The introduction of acyl groups into a compound or substance, usually achieved with an acyl halide or a carboxylic acid anhydride. Food chemists use acylation to modify starches — improving freeze-thaw stability, paste clarity and texture — and to alter proteins’ solubility, emulsifying power and heat stability. The degree of substitution is a precise control dial: light acylation tweaks functionality while preserving the ingredient’s character, whereas heavy modification can change nutritional and sensory properties. It belongs to the same modification family as acetylation, differing in the size and nature of the group attached.