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Cooking can adversely affect chemical characteristics of edible oils. The purpose of this paper is to determine biochemical changes due to cooking in commonly used Indian fats and oils through an experimental study.

Changes in chemical properties of various edible oils [Indian ghee (clarified butter), hydrogenated oil, coconut oil, mustard‐rapeseed oil, groundnut oil, soyabean oil, cottonseed oil and sunflower oil] were studied. Oils were subjected to various cooking methods (shallow frying, sautéing, single deep frying and multiple deep fryings) using an inert substance. Peroxide content was estimated as index of fatty‐acid oxidation, free fatty acids, iodine value for determination of fatty‐acid unsaturation and trans‐fatty acids at baseline and after cooking using colorimetric and gas‐liquid chromatography methods. Three samples were analyzed for each process (n = 144). Significance of change was determined using t‐test.

There was a significant increase in peroxide content (mEq/L) of Indian ghee from 1.83±0.03 at baseline to 4.5–6.6 by different cooking methods, hydrogenated oil (0.45±0.07 to 1.7–8.5), coconut oil (1.01±0.01 to 3.2–9.2), mustard‐rapeseed oil (0.90±0.01 to 2.1–5.3), groundnut oil (0.96±0.01 to 1.9–3.7), soyabean oil (0.86±0.02 to 1.9–3.4), cottonseed oil (0.71±0.01 to 2.9–6.4) and sunflower oil (1.09±0.01 to 2.3–10.2) (p<0.05). Free fatty acid content (g/100 g) was in undetectable amounts in all the fats at baseline and increased in Indian ghee (0.16–0.22), hydrogenated oil (0.09–0.23), coconut oil (0.09–1.39), mustard‐rapeseed oil (0.07–0.19), groundnut oil (0.09–0.18), soyabean oil (0.06–0.12), cottonseed oil (0.09–0.22) and sunflower oil (0.08–0.13). Trans‐fatty acids increased from 0.1% at baseline to 14.5% after sautéing and shallow frying and 15.8–16.8% after deep frying in hydrogenated oils (p<0.01). The iodine value decreased, indicating a decrease in unsaturated fats, insignificantly. The largest amount of oxidation was observed by shallow frying and free‐fatty‐acid formation by multiple deep frying. Hydrogenated, coconut and sunflower oils were the most susceptible to oxidation and soyabean oil the most resistant. Single deep frying caused the least changes in chemical composition of various fats and oils. Indian cooking practices significantly increase the peroxides, free fatty acids and trans‐fatty acids in edible oils and fats. Single deep frying appears to be the least harmful method and soyabean oil the least susceptible to degradation.

The paper offers an experimental study to determine biochemical changes due to cooking in commonly used Indian fats and oils.