Papain

Papain is tapped, not fermented. The unripe green fruit of Carica papaya L. is scored on the tree, the latex that weeps from the cut is collected, dried and then refined and spray-dried into the powder that trades as papain, CAS 9001-73-4, EC 3.4.22.2, a cysteine endopeptidase of peptidase family C1 and formerly listed as EC 3.4.4.10. UniProt P00784 describes a 345-residue precursor whose mature chain runs from residue 134 to 345, giving a 212 amino acid enzyme held by three disulfide bonds and working through a catalytic cysteine-histidine dyad. Specificity is broad, with a preference for a bulky hydrophobic side chain at the P2 position and a refusal to accept valine at P1'. What matters commercially is that the article of trade is not a single protein: EFSA's food-enzyme assessments describe papain as a cysteine endopeptidase complex containing papain (EC 3.4.22.2), chymopapain (EC 3.4.22.6), caricain (EC 3.4.22.30) and glycyl endopeptidase (EC 3.4.22.25), sharing 62 to 81 per cent sequence identity. A buyer specifying 'papain' is buying that complex, and any allergen or purity assessment has to be built on all four. The enzyme is sold on activity, and activity is only meaningful once the unit and the method are named. The tyrosine unit is the common basis: one TU is the amount of enzyme that releases one microgram of L-tyrosine equivalents from casein per minute under the conditions of the assay, read spectrophotometrically at 280 nm. Commercial food-grade batches assessed by EFSA against that method averaged roughly 1,060 TU/mg. USP and NF papain units, FCC papain units and milk-clotting units are also quoted in this trade and none of them convert cleanly into the others, so a contract that names one unit and a certificate that reports another cannot be reconciled without a cross-assay. Papain is relatively heat-resistant for a protease, with a reported optimum temperature range of 60 to 70 C, which is what makes it useful in meat tenderising, protein hydrolysate manufacture, beer chill-proofing and dough conditioning. The active site is a reduced thiol, so the enzyme is activated by cysteine and by chelators such as EDTA and knocked down by oxidising agents, heavy metals, E-64 and cystatin-family proteins. Purity follows the general specification applied to food enzyme preparations: lead 5 mg/kg maximum, total coliforms 30 CFU/g maximum, Salmonella and E. coli absent in 25 g, and no antimicrobial activity. On allergens the honest answer is more complicated than 'plant-derived, therefore clean'. Papaya appears on neither the EU Regulation 1169/2011 Annex II list of fourteen nor the US FALCPA and FASTER Act list of nine, so there is no mandatory allergen declaration in most markets. But papain and chymopapain, the latter catalogued as Cari p 2, are recognised papaya food allergens, papain is a documented occupational respiratory sensitiser causing rhinitis and asthma among people who handle enzyme dust, and EFSA records cross-reactivity with bromelain, actinidins and mite allergens, which matters directly if papain and bromelain are going into the same multi-enzyme blend. Treat it as an allergenic protein dust in the plant, specify low-dust or granulated grades, and name the papaya source on the ingredient statement even where it is not compelled. The carrier is the other declaration risk: enzymes are standardised down onto a diluent, and while maltodextrin and starch are the defaults, lactose has historically been used as an enzyme diluent and would bring a milk declaration with it. Thovek ships lactose-free and gluten-free unless the buyer specifies otherwise, states the carrier on the specification and the CoA, and will not change it between lots without written agreement. Casein appears only as the laboratory assay substrate; no milk protein enters the product. The material is vegan and vegetarian with no bovine, porcine, fish, crustacean, molluscan or other marine input, and because it is extracted from the plant rather than fermented, no production micro-organism is involved at any stage.