Fast method for testing the sweetness of fruit

17 Jun 2002

A faster way of determining the sweetness of fruit that could save the food industry money has been developed at Central Queensland University in Australia. A prototype system is currently sorting melons for one of the country's largest fresh-food suppliers.

The work, published this week in the Institute of Physics' journal Measurement Science and Technology, could lead the way to the replacement of current techniques where light is shone at a the fruit sample as it passes along a conveyor belt and a probe measures the light that passes through the sample and into the detector. This gives a measurement of the quality of the flesh of the fruit.

However, some of the light can be reflected by the surface of the fruit, causing unreliable results. The only way to exclude this is by physically creating optical barriers to prevent the extra light entering the detector. Unfortunately these barriers make contact with the fruit, slowing down the detection process.

The new technique uses a quartz-tungsten-halogen light source to illuminate the fruit and an acceptance probe to measure the incoming light. The probe houses a mirror to direct incoming light to the optical fiber of a sensor. The alignment of light source and probe means that any unwanted reflected light does not fall within the angle of acceptance of the fiber optic and is not transmitted to the detector. The researchers say that this is the first non-contact way of assessing the quality of fruit and their results show that this process is as accurate as any contact design currently in use.

Colin Greenshill said: "Current techniques for classifying fruit that need to make contact with the sample slow the whole process down. The rapid sorting capability of the new method can double the number of fruit being tested each second."