Electronic nose can select produce with appealing aromas

In order to overcome these fluctuations, researchers from the Agro-Food Quality Improvement Group at the Universitat Jaume I (UJI) have developed a statistical methodology which enables the aromatic characteristics of different samples of a product to be compared efficiently, so that the best quality items can be selected.

To date the samples analysed, both on the day and between days, underwent a series of fluctuations because "the environment, laboratory temperature, humidity, and so on exert a significant influence, which means that to ensure the evaluations are useful an extensive amount of correction work has to have been carried out through a methodology that can be transferred to other teams and products," explains Salvador Roselló, a researcher from the UJI.

This methodology, which corrects the fluctuations in the analyses on the day and between days, is based on Mercedes Valcárcel's thesis, entitled "Optimización del proceso de evaluación y selección de germoplasma de tomate por características de calidad organoléptica: uso de tecnología NIR y sensores electrónicos" (Optimization of the process of evaluating and selecting tomato germplasm according to organoleptic quality characteristics: use of NIR technology and electronic sensors).

The electronic smelling system is an instrument equipped with chemical sensors and a chemometric program for pattern recognition, which is able to recognise and compare individual or complex odours. Like the human olfactory system, its purpose is to relate the perceived aroma with a response that, after being stored in a memory unit, could serve as a model for subsequent analyses. Electronic noses have found one of their natural areas of application in the agro-food industry.

The electronic nose enables a large number of samples to be analysed while maintaining the overall aromatic impression. Until now, the two systems commonly used to analyse samples have been, as Roselló explained, "on the one hand, a tasting panel consisting of experts who provide information that is valuable but which is of limited use and very expensive, as only a few tastings can be made each day. The other system involves chemical analysis, via a gas-mass spectrometer, which provides information on all the volatile compounds in a product so that you can compare between variables. However, this information is too abstract and the global evaluation is lost."

The electronic nose takes interesting features from these two systems and tries to avoid some of their problems. "In an improvement programme, if you want to select a specific variety, sometimes you have hundreds or thousands of samples, because you're selecting a segregating generation, where there are quite different individuals, and what you really want is to select the best ones. This therefore completely rules out the use of a tasting panel. Analytic selection gives more information, but the overall impression is lost," explains the researcher. And as an example he points out that "in the case of tomatoes, there are more than 40 aromas involved but the number does not matter: the important thing is that as a whole they are perceived to be appropriate.

Another advantage of using this equipment is that samples can be frozen and evaluated gradually so that "in a period of some months, you may have evaluated significant numbers of samples." The research group at the UJI is applying the possibilities offered by the electronic nose in studies to improve varieties of tomatoes. "We also have experience in research with melons, so this experience would be easy to extrapolate to tomatoes. To work with other products, we would have to adjust the parameters the equipment works with," states Roselló. The Universitat Jaume I is working at present with several tomato and melon companies.

The electronic nose is particularly useful, as Roselló remarked, for seed companies, which need to select their plant material and to offer a differentiated product, and for this reason they devote significant amounts of resources to R&D. It could also be particularly useful to improve the quality control systems of food manufacturing firms.

All the electronic nose systems that currently exist on the market consist of three distinct parts. The first one involves taking the sample. Given the volatility of the substances involved, this process is based on the technique of static headspace. The volatile compounds, concentrated by heating in the steam phase which is on the sample (liquid or solid), are introduced into the sensor system that measures the different physical and chemical properties of the components of the aroma. It then converts the smell into a measurable signal which is processed by a computer by means of chemometric techniques and the results are plotted on a chart that represents the fingerprint of this odour. Thus, taking the sample, the set of sensors and the data processing system are the essential parts of any commercial electronic nose.