Physical and Physiological Changes in Low-Temperature-Stored Pitahaya Fruit (Hylocereus undatus)
Keywords:Color, respiration, ethanol, acetaldehyde, chilling injury, pitahaya.
Pitahaya fruit (Hylocereus undatus) is highly perishable, and so commercialization is limited. Refrigeration prolongs shelf life of fruits and vegetables. Nevertheless, some produce may be injured by low temperatures during storage. Studies on chilling injury in pitahaya fruit are scarce and this damage is mostly judged subjectively. This study was conducted to contribute to the knowledge and understanding of chilling injury in pitahaya, to eventually identify indicators that would be useful and consistent in describing degree of injury more objectively for future studies. Pitahaya fruits were stored at 4 ±2ºC and 8 ±2ºC for 5, 10, 16, or 21 d. At the end of each low-temperature storage period the fruits were removed from cold storage and kept at 26 ±2ºC and RH 72 ±2% for 0, 3, or 6 d. An additional group of fruits (used as reference) was kept under environmental conditions (6 d at 26±2ºC). At the end of each treatment period, external color, respiration rate, production of ethanol and acetaldehyde in pulp, and observable damage were assessed. Fruits not stored at low temperatures (reference) showed good color development (hue angle diminished from 45.09° to 17.5°) and good external appearance. However, external damage was exhibited in low-temperature-stored fruits at both low temperatures, although more intensely and sooner in fruits stored at 4ºC than in those stored at 8°C. For both temperatures, after 5, 10, or 16 d of cold storage, a moderate reduction of hue angle was registered (around 18.6° to 26.7°) when removed from low-temperature storage, indicating moderate development of color. In fruits stored for 21 d at 4ºC and ripening at 26±2°C, hue angle remained high (37.6º), indicating that the long period of cold storage inhibited natural reduction of hue angle, and so the development of the desirable external pinkish-red color did not occur. A 28% increase in respiration rate was also recorded, while production of ethanol and acetaldehyde increased 37 and 35 times. Also, external and internal appearance of the fruit deteriorated. In general, observable damage increased in fruits stored for longer periods, particularly at the lower temperature. It is suggested that external color (hue angle) and respiration rate are objective, useful, and consistent variables for measuring chilling injury in pitahaya fruits.