Danger of reused oil:
What Happens to Oil When it is Repeatedly Heated?
In frying the oil, it is usually heated to 170-220 °C (338-428 °F). When heated to these temperatures in the presence of oxygen (air), the oil undergoes chemical reactions such as hydrolysis, oxidation, and polymerization. In other words it changes its character. Degradation products can include free fatty acids, hydro-peroxides, and polymerized triglycerides. The oil viscosity increases, its color will grow darker, and rancidity begins to develop.
What is Rancidity?
Rancidity is the decomposition of fats, oils, and other lipids through oxidation. Oxidation of fats result in the replacement of an oxygen ion with a hydrogen ion in the fatty acid molecule. This substation destabilizes the molecule and makes it possible for other odd chemical fragments to find a place along the chain. Factors which accelerate fat oxidation are trace metals (iron, zinc, copper, etc.), salt, light, water, bacteria, and molds. Oxidation occurs primarily in unsaturated fats by a free-radical-mediated process. These chemical reactions generate highly reactive molecules in rancid food which also may destroy nutrients in the food. Free radicals formed by fatty acids react with oxygen to generate peroxides that enter into a multitude of reactions, producing numerous compounds such as aldehydes, ketones, acids, esters, and polymerized fats.
Hazards of Prolonged Heating
The amounts of degradation products increase with the duration of heating at high temperatures. The toxicity of these degradation products present a health concern. Other contaminants such as polycyclic aromatic hydrocarbons may be concentrated by prolonged heating. Some of these have been found to be potential carcinogens. Certain types of plant oils such as peanut oil are sometimes contaminated by naturally occurring aflatoxin which is a human carcinogen. Peroxides and other by-products are also formed, indicating a change in the oil on a molecular level. Secondary breakdown products of peroxides and hydro-peroxides are rapidly formed by prolonged heating. Trans-fatty acids and a substance called acrylamide are also produced.
Health Effects
Thermal oxidation forms volatile and non-volatile decomposition products. The latter present the most risk to our health since they remain in the oil, are absorbed into fried foods, and are then ingested. Diets high in lipid oxidation and polymerization products (found in used frying oils) are associated with cellular alteration, reduced endothelial function, as well as LDL oxidation. Endothelial function is the normal biochemical processes carried out by the cells that line the inner surface of all blood vessels including arteries and veins as well as the internal lining of the heart and lymphatics. A diet high in frying oil content has been shown to induce glucose intolerance in rats. The presence of excess polar compounds and polymers in the frying oils were positively associated with the risk of hypertension.
In 2002, Swedish scientists discovered acrylamide formation in some starchy foods fried at high temperatures. This has since become a major concern in the food industry. Consistent evidence has shown that acrylamide is formed in foods with a high content of the free amino acid aspargine and of reducing sugars. The optimum condition for such formation is in potato chips since potatoes contain a very high concentration of aspargine. Once formed, the acrylamide can easily be absorbed by inhalation, ingestion, or skin absorption and reacts with proteins to form its metabolite glycidamide, an epoxide which can react with DNA. The effect of these reactions is the formation of hemoglobin adducts and neurotoxins. These adducts and toxins have led to serious health effects such as protein malfunction and muscle control problems.
Ingesting deep-fried oils has an effect on allergic reactions of the digestive tract, growth retardation, increased weight of the liver and kidneys and other biochemical reactions. Necrosis, dark red patches, and bleeding were found in rats fed a diet of food fried in used oil and concern has been raised that frying oil contained in many ready-made foods and snacks such as potato chips can change human serum levels and damage liver and kidneys.
Wah lou eh, read liao i dun dare to eat fried food liao...if fried at home ok , i think.
different ways of frying different taste but all sedup! how about roasted piglet, roasted chicken n roasted ducks?
:p
.. maybe biodegradable plastic bag 
