Hot water treatments for the control of rots on harvested litchi (Litchi chinensis Sonn.) fruit

Abstract

Punnetted litchis are prone to rot development. We examined the use of hot water treatments to control rots, with 2 min or 5 min dips at 48 °C, 50 °C or 52 °C in one experiment, and 1 min, 2 min, 3 min, 4 min or 5 min dips at 52 °C in another. We also compared the benefits of a 1 min 52 °C hot water dip with a 1 min 52 °C hot water spray. The most effective hot water dip was 1 min at 52 °C, which slowed the rate of rot development by approximately 15%. The hot water spray was equally effective as the hot water dip. On the basis of comparisons with other studies, a hot water spray was about half as effective as a hot benomyl dip. A model was used to simulate the temperature profiles within a 30 mm diameter spherical fruit during a 1 min dip at 52 °C. At the end of the dip there was a steep temperature decline from the surface to the center of the fruit, consistent with a heat pasteurization effect largely restricted to the pericarp. The hot water treatments caused immediate effects on pericarp colour, with a positive linear correlation between dip time at 52 °C and chroma, indicating disturbance of pericarp cells.