Natural flavourings from green chemistry for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 268

This technique works well when there is suffi cient water present such as in
fresh foliage or fl owers, but does require dried spices or berries to be pre-hydrated.
Recent studies (Lucchesi et al. 2004b; Perino-Issartier et al. 2010) have
demonstrated that the essential oils from rehydrated berries and dry spices can be
successfully isolated using microwave-assisted distillation and that the
composition of the oils is identical to those obtained by hydro-distillation.
However, it should also be noted that changing the microwave power can also
have an infl uence on oil composition (Günes and Alma 2008) and can ultimately
lead to product degradation similar to that seen in hydro-distillation.

12.2.4 Ultrasound assisted extraction of aroma molecules
The use of ultrasonics addresses the process effi ciency aspects of green chemistry.
Any process that can be carried out more effi ciently and in less time, by default
uses less energy and solvent to complete the same task. The use of ultrasonics has
been applied to solvent extraction predominantly using ethanol or aqueous ethanol
solutions and particularly where the ethanolic extract is being used directly in a
formulation such as an alcoholic beverage. This process can be easily scaled up
and industrial-scale extraction of sage and valerian has been demonstrated
(Valachovic et al. 2001). It should be noted that the use of ultrasound is not
specifi cally listed in Annex II of Regulation (EC) No. 1334/2008 (EC 2008) even
though it is used in the extraction of herbs and spices for beverage production.
Ultrasonic enhancement of extraction appears to have a number of distinct
mechanistic elements (Toma et al. 2001), increased swelling (hydration) of the
raw material, fragmentation of the tissue (particularly the oil glands) and increased
mass transfer of the active principles into the extraction solvent. Since this
technique is most often used with dried herbs and spices, all three elements are
important to the success of the extraction. Ultrasonic transducers operate across a
broad frequency range but a frequency of 20-30 kHz appears to give the greatest
increase in extraction effi ciency (Valachovic et al. 2001), largely as a result of the
greater fragmentation of the tissue.
Ultrasonic extraction may have the greatest use where the fl avour molecules
are particularly labile, an example of this would be the isolation of garlic oil.
Marked differences in composition of the garlic oil were observed in a study that
compared the use of three extraction techniques: simultaneous distillation/
extraction, microwave hydro-distillation and ultrasonic-assisted extraction (Toma
et al. 2001). The authors noted that:
Compared to simultaneous distillation-extraction and microwave hydro-
distillation, the ultrasonic assisted extraction procedure diminishes the
danger of thermal degradation of sensitive aroma compounds from garlic.
Moreover, the method is easy to carry out and could be applicable for large
scale industrial use .
In this work the ultrasonic extraction was carried out at 25°C. This suggested that
the main garlic precursor, allicin, produces the cyclic dithiins initially and that
these in turn degrade to form the acyclic compounds (Abu-Lafi et al. 2004).

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