Pg. 32-35 Litchi (Litchi Chinensis Sonn) Pericarp Colour Retention

The South African litchi industry is predominantly export orientated and pericarp (skin) colour retention is of primary importance, where export markets demand red fruit. Until now, gaseous sulphur treatments were thought to play a major role in the maintenance of this colour by firstly, fixing the anthocyanins, and secondly acting as a fungicide thus
preventing browning reactions. Sulphuring of fruit however, results in undesirable aftertastes, constitutes a health problem and is ineffective against some fungi. In addition, since sulphur-fixed anthocyanins are colourless, the sulphuring process is then reversed by dipping the fruit in low pH solutions. Depending on the pH of the solution, the anthocyanins reflect light at different wavelengths, ranging from red to blue. At a pH around 5.0, they may even be colourless due to the excessive loss of protons from their structure. The pH of the solution is thus critical and investigations are implicated,