Destructive quality measurements
Different methods for analyses of fruit and vegetable quality exists. Well-known measurement methods are measurement of soluble solids content (SSC) after juicing and measurement of firmness with a penetrometer. These methods are easy to perform under the condition that the right protocol is followed.
Unfortunately these mentioned methods are destructive for the fresh product. Consequently only a sample of produce can be measured. It is therefore very important that the sample is representative of the whole batch.
Non-destructive quality measurements
Non-destructive quality measurements of fruit and vegetables can be helpful to measure external and internal properties. It has the great advantage over destructive measurements that products can still be sold after inspection. In this way, it facilitates the grading of products based on their size, shape, maturity or ripeness.
Among the techniques used are vision systems and near infrared spectroscopy (NIR). In addition to NIR devices in sorting lines, several hand-held NIR devices are available. Handheld devices can also be used in the field to measure fruit maturity. A very interesting development is NIR hyperspectral imaging which provides spectral data as a set of images.
Size and shape measurements
Measure Soluble Solids Content
Titratable acid measurements
Measure the % dry matter
Measuring the sensory quality
Determining disorders and diseases
How to measure fruit firmness with an analogue penetrometer mounted on a drill stand
Choose the right probe size. Photo from WUR
Step 1: Choose the right probeDiameter 8 mm is commonly used for pear, plum and kiwi. Diameter 11 mm is commonly used for apple.
Peel the skin before the measurement. Photo from WUR
Step 2: Peel the skinThe skin should be peeled off such that a skinless area larger than the diameter of the probe is created.
Hold the fruit under the probe. Photo from WUR
Step 3: Stabilise the fruitHold the fruit stably on a hard surface under the probe.
Apply a constant force. Photo from WUR
Step 4: Apply a constant forceA constant equal force shall be applied. Make sure that you do not go too fast or too slow. Doing a proper measurement takes practice.
The probe should enter the fruit until the marking. Photo from WUR
Step 5: Penetrate deep enoughThe probe must penetrate the fruit until the circular line on the probe is reached. Not too shallow, not too deep.