Effects of some thermal treatments on polyphenoloxidase and peroxidase activities of banana (Musa cavendishii,var enana)

Polyphenoloxidase (EC 1.14.18.1) and peroxidase (EC 1.11.1.7) activities were evaluated during cold storage of banana (Musa cavendishii, L var enana). The effects of some thermal treatments (blanching of peeled bananas, microwave treatment of banana slices and storage of banana slices at ?24°C) were studied. Inactivation of both enzymes by blanching was very effective (96–100 %) at all maturity levels. Microwave treatment showed differing efficiency depending on banana ripeness, and produced non-enzymic darkening due to Maillard reactions mainly in green and full-yellow bananas. Freezing of fruit slices without previous thermal treatment produced different effects in polyphenoloxidase and peroxidase activities. It was concluded that immersion in boiling water of peeled bananas with 70 % green/30% yellow peel colour maturity index is the optimal pretreatment for the preservation of frozen banana slices.