Pears
Application
Simple penetration test of pears.
Test Objective
To quantify the difference between ripe and unripe pears through implementation of simple penetration principles.
Background
Pressure tests have traditionally been applied in the quantification of textural properties of pears. Correlation of instrumental mechanical measures with perceived sensory characteristics provides an objective method of quantifying subjective parameters. Quantification of textural properties is beneficial in:
- Determining optimum point of harvest
- Controlled ripening and storage
- Optimization of process operations (e.g., freezing, blanching, cooking, etc.)
- Indicator of potential mechanical injury (bruising)
- Control of raw materials through application of objective quality measures
- Conformance to customer requirements and supply of correctly ripened products
- Quantification of product shelf-life in relation to ripening
Method
Samples were taken from modified atmosphere packaging on day of purchase at ambient conditions. A small section of each fruit was removed (as in illustration) to give stable test surface through which to penetrate.
Reading
)
Click to enlarge
Parameters
| Hardness: | Peak positive value within first compression cycle. Direct indication of skin strength. Skin yields and ruptures prior to inner flesh penetration. |
| Skin Modulus: | Curve slope or gradient during penetration. Indicative of flesh rigidity and cell turgidity. |
| Work To Rupture Skin: | Area of graph. |
| Mean Of Internal Peaks: | Mean of positive peaks after skin rupture; indicative of internal cell structure. |
| Total Positive Area: | Work to complete penetration cycle, including that to initially rupture skin (e.g., sample consistency). |
| Adhesiveness: | Total negative area, indicative of work required to pull the probe from the sample. |
| Adhesive Force: | Peak negative force caused by “pinching” and suction of fleshy sample. |
Results
| Ripe | Unripe | |
| Hardness (Skin) (g): | 306 | 1045 |
| Skin Modulus (g/s): | 257.1 | 641.3 |
| Work To Rupture Skin (gs): | 186.2 | 866.2 |
| Mean Of Internal Peaks (g): | 220.8 | 573.2 |
| Total Positive Area (gs): | 3748.6 | 11072.2 |
| Adhesiveness (gs): | -121.8 | -386.1 |
| Adhesive Force (g): | -87 | -327 |
Discussion
The unripe pear is much harder than the ripe pear; it exhibits greater resistance to penetration by the 2mm Ř probe. The inner flesh of the ripe pear is much softer than the unripe pear, as shown by the mean of selected peaks, after rupture or yield of the skin.
Conclusion
This simple test clearly shows differences in pear ripeness.
Table 1: LFRA Texture Analyzer Test Settings
| Mode: | Measure force in compression |
| Plot: | Peak |
| Speed: | 0.5mm/s |
| Distance: | 10 |
| Option: | Normal |
| Trigger: | Auto 4g Trigger |
| Probe: 2mm Ř stainless steel probe, TA 39 | |
