Kinetic model of apple juice enzymatic browning in the presence of cyclodextrins:: The use of maltosyl-β-cyclodextrin as secondary antioxidant

Enzymatic browning reactions limit the commercial shelf life of apple juice, so that colour preservation during storage is one of the main objectives of fruit processors. In this paper, the colour of fresh apple juice was evaluated in the presence of different types of cyclodextrins (CDs) (alpha-CD, beta-CD, gamma-CD and maltosyl-beta-CD), compounds that bind or complex polyphenol oxidase substrates. The effectiveness of CDs as browning inhibitors was determined as the difference between the colours observed in the CD-treated sample and the controls, using the colour space CIE-L*, a*, b* system. Although the effect of CDs on apple juice enzymatic browning has been studied, the action mechanism involved remains a subject of controversy. In this work, we have kinetically modelled apple juice enzymatic browning in the absence and presence of maltosyl-beta-CD. The complexation constant between the mixtures of diphenols present in apple juice and maltosyl-beta-CD was calculated (K-c = 4.09 mM(-1)). Different concentrations of maltosyl-beta-CD modified the evolution of lightness (L*), total colour (Delta E*) and hue angle (H*) because of the higher affinity constant it shows for the compounds responsible for apple juice browning than do alpha-CD, beta-CD and gamma-CD. Moreover, in this paper we show that maltosyl-beta-CD can enhance the ability of ascorbic acid to prevent the enzymatic browning due to the protective effect of maltosyl-beta-CD against ascorbic acid oxidation. Hence, maltosyl-beta-CD seems to act as a "secondary antioxidant", reducing apple juice browning and enhancing the naturally occurring antioxidant capacity of a food. (c) 2006 Elsevier Ltd. All rights reserved.