Texture Testing for the Fruits and Vegetables Sector
Texture is a critical quality attribute to all fruits and vegetables, whether it is to assess ripeness or functional performance in their processed forms.
Evaluating the texture of fruits and vegetables, whether fresh or after post-harvest treatments and processing, shows there is a clear link between the anticipated texture of these food products and their quality.
- Ripe, juicy tomatoes
- Crunchy apples
- Succulent oranges
These are all now commonly associated as the norm for the acceptable state, feel and taste of these foods. If a strawberry is too soft, it is no longer desirable, therefore sensory characteristics must be continually evaluated to monitor quality standards in order to, for example, establish the optimum time to pick the best crop and produce a consistently good finished product.
Texture Measurement Solution
Texture measurement provides the solution by putting values to traditionally subjective characteristics of foods.
Using mechanical means, through the use of an FTC texture analyzer and appropriate fixture, it is possible to imitate the actions undertaken by a person when consuming the product to measure the following attributes;
- Crispness
- Hardness
- Juiciness
- Toughness
- Mealiness
- Fibrousness
These characteristics can be measured and compared throughout production and processing to assess the changes in texture. Different varieties of the same type of fruit or vegetable, for example, pears, can be easily examined to determine differences in texture.
Acpplications for the Fruit & Vegetables sector
Finding the right test
Fruits and vegetables differ significantly in texture between one another, therefore a range of texture test techniques are available in which to accurately assess their characteristics;
- Back Extrusion
- Bulk Analysis
- Multiple Point Analysis
- Penetration
- Shearing
- Compression
- Breaking
Back Extrusion
Used for softer foods such as pastes and liquids, which can be tested in their own packaging.
Viscous liquids and semi-solid liquids are displaced in a controlled manner in order to assess characteristics such as flow, thinning and thickening, consistency, viscosity, adhesiveness and spreadability.
Application examples include;
- Assess pumpability of vegetable purees
- Optimize viscosity of fruit toppings
- Assess changes to texture of broccoli and cauliflower florets during low temperature blanching
Bulk Analysis
Where measurement of one sample is either not practical or would not adequately represent how the consumer handles the product, it is possible to assess the sample in bulk form.
The Kramer Shear Cell faithfully reproduces the actions of consumption by shearing, compressing and extruding the sample, measuring them together and providing increased reproducibility in a highly variable product.
Application examples include;
- Chopped tomato integrity test
- Bulk evaluation of cooked potato
- Measuring soft fruits, such as strawberries to predict final product integrity
- Batch optimization and oven design of roasted vegetables
Multiple Point Analysis
Used to test multiple points on one sample where texture and form may vary considerably from one area to the next to measure properties such as firmness, gel strength and maturity.
Application examples include;
- Measure set properties of fruit jams
- Skin toughness of cooked pulses
- Firmness of haricot beans post cooking
Penetration
Small cylinders, balls, needles and cones are used to penetrate into a samples surface imitating biting in the mouth. This evaluates the ripeness and cook quality of fruits and vegetables by determining their firmness.
Application examples include;
- Skin toughness of berries
- Hardness of cooked carrots
Shearing
Cross-sections of samples can be evaluated by slicing through them with blades and wires imitating the actions applied by the front incisor teeth. Attributes assessed include bite strength, cook quality, tenderness and toughness.
Depending on the blade geometry, many actions are performed on the sample, including shearing, tearing and compression. Product texture variations are measured by slicing through the whole sample.
Application examples include;
- Shear through apple slices to assess crispness as a measure of freshness
- Cut through broccoli to predict final cook quality
- Measure bite characteristics of bananas
- Cross-sectional changes in bite force along length of asparagus stem
- Firmness of potato tuber
Compression
Squashing solid and self-supporting samples enables a number of textural properties to be evaluated, including hardness, springiness and fracturability.
Juiciness is another common trait of fruits, which is a critical factor in determining its acceptance among consumers. This is effectively measured by compression using the FTC succulometer cell (432-255). The cell squeezes the juice from food to measure its succulence.
When using a compression probe, it is recommended that the probe has a greater surface area than that of the sample being tested.
Application examples include;
- Succulence of sweetcorn, oranges, apples etc
- Hardness of seeds
- Softening of cooked potato to assess suitability for mashing and puree production
Breaking
This test measures the fracture properties of brittle solids that have a bar type structure and is an ideal measure of crispness in fruits and vegetables. Supported at either end, a force is applied at the centre by a knife edge until failure occurs to ascertain break strength, or until deformation to a specified point is reached to measure flexure properties.
Application examples include;
- Measure flexure properties of asparagus to assess freshness throughout storage
- Test fracture of celery as a measure of freshness and suitable crop harvesting
