CONTROLLED ATMOSPHERE STORAGE OF LONGAN
SCIENTIFIC NAME: Euphoria longana
FAMILY: Sapindaceae
1. INTRODUCTION
Presently, the post-harvest life of longan fruit is prolonged by storing fruit under refrigeration (Watson, 1984; Olszack, 1986). Controlled atmospheres have also been used with varying success to prolong storage life of many temperate and some tropical fruit (Hardenburg, 1969); Dewey, 1977; Smock, 1979; Kader, 1980) and may also serve as a means of extending storage life of longan.
No studies appear to have been reported regarding controlled atmosphere storage of longans. The purpose of the following investigation was to establish if an alteration in atmospheric composition could delay deterioration of longan skin and pulp characteristics.
2. DISCUSSION
Controlled atmospheres did not markedly alter the storage characteristics of longans held at 10°C. Disease did not develop at this temperature, which is in agreement with earlier temperature studies performed with longan (cv. Biew Kiew) (O'Hare and Prasad, unpublished). High oxygen atmospheres appeared to maintain skin colour slightly closer to that of fruit at harvest (0 days). Carbon dioxide levels did not have any effect in this regard.
The principle differences in skin colour were indicated by a-values (redness) of fruit. L and b values generally did not differ between different atmospheres. The reason behind a-value differences can only be speculated at this stage, but may be associated with an increase in the oxidation rate of rising anthocyanin levels induced by low temperature (O'Hare, unpublished).
Despite these differences in a-values, no differences between treatments could be detected by a visual assessment (data not shown). Earlier comparisons of visual assessment and CIE-Lab values (O'Hare and Prasad, unpublished) showed high correlation between band L-values, but not with a-values. Considering that no skin colour differences occurred generally with the L and b values in the present experiment, it is considered that controlled atmospheres do not significantly enhance the visual quality of longan fruit held under 100°C.
Low oxygen atmospheres did tend to maintain the eating quality of longans at a significantly higher level than fruit held under high oxygen. This difference, however, was only slight, with fruit rating between 7 (like moderately) and 8 (like very much). This difference in pulp acceptability was probably due to a slowing of metabolism under low oxygen conditions. This is a common feature that has been recognised in other fruit (Metliskii et al., 1983).
Although CA did not appear to markedly enhance the storage characteristics of longan in the present experiment, it is possible that differences between treatments may be greater if fruit are held in storage for a longer period (e.g. 20 days). The present data suggests that controlled atmospheres hold no benefit to longan storage if fruit are only held for a 12-day period.
DATE: January 1990
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