Date of manufacture of food items fried in oil should be checked before buying because oils become rancid due to

The date of manufacture for fried food items is critical because fats and oils undergo oxidation when exposed to air over time [1]. This chemical process, known as oxidative rancidity, occurs when oxygen reacts with the unsaturated fatty acids in the oil, leading to the formation of volatile compounds that alter the food's smell and taste [4]. Fried foods are particularly susceptible because the frying process involves high temperatures and exposure to oxygen, which can accelerate lipid deterioration [1]. To combat this, manufacturers often use antioxidants or flush packaging with inert gases like nitrogen to displace oxygen and slow down the oxidation rate [1]. In contrast, hydrogenation is a process used industrially to saturate oils and actually prevent them from turning rancid by increasing their stability [3]. Therefore, checking the manufacturing date ensures the oil has not yet reached a state of significant oxidation.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > 1.3.2 Rancidity > p. 13
2. [3] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.3.3 Addition Reaction > p. 71
3. [4] https://pmc.ncbi.nlm.nih.gov/articles/PMC10307983/
4. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 29: Environment Issues and Health Effects > 29.1.8. Transfat > p. 414