Postharvest Biology and Technology 52 (2009) 294–299 Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio Postharvest physiology and browning of longkong (Aglaia dookkoo Griff.) fruit under ambient conditions I. Lichanporn, V. Srilaong ∗ , C. Wongs-Aree, S. Kanlayanarat Division of Postharvest Technology, School of Bioresources and Technology, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand article info Article history: Received 16 September 2008 Accepted 3 January 2009 Keywords: Longkong Browning Phenolic content PAL PPO POD abstract Longkong (Aglaia dookkoo Griff.) fruit rapidly loses its yellow skin color and turns brown after harvest. We aimed to elucidate the postharvest physiology and browning mechanism of longkong fruit stored at a 70–85% RH and at room temperature (25 ◦ C). The respiration rate slightly decreased with progressive fruit browning, while ethylene production was dramatically increased. Preliminary experiments showed that ethylene treatment markedly increased peel browning, suggesting that this is induced by ethylene. The peel L-value continuously decreased during storage, in relation to the severity of peel browning. The peel surface morphological data indicated that the ultrastructure of longkong peel collapsed after harvest, especially around brown areas. The total phenolic content of peel tissue rapidly increased, concomitant with rapid increases in phenylalanine ammonia lyase (PAL) activity and browning score on day 2. Tissue from the lower part of the fruit had higher total phenolic contents, as well as polyphenol oxidase (PPO) and PAL activities, compared to the top and middle parts of the fruit; however, peroxidase (POD) activity slightly changed during storage, possibly independent of phenol oxidation. The browning of longkong peel was not associated with changes in soluble solids contents, titratable acidity or ascorbic acid levels. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Longkong (Aglaia dookkoo Griff.) belongs to the Meliaceae fam- ily and originates from the South of Thailand. It is an economically important plant in the peninsula of Thailand, widely distributed from the South through the East, and is also cultivated in Australia, Sri Lanka, Vietnam, Myanmar, India, and Puerto Rico (Paull, 2004). The fruit contains a variety of nutrients, including proteins and car- bohydrates, a low fat content and a high percentage of vitamins and minerals (Sabah, 2004). The fruit pulp is aromatic and juicy, and has a taste that is simultaneously slightly sour and sweet. The skin of young fruit is pale green, and turns yellow when ripe, frequently with brown blemishes, and the fruit has a brittle skin. Longkong fruit develop in clusters of between 15 and 25 fruit per bunch, and consist of green seeds covered by white, translucent flesh. The fruit has five separate segments, with one to five seeds each. During ripening, astringency in the flesh declines, while the sugar con- tent increases approximately 6-fold (Paull et al., 1987). The sweet and sour taste of longkong, combined with its faintly aromatic and nutritious qualities, make this fruit a potentially valuable export. Longkong fruit deteriorates rapidly after harvest due to peri- carp browning, which reduces its marketable value. Postharvest browning of fruit and vegetables is primarily attributed to the ∗ Corresponding author. Tel.: +66 2 470 7726; fax: +66 2 452 3750. E-mail address: varit.sri@kmutt.ac.th (V. Srilaong). oxidation of phenolic compounds by polyphenol oxidase (PPO) (Walker, 1995) and/or peroxidase (POD) (Jiang, 1999; Jiang and Li, 2001). In addition, the activity of phenylalanine ammonia lyase (PAL) converts phenylalanine to free phenolic substrates for PPO (Camm and Towers, 1977). PPO can promote enzymatic browning by catalyzing the oxidation of mono- and di-phenols to o-quinones. These quinones polymerize to produce brown pigments (McEvily et al., 1992). Lin et al. (1988), Chen and Wang (1989), and Underhill and Critchley (1995) have reported an increase in POD activity dur- ing litchi pericarp browning. POD can catalyze the oxidation of many kinds of phenols in the presence of oxygen, which results in enzymatic browning of harvested fruit, such as pear (Richard and Gauillard, 1997), pineapple (Selvarajah et al., 1998), and peach (Stutte, 1989). Moreover, fruit tissue browning is also a result of cellular breakdown, leading to the mixing of browning-related enzymes and their substrates, which results in enzymatic oxida- tion in the presence of oxygen (Ju and Zhu, 1988). Little is known about the enzymatic browning of the longkong pericarp and so the objectives of this research were to study the physiological changes of the fruit after harvest and the mechanisms involved in browning during storage of the fruit at ambient temperatures. 2. Materials and methods 2.1. Plant material Bunches of longkong (A. dookkoo Griff.) fruit at commercial maturity were harvested from a local orchard in Chantaburi 0925-5214/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2009.01.003