Oxidative (O_2 + unsaturated FA → hydroperoxides → off-flavour); accelerated by heat, light, metals; prevented by antioxidants (BHA/BHT, Vit E) & cool dark storage.
Hydrolytic (lipase + moisture).
Reversion (early off-flavour in linoleic oils).
Deep-Fat Frying
Ideal frying range 177-191^{\circ}\text{C} ( 350-375^{\circ}\text{F}).
High smoke-point neutral oil; low free FA; minimal emulsifiers.
Quality indicators: golden colour, crisp surface, minimal fat uptake.
Oil care: filter daily, maintain temp, avoid water/salt, replace when dark, viscous, foamy, smoke point drops.
Safety: never add wet food; smother grease fires (lid, \mathrm{NaHCO}_3); no water.
Emulsions, Foams, Salad Dressings
Dispersed vs continuous phase; require emulsifiers (lecithin, proteins, gums).