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J. Agric. Food Chem. 2011, 59, 342–348 DOI:10.1021/jf102511z
Polyphenol Oxidase and Peroxidase Expression in Four Pineapple Varieties (Ananas comosus L.) after a Chilling Injury ASTRID-KIM RAIMBAULT,†,§ PAUL-ALEX MARIE-ALPHONSINE,† JEAN-PIERRE HORRY,‡ MADLYN FRANCOIS-HAUGRIN,† KARELL ROMUALD,† AND ALAIN SOLER*,† † CIRAD, PERSYST, UR: Banana, Plantain and Pineapple cropping systems, P^ ole de Recherche Agroenvironnementale de la Martinique, 97285 Le Lamentin, Martinique, and ‡CIRAD, BIOS, UR: Genetic improvement of vegetatively propagated crops, Avenue Agropolis, TA A-75/02, B^at. 2, Bur. 29, 34398 Montpellier Cedex 5, France. § Present address: Universite´ Paris Est-Cre´teil, Laboratoire d’e´cophysiologie mole´culaire, IBIOS -IBIOEMCO, UMR : 7618, 61 av. du ge´ne´ral de Gaulle, F-94010 Cre´teil.
Pineapple internal browning (IB) is a chilling injury that produces enzymatic browning associated with flesh translucency. Pineapple biodiversity allowed the investigation of how polyphenol oxidase (PPO) and peroxidase (POD) activities with their different isoforms are involved in the IB mechanism. Fruits of four varieties that expressed IB symptoms differently, Smooth Cayenne (SCay) and the hybrids MD2, Flhoran 41 (Flh 41), and Flhoran 53 (Flh 53), were stressed by cold. The susceptible varieties showed classical brown spots but different patterns of IB, whereas MD2 and controls showed no IB. Enzymatic activities were measured on fruit protein extracts and PPO and POD isoforms separated on mini-gels (PhastSystem). Only PPO activity was significantly enhanced in the presence of IB. Up to six PPO isoforms were identified in the susceptible varieties. PPO was barely detectable in the nonsusceptible variety MD2 and in controls. The number of PPO isoforms and the total PPO activity after chilling are varietal characteristics. KEYWORDS: Internal browning; chilling injury; polyphenol oxidase; peroxidase; pineapple varieties
INTRODUCTION
Browning of the flesh in stressed or injured fruits and vegetables is a common symptom linked to polyphenol oxidase (PPO) or peroxidase (POD) activity (1). Quinone products resulting from phenol oxidation tend to polymerize into brown compounds that bind with amino acid groups of cellular proteins (2). Under normal cold-storage conditions, pineapples are maintained at a temperature of 8 °C. Pineapple internal browning (IB), also known as blackheart or endogenous brown spots, develops to a greater or lesser extent depending on the cold stress intensity undergone by the fruit. IB has also been shown to depend on the fruit susceptibility, which, in turn, depends on the maturity stage, the nutritional status, and the variety (3-5). IB was found to be inducible above the usual storage temperatures, but the higher the temperature, the fewer the symptoms (5). Flesh translucency is a symptom associated with IB and other chilling injuries. At a temperature of
