Polyphenoloxidase inactivation by light exposure in model systems and apple derivatives

Photo-Induced Modification of Food Protein Structure and Functionality

“…However, it is clear that for a given light radiation, the higher the intensity of the light, the higher the extent of protein structure modifications. For instance, when the effects of both UV-C and PL were investigated on polyphenoloxidase and pectin lyase in a wide range of light doses, the same mechanism of structural modification was detected but with different extents depending on light dose [56,63]. Similar results were also observed upon PL treatment of gluten, egg white and polyphenoloxidase [61,62,72].…”

“…Enzymatic activity was thus analysed on the extract of the entire plant tissue and is likely to be the result of activation/inactivation of genes encoding enzymes rather than to a specific photoreaction involving enzymes. However, when pectolytic enzymes and polyphenoloxidase were extracted from a thin surface layer of UV-C-treated apple slices (4 kJ m -2 ), their Similarly, polyphenoloxidase in mango nectar and apple juice was reported to be inactivated by UV-C treatments [33,42,63]. These results suggest that there is not only a metabolic response of the wound tissue to irradiation but also a direct photo-induced modification of enzyme activity.…”

“…By contrast, densely packed globular proteins show higher modification than random coil proteins. Globular proteins, such as lactoglobulin, polyphenoloxidase, lysozyme and egg white proteins, typically undergo unfolding [19,56,60,63,104]. The higher photosensitivity of globular proteins can be attributed to the facile transfer of oxidising equivalents among vicinal reactive sites within the molecule.…”

“…The latter indicate that low-intensity treatments can modify the conformation of the active site of the enzyme, leading to an overall activity increase [82]. By contrast, higher intensity treatments would be associated with non-reversible structural changes, including protein aggregation and fragmentation, resulting in enzyme inactivation [56,63]. In the case of soy lipoxygenase, the dose of PL resulted to be the main factor governing the extent of protein fragmentation [4].…”

Inactivation of pectic lyases by light exposure in model systems and fresh-cut apple

“…The enzyme pectin methyl esterase in orange juice was indicated to be not affected by UV-C treatment, whilst polyphenoloxidase in mango nectar and alkaline phosphatase were reported to lose their activity (Guerrero-Beltràn & Barbosa-Cànovas, 2006;Keyser et al, 2008;Tran, & Farid, 2004). More recently, UV-C light was shown to inactivate mushroom polyphenoloxidase by inducing protein aggregation (Manzocco, Quarta & Dri, 2009). …”