Anthocyanidin separation in exocarps of ‘Mauritius’ litchi (Litchi chinensis Sonn.) following methods to improve rind colour

Abstract

Litchi or lychee (Litchi chinensis Sonn.) fruit rinds are red due to the presence of water-soluble, vacuole-bound anthocyanin pigments. After harvest, these pigments decompose rapidly unless treated. Treatment with steam (95°C) for two seconds, followed by subsequent immersion in a zero pH solution for four minutes resulted in rinds that were still red after 28 days of storage at 1 °C. Spectrophotometric analysis of individual anthocyanidin pigments showed that only cyanidin and pelargonidin are present in ‘Mauritius’ litchi fruit rinds. However, four distinct anthocyanins were separated by high performance liquid chromatography from rinds of some fruit, while no additional compounds were found in rinds of fruit immersed in a zero pH solution when compared to untreated control fruit. This confirmed that preservation of litchi rind colour after immersion in zero pH is not the result of copigmentation but is simply a pH effect. On the other hand, a two second steam (95°C) treatment, resulted in the breakdown of anthocyanins while immersion of fruit in a zero pH solution not only enhanced rind colour, but also lead to elevated anthocyanin concentrations.