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1、The electronic nose applied to dairy productsAbstractThe state-of-the-art and current trends in the development of “aroma” analysis with electronic noses are reviewed with special reference to applications to dairy-products. Some of the reported problems with electronic noses have recently been redu
2、ced, e.g. the correction/reduction of signal drift, the influence of humidity and temperature. New promising and reproducible sensor manufacturing techniques are being implemented, e.g. electro-spray for QMB sensor production. The development of more selective and sensitive sensors, especially of QM
3、B and conducting polymer (CP) type, should improve their applicability. Interesting novel sampling techniques, such as SPME or SBSE,offer more possibilities for the analysis of semi-volatile compounds which are generally more odoriferous. However, standard calibration procedures and reference materi
4、als are not yet available. Although they are normally less powerful than human noses, electronic noses offer some significant advantages in the analysis of volatiles, for example, in instrumental classifications based on hedonic or sensory analyses and in potentially automated on-line monitoring of
5、volatiles. Several groups have explored the application of different electronic noses in the investigation of various aspects of dairy products. The present review includes as examples the evaluation of Swiss and Cheddar cheese aroma, the assessment of the ripening of Pecorino Toscano cheese (ewes),
6、 the detection of mould in Parmesan cheese, the classification of milk by trademark, by fat level and by preservation process, the classification and the quantification of off-flavours in milk, the evaluation of Maillard reactions during heating processes in block-milk, as well as the identification
7、 of single strains of disinfectantresistant bacteria in mixed cultures in milk.Since the first applications of solid state gas sensors in arrays, some twenty years ago, “electronic noses” have undergone a great deal of development. Around a thousand articles on this subject have been published over
8、the last 4 years, mainly in relation to the food and beverage industry1, but also concerning environmental, agricultural, and medical topics, in the automotive industry, etc. However, the number of studies dedicated to dairy products is still very limited, probably due to the complexity of their mat
9、rices.The aim of the present paper is to review recent exploratory studies of electronic noses applied to dairy products, in order to perceive the prospects and trends in this field.Traditionally in the food industry, monitoring of products in terms of quality and control of production processes (e.
10、g.mixing, heating, drying, cooking, baking, extruding, fermenting,etc.) are performed via physicochemical measurements,i.e. pH-value, colour, concentration of given chemi-cals or biomolecules generally determined by spectroscopy(e.g. FTIR, NIR, UV-Vis, etc.) 2 and this despite the extreme importance
11、 of aroma as an indicator of quality and product conformity. This was mainly due to the lack of reliable odour assessing instruments and the practical impossibility of employing sensory panels to the continuous monitoring of aroma. Electronic noses have the potential to fulfil this task. Compared to
12、 sensory panels the main advantage of electronic noses is that once calibrated they can perform odour assessment on a continuous basis with a minimal cost. Furthermore, once established this technique does not require trained personnel like a sensory panel does, is not subject to individual breakdow
13、n or variation of sensitivity3, is not overloaded under normal operation and takes comparatively very little time.Before the advent of electronic noses the only possible instrumental analysis of “aroma” (the mixture of volatiles present in the headspace of a product) was the identification/quantific
14、ation of individual chemical compounds, after a separation step (e.g. GCMS, GCFID, etc.). However,the relationship between this sequential analysis and the perception of the global aroma of a product is not easily established since the rules governing the combination of individual chemical compounds
15、 in the generation of odours are not yet fully understood 46.It should be kept in mind that instrumental analyses,whether classical such as GCMS, etc. or by electronic nose are performed not only on odorous volatiles but also on non-odorous compounds occurring in the headspace. This can be interesti
16、ng when analysing hazardous non-odorous compounds (e.g. carcinogens, toxins, solvents) but also implies that instrumentally performed classifications/analyses might not be based on aroma relevant molecules. Furthermore,hedonic assessment can not be performed by any instrument. Classification models have to be defined based on the results of sensory panels prior to performing analyses with odour significance.2. The electronic nose conceptThe name “electronic nose” co
