Electronic noses, sophisticated sensors that create digital fingerprints of smells, are being used by an increasing number of industries for quality control and product development. Food manufacturers may now be about to follow suit.

One of the most important objectives of food production is to achieve a uniform, high quality of both raw materials and the final product. A particular concern for fruit processors is the systematic determination of fruit ripeness under harvest and post-harvest conditions, because variability in ripeness is perceived by consumers as a lack of quality. Engineers have recently devised an "electronic nose" that will help both the fruit processors, and ordinary shoppers, solve the perennial problem of how to determine the ripeness of fruit consistently.

Unlike most of the traditional methods that assess fruit ripeness by testing a piece of fruit to destruction, the electronic nose calculates the exact ripeness of the fruit by its smell. Once it has been 'trained' on a particular fruit it does not require a skilled operator and can obtain the results in a few seconds with over 92% accuracy.

Of all the human senses, smell has always been the most arbitrary to define. Understanding how the sense of smell functions has long been the goal of researchers. The odour of a food comprises many chemical substances that give it its unique quality and character. The ability to reliably measure and identify optimal flavour development and constant taste characteristics is therefore crucial in the development of many products. Traditionally, this difficult task has been the main prerogative of sensory panels, people whose individual assessments will always include personal appreciation. Analytical techniques are sometimes used but data is often difficult to correlate with sensory information and is costly to produce.

Measurement by the electronic nose is by contrast objective, repeatable, highly accurate and relatively cheap. Interpretation is simple, quick, and in real-time. Like the human sense of smell, the electronic nose learns by experience and improves the more it is used. It is designed to analyse, recognise, and identify volatile chemicals at low (parts per billion) levels. The technology is based on the absorption and desorption (passing through) of volatile chemicals onto an array of sensors, which exhibit specific changes in electrical resistance, measurable across each sensor element, on exposure to different odours and aromas.

Work in this area has concentrated on the ripeness of bananas and apples, but the technology can easily be applied to most other fruits. It has also been used to test the quality of coffee, beer and wine. This could be just a scent of things to come.

FOOD TODAY 09/1999