Development of a handheld precision penetrometer system for fruit firmness measurement

A novel design for a handheld precision penetrometer with control of probe speed, angle and depth of penetration was developed and used to measure the firmness of rose apple and jujube samples. Its performance was compared with two traditional handheld penetrometers used in the produce industry, one with an analog force gauge and the other with a digital force gauge. The prototype instrument had penetration speeds of 4.49, 3.23 and 2.10 mm s−1 when the force resisted at the probe tip were 0, 50 and 100 N, respectively. A performance study involving four human operators showed the prototype instrument performance was superior to either of the traditional penetrometers in terms of measurement precision. For rose apple samples, the range of error in firmness value were 0-9.81 N, 0-7.10 N and 0-1.60 N for traditional analog, manual digital and the prototype instrument, respectively. For jujube samples, the range of error in firmness value were 0-9.81 N, 0.20-10.00 N and 0-2.60 N for traditional analog, manual digital and the prototype instrument, respectively. Comparison in firmness value among four operators by statistical analysis with a paired sample t-test found that the effect of operator on firmness value was significant when measuring firmness on rose apple samples by traditional analog and manual digital instruments. There was no significant influence of operator when measuring firmness on rose apple and jujube samples by the prototype instrument.