Pg. 64-65 Establishment of a total soluble solid-based harvest maturity threshold parameter for ‘Mauritius’ litchi fruit

Currently, the total soluble solid content/titratable acid ratio (TSS/TA) of South African ‘Mauritius’ litchi fruit is used as an unofficial maturity parameter. Originally, a TSS/TA ratio of 20:1 was proposed, but this was later increased to 25: 1. However, in practice this value only serves as a broad guideline and subjective tasting remains the decisive tool used by the Perishable Product Export Control Board (PPECB). The aim of the present study was to determine whether a relationship exists between the TSS of ‘Mauritius’ litchi fruit and taste. To do this, individually picked and bunch harvested fruit were sampled from an orchard in the Nelspruit area on seven dates during December 2014. The results indicated that fruit with a TSS content lower than 19°brix had unacceptable taste while those with a TSS content between 19 and 20°brix were borderline. Fruit with a TSS content higher than 20°brix had acceptable taste. In terms of the TSS :TA ratio, the corresponding value was about 27: 1 which is two units higher than the currently used value of 25: 1. From the results it would appear that TSS on its own may serve as a fast maturity parameter for ‘Mauritius’ litchi fruit. It is provisionally recommended that a mean threshold of 20.5°brix be used. It is further recommended that the TSS of 10 fruit be individually measured to obtain the above value. It is also recommended that this procedure be used on selectively picked fruit only and not on bunched picked fruit. It would further appear that a mean fruit mass of around 24 g may serve as an additional indicator that the TSS level is approaching 20°brix. However, the minimum TSS level of
later harvested bunch picked size/colour sorted samples may possibly be reduced to 18°brix at the time when the TA content is dropping fast. Further research is indicated so as to refine the method and to determine what effect harvesting procedures, climate and horticultural practices have on the observed trends.