Testing fruits of non-homogenous nature or variable texture, such as water melons where there is a high seed content, is not only tricky by any puncture, shearing or compression method, but often results in low reproducibility and misleading data.
In any of these tests, the data may show wide variances between maximum and minimum force resistance, depending upon whether the probe or fixture meets with less or more seeds or variable texture when tested. By penetrating the product in several areas at the same time, the Multiple Puncture Probe produces an averaging effect and is therefore more representative.
Measuring Flesh firmness of non-homogeneous fruits
Using several testing pins, attached to the TA.XTplus Texture Analyser (as shown above), melons, for example, of different varieties, root stocks and post-harvest storage times can be compared. The testing method also offers flexibility. When forces are created above the capacity of the load cell being used in the TA.XTplus, the operator can adapt the test by removing pins and reducing the contact area, if necessary.
However, the more probes that are used in the test, the more reproducible the results. The central pins may, in the case of water melons, be removed so as to avoid the hard core which would otherwise give mis-representative results. The outer ring of pins are then ideally located as they can puncture the heart of the melon yet avoid the majority of the seeds.
Preparation would involve cutting the melon in half and removing the blossom end with a sharp knife to provide extra stability. The melon is then presented to the Texture Analyser and levelled if necessary to ensure a flat testing surface. The multi-penetration test is commenced and the area under the curve taken as average flesh firmness.
