Post Harvest Management of Horticultural Crops

Degreening

Degreening

Post harvest treatment of citrus fruits with ethylene under controlled conditions hastens the loss of chlorophyll, a process known as ‘degreening’. Degreening consists of chlorophyll degradation to allow the expression of natural pigments masked by the green colour. Eg. Yellowing of citrus fruits. Degreening process can be hastened by applying ethylene and done mainly in non-climacteric fruits like citrus. On a small scale dip treatment in ethrel solution also bring about degreening . The concentration of ethylene required and time of exposure is significantly high in case of degreening when compared to ripening.



The main causes for greening are climatic conditions before harvest. For example, citrus often reaches commercial maturity with traces of green colour on the epidermis (flavedo). Although not different from fruits with colour, consumers sense that they are not ripe enough and have not reached their full flavor. Exposure to low temperature during maturation is necessary for an orange-coloured peel to develop. Hence fruit grown in low altitude tropics fail to degreen completely.


Degreening is done by 2 methods

1. Exposing to ethylene - Degreening is done at 25-300C and 85-95% RH with ethylene gas trickled into room to achieve 20-30 PPM or 10 µL L-1 for 24-72 hr. with regular ventilation of the chamber to prevent CO2 build up and injury. In batch process it is at 20-200 µL ethylene L-1. Trickle process is faster than batch process; since degreening condition accelerate deterioration and decay of citrus fruits. This is most popular methods
Citrus fruits are exposed from 1-3 days (depending on degree of greening) to an atmosphere containing ethylene (5-10 ppm) under controlled ventilation, 20-260C and 90-95% RH. Conditions for degreening are specific to the production area.

2. Artificial colouring - When weather is not conducive for the development for colour in orange; legally permitted dye can be used to colour the peel of the fruits like orange, with Citrus Red No.2 (1-2(2,5-dimethoxy phenylazo)2-napththol) this process is called as ‘Colour Add’. It is used on mature fruit which are not intended to processing. Dye is applied to fruit by dip at 490C for 4 min. for oranges. Rinsed enough to prevent bleeding and residue tolerance is 2ppm / 2 mg kg-1 of fruit.