Utilizing the IAD index to determine internal quality attributes of apples at harvest and after storage

A hand-held instrument (DA Meter, Sinteleia, Bolonga, Italy) which measures chlorophyll nondestructively and gives an IAD index (index of the absorption difference between 670 and 720 nm), was used to measure quality attributes of three cultivars of apples. A preharvest study conducted in a ‘Starking’ apple orchard found determination coefficients of r2 values of 0.79 to 0.64 between the IAD index and starch levels, firmness, TSS and TA of fruit. Three orchards of ‘Starking’, ‘Granny Smith’ and ‘Pink Lady’ apples were sampled during commercial harvest and the apples held in air storage for up to six months. The IAD index measured either at harvest or at removal from storage was correlated with TSS, TA and firmness of the apples. The r2 values were best for TSS (0.76) and poorest for firmness (0.51). Moreover, the measurement at harvest and at removal from storage gave similar prediction coefficients for quality attributes. This measurement can be used to sort at harvest for different quality classes after storage, or at removal from storage for different marketing classes.

► The DA-meter was used to follow on-tree ripening of ‘Starking’ apples.
► Determination coefficients r2 between IAD and starch or firmness were 0.73 and 0.79.
► Three cultivars from three orchards were harvested and stored for up to six months.
► IAD at harvest or at removal from storage was correlated with quality parameters.
► The r2 values were best for TSS and poorest for firmness.
► IAD can be used to sort apples at harvest or before marketing into different ripeness classes.