A low-cost handheld apparatus for inspection of peach firmness by sensing fruit resistance

Abstract

The determination of peach firmness plays a significant role in evaluating the harvest time, ripeness, and shelf life, which guide transportation and distribution. Traditionally, a handheld penetrometer is used to determine objectively the firmness of peaches by measuring the maximum force required by a probe to penetrate a sample to a prespecified depth. However, the measurement results are affected by the operator. To solve this problem, many apparatuses have been developed. But they are either not portable enough for on-site usage or expensive. Therefore, a low-cost handheld prototype apparatus was developed for measuring peach firmness by sensing the resistance of fruit. With a designed mechanical structure, this prototype can minimize the impact of operators. Compared with penetrometers, this prototype caused just a slight concavity. A series of experiments were conducted to calibrate and evaluate this prototype. First, the prototype was calibrated by compressing its probe with a texture analyzer, and then, its precision was verified by measuring four Shore A hardness blocks. The results showed that the readings of the prototype were linearly correlated with the force applied by the texture analyzer with R2 = 0.9998 (p < 0.01) and could be converted to force values by the regression equation. In addition, the repeatability index (CVp) and the reproducibility index (CVd) of the prototype were all less than 0.5%, which indicated that the prototype had good repeatability and reproducibility. Finally, the prototype was validated by measuring the firmness of 210 peaches during 14 days after picking, and its readings were compared with two reference parameters extracted from the force–displacement curve recorded by the texture analyzer. The results showed that the readings of the prototype were significantly logarithmically correlated with the reference parameters, especially the initial slope with R2 = 0.8971 (p < 0.01), which indicated that the developed apparatus could detect peach firmness.