Kensington Pride or 'Bowen' mangoes have the unfortunate attribute of producing a lot of sap at harvest. This sap can be extremely damaging to the skin of the mango, and in severe cases, can make the fruit totally unsaleable.
In less severe cases, the fruit is left with an unsightly blemish (usually near the stem end) which is commonly mistaken by consumers as a fruit rot.
Sap damage will occur wherever sap makes contact with the fruit and penetrates the skin. Entry is usually made through the lenticels (breathing pores of the fruit) and will occur within five seconds of contact. Once this has occurred, the damage is largely irreversible and the symptoms of sapburn will develop.
Currently, mangoes are usually harvested with the stem attached. This inhibits the release of sap from the mango and prevents sapburn occurring prior to transfer to the packing shed. Once at the packing shed, the stems are removed manually and the fruit are then placed up-side-down on racks to allow the excess sap to drain.
Despite these precautions, sapburn still occurs and is the most serious postharvest problem of the mango industry and the major reason for rejecting or downgrading fruit. In economic terms, this means less return for farmers, wholesalers and retailers and lower quality fruit for the consumer.
Mango sap is basically comprised of two parts: an oil fraction and a protein fraction. QDPI postharvest trials at Walkamin Research Station have shown that the mango skin is damaged exclusively by the oil fraction. This part is largely released in the first 30 seconds after stem removal, and this is the most likely time that injury will occur. Sap released in the first 10 seconds has been found to have an oil content of greater than 50% of the total sap, which emphasises the extreme care that should be taken at this time.
After this point, the oil content drops exponentially, so that by about five minutes, the sap consists mainly of protein. This protein alone is non-damaging and is responsible for the clear glaze that is sometimes seen on mangoes in the marketplace.
QDPI researchers and engineers together with a local firm have been currently looking at methods of overcoming this problem and are confident that a commercial 'desapping' machine will be feasible in the near future.
A process has been developed to incorporate both physical and chemical protection of the mango based on inherent properties of the sap.
At this stage, the equipment is still in the prototype phase and further development is occurring. Full commercial trials will be conducted with the prototype equipment in the next mango season.
It is confidently anticipated that mango sap injury caused in the packing shed will be largely eradicated with the introduction of this technology, and that an increase in quality fruit on the market floor will directly result.
DATE: July 1991
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