The key difference between hydrolytic and oxidative rancidity is that hydrolytic rancidity refers to the odor that develops when triglycerides undergo hydrolysis and the release of the free fatty acids, whereas oxidative rancidity is the chemical reaction of the oil with oxygen.
Rancidification is a chemical process that involves complete or incomplete oxidation or hydrolysis of fats and oils upon exposure to air, light, or moisture or through the microbial activity that results in an unpleasant taste and odor. Therefore, this chemical reaction that takes place in food can cause undesirable odors and flavors. According to the mode of action, there are three types of rancidification as hydrolytic, oxidative, and microbial rancidity.
CONTENTS
1. Overview and Key Difference
2. What is Hydrolytic Rancidity
3. What is Oxidative Rancidity
4. Hydrolytic vs Oxidative Rancidity in Tabular Form
5. Summary – Hydrolytic vs Oxidative Rancidity
What is Hydrolytic Rancidity?
Hydrolytic rancidity is the development of an unpleasant odor upon the hydrolysis of triglycerides, releasing their free fatty acids. This is a chemical reaction where the lipid usually reacts with water. This reaction particularly requires a catalyst. Moreover, this chemical reaction leads to the formation of free fatty acids and glycerol.
Furthermore, some short-chain fatty acids that are present in lipids (e.g. butyric acid) can be malodorous (meaning, they can already have a particular odor). In addition, when short-chain fatty acids form in lipids, these fatty acids can act as catalysts themselves, which can further accelerate the chemical reaction. Therefore, we can name this type of chemical reaction as an autocatalysis process.
What is Oxidative Rancidity?
Oxidative rancidity is a chemical process where oils are degraded by oxygen in the air. Usually, unsaturated fatty acids have double bonds between carbon atoms. These double bonds can be cleaved by free radical chemical reactions, where the cleavage reaction also involves molecular oxygen.
Typically, oxidative rancidity can cause the release of malodorous and highly volatile aldehydes and ketones. Since these reactions are free radical chemical reactions, they can be catalyzed by sunlight. Primarily, oxidation takes place along unsaturated fats.
For example, we usually keep meat under refrigeration or in a frozen state; if not, oxidative rancidity can occur. However, even though we keep meat in the fridge, polyunsaturated fat can still continue to oxidize; therefore, the fat will slowly become rancid. This fat oxidation process can lead to rancidity, which begins immediately when animals are slaughtered, and the fat on muscle surfaces are exposed to the oxygen of the air. Moreover, this chemical reaction typically continues during the refrigeration at a very low speed because the meat is at a very low temperature.
Figure 01: Simple Pathway of Oxidative Rancidity
We can prevent food from undergoing oxidative rancidity by using light-proof packaging, using an oxygen-free atmosphere around the food and through the addition of antioxidants. These antioxidants are often used as preservatives to delay the development of rancidity. There are some natural antioxidants that we can use as well; these include ascorbic acid and tocopherols.
What is the Difference Between Hydrolytic and Oxidative Rancidity?
Rancidity or rancidification is the formation of an unpleasant odor due to the complete or partial degradation of lipids. The key difference between hydrolytic and oxidative rancidity is that hydrolytic rancidity refers to the odor that develops when triglycerides undergo hydrolysis and release free fatty acids, whereas oxidative rancidity is the chemical reaction of oil with oxygen.
The following infographic lists the differences between hydrolytic and oxidative rancidity in tabular form.
Summary – Hydrolytic vs Oxidative Rancidity
Rancidity or rancidification is the formation of an unpleasant odor due to the complete or partial degradation of lipids. There are three ways of rancidity as hydrolytic, oxidative, and microbial rancidity. The key difference between hydrolytic and oxidative rancidity is that hydrolytic rancidity refers to the odor that develops when triglycerides undergo hydrolysis and release free fatty acids whereas oxidative rancidity is the chemical reaction of oil with oxygen.
Reference:
1. “Rancidification.” Wikipedia, Wikimedia Foundation.
Image Courtesy:
1. “Lipid peroxidation” By Tim Vickers, after Young IS, McEneny J (2001). “Lipoprotein oxidation and atherosclerosis” Biochem Soc Trans 29 (Pt 2): 358–62. PMID 11356183. Vectorized by Fvasconcellos. – w:Image: Lipid peroxidation v2.png (Public Domain) via Commons Wikimedia