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INTRODUCTION
During the 1984-85 season, experiments were carried out on lychee fruit using Menthene® and Vaporgard®, an antitranspirant to determine its effectiveness in retaining fresh fruit quality by inhibition of moisture loss (Brown, 1985). Although the results of these experiments did not support the possible commercial use of these products, Menthene at low concentrations (0.1- 1.0% improved the red colour of lychee fruit and inhibited browning of the skin by slowing down the rate of transpiration. Other experimental work using Freshglo®, a commercial wax emulsion (unpublished data) showed that this product also reduced the rate of transpiration and the postharvest loss of fresh quality.

A third product, Semperfresh®, a polysaccharide powder, had also been used experimentally on mango fruit (Peacock and Wilson, 1986 unpublished), with variable success, to extend the postharvest life of that fruit.

The experiments reported here were carried out to determine the effects of using these products to protect the postharvest quality and extend the shelf-life of rambutan fruit.

MATERIAL AND METHODS
Rambutans grown in North Queensland were harvested randomly from selected trees, but with the sample being biased towards representing the average size and coloured fruit on the tree at the time of harvest.

Samples were then transported by air to the Brisbane laboratory within 24-36 hours. At the laboratory fruit were sorted, labelled, and treated with solutions of (i) Semperfresh® , (ii) Freshglo® and (iii) Menthene at the following concentrations: 0; 0.15%; 0.31%; 0.62%; 1.25%; 2.50% and 5.0%. Seven punnets of untreated fruit were overwrapped with PVC cling wrap as controls. Fruit were then stored at 20°C under 90% RH.

At daily intervals assessments were made for:
1. Percent weight loss, by weighing punnets on a top loading balance;
2. Skin discolouration, by a panel of four assessors using the scale 0-4, where 0 = no discolouration and 4 = severe discolouration;
3. Skin rots, by a panel of four assessors using the scale 0-4, where 0 = no rots and 4 = severe rots;
4. General appearance, by a panel of four assessors using the standard hedonic scale 1- 9 (1 = dislike extremely; 9 = like extremely).

After storage at 20°C under 90% RH for seven days, final assessments were made on the fruit for:
1. Off-odours, by a panel of four assessors using the scale 0-4, where 0 = no off-odours and 4 = severe off odours;
2. General appearance, flavour, texture, general acceptability, by a panel of four assessors all using the standard hedonic scale 1-9.

RESULTS
The untreated, PVC overwrapped punnet lost much less weight compared to other treatments, with storage time (total weight loss 5.6%). The unwrapped control, however, displayed the most weight loss over the time elapsed, (total weight loss 29.3%).

Fruit treated with Semperfresh, and Menthene displayed a slight drop in total weight loss as the concentration of product used was increased; weight loss was less than the unwrapped control total weight loss, indicating that these products were of some benefit in reducing weight loss at the higher concentrations. The fruit treated with Freshglo, however, exhibited no apparent change in total weight loss regardless of the treatment concentration used, and were only slightly lower than that of the unwrapped control, indicating that this product is of little use in controlling weight loss.

From the skin discolouration data it can be shown that the treated PVC overwrapped punnet exhibited reduced discolouration with time compared with all other treatments, (regardless of concentration of dip used), including the unwrapped control. It should also be noted that in the PVC overwrapped control there was no evidence of the spinterns becoming brittle and desiccated (even after 12 days storage), compared to all other treatments where the spinterns became brittle and desiccated after 2 to 3 days storage at 20°C.

It is evident from the skin rot data that if a postharvest fungicidal treatment (e.g. heated Benlate, 500 ppm a.c. Benomyl at 52°C for 2 minutes) is not applied to the fruit after harvest, then the application of postharvest teatments such as solutions of Semperfresh, Freshglo and Menthene, as well as overwrapping punnets with PVC cling wrap before storage is of no benefit in the prevention of rots. Also, as the concentration of the post harvest treatments of Semperfresh, Freshglo, and Menthene increased, so the incidence of rots increased.

The general appearance data indicated that the application of the postharvest treatments to the fruit, regardless of concentration used, did not improve general appearance compared to the unwrapped control fruit. The general appearance of the treated fruit and that of the unwrapped control fruit after the 12 day storage period, had degenerated to a greater extent than did the fruit overwrapped by PVC cling wrap. The sensory assessments of off-odour, flavour, texture, and general acceptability made after 7 days storage at 20°C under 90% indicated that for:
1. Off-odour
Both controls, PVC overwrapped and unwrapped, exhibited minimal development of off odours after 7 days storage.

Fully treated with solutions of Semperfresh and Freshglo displayed no apparent increase in off-odour development as the treatment concentration increased, but did exhibit a slightly higher overall incidence of this parameter when compared to the control. However, the fruit treated with Menthene showed an increase in off-odours as the treatment concentration increased.

2. Flavour
The punnet-packed, PVC overwrapped fruit were more acceptable to the panel than were the unwrapped controls and treated fruit. Fruit treated in solutions of Semperfresh showed a slight increase in panel preference with increase in treatment concentrations used. (This could be attributed to Semperfresh acting as an individual "wrap" for fruit in a similar manner to PVC cling wrap). The fruit treated with Freshglo solutions displayed no apparent increase or decrease in flavour as the treatment concentration increased. The fruit treated with Menthene however, displayed a distinct decrease in panel preference with increased treatment concentration used. None of the treated fruit, although showing either some or no increase in panel preference, were as favoured as the untreated control fruit by the panel.

3. Texture
There was no apparent textural difference detected by the panel between either of the control treatments. Fruit treated with solutions of Semperfresh displayed a slight increase in texture, as the treatment concentration increased, while fruit treated with solutions of Freshglo and Menthene showed a slight decrease in texture as the treatment concentrations increased (variability in the results could be attributed to sampling and tasting errors due to lack of suitable fruit).

4. Conclusion
This experiment was designed to supplement the data obtained for lychees in the 1984/85 season, however, care must be taken in interpreting the results, because of the limited sample size and lack of replication.

The following conclusions summarise the main findings of the experiment:

1. PVC cling wrapping of punnets is a preferable method of handling fruit for the control of weight loss;

2. Solutions of Semperfresh, Freshglo, and Menthene had little effect on preventing skin discolouration and spintern desiccation. PVC overwrapping of fruit is the most desirable method of overcoming these problems.

3. Postharvest skin rots were not controlled by application of any of the treatments. The only effective method of control being that of an approved postharvest fungicidal dip.

4. The application of solutions of various concentrations of Semperfresh, Freshglo and Menthene to fruit did not protect postharvest fruit quality as well as the PVC cling wrap in terms of general appearance, off odour, flavour, texture, general acceptability.

Finally, from an overview of the results it is considered that the three products Semperfresh, Freshglo and Menthene do not sufficiently protect postharvest quality and extend shelf-life of rambutan fruit and it is not recommended that these be used as a postharvest treatment on this fruit.

References
Brown B. I. 1985. Report on Postharvest Experiments on Lychee - Queensland 1984/85 Season. Queensland Department of Primary Industries Postharvest Report.

Peacock, B. C. and Wilson, P. R. 1986. A preliminary evaluation of Semperfresh fruit coating for prolonging the storage life of mangoes (unpublished data).

DATE: January 1988

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