Maturity indices ofCanarium indicum(Burseraceae) nuts

Abstract

Many tree nuts are harvested from the ground following abscission, but some are harvested directly from trees when fruit is mature. Canarium indicum (Burseraceae) is a tropical nut indigenous to lowland rainforest of Melanesia that has great potential for commercialization. The nut is enclosed in a fleshy mesocarp that turns from green to purple before abscission and is usually gathered from the forest floor. Maturity of other nuts is often related to oil content and there may be a relationship between C. indicum fruit colour, kernel oil content and maturity. We observed the timing of colour change of fruit of C. indicum on trees over 8 weeks. We also compared the colour change in fruit at the top of the tree and the bottom of the tree over 8 weeks. Oil was extracted from kernels of purple, half-purple and green fruit with a Soxhlet-type apparatus. Kernels in each fruit colour category were weighed to obtain mean kernel weight in each colour category. Around 80% of C. indicum fruit ripened from green to purple and abscised over a period of 8 weeks. Fruit ripened first at the top of the tree. Purple or half-purple fruit of C. indicum produced kernels with a significantly higher oil content than green fruit (76.6 and 76.3% compared with 72.8%). Kernels from green fruits were small, shrivelled and weighed significantly less than kernels from purple and half-purple fruit. These results demonstrate that fruit colour of C. indicum is a suitable indicator of kernel maturity and oil content. Purple to half-purple fruit colour is a suitable harvest standard.