Steam blanching effect on polyphenoloxidase, peroxidase and colour of mango (Mangifera indica L.) slices

Abstract

The heat stability of peroxidase (POD) and polyphenoloxidase (PPO) was investigated in mango (Mangifera indica L.) slices, and the relative colour was studied after different steam blanching times. There was complete inactivation after 5 min for POD and 7 min for PPO. Steam blanching of 3 min gave residual activity of 2.85% and 8.33% for PPO and POD, respectively, and when compared with samples blanched for 5 min had no effect on colour over 20 days of storage. Correlation was found between activities of PPO, POD and colour change over 20 days. After 7 min steam blanching the browning index was stable but less than at 3 and 5 min because non-enzymic browning had occurred. This research suggests that yellowness (b) and lightness (L) values contribute positively to the browning index (BI), compared to redness (a).

Introduction

With a world production exceeding 2.6 × 10⁷ ton, mango (Mangifera indica L.) is one of the most important fruit produced in tropical regions (Berardini et al., 2005, Jasim et al., 2005, Sreenath et al., 1995, Tharanathan et al., 2006). Recognised for its delicious taste and exotic flavour, mango is a rich source of carotenoids and provides high vitamin A content (FAOSTAT, 2005, Manohar et al., 1990, Pott et al., 2003, Sreenath et al., 1995). Furthermore, high quality dietary fibre (pectin), flavol O- and xanthone C-glycosides have been found in mango peels (Berardini et al., 2005, Schieber et al., 2003).

Conventional methods of thermal processing such as pasteurisation, sterilisation and blanching often lead to a number of undesirable changes in foods, including loss of colour, flavour, texture and functionality. Although blanching is an excellent tool for inactivating enzymes, it is also accompanied by reduction of sensory and nutrient quality in many foods, mainly due to Maillard reaction and caramelisation/nonenzymatic browning (Baron et al., 2006, Deliza et al., 2005, Hoover, 1997, Nicoli et al., 1991). In many juice products, pasteurisation is used to prevent microorganisms growth as well as reducing the activity of naturally-occurring enzymes (Arogba et al., 1998, Yen and Lin, 1996). Polyphenoloxidase (PPO) and peroxidase (POD) have been identified as responsible for browning reactions (Toma´s-Barbera´n & Espı´n, 2001).

Mango PPO (EC 1.14.18.1), which is a copper-containing enzyme, has been associated with the conversion of phenolic compounds to quinones and their products’ polymerization. It is involved in the browning of injured, peeled or diseased fruit tissues, causing undesirable quality changes during handling, processing and storage (Arogba et al., 1998, Nicoli et al., 1991, Park et al., 1980, Prabha and Patwardhan, 1982, Toma´s-Barbera´n and Espı´n, 2001). PPO enzymes lead to the formation of undesirable brown pigments and off-flavoured products (Yemenicioglu, Özkan, & Cemeroglu, 1999). Two kinds of reactions generated by PPO are the hydroxylation of monophenols to O-diphenol and the oxidation of O-diphenol to O-quinone (Toma´s-Barbera´n & Espı´n, 2001).

POD (EC 1.11.1.7), mostly in isoenzyme forms and also one of the most thermostable enzymes, is responsible for performing single-electron oxidation on a wide variety of compounds, in the presence of hydrogen peroxide. An empirical interdependence between prevention of off-flavour development and inactivation of POD enzyme in frozen vegetables has been highlighted (Yemenicioglu et al., 1999). Furthermore, the synergistic activity of PPO and POD is due to the generation of hydrogen peroxide during the oxidation of phenolic compounds in PPO-catalysed reactions (Khan and Robinson, 1994, Sugai and Tadini, 2006, Toma´s-Barbera´n and Espı´n, 2001).

Mango PPO and POD have been extracted and characterised. Due to the importance of colour preservation of the raw material before any processing, the inactivation of naturally-occurring enzymes including PPO and POD is key. The aim of this study was to inactivate the PPO and POD of mango slices using steam blanching. The effect of this method on colour change was also investigated.