What is rancidity
The rancidity is a natural process of chemical decomposition which fats, oils and other lipids face.
In the food field it is an undesirable phenomenon, which leads to a decay of the organoleptic characteristics and represents a potential danger for the consumer's health.
Causes
Lipolytic (or hydrolytic) rancidity is caused by lipase enzymes, which attack triglycerides by removing fatty acids from glycerol; the presence of these nutrients in the free state, and in particular short-chain fatty acids, gives the food unpleasant smells and flavors (butyric acid, for example, is responsible for the bad aroma of rancid butter). The free fatty acids, and in particular the unsaturated ones, are also the substrate of the so-called oxidative rancidity, from which they originate peroxides which propagate with a radical chain mechanism. Oxidative rancidity leads to the formation of chemical compounds of various types, characterized by unpleasant smells and tastes, and to a decay of the nutritional characteristics of the food (significant loss of fat-soluble vitamins).
Prevent food rancidity
The rancidity can be favored by various elements, first of all the content in polyunsaturated fatty acids.
| Factors that favor rancidity | Factors that hinder rancidity |
| Richness in unsaturated fatty acids | Absence of saturated fatty acids |
| High humidity | Low humidity |
| High temperatures | Low temperatures |
Availability of oxygen (air) Long storage times | Addition of inert gases such as nitrogen (industrial area), well closed container after use (domestic) |
| Light (transparent glass) | Absence of light (dark glass) |
Presence of organic catalysts (such as chlorophyll and porphyrins) and inorganic ones, such as traces of copper, iron, lead, cobalt, etc. | Absence of catalysts and abundance of antioxidant compounds such as vitamin E, carotenoids, polyphenols, vitamin C and flavonoids. The fat pigs, for example, go rancid quickly due to the almost total absence of natural antioxidants. |
To prevent rancidity, the food industry usually adds antioxidants to products particularly rich in lipids; these include ascorbic acid, ascorbyl palmitate, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and propyl gallate. Other preservatives, such as ethylenediaminetetraacetic acid (EDTA), avoid oxidation due to inorganic catalysts, sequestering metal atoms.
According to what has been said, the oils most susceptible to rancidity are those friends of our health (grapeseed oil, hemp oil, linseed oil and other oils rich in omega-3 and omega-6). If they are not produced by cold pressing and properly stored, these oils can become rancid and cause health problems for those who consume them. For example, the presence of mutagenic agents may predispose to the risk of colon and digestive tract cancer. We must not forget, moreover, that the same phenomena of oxidation responsible for the rancidity can occur in an important way inside the body (where there is plenty of oxygen). For this reason it is advisable to combine the integration of omega-3 and omega-6 with that of tocopherols (vitamin E).
