Chemistry, asked by shivangi8888, 1 year ago

why do edible oil show rancidity when stored for longtime

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Answered by Anonymous
2
Oils go rancid through a chemical reaction that causes the fat molecules in the oil to break down. The whole process is sped up by exposure to air, light and heat.
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Answered by beast14
12
When edible oil is stored for a long time it undergoes oxidation and become s rancid . Fats in the oil have carbon -carbon double bond in their structure .These bonds r broken by oxygen that's why edible oil becomes rancid.Why do edible oils show rancidity when stored for a long period?

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6 ANSWERS



Maryann Barretto

Answered Aug 27

When edible oil is stored for a long time it undergoes oxidation and become s rancid . Fats in the oil have carbon -carbon double bond in their structure .These bonds r broken by oxygen that's why edible oil becomes rancid.

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Emily Taylor Carden, Chief Executive Officer

Answered Aug 2

The short answer is, we live in an oxygen-rich atmosphere, and oxygen likes to react with other things. This is called oxidation (when it’s not happening as combustion). One of the things it likes to react with is oil. We don’t like the smell that rancid (oxidated) oils produce, or the taste, so it’s probably evolutionarily advantageous for us to avoid rancid things - very likely we evolved to avoid rancid meat, which also contains oxidated fats, but our modern technologies of producing vegetable oils provide new places to sniff and taste that old, familiar, nasty rancid flavor.

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Gary Karaff

Answered Aug 28

Originally Answered: Why does edible oil show rancidity when stored for a long period?

All vegetable oils and waxes as well as animal fats will eventually oxidize and become rancid over time as the chemical bonds that hold the oil molecule degrades and reacts with free oxygen in the headspace above the oi. The degradation process is accelerated when exposed to high temperature, UV light, certain microbes as well as contact with moisture and reactive metals (iron, copper, nickel, etc.) during manufacturer, storage and end use. Most oils are processed and stored under a nitrogen headspace to avoid oxygen degradation.

The chemical composition or fatty acid profile of an oil is a major contributor to the relative susceptibility of an oil to rancidity. Oils that are composed of higher levels of saturated fatty acids will be more resistant to rancidity whereas oils with higher levels of unsaturated fatty acids (mono and poly) contain more active carbon-carbon sites and, as such, are more prone to oxidation.

In a practical context, the denser and higher the melt point of the oil or fat, (wax, tallow, lard, shortening, butter) as compared to a liquid oil or fat, (fry oil, cooking oil or salad oil) the greater the shelf life before rancidity.

The relative state of rancidity is determined by measuring the primary breakdown components of oxidation using the PV (Peroxide Value) method and secondary components using the AV (Anisidine Value) method.

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Jovi George, Masters Applied Chemistry

Answered Aug 28

Originally Answered: Why does edible oil show rancidity when stored for a long period?

Blame it on the unsaturated acids in the oil. On exposed to oxygen, the unsaturated acids react with oxygen and breaks off at the double bond between the carbons. The resulting product will be an aldehyde. (That's the first product that is formed. Aldehydes can react again and become an acid) Aldehydes smell bad. Very bad. Also Aldehydes can make one sick. If you cook with rancid oil, you are most likely to get am upset tummy.

Oils with more unsaturated fatty acids like olive oil go rancid very fast. Oils with more saturated acids like coconut become rancid very slow. Oils contains natural anti oxidants which removes the oxygen that get into the oil. But during the refining, most of the antioxidants gets removed. So a refined oil can go rancid faster than am unrefined .

I hope this will help you

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