ARS | Publication request: Practical implications of probe- and sample-related variables in puncture testing of clingstone peaches

Submitted to: International Congress on Engineering and Food
Publication Type: Proceedings
Publication Acceptance Date: December 20, 2010
Publication Date: N/A

Interpretive Summary: Fruit processors have long used hand-held devices to test the firmness of fruit in the field. One such device, the Magness-Taylor penetrometer, has a slightly curved tip that is 7.9 mm in diameter. A typical probe used in the laboratory for instrumented firmness measurement is a flat-tipped cylinder. The purpose of this study was to compare the firmness and energy readings for clingstone peaches measured with a Magness-Taylor probe and two flat-tipped cylindrical probes, all mounted on a laboratory instrument. Puncture position, probe approach, and fruit configuration (whole fruit vs. half fruit) were examined, in addition to probe type. For both peak firmness and peak energy, the Magness-Taylor probe gave similar results to those of a flat-tipped probe of similar diameter. In general, probe position and approach did not significantly affect either metric. While peak firmness was not affected by fruit configuration, half-fruit exhibited significantly higher peak energy than did whole-fruit. The presumed cause of this difference was that the half-peaches deformed outward before the probe punctured the flesh. The conclusion of this study was that processors may use either the Magness-Taylor probe or a flat-tipped cylindrical probe of comparable diameter and obtain statistically similar results. Probe position, probe approach, and fruit configuration are also not significant sources of variation for the measurement of peak firmness in clingstone peaches. However, peak energy differs between whole-peaches and half-peaches if half-peaches are not securely affixed to the platform and depends on probe approach if a flat-tip probe is used.

Technical Abstract: Fruit processors want to correlate processing-relevant field measurements (such as the Magness-Taylor penetrometer test) with similar measurements (such as the puncture test) obtained on laboratory instruments. The objective of this work was to compare a Magness-Taylor probe to standard, flat-tipped puncture probes by investigating the effects of four controlled variables (probe type, probe position, fruit configuration, and probe approach) on two response variables (peak firmness and peak energy) relevant to the assessment of peach (Prunus persica) processing quality. The probe types used were 3 mm diameter cylindrical flat-tip, 8 mm diameter cylindrical flat-tip, and 7.9 mm diameter Magness-Taylor-tip. The probe positions were the corners of an equilateral triangle centered at the cheek of the fruit; fruit configuration was either whole-fruit or half-fruit. For whole peaches, probe approach was varied between perpendicular-to-the-fruit and perpendicular-to-the-platform (that is, oblique to the fruit due to the fruit’s curvature). For both metrics (peak firmness and peak energy), the Magness-Taylor-tip probe was not significantly different (a = 0.05) from the 8 mm diameter cylindrical flat-tip probe. In general, probe position and approach did not significantly affect either metric. While peak firmness was not affected by fruit configuration, half-fruit exhibited significantly higher peak energy than did whole-fruit. The presumed cause of this difference was that the half-peaches deformed laterally before the probe punctured the flesh. For laboratory measurement of puncture peak firmness of clingstone peaches, processors may use either the Magness-Taylor probe or a flat-tipped cylindrical probe of comparable diameter and obtain statistically similar results. Probe position, probe approach, and fruit configuration are also not significant sources of variation for peak firmness. However, peak energy differs between whole-peaches and half-peaches if half-peaches are not securely affixed to the platform and depends on probe approach if a flat-tip probe is used.