PTR-MS in the Food Sciences

Volatile compounds play a fundamental role in food seience and technology. In part, this is because they are released when foods and drinks are consumed, and are hence involved in aroma and flavour which are intimately linked to our enjoyment, palatability and perception of food. Aroma volatiles that reach the olfactory epithelium, via orthonasal and retronasal pathways, play not only a major role in our enjoyment of food (and drink), but also allow us to assess food quality or to detect subtle changes in food products as a result of modifications in ingredients and production. Volatile organic compounds (VOCs) are also emitted directly from food which can, for example, give us information about ripening processes (e.g. cheese or fruits) and the effects of storage. 

Proton Transfer Reaction Mass Spectrometry Principles and Applications, First Edition. Andrew M. Ellis and Christopher A. Mayhew. 2014 Andrew M. Ellis and Christopher A. Mayhew. Published 2014 by John Wiley Sons, Ltd. 

---

Even with this simplified instrument, PTR-MS/GC-MS systems are still not in regular use, possibly because the real advantage of PTR-MS in the Food Sciences is not necessarily in the identification of the VOCs but in its real-time rapid monitoring and fingerprinting capabilities. The latter s capability can be used for fast classification of foods (e.g. geographical origin) or for determining food quality and this is the subject of the next section. 

PTR-MS has been applied to monitor emission of VOCs in the field of food research. The potential utility of PTR-MS in food science was first recognized by its initiating research team in Innsbruck. Now there are many investigations on the flavor studies and on the assessment of food quality. 

PTR-MS has become a remarkably versatile tool, with applications in many areas of science and technology. A review of the research literature at the time of writing indicates that approximately 50% of all reported activities are based on studying VOCs (anthropogenic and biogenic) in the environment, and in particular for atmospheric science. Approximately 30% of publications are based in the area of food science/technology while another major field of application is to be found in the health sciences, representing approximately 15%... 

The second part of the book, which spans Chapters 5-9, turns its attention to some of the many applications of PTR-MS. Here we want to demonstrate the scope and benefits, as well as the limitations, of PTR-MS. Our aim here has been to give a thorough but not exhaustive coverage of applied PTR-MS. We particularly want to try and show that PTR-MS, while already in widespread use, is rapidly finding new avenues where it can be applied. Four key areas of application will be described, namely environmental science, topics associated with food/drinks, medicine and homeland security, and each of these receives a dedicated chapter (Chapters 5-8). A short chapter (Chapter 9) will also deal with the applications of PTR-MS in liquid analysis. Chapters 5-9 build upon the material presented in Chapters 1-4 and are essentially self-contained reviews of the specific topics mentioned above. Consequently, the reader can dip into those that are of particular interest to him/her and if desired can safely ignore those of more peripheral interest. 

Besides good sensitivity, the MI-PTR-MS also has a wide linear dynamic range for all the VOCs analyzed in water and seawater. The data in Table 28.2 illustrate a linear response of up to four orders of magnitude, suggesting that the MI-PTR-MS can quantify VOCs with various concentrations dissolved in water. However, as to MI-PTR-MS technique, compared with direct inlet PTR-MS as used in atmospheric monitoring and food science, its deficiency is a much slower response time even up to several minutes. 

---