An Automatic Handheld Device for Firmness Measurement of Fruit with Edible Peel Based on Resistance Sensing: A Case Study of Peaches

HighlightsA handheld device was developed for automatic on-site measurement of fruit firmness.The prototype device achieved better performance than a typical commercial penetrometer.Two commonly used firmness-related parameters could be predicted based on the prototype readings.The distribution and changes of firmness could be visualized based on 3D models of the prototype readings.Abstract. Firmness is an important indicator of fruit quality. The devices for on-site fruit firmness measurement need to be portable, low-cost, lightweight, reliable, and flexible. Existing portable devices can provide firmness-related parameters, but their measurement results cannot be converted to each other. Their measurement results are also susceptible to operator error due to the manual measurement process. To solve this problem, a prototype handheld device was developed based on sensing fruit resistance to achieve automatic on-site firmness measurement of fruit with edible peel and provide commonly used firmness-related parameters. The prototype’s precision was verified by analyzing the repeatability and reproducibility of the measurement results with four Shore hardness blocks. The relative standard deviations (RSDs) of the results obtained by the same operator were less than 0.61%, and there was no significant difference among the results obtained by different operators (p < 0.05), which indicated that the prototype could provide reliable measurement results. A case study of peaches was performed, and the results showed that (1) the prototype had better performance than a commercial penetrometer, (2) two commonly used firmness-related parameters could be predicted based on regression models between a texture analyzer and the prototype readings (R2P = 0.908 and RMSEP = 4.191 N for maximum force; R2P = 0.923 and RMSEP = 1.613 N mm-1 for initial slope), (3) changes in the prototype readings for peaches during growth corresponded with the growth characteristics, and (4) the distribution and changes of peach firmness over time could be visualized based on 3D models of the prototype readings. Keywords: Automatic, Fruit firmness, Handheld device, High precision, Peach.