Sensory methods analytical

The combination of sensory evaluation with analytical approaches is required to identify perceptible changes and to identify the potential chemical changes that may be causing the sensory effect. Low concentrations of compounds responsible for changes in food characteristics may not be detectable by even the most sensitive analytical methods but, in combination with appropriately applied sensory methods, the clues provided by both techniques may help identify the problem, provide indications to the cause, and suggest clues for the source of the problem. 

Off-flavors in food packages are not only a legal but also often an economic problem, when market recalls have to be made. This chapter describes the different kinds, origins and development of off-flavors and deals with solutions for off-flavor problems arising from interactions between packaging and food. The text covers the sensory and analytical methods used for off-flavor-investigations and describes several case studies. 

In this process the acetic fermentation takes place in a more or less open container (usually a vinegar vat in the cellar). The primary product stays in the open container until acetic fermentation starts, i.e. a mother of vinegar, or film consisting of vinegar bacteria, moulds and slime fungi, is formed. In this method it is not possible to control the fermentation or the temperature. The quality of the vinegar produced does not always meet current sensory and analytical requirements. 

Human olfaction measurement considers the odour as a global concept and provides the true dimensions of the human perception. Yet, physiological differences in the smelling of various people often lead to subjective results with large uncertainties. Analytical techniques identify the various volatile compounds involved in the odour and give their chemical concentration. They have better scientific standing than sensory methods. However, the chemical composition of the gas mixture doesn t represent the odour perception. 

Flavour can be analyzed either using sensory methods or with analytical instruments such as gas-chromatography (GC). Separating and analyzing a mixture of volatile compounds in foods without decomposition is an important feature of this latter technique. As most flavour compounds in foods are volatile, simplified GC methods may offer an appropriate technique for the separation and characterisation of volatiles in different food matrices. 

The objective of modern flavor analysis is to qualitatively and quantitatively determine the flavor profile imparted by nature and thus to identify those substances responsible for the flavor of a food. In recent years, a combination of sensory methods and instrumental analytical procedures has made a major contribution toward reaching this objective. Thanks in particular to the concept of odor activity value, which has been steadily refined at the German Research Institute for Food Chemistry in Garching (Technical University of Munich) during the past decade, it is today possible to make well-founded statements about the odor activity of volatile flavor compounds in foods (112-116). With the aid of the odor activity value concept, it is possible to identify those components of the extremely complicated flavor profiles that are of key importance for the specific flavor of a food. 

In recent studies, potent aroma compounds have been identified using various gas chromatography-olfactometry (GCO) techniques, such as Charm Analysis and aroma extract dilution analysis (AEDA) (7,8). The flavor compounds that are identified by these methods are significant contributors to the sensory profile. In some cases, these sensory-directed analytical techniques have enabled the discovery of new character impact compounds. However, in other instances, key aroma chemicals have been identified that, while potent and significant to flavor, do not impart character impact. For example, in dairy products, chocolate, and kiwifmit, these flavor types appear to be produced by a complex blend of noncharacterizing key aroma compounds. 

The development of precise and reproducible methods of sensory analysis is prerequisite to the determination of what causes flavor, or the study of flavor chemistry. Knowing what chemical compounds are responsible for flavor allows the development of analytical techniques using chemistry rather than human subjects to characterize flavor (38,39). Routine analysis in most food production for the quaUty control of flavor is rare (40). Once standards for each flavor quaUty have been synthesized or isolated, they can also be used to train people to do more rigorous descriptive analyses. 

This example demonstrates the most challenging problem of flavor chemistry, ie, each flavor problem may require its own analytical approach however, a sensory analysis is always required. The remaining unknown odorants demand the most sensitive and selective techniques, and methods of concentration and isolation that preserve the sensory properties of complex and often dehcate flavors. Furthermore, some of the subtle odors in one system will be first identified in very different systems, like o-amino acetophenone in weasels and fox grapes. 

Liquid membrane type ion-seleetive electrodes (ISEs) provide one of the most versatile sensing methods because it is possible to customize the sensory elements to suit the structure of the analyte. A wealth of different synthetic and natural ionophores has been developed, in the past 30 years, for use in liquid membrane type ISEs for various inorganic and organic ions [1], In extensive studies [2-4], the response mechanism of these ISEs has been interpreted in terms of thermodynamics and kinetics. However, there have been few achievements in the characterization of the processes occurring at the surface of ISEs at molecular level. 

Coupled with successful primary prevention are ongoing monitoring programs for the organisms and their toxins, both in the environment and in the seafood. The molluscan shellfish (i.e., oysters, clams, mussels, and scallops) are the species associated with shellfish poisonings. The absence of characteristics such as abnormal taste, smell, or appearance precludes sensory inspection for these toxins. Instead, ensuring seafood safety relies on testing seawater and the seafood itself The assays used to detect toxins in seafood have evolved as analytic methods and instrumentation have improved. The American Public... 

Several analytical devices have found application as test sensors or, more generally, as electronic tongues for characterizing foods or food ingredients, being able to provide information related to the human sensorial perception or to other important features. There are some examples of electronic tongues based on optical techniques as well as on mass measurements, but the analytical methods that have been most widely exploited in this field are, without any doubt, the electrochemical ones, as shown in Fig. 2.6. 

Volume 16 Multivariate Analysis of Data in Sensory Science, edited by T. Naes and E. Risvik Volume 17 Data Analysis for Hyphenated Techniques, by E.J. Karjalainen and U.P. Karjalainen Volume 18 Signal Treatment and Signal Analysis in NMR, edited by D.N. Rutledge Volume 19 Robustness of Analytical Chemical Methods and Pharmaceutical Technological Products, edited by M.M.W.B. Hendriks, J.H. de Boer and A.K. Smilde... 

In addition to sensory and physical properties, the content of certain typical components is determined. Problems concerning the natural, botanical, and geographical origins of these products are also solved by using modern chromatographic methods such as enantiomer separations [843-843c], and spectroscopic analytical techniques such as isotope ratio mass spectrometry (IRMS) [844-844b],... 

Supported by the overall development in all fields of analysis during the past few decades, a precise analytical methodology has been developed for the different aspects of quality control, comprising physicochemical, biotechnological, sensory and microbiological methods. In order to meet the sense of the quality control system and by that the customers requirements, all methods applied have to be validated by adequate quality assurance tools. 

In order to set up an analytical method based on factor scores or analytical deviation in a Q.A. environment, several precautions would need to be followed. For instance, changes in raw materials would need to be monitored and either new reference materials used or factor analyses repeated. Changes in chromatographic conditions would require a system which allowed constant updating to avoid shift in factor scores. While the peak ratio technique is the simpler of the two, factor scores provide a more sophisticated method which can be used where overlap of components does not lend itself to the simpler methods. These two techniques for deriving the concentrations of the multicomponents in a mixture were shown to predict sensory response when one multicomponent was altered. However it also could be used in a multidimensional formula to predict response when more than one multicomponent has been altered. 

---