Enzyme Tenderisation — Papain, Bromelain, Actinidin

Proteolytic enzymes from certain fruits — papain from papaya, bromelain from pineapple, actinidin from kiwi fruit — can tenderise meat by hydrolysing the peptide bonds in myofibrillar proteins and collagen, breaking down muscle fibre structure from the outside in. These cysteine proteases are the biochemical basis of traditional marinades in tropical and Pacific cuisines that use fruit as a tenderising agent. The mechanism is enzymatic hydrolysis: each protease cleaves specific peptide bonds within the protein structure, reducing long, organised protein chains into shorter fragments. Myosin and actin — the primary structural proteins of muscle — are both substrates for these enzymes, producing a textural softening that mimics extended mechanical or thermal tenderisation. Collagen fibres are also partially hydrolysed, weakening the connective tissue matrix. Temperature governs enzyme activity: all three enzymes are most active at 50–60°C, well above typical marinating temperatures, meaning their tenderising effect at refrigerator temperature (4°C) is modest. Commercial tenderising powders exploit this by applying enzyme-coated meat that is then cooked — the enzyme activates in the range of 50–60°C during cooking, tenderising the meat from within before fully denaturing above 65–70°C (the temperature at which enzyme proteins themselves unfold and lose function). The critical limitation is surface-specific action: enzymes are large molecules that cannot diffuse deeply into muscle tissue under normal marinating conditions. They act primarily on the outer 2–3mm of the meat surface, leaving the interior unchanged. Excessive contact time or high enzyme concentration produces an unpleasantly mushy, mealy surface texture while the interior remains untouched. Fresh fruit must be used — heat processing (canning, cooking the marinade) denatures the enzymes entirely. This is why fresh pineapple juice breaks down gelatin and prevents setting, while canned pineapple juice does not.