Latency properties of polyphenol oxidase in two avocado cultivars differing in their rate of browning

Abstract

Differences in the degree of browning of two cultivars of avocado, Lerman and Fuerte, were investigated by studying the relative activities of buffer-soluble ("soluble'') and detergent-soluble ("bound") forms of the enzyme polyphenoloxidase (PPO). The soluble form was found to exist in a latent as well as an active state. Different isoenzyme patterns were shown to exist for soluble and bound-PPO as determined by gel electrophoresis and electrofocusing. Sodium dodecylsulphate increased the PPO activity and the protein extracted from the acetone powder without releasing any additional isoenzymes. It did, however, activate latent PPO in the crude and partially purified PPO fractions. The ratios between soluble/bound and between active/latent forms of the PPO enzyme were similar in both avocado cultivars studied. It was therefore concluded that differences in the rate of browning between the two cultivars were accountable more in terms of total and specific activity of PPO rather than in the proportion of the enzyme in bound or latent forms.

Effect of chitosan and sodium alginate edible coatings on the postharvest quality of fresh-cut nectarines during storage

“…The increase in PPO activity might be due to the activation of soluble tyrosinase forms existing in a latent state, which can be activated during storage by several factors [33]. In this study we noted that the PPO activity was different depending on the type of treatment used; in particular, after 9 days of storage the highest PPO activity was observed in chitosan-and chitosan + alginate-coated samples.…”

Browning, polyphenol oxidase activity and headspace gas composition during storage of minimally processed pears using modified atmosphere packaging

“…The increase might be due to the activation of soluble tyrosinase forms existing in a latent state, which would otherwise be masked. 22 The latent forms of the enzyme might be effectively activated during storage by several factors, such as proteolysis, detergents or denaturing agents, liberated by means of cell disruption and subsequent decompartmentalisation of enzymes, substrates and other substances present in cell vacuoles. According to this, the more important the visual perception of tissue breakdown, the greater the increases in PPO activity throughout time.…”

Avocado Fruit Development and Ripening Physiology

“…The symptom is more predominant towards the end of the season. Both disorders involve browning reactions, and as such implicate in particular the enzyme polyphenol oxidase (PPO) (Kahn 1975), and phenolics (Kahn 1977). Zauberman et al (1985) were unable to find a role for peroxidase where disorders were associated with low temperatures.…”