Postharvest control of litchi pericarp browning (cv. Kwai Mi) by combined treatments of chitosan and organic acids

The combined use of organic acids and chitosan may stabilise the colour of litchi fruit after harvest (Litchi chinensis Sonn cv. Kwai Mi). While homogeneous responses were obtained from acid-chitosan treatments performed at pH 0.8, the response to treatments performed at pH 1 or 1.3 appeared less consistent and predictable. Treatment effectiveness depended on the conditions of coating application. Humidifying fruit prior to treatment favoured acid impregnation at a given storage temperature. The extent of browning may be estimated from an acid impregnation index (AII), defined as the titratable acidity-to-postharvest weight loss (in %) ratio. Results suggest that the response to acid-chitosan treatment is partially physiology-dependent (pericarp water content) and that treatments at higher pH (above 1) may be considered, provided that treatment and storage conditions are properly controlled.