Chapter 14
Modeling Aroma Release from Foods Using Physicochemical Parameters Rob S. T. Linforth,Ε.N.Friel, and Andrew J. Taylor
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 24, 2016 | http://pubs.acs.org Publication Date: September 7, 2000 | doi: 10.1021/bk-2000-0763.ch014
Samworth Flavour Laboratory, Division of Food Sciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, United Kingdom
Models have been developed (based on physicochemical parameters) to predict the temporal changes of volatile concentration in breath from the nose when gelatin/sucrose gels were eaten. Breath volatile concentrations were determined experimentally, using the M S Nose™ and these values were correlated with physicochemical parameters of the volatiles using an empirical process contained in a chemical modeling program. The models predict both the maximum release intensity (mg/m ) and temporal aspects such as the time to maximum intensity and persistence. The physicochemical parameters used to generate the models were Log Ρ (the octanol water partition coefficient), Log p (vapor pressure), and the Hartree energy (the energy required to separate all of the electrons and nuclei of the molecule infinitely far apart), all of which can be estimated by calculation. A wide range of compounds with different functionalities were used in these experiments in order, to build a robust model capable of predicting release with good predictive power. 3
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One of the major research areas in flavor science is the understanding of how volatile flavor compounds are released and transported to the flavor sensors during the eating process. Release behavior in vivo depends both on the interactions of volatile compounds with the food matrix and the interactions that occur between volatiles and the lining of the mouth, throat, and nose. Some interactions affect all volatiles equally; other interactions depend on the specific physicochemical properties of the volatile molecules. The actual release of volatile compounds can be followed in vivo by monitoring the expired air from the nose of a person as they eat a food using the API-mass spectrometric interface, developed in our laboratory (7). This is now commercially available as the M S Nose™'. This system allows us to study the release of several
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© 2000 American Chemical Society
Roberts and Taylor; Flavor Release ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
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volatiles directly and simultaneously (2) and, from the data obtained, release curves for each volatile can be constructed. The principles of API-MS are discussed elsewhere in this book. Rather than just measure volatile release in vivo, it would be desirable to predict release based on the composition of the food sample and, for this, models are needed. There are many different approaches to model production for flavor release (3). One approach is to identify the mechanisms (melting, diffusion, etc.) involved in volatile release for a particular food system and develop appropriate models to describe the release behavior. These models are complex and involve consideration of many factors, such as the air-water partition coefficient, the octanol-water partition coefficient (Log P), surface area, temperature, as well as mass transfer coefficients for the movement of compounds from the matrix into the aqueous/saliva phase (4). Mechanistic models have been produced to describe release of volatile compounds from matrices such as boiled sweets (5) or from gelatin/sucrose gels of different compositions (6). Computer simulations have been created to predict the rate of loss of aroma compounds from chewing gum during eating (7) or the overall flavor release from food into the air phase (8). Model-mouth headspace systems have also been used to study volatile release and subsequently generated models to show how the matrix affects aroma release (9). For all these models, it is necessary to establish values for key parameters like vapor pressure, mass transfer in the liquid and gas phases, and change in surface area with time in-mouth. Although some values can be found in the literature, others have to be determined experimentally. There are currently no published models, that attempt to predict the changes in intensity of aroma compounds in the nose over the eating time course. Quantitative Structure Property Relationships (QSPR) can be used to construct models that relate the behavior of a compound (e.g. volatile release) to a range of physicochemical parameters (10) using statistical analysis. This is a different approach to the models described above, where mathematical equations are generated on the basis of defined mechanisms based on theoretical considerations (e.g. the mass transfer coefficient, sample melting point etc.). In QSPR, all of the physicochemical parameters used in the model can usually estimated by calculation, which avoid the need for further experimentation before a prediction can be made. QSPR's have been widely used in the pharmaceutical industry to optimize drug design, as synthesis and evaluation trials are expensive. They have also been used to produce models that describe the physical behavior of compounds such as the air-water partition coefficient (77). This paper presents models derived using a QSPR approach to aroma release from gelatin gels during eating.
Materials and Methods Gelatin gels were prepared by melting hydrated gelatin (bloom strength 250) in a water bath (60°C) before mixing it with a solution of sucrose and glucose (which had been boiled and cooled to
