Resumo

MEJIA-DORIA, Clara M et al. Kinetic characterization of the polyphenol oxidase enzyme in six ripening stages in lulo (Solanum quitoense Lam.) var. Castilla. Actu Biol [online]. 2014, vol.36, n.101, pp.107-117. ISSN 0304-3584.

Enzymatic browning is a problem that affects fruits due to its negative effects on nutritional and organoleptic characteristics. This process is catalyzed by enzymes with polyphenol oxidase activity (PPOs; PFO: EC 1.10.3.1, 1.10.3.2 y/o 1.14.18.1) and varies depending on the species, cultivar, maturity and specific plant phenological stage. In lulo (Solanum quitoense Lam.), with a cultivated area in Colombia of 4868 hectares and an annual production of 38910 tons, it is an important problem because of the relevance of this crop for the national economy. However, the properties of this enzyme in lulo have not been adequately studied. In order to understand the behavior of the enzyme in lulo fruits, several physicochemical and kinetic characteristics were evaluated. The study was conducted on the six commercially defined maturation stages (0 to 5). We determined the optimum functional characteristics for PPO activity in terms of temperature, pH, substrate concentration and amount of the enzyme, through spectrophotometric assay (A_{412 nm}) using catechol as a substrate. Kinetic studies showed variability in the parameters KM (1.16 ± 0.07 - 5.71 ± 0.14) and V_máx (30.212 ± 1.77 - 188.679 ± 14.26), depending on the maturation stage. The lulo fruits in maturation stages 3 and 4 were those with lower PFO enzyme activity, suggesting that these may be the stage in which they can be harvested to minimize the enzymatic browning process.

Palavras-chave : Solanum quitoense; enzymatic browning; polyphenol oxidase; kinetic parameters; enzymatic activity; spectrophotometric assay; maturation stages.

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