Kiwifruit and apricot firmness measurement by the non-contact laser air-puff method

The laser air-puff method was investigated for non-destructive firmness measurements on kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson cv. Hayward) and apricot (Prunus armeniaca L. cv. CluthaGold). The method involves delivering a sharp puff of air onto a stationary fruit whilst recording the resulting surface deformation with a laser displacement sensor. At a 65-kPa maximum puff pressure the deformations on both kiwifruit and apricots ranged from 0.1 mm for hard fruit to about 1 mm for very soft. A fruit stiffness value (Epuff) was calculated from the maximum deformation and compared with penetrometer firmness (Fpen) on cool-stored kiwifruit and mixed maturity apricots. Two measurements were made on opposite sides of each fruit using each technique and were averaged before regression analysis. Reasonable regression results (R 0.80, s=2.1 N) were obtained between Fpen and Epuff on kiwifruit over the penetrometer firmness range 0–30 N. The relationship showed a trend of increasing scatter with increasing kiwifruit firmness. With apricots, over a greater penetrometer range (0–80 N), the relationship between Fpen and Epuff was best described by a simple power law regression (R 2 0.80, s=8.2 N). Both sets of fruit results suggest the laser air-puff method is only suitable for coarse screening of fruit into two penetrometer firmness classes. Improved correlations may be possible by using higher puff pressures and/or more measurements per fruit. © 2000 Elsevier Science B.V. All rights reserved.