Non-invasive Assessment of Firmness and NIR Sugar (TSS) Measurement in Apple, Pear and Kiwi Fruit

A comparison of the non-invasive 'intelligent firmness detector' (IFD) with two standard destructive techniques for measuring fruit firmness of peeled fruit, viz. a hand-held (Bareiss) and the ART penetrometer, showed the least variation of the IFD or best reproducibility of SE of +/- 1-2 elasticity units with firm cv. 'Braeburn' apples, equivalent to conventional hand penetrometer values of +/- 0.12 kg/cm(2). Correlations of the IFD with hand-held values ranged from r (2) = 0.47-0.54 for cv. 'Lucas' pear, 0.55-0.75 for stored cv. 'Elstar' apple to 0.68 (ART) and 0.75 (handheld penetrometer) for retail cv. 'Hayward' kiwi fruit. Shrivelled fruit showed larger elasticity values possibly due to the firm ridges, which develop in the peel during shrinkage of those fruit. The IFD software corrects viz. removes artificially firm values, if the pressure sensor hits the pedicel rather than the fruit. A second comparison for total soluble solids (TSS/sugar/sweetness/taste) values of the non-invasive 'intelligent fruit analyser' (IFA) with conventional, destructive refractometry showed a good correlation with a coefficient of determination of r (2) = 0.87 with cv. 'Elstar'. Non-destructive IFA sugar/TSS values were within ca. 4 % of those obtained by the destructive refractometer, e.g. an accuracy of +/- 0.6 % sugar/TSS in apple fruit with 14-17 % sugar. The work showed that non-invasive fruit firmness determination with the IFD requires only a single calibration for all fruit species and future measurements, non-invasive sugar determination with the IFA requires regression curves in the grading machine for each fruit species, cultivar, provenience and year, or alternatively a large number of stored values, and neither bruises nor heat damage were observed on fruit measured properly by the IFD or IFA.