Assessment of the use of the DA meter to increase the rigour of fruit sampling for release date determination in strip-picked orchards and to generate additional information for packhouses on the maturity of select pick fruit

The objective of this trial was to determine if the DA meter (Sinteleia, Bologna, Italy) can be used as an additional device to determine maturity in apples.

A sample of 120 uniformly sized fruit were harvested weekly per orchard (2 orchards per cultivar per season, 8 in total), starting 4/5 weeks before until 2 weeks after commercial harvest. Using a delta absorbance (DA) meter, the index of absorption difference (I_AD) was measured on marked areas of the fruit whilst still attached to the tree. The skin ground colour, red colour intensity, firmness, starch breakdown, total soluble solids (TSS) and titratable acidity (TA) were determined and correlated to the respective I_AD readings. Fruit were also harvested from each orchard and cold-stored. The I_AD values at harvest and after storage were correlated to fruit quality and disorders after storage.

During the sampling period, as well as at harvest, good associations were found between the I_AD and starch breakdown percentage of ‘Bigbucks’ apples. For ‘Golden Delicious’ apples, there was a negative correlation between the I_AD at harvest and senescent scald after shelf-life. For ‘Cripps’ Pink’ apples, there was a positive correlation between the I_AD at harvest and superficial scald incidence after storage.

With further verification, the DA meter could be used commercially as an additional tool to non-destructively track maturity and ripening of ‘Bigbucks’ apples.  The I_AD of ‘Golden Delicious’ and ‘Cripps’ Pink’ apples at harvest may also serve as a predictor for senescent scald and superficial scald, respectively.

The DA meter has the potential to track the starch breakdown of ‘Bigbucks’ apples during pre-harvest period and may serve as a pre-sorting device to reduce mixed maturities in cartons.