Oxidative Rancidity Mechanism

What is oxidative rancidity?

Over time, foods will lose their nutritional value as they break down—vitamin A, C and E as well as other ingredients and amino acids are destroyed. Degradation, or spoilage, in a product does not only involve the production of either peroxides, malonaldehydes, alkenals or free fatty acids, it usually involves the generation of all four of these compounds or at least a combination thereof. These compounds are generated as fats and oils get oxidized, which is a natural outcome of exposure to air, light, moisture or certain bacteria. An accumulation of these compounds in your product can lead to an unpleasant taste and odor that needs to be avoided to keep your products marketable.

Every natural product has some innate ability to withstand oxidation. This innate ability is commonly attributed to the presence of antioxidants. Manufactured products can have antioxidants added to them, along with stabilizers and other nutrients to slow down the oxidative process. So, as a product is harvested or first manufactured, the initial oxidation is slow, while antioxidants and stabilizers, etc. fight oxidants to maintain the freshness of the material. During this period, lipid peroxides increase slowly and antioxidants and nutrients begin to decrease.

Decreasing nutrients and increasing degradents over time

What are the steps of an oxidative rancidity mechanism?

Food stability researchers have extensively studied the mechanisms by which fats and oils are oxidized to cause rancidity. Three steps are recognized in process of oxidation of food (i.e., autoxidation or free radical) and there are two different reactions typical of each step that can occur:

The rate of these reactions depends on several factors:

• The nature of the fat
• The level of moisture in the product
• The presence of prooxidants, antioxidants, energy inputs (light or heat), enzymes that catalyze lipid oxidation in food

There is an initial phase where oxidation occurs very slowly, or not at all. After initiation and under favorable conditions, the rate of free radical reactions increases very rapidly because they are self-catalyzing. This rapid phase continues until the substrate is depleted or, until conditions are changed to quench the reactions.

Adding antioxidants such as ethoxyquin, tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), or butylated hydroxytoluene (BHT) will usually delay induction time by interacting with free radicals and converting them to inactive forms.

How do you measure an oxidation in food?

Lipid oxidation in food is generally measured based on the first relatively stable products of the reactions: peroxides and hydroperoxides. The “peroxide value” measurement is used to determine the quantity of these species in foods and is one of the most sensitive techniques during the early stages of lipid oxidation. However, in later stages of the process, the peroxides themselves degrade via a series of complex reactions to organic acids, alcohols and aldehydes or alkenals.

Many of these secondary products are strongly flavored (painty or cardboard-like) and lead to stale tastes that decrease palatability. During the later stages of oxidation, other methods must be used to measure the secondary reaction products.

MP Bio offers 6 different SafTest Test Kits to assess oxidative rancidity in your products: