Fruit and vegetable

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.

Test methods for the fruit and vegetable sector

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. Common consumer sensory texture descriptions, especially fresh produce, are:

• 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. Pea texture for harvest is a specialised field, which requires a tenderometer.

Bulk analysis

• Chopped tomato integrity test
• Bulk evaluation of cooked potato, canned mushrooms
• Measuring soft fruits, such as strawberries to predict final product integrity
• Batch optimization and oven design of roasted vegetables
• Pea maturity using a tenderometer

Compression

Deformation tests using compression platens (ideally larger than the deformed sample) are useful for assessing the integrity of cooked potatoes. Squashing solid and self-supporting samples enables a number of textural properties to be evaluated, including hardness, springiness and fracturability.

• Succulence of sweetcorn, oranges, apples etc., using the succulometer
• Hardness of seeds
• Softening of cooked potato to assess suitability for mashing and puree production
• Avocado firmness for freshness grading

Extrusion (back extrusion)

Use back extrusion to measure flow and spoonability of thick purees and fruit pulps.

• Assess pumpability of vegetable purees
• Optimize the texture of fruit toppings: flow, firmness and consistency

Penetration and puncture

Small cylinders, balls, needles and cones are used to penetrate into a sample’s surface imitating biting in the mouth. This evaluates the ripeness and cook quality of fruits and vegetables by determining their firmness.

• Apple ripeness by Magness-Taylor penetrometry method
• Skin toughness of berries
• Hardness of cooked carrots
• Onion bulb puncture test, by spherical probe

Multiple point penetration

Multiple point analysis of jam allows for different particulates when measuring set firmness. 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

Shear

• Shearing 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
• Assess changes to texture of broccoli and cauliflower florets during low temperature blanchings

Snap, bend and break

Measuring flexure properties using a three point bend determines freshness and crispness of vegetables, such as asparagus.

• Measure flexure properties of asparagus to assess freshness throughout storage
• Test fracture of celery as a measure of freshness and suitable crop harvesting