Page 76 - SA Fruit Journal VOLUME 14

is part of the standard handling procedure for grapefruit exported to Japan and should be implemented by anybody wishing to risk exporting grapefruit under an extended cold treatment regime.Postharvest shock conditioningAlthough not developed to the point of be- ing a practical standard recommendation, exploratory trials have indicated that vari- ous shock treatments may also be useful in conditioning grapefruit such that sensitivity to chilling injury is reduced. In these trials Marsh grapefruit was shock-treated by expo- sure to a high temperature (35°C) or a high level of CO2 (10%) for 3 days prior to cold treatment (-0.6°C for 22 days). The incidence of chilling injury was dramatically reduced relative to control fruit that was conditioned through wilting at ambient temperatures for 3d, but the incidence of decay was increased by the high temperature treatment.The role of TBZIt is known that inclusion of thiabendazole (TBZ) in citrus wax applied to grapefruit can significantly reduce the incidence of chilling injury. Inclusion of TBZ is also a good stand- ard packhouse procedure and should be used if anybody wishes to risk exporting grape- fruit under these extended cold sterilisation conditions.Precooling and storageA critical factor affecting the extent of chill- ing injury of grapefruit, is the duration of exposure to temperatures below 4.5°C. This exposure period is cumulative and can oc- cur during precooling (the period prior to loading during which the temperature of the fruit is reduced to the cold sterilisation level), the cold sterilisation treatment itself and post-shipping storage. Precooling for 3d is a compulsory component of the disinfes- tation treatment, but any other pre-loadingstorage at temperatures below 4.5°C should be avoided. Storage of grapefruit after ship- ping should be at an “intermediate storage temperature” of 7 to 8°C and should be kept to the minimum necessary duration.The role of waxesThe main purpose of a wax emulsion is to:• Protect fruit against moisture loss, which results in longer shelf life and less weight loss of the fruit.• To provide shine to the fruit at the point of sale. It is important to note that this shine needs to be sustained throughout the chain of distribution (some waxes break down more rapidly than others).• Provide a barrier of protection against chill- ing injury and fungi.The type of wax that you choose and the way in which you apply the wax will have a sig- nificant influence on the above points. Choosing the right wax: The “lighter” waxes (e.g. lower solids or carnauba based waxes) offer less resistance to gas transfer (respira- tion) than “heavier” waxes (e.g. shellac or high solids polyethylene based waxes). Thus light wax emulsions will protect fruit with sensitive rinds far better than a heavier wax emulsion and will also allow for better colour development. On the other hand lighter wax- es break down more quickly, and are there- fore not suitable for long storage programs, especially cold sterilisation programs.Research has indicated that “heavy wax- es” that slow down breathing (respiration) and retain a high level of CO2 (10%+) on the surface of the fruit, reduce the incidence of CI. Unfortunately the use of heavy waxes may increase the incidence of postharvest rind pitting on sensitive fruit. Nonetheless, the high risk of chilling injury on grapefruit under conditions of extended sterilisation, make it appropriate to consider preferentially using such waxes when exporting to markets that require such extended cold treatment.Wax application: Uneven waxing, under- waxing and over-waxing all have a deleteri- ous effect on fruit quality. The wax barrier need not be thick, and in fact a very thin bar- rier provides enough of an integral film to prevent most of the moisture loss without interfering with the respiration process.NB: Adhere to the wax manufacturer’s rec- ommended application rate – adhere to the product label instructions. Please note:• Fruit should be dry before waxing. Where possible the packhouse should use a hot water bath for fungicide application as this helps the drying of fruit before waxing.• Fruit must move evenly through the wax- ing unit and flow of fruit entering the pack- ing line must be consistent.• When fruit leaves the waxing unit, all parts of the fruit needs to be covered with a film of wax. Examine fruit after the waxing unit regularly.• Brushes in the wax applicator must be in good condition and should rotate at a speed of about 90 rpm. The last brush in the wax applicator should always be wet, so as not to remove wax from the fruit.Over-application• Inhibits the breathing (respiration) of the fruit.• The movement of oxygen and CO2 on the surface of the fruit is inhibited resulting in poor colour development and off-flavours caused by the process of an aerobic fermen- tation.• Inhibits colour break.• Encourages rind disorders on sensitive fruit.• Unnecessary expense!!Under-application• Excessive weight loss and shrinkage of fruit.• Poor shelf life / storage.• Susceptibility to chilling injury.TECHNOLOGY 73 FEB | MARCH 2015