Rancidity in edible oils: How it affects your health and why you should avoid using them

Rancidity in edible oils is a silent but significant problem affecting quality, flavour, and safety. It occurs when oils degrade due to exposure to oxygen, light, heat, or moisture. This degradation leads to the formation of harmful compounds like free radicals, aldehydes, and ketones. While rancid oils may not always appear visibly different, consuming them can pose health risks.

This article explores what causes rancidity, how it impacts health, proper storage practices, and why you should always prioritize fresh oils.

What causes rancidity in edible oils?

Rancidity is caused by three primary chemical processes:

Oxidative rancidity:

• Occurs when oils are exposed to oxygen.
• Results in the breakdown of unsaturated fats, forming harmful by-products.

Hydrolytic rancidity:

• Triggered by water reacting with triglycerides, releasing free fatty acids.
• Common in oils stored in humid conditions.

Microbial rancidity:

• Caused by microbial activity, particularly in unrefined oils or oils stored improperly.

External factors like light, heat, and air accelerate these processes, making proper storage essential to extending the shelf life of edible oils.

Rancidity in edible oils: Health risks

Using rancid oils is harmful to your health for several reasons:

Oxidative stress:

• Rancid oils generate free radicals, damaging cells and tissues.
• This oxidative stress contributes to chronic illnesses like cancer and cardiovascular disease.

Inflammation:

• Degraded oils promote inflammation, worsening conditions like diabetes and arthritis.

Liver toxicity:

• Rancid oils strain the liver, impairing detoxification processes.

Nutritional loss:

• The degradation of essential fatty acids reduces the oil’s nutritional value.

Can rancid oils be used for other purposes?

No, rancid oils are not safe for consumption or topical use. The degraded compounds can irritate the skin or cause allergic reactions. Additionally, using rancid oil for cooking or cosmetics introduces harmful toxins to the body. It’s best to discard rancid oils responsibly to avoid health and environmental hazards.

Rancidity in edible oils: Shelf life of common edible oils

The shelf life of edible oils depends on their composition and storage. Below is a guide to popular oils and their durability:

• Coconut oil: 1–2 years (refined), 6 months (unrefined). Its high saturated fat content makes it stable.
• Groundnut (Peanut) oil: 6 months to 1 year. Prone to oxidation if exposed to air and light.
• Sesame oil: 6 months (unrefined), up to 2 years (refined). Contains natural antioxidants like sesamol.
• Rapeseed (Canola) oil: 6 months to 1 year. Requires refrigeration once opened.
• Mustard oil: 6–8 months. Its strong flavour deteriorates quickly without proper storage.
• Sunflower oil: 6 months to 1 year. Highly unsaturated, making it prone to rancidity.
• Olive oil: 18–24 months (extra virgin), 1 year (refined). Oxidation occurs faster in light and heat.

How proper storage prevents rancidity in edible oils

Storing oils properly is crucial to slowing down the rancidity process. Factors like container type and material significantly affect their longevity.

Opaque containers vs. transparent bottles

1. Opaque containers:

• These block light, which is a major factor in accelerating oxidation.
• Dark glass bottles, ceramic jars, or coloured plastic are ideal for light-sensitive oils like olive, sesame, and sunflower.

• Stainless steel containers are the gold standard for storing oils.

2. Transparent bottles:

• These allow light to penetrate, hastening degradation.
• Oils in transparent containers should be stored in dark places or wrapped in opaque materials for protection.

Research insight: A study in the Journal of Food Science revealed that oils stored in opaque containers retained their quality longer due to reduced peroxide formation.

Using stainless steel containers

Stainless steel containers are highly effective for storing edible oils because they:

• Block light completely, preventing photo-oxidation.
• Are airtight, minimizing exposure to air and moisture.
• Are durable, non-reactive, and safe, unlike plastic.

Stainless steel is particularly useful for oils like sesame, mustard, and groundnut, which are prone to oxidation when stored improperly.

How to detect rancidity in edible oils

Rancidity isn’t always visible but can be identified through:

1. Smell: A sour or sharp odour indicates oxidation.
2. Taste: A bitter, metallic flavour is a strong sign.
3. Colour: Darkening or cloudiness suggests the oil has degraded.
4. Texture: Thickened or sticky oil indicates rancidity.

Medical research on rancidity in edible oils

Scientific studies highlight the dangers of rancid oils:

• Oxidative stress and DNA damage: The Journal of Food Science and Technology found that rancid oils generate free radicals, which harm DNA and proteins.

• Cardiovascular risks: Research in the Journal of Clinical Lipidology shows that oxidized oils increase LDL cholesterol, raising the risk of heart disease.

• Carcinogenic compounds: A study in the European Journal of Cancer Prevention identified aldehydes in rancid oils as potential carcinogens.

Practical tips to extend oil shelf life

1. Store oils in proper containers: Use opaque glass, stainless steel, or ceramic jars for storage. Avoid clear bottles unless stored in dark areas.

2. Refrigeration: Oils high in polyunsaturated fats, like flaxseed and canola, benefit from refrigeration.

3. Buy smaller quantities: Purchase quantities you can use within their shelf life to minimize waste.

4. Minimize reheating: Repeated heating accelerates oxidation, especially for frying oils.

5. Use antioxidants: Add natural stabilizers like rosemary extract to slow rancidity.

Why expiry dates matter

All oils have an expiry date that reflects their safe consumption period. Even under perfect storage conditions, natural chemical reactions eventually degrade oil quality. Always check the label and discard oils past their expiration date to avoid health risks.

Conclusion: Rancidity in edible oils

Rancidity in edible oils is a serious issue that affects health and quality. By understanding the causes of rancidity, the role of proper storage, and the shelf life of different oils, you can ensure safe and flavourful cooking. Opt for opaque or stainless steel containers and store oils in cool, dark places to maximize their freshness.

Remember, when it comes to edible oils, freshness and quality should never be compromised. Discard rancid oils and prioritize proper storage to protect your health and enjoy the full benefits of high-quality oils.

Image Courtesy: ACCENTERRA

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