No studies of the acute, short-term, or long-term effects from ingestion or oral administration of the pure enzyme papain have been found by the Select Committee. The acute oral LD50 of a commercial preparation of papain has been reported to be more than 10g per kg for mice. The apparent acute oral toxicity is low when compared with the ususal levels of human exposure which appear to be of the order of 2 to 25mg per day. Commercial papains are only standardized for their proteolytic activity and the various methods of preparation may result in the presence of other macromolecules, such as protein and carbohydrate, as well as minerals. The relationship between food grade papain and that used by the investigators in the biological studies evaluated in this report is not known but their gross similarity can be assumed.
The proteolytic activity of papain is destroyed by extremes of pH and by heat. Cooking converts the enzyme to an inactivate protein. Little is known about the nature and properties of the inactivated enzyme, or the other protein and non-protein portions of commercial preparations, but there is no evidence that they produce deleterious effects when ingested with food.
Allergies to papain have been reported but the incidence is low and the slight reactions reported appear to be confined to workers exposed to papain in air-borne dust.
In common with other proteolytic enzymes, papain digests the mucosa and the musculature of tissues in contact with the active enzyme for an appreciable period. Because there is no food use of papain that could result in the enzyme preparation occurring in sufficient amount in foods to produce these effects, this property does not pose a dietary hazard.
In view of the foregoing, the Select Committee concludes that: There is no evidence in the available information on papain that demonstrates, or suggests reasonable grounds to suspect, a hazard to the public when it is used at levels that are now current or that might reasonably be expected in the future.