acid protease

A protein-digesting enzyme that works best in strongly acidic conditions, with pepsin in the human stomach as the classic example. Secreted as the inactive precursor pepsinogen, it switches on when stomach acid drops the pH below about 3, then dismantles dietary proteins into peptides for further digestion downstream. Food technologists use microbial acid proteases from fungi such as Aspergillus for purposes far beyond digestion: they tenderize meat, accelerate cheese ripening, clarify chill haze in beer, and improve the solubility of plant proteins. Because each acid protease has a preferred pH window and cleavage pattern, manufacturers select the source organism to match the process, whether that means the fierce acidity of the stomach or the milder acidity of a fermenting sausage.