For isolating food and plant volatiles

BUTTERY UNG Methods for Isolating Food and Plant Volatiles... 

Buttery, R. G. Ling, L. C. Methods for Isolating Food and Plant Volatiles. In Biotechnology for Improved Foods and Flavors Takeoka, G. R., Teranishi, R., Williams, R J., Kobayashi, A., Eds. ACS Symposium Series 637 American Chemical Society Washington, DC, 1996 pp 240—248. 

R. G. Buttery and L. C. Ling, Methods for isolating food and plant volatiles. Biotechnology for Improved Foods and Havors (G. R. Takeoka, R. Teranishi, P. J. Williams, and A. Kobayashi, eds.), American Chemical Society, Washington, DC, 1996, p. 240. 

This chapter discusses some more recent variations of methods for isolation of volatiles fiom food and plant materials. For particular problems there are advantages to each of the three main types of isolation methods, direct extraction, steam distillation and dynamic headspace. Direct solvent extraction is the only method which is reasonably efficient in isolating components of both high and low water solubility. Because food and plant volatiles are usually water soluble at their ppm concentrations their isolation by steam distillation does not fit the theory s required non-miscible conditions and this may be better considered a type of dynamic headspace isolation. By atkpting ideas fiom a recently published direct solvent extraction metiiod, which used excess sodiiun fate to bind all water in aqueous foods, the authors discovered an effective dynamic headspace meAod for isolating Furaneol and other water soluble volatiles. 

Extraction of Essential Oils from Plants. Essential oils are aromatic substances widely used in the perfume industry, the pharmaceutical sector, and the food and human nutrition field. They are mixtures of more than 200 compounds that can be grouped basically into two fractions a volatile fraction, which constitutes 90-95% of the whole oil, and a nonvolatile residue, which constitutes the remaining 5-10%. The isolation, concentration, and purification of essential oils have been important processes for many years, as a consequence of the widespread use of these compounds. The common methods used are mainly based on solvent extraction and steam distillation. SFE has been used for the extraction of essential oils from plants, in an attempt to avoid the drawbacks linked to conventional techniques (57). Such is the case with the extraction of flavor and fragrance compounds, such as those from rose (58), rosemary (59), peppermint (60), eucalyptus (61), and guajava (62). The on-line coupling of the extraction and separation ietermi-nation steps (by SFE-GC-FID) has been proposed successfully for the analysis of herbs (63) and for vetiver essential oil (64). 

Static headspace isolation normally involves taking a sample of the equilibrium headspace (a few ml) immediately above the food. This can be directly injected onto the GC column or more usually first concentrated on an adsorbent trap. The GC analysis of this small sample can give useful information such as the detection of rancidity in a food by measuring hexanal concentration (20). Static headspace can also be useful for the analysis of very volatile compounds such as acetaldehyde and dimethyl sulfide. However, in order to get enough material into the headspace, the sample frequently has to be heated to 60-100° C which, in some cases, could give an unrealistic picture of the volatiles of the food or plant material. Static headspace is a very rapid method, but it does not give a comprehensive analysis of the volatiles, and in the case of foods, may miss the most important. 

The phenylpropanoids rrans-anethole (61) and rran -cinnamaldehyde (62) are used as flavoring agents in foods in the United States and some other countries [20]. tranj-Cinnamaldehyde (62) Avas isolated from Cinnamomum osmophloeum Kanehira (Lauraceae) as a sweet principle, while tra/w-anethole (61) was isolated as the volatile oil constituent responsible for the sweet taste of several plant species, as listed in Table 1 [92]. These two compounds occur widely in the plant kingdom. Therefore, it is necessary to rule out their presence in any candidate sweet plant by a dereplication procedure in a natural product sweetener discovery program using gas chromatography-mass spectrometry (GC/MS) [46,47]. 

---