Maturity

Science programme: Optimising fruit & crop growth

Horticultural or harvestable maturity is a stage of development after storage or transport when fruit is ready for use by consumers. Quality at maturity depends on harvesting, storing and transporting fruit to a consumer in its best possible state.

New Zealand is in an excellent position to carry out high quality control of harvest maturity because much of our crop is exported, and is subject to controls such as the Horticulture Export Authority.

Maturity is affected by fruit disorders, colour, sugar/acids, texture, flavour and ripening. A maturity index is used to determine when a fruit should be harvested. For example, in avocado, dry matter content or oil or water content are accepted worldwide standards to determine the time of harvest. Apples are measured by background skin colour, starch pattern index by iodine staining, and internal ethylene concentration.

Possible harvest indices include: SSC (Brix), acidity, dry matter, skin or flesh colour, firmness, flavour, biochemical or molecular markers. The indices used to determine maturity vary by fruit but must be relatively simple and rapid to obtain and analyse.

Examples of current indices used are:

• Apple: starch pattern indices, background skin colour, firmness
• Pear: firmness and starch pattern indices
• Kiwifruit: dry matter, flesh colour
• Avocado: dry matter (which correlates strongly with oil content)
• Persimmon: skin colour
• Citrus: SSC.

Many fruit industries are re-examining their method of deciding harvest maturity in order to find a better way to deliver better quality fruit to the market.

Research is focused on improving fruit quality in terms of taste, improved firmness or texture. Pre- and post-harvest plant physiologists at HortResearch are working on:

• New apple cultivars: determining the maturity indices for each new cultivar.
• Avocados: fruit is currently harvested on the basis of a minimum dry matter level. In collaboration with researchers in California and a NZ packhouse, we have introduced a new, rapid and safer means of measuring dry matter. The Hofshi coring device is currently being evaluated by the Avocado Industry Council. Our current government-funded work is also examining the levels of oils in fruit of a wide range of maturities over a range of regions in New Zealand, with the aim of increasing our understanding of fruit and oil quality. This also includes the levels of health-promoting components in the oil over the commercial season, and in a range of avocado cultivars.
• Postharvest storage trials: these are often aimed at optimising fruit quality following a storage period. When seeking to increase the storage duration of say, avocados, early, mid and late season fruit are used. At the point of harvest maturity fruit is measured to provide improved understanding of the interaction of maturity with postharvest handling. These maturity stages are highly likely to influence the incidence of disorders, storage potential, and rate of softening of the crop.
• Kiwifruit: preharvest scientists are working to reduce variability by manipulating preharvest factors such as spread of flowering. Another means of dealing with variability is that of sorting fruit non-destructively after they are harvested. Current areas under examination are the use of density and NIR (Near Infrared) technologies to determine maturity of avocados and summerfruit. This could mean that fruit could be graded in the packhouse into dry matter categories, which potentially may be sold to different clients on the basis of taste, or stored or shipped differently.