Development of rind and pulp mineral content parameters as indicators of storage potential for subtropical fruits.
Kruger F. J., Snjider B., Freeman T., Fraser C.
Author Affiliation: Private Bag X11208 Nelspruit 1200, South Africa.
SA Fruit Journal 2 : 39-41, 43
Abstract : Studies conducted in South Africa in the late 1990s identified maturity and fruit mineral composition as the key factors affecting storage potential of avocados. Recommendations emanating from the studies were introduced and applied with success. This approach has since been extended to the mango and citrus industries, and trials have recently been conducted in these crops. In this paper, changes in the mineral contents of avocado, citrus and mango fruits during growth and maturation are discussed. In citrus fruits, mineral composition varies according to position within the tree canopy. Grapefruits in the outer canopy had a third more Ca in the rind than fruits within the canopy and similar results were obtained for B. Also, the shaded side of outer fruits contained more B than the side exposed to the sun. Eastern fruits contained more Ca and B fruits than western fruits. In contrast to these immobile elements, mobile elements such as P and K generally showed the opposite patterns. The rind of subtropical fruits usually contains more N (and other elements) than the pulp. In mango, the N content of the skin, which declined from October until harvest in January, remained around 20% higher than that of the pulp. An avocado with good storage potential should have a pulp N content of about 1.7% during October and this falls to below 1% by January and remains low until harvest. Avocados with a pulp N content above 2% in October may mature too rapidly resulting in poor storage potential. The same applies to fruits in which the N content fails to drop below 1% by February, or increases during the late season.