Rancidification

Rancidity is, the state, divided into the fats and other lipids by oxidation or by lipolytic enzymes (lipases ).

Course

The destruction of plant and animal fats, which in the early stages by smell and taste impairment ( rancidity ) can be perceived, is due in large part to chemical changes caused by the action of atmospheric oxygen. The process is accompanied by drying (butter) or frequently by mold ( cut surfaces ). Slowly at room temperature, with increasing temperature faster running oxidation processes are known as autoxidation and lipid peroxidation as well. You start with radical reactions of unsaturated fatty acids and result in a multi-step process to a wide variety of degradation products, in particular peroxides, alcohols, aldehydes and carboxylic acids. Most susceptible to spoilage are fats with a high content of unsaturated fatty acid residues. The oxidation potential of simple (unsaturated) oleic acid residues lies about a factor of 100 higher than that of ( saturated ) stearic acid residues in polyunsaturated linoleic acid residues even by a factor of 1200 in linolenic acid residues by a factor of 2500th Therefore, it should you, store them for example linseed oil or walnut oil, which have a high content of glycerides of linolenic and linoleic acid as possible in the refrigerator or heat. Oils with a high percentage of linoleic acid residues, such as conventional sunflower or safflower oil, should be used only to vapors at low temperatures. Oils with a high content of glycerides of oleic acid, like olive and canola oil, but peanut oil and so-called high-oleic sunflower oil, on the other hand can be used for frying and deep-frying at temperatures up to 170 ° C and are a sensible alternative to saturated fats is which are higher heatable and longer and therefore particularly in the gastronomic field are used, should be from a nutritional point of view but as little as possible consumed.

Not from rancidity, but of otherwise damage by, for example mold, it is called the microbiological infestation by fungi or bacteria. Pure fats are anhydrous and ruin only by the above- described oxygen reaction. Water-in -oil emulsions such as butter (compared to pure butter fat) and margarine or oil-in -water emulsions such as cream, milk and mayonnaise on the other hand can be attacked by microorganisms and destroy by the same applies for longer with water in Contact seasoned points of pure fats, for example in the form of condensation. The higher the water content in a fat-water mixture, the faster a bacterial strain can be established.

Follow

The reaction products are often foul- smelling or bad -tasting substances (among free fatty acids), the food and edible oils make them unpalatable. Some foods ( such as linseed oil and walnut oil) Shelf rancid very quickly. The particularly fast becoming rancid fats and oils contain a high proportion of triglycerides of unsaturated fatty acids (mostly linoleic acid and linolenic acid ). In addition to the oxidation of the unsaturated bond is carried out in polyunsaturated fat and an oxidative cross-linking (such as linseed oil to oxidize Linoxin ). In the industrial production of margarine, the double bonds are saturated through hydrogen reduction. This increases the shelf life expiration date, even if this means that most of the essential fatty acid residues are hydrogenated to saturated fatty acid radicals, which can only be used to a lesser extent in cell membranes as membrane lipids, but serve mainly as storage fats.

The process forms of food sometimes an airtight and watertight bark on the surface and also acts in the drying of oil paint with. Butter is yellowish- translucent to dark and cracked. Edible oil is thick and eventually getting tougher.

Health effects

Already prevents rancid smell (and taste) that are eaten rancid products because it excites disgust. Problem but it could be with spicy food if you do not perceive the rancidity before consumption. It then depends on the quantity, but usually there are at most digestive problems, and pre-loaded individuals ( eg gall bladder ) more affected. Only in the extreme form of fat spoilage, with very strongly heated oil - depending on the oil at about 400 ° C - when grilling food as incurred increased polycyclic aromatic hydrocarbons ( PAHs) which are carcinogenic in laboratory tests. Critical to see is also a multiple of strong heating of the same fat, such as in deep fryers. The accelerated by heat reaction leads to an ever increasing saturation of the amount of oil decomposition products which may be harmful. Therefore, one should pay attention to natural disgust reactions when eating fried food, hitting automatically alarm before reaching harmful levels of decomposition material in the oil. The dose makes the poison - a poison accumulation by repeated eating of more or less decomposed fats should be avoided at all costs.

On pure fats and oils molds and bacteria can not grow, so only emulsions with water, such as mayonnaise, butter and similar fatty products are affected. One no longer rancid to be named, but already microbiological load can cause a variety of symptoms, diseases or toxic accumulations in the body, depending on which germs were in the ingested fat mixture.

Protection

Delicate oils and fats, so fats linked with a high proportion of polyunsaturated fatty acids in the triglyceride are kept refrigerated in closed containers. Conveniently, the use of vessels, the opaque ( sheet ) or little translucent ( dark glass), which extends the shelf life. Freeze protects well, but with sensory deterioration most likely to occur with repeated freezing. In particular, in water-containing fat blends can increase the microbiological susceptibility by increased freezing, ie, the product is then more susceptible to germs and is more heavily loaded with them. Antioxidants, such as carotene, ascorbic acid and tocopherol, which can be added to foods to make these more durable.

Intended application

In contrast, raw milk cheese, the milk fat is decomposed by the milk itself lipases during ripening. The final products improve significantly weaker concentration than the rancid flavor of the cheese.