues and, if not eradicated, they are fatal. A benign neoplasm can also be deadly when it forms a tumor that grows and compresses vital organs.
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13. How different are the concepts of neoplasia, tumors and cancer?
Not every tumor is neoplastic and not every neoplasia creates a tumor. A tumor is the generic name given to the abnormal increase in mass or volume of any area of the body (for example, the enlarged tonsils during throat infection are a type of tumor, any inflammation creating a swelled area is characteristic of a tumor, etc.). Neoplasias can form tumors, some of them very large, through the accumulation of neoplastic cells in the region where the neoplasia began or in distant areas. Cancer is a synonym for malignant neoplasia.
14. What is cancer?
Cancers are malignant neoplasias, that is, the abnormal and uncontrolled proliferation of cells that can spread to other sites of the body. Cancer spreading over distances usually occurs through blood or lymphatic vessels.
15. How do neoplasias appear?
Neoplasias appear due to DNA mutations in genes that regulate cellular proliferation, thus making the cell lose its capacity to control and limit its division by mitosis. The cell then divides continuously and uncontrollably and this defect is transmitted to its daughter cells.
16. What are carcinogens?
Carcinogens are factors capable of producing neoplasms. Any mutagen, a substance that can induce DNA mutation, is a potential carcinogen. Examples of carcinogens are radiation, nitrous acid, many substances inhaled through tobacco smoking and the human papilloma virus (HPV).
17. How do the cells of neoplastic tumors obtain oxygen and nutrients and release waste?
In neoplastic tumors, a phenomenon called angiogenesis occurs. Angiogenesis is the formation of new blood vessels. Neoplastic cells induce the formation of new blood vessels to irrigate and drain neoplastic tissue.
Angiogenesis is important because tumor growth depends on it. A lot of research on cancer has tried to discover natural and synthetic substances to inhibit angiogenesis.
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18. What are the main types of cancer that affect humans?
Excluding skin cancer, which is the most easily detected type and therefore the type with the largest number of registered cases, the main types of cancer in men are prostate cancer, lung cancer, and stomach cancer. In women, breast cancer, colon and rectal cancer and lung cancer have high rates. Other common cancers are ovarian cancer, pancreatic cancer, liver cancer, esophageal cancer, brain cancer and leukemia and lymphoma (blood cancers).
Epithelial cancers, of the skin as well as of the internal organs, are more common because epithelial tissues are more exposed to carcinogens.
The proportional incidence of the many types of cancer varies according to the population studied.
19. What is the main risk factor for lung cancer?
The main risk factor for lung cancer is tobacco smoking. The large number of cases of this type of cancer is due to the large number of smokers worldwide.
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20. What is the main risk factor for skin cancer?
The main risk factor for skin cancer is the exposure of the skin to sun without protection against ultraviolet radiation (a potential carcinogen).
The most lethal skin cancer is melanoma.
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21. How is cancer usually treated?
If the cancer is in its initial stage, treatment is often done by the surgical removal of neoplastic tissue. Cancers that have already spread are often treated with radiation (radiotherapy) and anti-mitotic drugs (chemotherapy).
Alzheimer’s and Parkinson’s Diseases
22. What are the main degenerative diseases of the nervous system?
The main degenerative diseases of the nervous system are Alzheimer’s disease and Parkinson’s disease.
Degenerative diseases of the nervous system are caused by progressive tissue degradation or the loss of neurons in some regions of the nervous system.
23. What is Alzheimer’s disease?
Alzheimer’s disease is a degenerative disease of the central nervous system in which the patient develops progressive dementia and an alteration of mental functions.
The disease generally appears after 40 years of age and is more frequent in the elderly. Image studies of the brain show broad loss of brain tissue. (Alzheimer’s disease should not be confused with other types of mental deterioration common in the elderly.)
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24. What is Parkinson’s disease?
Parkinson’s disease is a degenerative disease of the nervous system in which the main manifestations are progressive motor disturbances, such as tremors of feet, hands and mandibles (jaws) and walking and balance impairments. Parkinson’s disease is due to the degeneration of dopaminergic motor neurons, which are motor neurons that use dopamine as a neurotransmitter, located in a specific region of the brain, the mesencephalon. Such degeneration creates a deficiency of dopamine in the nervous system. (Parkinson’s disease should not be confused with other causes of tremors, such as the use of some medicines.)
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