Proteases hydrolyze proteins into simpler compounds such as peptides and amino acids. Enzymes exert two basic types of action on proteins--endo and exo. Endo action splits the polymer randomly anywhere along its chain, which contributes to dough relaxation, prevents shrink-back and improves bread volume and gas retention. In addition, endo action increases bakery throughput. Exo action cleaves a specific terminal group, such as an amino acid or a di- or tri-peptide, on the protein polymer. Free-amino acids contribute to browning and may reduce bitter peptides, thereby modifying flavor.
Proteases are derived from animal, botanical and microbial sources, although animal proteases such as pancreatin, trypsin and chymotrypsin are rarely used in baking because of the expense involved and their non-kosher status. Botanical sources include papain, bromelain and ficin, none of which have amylase or pentosanase activity. Of these, bromelain and papain are used most frequently. The most common sources of fungal proteases are Aspergillus oryzae and Aspergillus niger, which are neutral to acid pH applications, relatively slow-acting, and may have significant amylase and pentosanase-side activity. Other common sources of microbial proteases are Bacillus subtilis and licheniformis, which are used in neutral to mildly alkaline applications and may have significant amylase.