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- Characterization on extraction conditions for 'starking" apple polyphenolox1dase (ppo)Publication . Rocha, A. M. C. N; Cano, M. P.; Galeazzi, A. M.; Morais, Alcina M. M. B.
- Polyphenoloxidase activity and total phenolic content as related to browning of minimally processed ‘Jonagored’ applePublication . Rocha, Ada MCN; Morais, Alcina M. M. B.Phenolic content, polyphenoloxidase (PPO) activity and browning have been reported by different authors to vary in different ways, depending on cultivar, picking maturity, storage conditions, etc. Numerous authors have attempted to correlate browning results with the phenolic content and/or enzymatic activity of apples, but data published in the literature are divergent as to which of the two factors, ie the enzyme or the substrate, plays the decisive role in the overall phenomenon of enzymatic browning. The aim of this work was to follow the PPO activity and phenolic content of minimally processed apple (cv ‘Jonagored’) during cold storage and to establish a potential relationship with enzymatic browning. Increasing storage time of minimally processed apple seemed to result in an increase in PPO activity. No changes (P > 0.05) in total phenolic content were observed during storage. Colour degradation of apple cubes, as indicated by changes in colour parameters, was found to be highly correlated with PPO activity. Browning of ‘Jonagored’ apple cubes during storage was found to be moderately correlated with PPO activity. No correlation was found between the browning index and the total phenolic content.
- Characterization of polyphenoloxidase (PPO) extracted from "Jonagored" applePublication . Rocha, A.M.C.N.; Morais, A. M. M. B.Polyphenoloxidase (PPO) was extracted from apple (cv. Jonagored) with addition of 2% PVP and 0.25% Triton X100 to the extraction buffer containing phenolic adsorbents. Experiments were performed to evaluate the affinity and specificity towards several substrates. ‘Jonagored’ apple PPO was found to have higher specificity (lower Km) towards L-dopa, 4-methylcatechol and (+) catechin than other phenols tested, but the highest activity level was obtained with p-cresol. The ratio Vmax/Km indicates that p-cresol followed by L-dopa and 4-methylcatechol are the best substrates for ‘Jonagored’ apple PPO. The enzyme activity showed two pH optima, at 5.0 and 7.5, at room temperature, with the main peak at pH 7.5 and the secondary one at pH 5.0 when catechol was the substrate.