Life Sci. 1993 ; 53(17): 1383-9.

Antimicrobial and antioxidant activities of unripe papaya.

Osato JA, Santiago LA, Remo GM, Cuadra MS, Mori A.

Sun-O International Inc., Gifu, Japan.

The meat, seed and pulp of Carica papaya Linn., a popular traditional medicinal herb grown in the tropics, was shown by the agar-cup method to be bacteriostatic against several enteropathogens such as Bacillus subtilis, Enterobacter cloacae, Escherichia coli, Salmonella typhi, Staphylococcus aureus, Proteus vulgaris, Pseudomonas aeruginosa, and Klebsiella pneumoniae. The same parts of papaya were unequivocably demonstrated by electron spin resonance spectrometry to scavenge 1,1-diphenyl-2-picrylhydrazyl (5.8 x 10(14) spins/ml), hydroxyl (5.1 x 10(14) spins/ml) and superoxide (1.2 x 10(14) spins/ml) radicals with the seed giving the highest activity at concentrations (IC50) of 2.1, 10.0 and 8.7 mg/ml, respectively. The superoxide dismutase (SOD)-like activity in the meat, seed and pulp amounts to about 32, 98 and 33 units/ml; comparable to those of soybean paste miso, rice bran and baker's yeast. Vitamin C, malic acid, citric acid and glucose are some of the possible antioxidative components in papaya. Our study correlates the bacteriostatic activity of papaya with its scavenging action on superoxide and hydroxyl radicals which could be part of the cellular metabolism of such enteropathogens. This is indicative of the pathophysiological role of these reactive oxygen species in gastrointestinal diseases and papaya's ability to counteract the oxidative stress.