Rancidity Meaning, Types, Effects and Prevention Explained
Rancidity is a condition and process involving changes in taste, smell and nutritional value of fats and oils due to hydrolytic, oxidative and microbial mechanisms. This article discusses rancidity meaning, types, effects and prevention, as outlined below;
-Rancidity Meaning and Examples
Rancidity Meaning and Examples
Rancidity is a process and condition whereby fats, oils, and other substances containing lipids, deteriorate and develop unpleasant taste and/or smell, as a result of auto-oxidative or hydrolytic reactions . An example of rancidity is the souring of vegetable on long-term exposure to air.
It is fairly correct to describe rancidity as in indication of biodegradation of lipids. Causes of rancidity include light, heat and oxygen exposures.
Along with the physical changes in odor and taste, rancidity leads to chemical changes in the composition, quality and nutritional value of fats and oils.
The mechanism of rancidity generally involves reaction between unsaturated fatty acids, and oxygen. Volatile products of this reaction are the reason behind the unpleasant taste and smell that may be observed afterward.
Depending on the specific reaction pathway(s), rancidity could be classified as oxidative, hydrolytic or microbial.
Factors that contribute to rancidity in food and other lipid materials are;
1. High temperature
2. Exposure to light
3. Exposure to oxygen
4. Presence of unsaturated fatty acid (the substrate)
5. Presence of microbes and chemical/enzymatic catalyst(s)
Examples of rancidity are;
1. Souring of exposed vegetable oils and animal fats
2. Development of stale taste/odor in packaged, processed foods like salad dressing, fries and snacks
3. Souring of diary products like cheese and butter
Types of Rancidity
Types of rancidity are; oxidative, hydrolytic, and microbial rancidities respectively.
1). Oxidative Rancidity (as one of the Types of Rancidity)
As the name implies, oxidative rancidity is a type of rancidity that is chiefly driven by the exposure of fats and oils to oxygen, which reacts with their organic constituents to produce volatile compounds that have unpleasant odor and taste.
The mechanism behind oxidative rancidity is simply oxidation. In the process, oxygen molecules become integrated into the chemical structure of the affected fatty acids, thereby degrading their nutritional value and quality.
Fatty acids are generally prone to oxidation because of the presence of a carbon-carbon double bond in their chemical structure, which oxygen may attack and break.
Multiple stages of chemical reaction can be identified in the oxidative rancidity mechanism.
On initial reaction with fatty acids, oxygen molecules break the double bonds to form free radicals with high reactivity. The high reactivity of these radicals causes them to further react with unaffected fatty acid compounds, in a chain reaction series.
Final products of oxidative rancidity are hydroperoxides, which decompose to yield alcohols like pentanol, ketones like 2-pentanone, and aldehydes like pentanal . These decomposition products are odorous and sour-tasting.
Predictably, one of the primary factors that affect oxidative rancidity is the availability of oxygen, which could be high if the lipid substance is exposed to air. Other factors like light and temperature also play roles in facilitating or inhibiting this type of rancidity.
Applicable measures for prevention of oxidative rancidity include airtight packaging, optimal storage conditions (dark, cool), and antioxidant preservatives like ascorbic acid.
2). Hydrolytic Rancidity
Hydrolytic rancidity is a type of rancidity that occurs due to the deteriorative reaction of lipids with water.
The occurrence/development of hydrolytic rancidity can be attributed to the hydrolysis of lipids, during which their fatty acid compounds are broken down by water molecules. When this occurs free fatty acids are released, which cause the observable unpleasant odor and taste .
A group of enzymes called lipases also play a role in hydrolytic rancidity. These enzymes may occur naturally in fat, or they may be introduced while fatty substances are being processed, or stored.
Lipases catalyze the hydrolysis of lipids by attacking esterified bonds, so that the lipids are hydrolyzed and degraded into glycerol and free fatty acids.
The likelihood of hydrolytic rancidity is high in lipids (including food materials) that contain significant amount of water.
3). Microbial Rancidity (as one of the Types of Rancidity)
Microbial rancidity is the souring of fatty and oily food as a result of the metabolic activities of microorganisms.
There are multiple ways by which microbes can get into lipids to cause rancidity, especially since these microbes are abundant is most environments.
Examples of microorganisms behind microbial rancidity are yeasts like Rhodotorula; bacteria like Clostridium; and molds like Fusarium, which could operate either independently or collaboratively.
As decomposers, these microbes play their role in the food chain by degrading biomass, which serves as a source of nutrients and bioenergy to them.
Microbial rancidity is effective because microorganisms are ecologically resilient and versatile, so that they can reproduce rapidly on any degradable substrate.
It must be noted that microbes cause rancidity through the biochemical effect of their enzymes, among which are lipases that breakdown and transform lipids into glycerol and free fatty acid.
Factors like moisture content, pH, oxygen availability and temperature, all influence the effectiveness of microbes at degrading lipids.
Rancidity In Food Production
Rancidity in food production is discussed in terms of rancidity of fat and oil food products, respectively.
1). Rancidity of Fat
Rancidity of fat results from chemical degradation by oxidants, hydrolytic agents, and/or microbes that react with lipids and break their esterified bonds.
The causes of rancidity of fat range from air exposure and microbial action to light and above-room temperature conditions.
Changes that can be observed in rancid fats include sour or bitter taste, unpleasant smell, low nutrient-value, sticky, grainy, greasy or slimy texture, and color alteration.
Prevention of fat rancidity can be achieved through optimal storage, air-tight packaging, and use of antioxidants.
2). Rancidity of Oil
Rancidity of oil is a major challenge for storage of oil/oily products in the food industry.
Oxidative and/or hydrolytic mechanisms could lead to oil rancidity.
The oxidative pathway is fairly common for rancidity of oil, because oil comprises of fatty acids with breakable carbon-carbon double bonds.
Heat and light-exposure also play roles in making oil rancid.
Rancidity of oil can be detected through the development of stale taste and smell, with sticky, thicker texture and increased cloudiness or opacity.
Measures that could be taken to prevent oil rancidity are; moisture content-restriction, airtight, dark/opaque packaging, optimal storage and antioxidant addition (like butylated hydroxytoluene; BHT).
Effects of Rancidity
Effects of rancidity are;
1. Stale, rancid taste
2. Unpleasant/uncharacteristic smell
3. Textural changes
4. Color and opacity alteration
5. Loss of nutritional value
Prevention of Rancidity
Prevention of rancidity in fats and oils can be achieved through;
1. Avoidance of high temperature through refrigeration
2. Optimal storage with low exposure to air and light
3. Airtight, opaque packaging
4. Addition of antioxidants like vitamins C (ascorbic acid) and E (tocopherol) 
5. Early consumption of fatty and oily food products
Rancidity is a type if organic deterioration whereby fats and oils lose their quality and nutritional value due to hydrolysis, oxidation, and microbial metabolism.
Factors that contribute to rancidity in food and other lipid materials are; temperature, light, air exposure, presence of microbes and enzymes.
Examples of rancidity are; souring of exposed vegetable oils and animal fats, development of stale taste/odor in packaged or processed foods, and souring of diary products like cheese.
Types of rancidity are;
1. Oxidative Rancidity
2. Hydrolytic Rancidity
3. Microbial Rancidity
Rancidity in food production can be discussed in terms of;
1. Rancidity of Fat
2. Rancidity of Oil
Effects of rancidity are; stale/rancid taste, unpleasant smell, texture changes, color/opacity alteration, and loss of nutritional value.
Prevention of rancidity in fats and oils can be achieved through; refrigeration, optimal storage, airtight packaging, antioxidant addition, and early consumption.
1). Bynum, D. G.; Senyk, G. F.; Barbano, D. M. (1984). "Determination of Free Fatty Acid Content of Cheddar Cheese by a Copper Soap Method." Journal of Dairy Science, Volume 67, Issue 7, July 1984, Pages 1521-1524. Available at: https://doi.org/10.3168/jds.S0022-0302(84)81470-8. (Accessed 23 May 2023).
2). Frankel, E. N. (1996). "Antioxidants in lipid foods and their impact on food quality." Food Chemistry, Volume 57, Issue 1, September 1996, Pages 51-55. Available at: https://doi.org/10.1016/0308-8146(96)00067-2. (Accessed 23 May 2023).
3). Gorji, G. S.; Calingacion, M.; Smyth, H. E.; Fitzgerald, M. (2019). "Comprehensive profiling of lipid oxidation volatile compounds during storage of mayonnaise." J Food Sci Technol. 2019 Sep;56(9):4076-4090. Available at: https://doi.org/10.1007/s13197-019-03876-6. (Accessed 23 May 2023).
4). Mahmud, N. R. A. (2019). "RANCIDITY OF TRADITIONAL COCONUT OIL: MICROBIAL CONTAMINANT AND FREE FATTY ACID CONTENT." Available at: https://www.researchgate.net/publication/344594760_RANCIDITY_OF_TRADITIONAL_COCONUT_OIL_MICROBIAL_CONTAMINANT_AND_FREE_FATTY_ACID_CONTENT. (Accessed 23 May 2023).