TECHNICAL CONSIDERATIONS IN PACKAGING MATERIALS AND TABLE GRAPES
The Box,the Table grapes, the Materials in the box in contact with the grapes , the so2 sheet and the liner bag constitute an integral system.That system must work in perfect balance to have good qaultiy of table grapes during and after post harvest.
The system must prevent attack of fungus, must keep good color stems and berries and shape (commercial quality).
The way to keep all these elements in perfect conditions din post harvest is taking care of the corrent use of this elements to prevent quality loses. The most important factors to take in conderation are.
- Percentage of Moisture in the box
- SO2 Release concentration
- Residues Levels
- Temperature
The Botrytis is controlled by the SO2 sheet. This one has a chemical Product called sodium Metabisulfite. The chemical product reacts with moisture (water) to relaease the SO2 gas.The chemical reaction happens as Follow:
Na2SO5 + H2O + ½ O2 Na2So4 +H2O + SO2
To react in the table grapes box the moisture must be enough and depending the level of moisture, the concentration of SO2 released by the SO2 sheet. High concentrations of SO2 can damage the table grapes producing bleaching, dry stems, loss of berry color and/or weak and dry stems.
The box ventilation (liner bags ventilaion percentage) will decide the quantity of the moisture in the box and the percentage of exchange air with the exterior.If the ventilation is high, the bos will loose moisture and SO2 gas and the grapes will have damage and loss of quality.But the Time to Cool the box will be lower to reach 0 celcius degrees.
If the ventilation is poor, the quantity of moisture will be too high and the SO2 cencentration will be high as well producing bleaching in the grapesand SO2 damage on the surface of the berries and stems.That is way the right Level of ventilation is matter of several studies in different countries and reseach institutes.
It is coincident following all the studies made around the world, the right ventilation is 0.3%, keeping the right level of moisture in the box to keep the grapes fresh and also right levels of SO2 to control and prevent fungus.This formula will have more or less importance in different cultivars, being the most susceptible to bleaching Thompson seedless but most notorious red and black Cultivars.
The SO2 sheet performance and technology involved in its desigh will play a fundamental role in the system.As we mentioned before, high concentrations of gas can damage grapes, low concentrations won’t protect grapes against the fungus, the balance in the release is fundamental. As a result of the same, the SO2 sheet leave chemical residues in the grapes, and the level or concentration of those residues can be incident in the commerical quality of the grapes as in human health.
Residues levels also can be read as in MRLs and defined as the maximum concentration of pesticide residue (expressed as millgrams of residue per kilograms of food/animal feeding stuff) likely to occur in or on food and feeding stuffs after the use of pesticides according to Good Agricultural Practice (GAP) , i.e when the pesticide has been applied in line with the product label recommendations and in keeping with local environmental and other conditions.
The MRL is defined by the EU as Following:
All pesticide/fungus/commodity combinations without an established MRL= 0.01Mg/Kg.(10ppm). The Na2SO4 belong to that group. Find more info at the following source www.efsa.eu.int
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