THE EFFECT OF FRUIT MATURITY AND STORAGE DURATION ON FRICTION DISCOLOURATION OF ‘PACKHAM’S TRIUMPH’ AND ‘DOYENNE DU COMICE’ PEARS

Abstract

Friction discolouration (FD) is causing the South African pear industry multi-million rand losses due to blemished fruit being rejected for the export market and being sold locally. The occurrence of FD was studied over two seasons using ‘Packham’s Triumph’ and ‘Doyenne du Comice’ (Pyrus communis) fruit. The influence of fruit maturity and storage duration were investigated by harvesting over three maturities and storing fruit for up to three months. FD was induced using a modified laboratory shaker that was shown to closely mimic pack line damage. Polyphenol oxidase (PPO) activity and total phenolics (TP) content were also evaluated. ‘Doyenne du Comice’ was more prone to FD than ‘Packham’s Triumph’. Harvest maturity significantly influenced FD susceptibility, with the middle picking maturity generally giving higher FD ratings. Increasing storage duration generally increased FD ratings, although not consistently. PPO activity was not influenced by harvest maturity, but was influenced by storage duration. In ‘Packham’s Triumph’, the TP content was not affected by harvest maturity or storage duration, whereas both these factors significantly influenced TP content in ‘Doyenne du Comice’. Susceptibility to development of FD symptoms is not easily linked to either PPO activity or TP content, and seasonal differences in susceptibility make prediction of possible levels of FD very difficult. INTRODUCTION Friction discolouration (FD) is a well known and serious postharvest problem in the pear industry (Wang and Mellenthin, 1973; Mellenthin and Wang, 1974). The reduction of visual quality is one of the foremost causes for consumer discontent (Raese, 1989). FD is also referred to as skin browning, abrasion marks, belt burns and friction bruises (Smith, 1946). This disorder is characterised by diffuse brown skin discolourations, especially at high points on irregular fruit surfaces (Meheriuk et al., 1994). Such discolourations are induced by a number of mechanical injuries that fruit are subjected to during harvest, packing, transportation and marketing (Mitcham et al., 2001; Feng et al., 2004), followed by biochemical reactions that lead to browning (JimenezAtienzar et al., 2004). The effect of fruit maturity on susceptibility to skin discolouration has been studied in ‘Bartlett’ (Mitcham et al., 2001), ‘Doyenne du Comice’ (Amarante et al., 2001a) and an array of cultivars by both Kvale (1979, 1988) and Amiot et al. (1995). It has been reported that the timely harvesting of the fruit might influence the degree to which this disorder is experienced. It is commonly accepted that both bruising and frictional forces give rise to the skin browning, at epidermal level (Mitcham et al., 2001). Storage duration as a controllable component in the post harvest chain has been studied by a number of researchers (Mellenthin and Wang, 1974; Kvale, 1988; Spanos and Wrolstad, 1990; Amiot et al., 1995; Mitcham et al., 2001). Polyphenol oxidase (PPO) enzyme activity is known to influences the extent and degree of browning of pear peel (Gauillard and Richard-Forget, 1997). Sufficient and