Pg. 12-14 Steam and Low pH Dips Improve Litchi (Litchi Chinesis Sonn) Pericarp Colour Retention

The red pericarp (skin) is an important attribute in the appeal of fresh litchi or lychee fruit in the market place. At room temperature, fruit will rapidly discolour due to breakdown of the anthocyanin pigments and are less attractive. In recent years fruit from several countries, including South Africa, have simply received a postharvest gaseous sulphur treatment to overcome browning. However, at best fruit are light green, yellow or pink and they never attain their initial red colour. In addition, several workers have examined the use of low pH solutions in conjunction with sulphur treatments, but the results were not too promising. Kaiser (1994) implemented a novel technique using boiling water to break down the cell membranes, followed by immersion in zero pH, thus eliminating the need for using sulphur. This red colour was retained, but the pulp browned. Steam was then substituted for boiling water and a 2 s treatment of steam (95°C) followed by immersion for 4 min in zero pH and then dipping in 1% Vaporgard® solution resulted in firm red fruit with no internal browning and acceptable taste (rated on a scale of 0- 5) after 28 days of cold storage at 1°C, compared with sulphur-treated fruit and controls. Consequently, commercial trials of this treatment are recommended.