Natural flavourings from green chemistry for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 265

Table 12.4 Fractionation of white and black pepper to produce aroma and heat-rich

extracts

% Piperine Essential oil (ml/100g)

Raw white pepper 5.0 3.1

Heavy fraction 56.0 1.5

Light fraction 0.8 109.4

Raw black pepper 5.6 3.4

Heavy fraction 63.8 1.1

Light fraction 0.6 94.0

12.2.2 Application of subcritical water as an alternative extraction solvent
for essential oils and aroma molecules
Water is already used as a solvent in as much as the production of essential oils by
steam distillation uses water in the vapour phase to volatilise the oils. Although
this process is entirely natural, the energy required to carry out distillation for up
to three hours is signifi cant and contributes to the production of greenhouse gases
and in most cases the use of fossil fuels. An alternative approach to using water as
an extraction solvent is to extract the botanical material with subcritical water
(water above boiling point but below critical point). The energy required to heat
water from 15°C to steam at 100°C is 2595 kJ/kg water compared with heating
water from 15°C to 150°C, which requires only 552 kJ/kg water and up to 75% of
this can be easily recycled. Pressurising water is not particularly energy-intensive
- only 4 kJ/kg water is needed to raise the pressure to 5 MPa (50 bar).
Subcritical water offers an alternative solvent at the opposite end of the polarity
spectrum to supercritical CO 2 and can therefore be seen as a complementary
technique (Srinivas and King 2010). Extraction using subcritical water does not
require overly complicated equipment (Fig. 12.4), although the recovery of the
essential oil from the water needs to be considered. In almost all laboratory trials
the essential oil is recovered either by secondary extraction with a solvent such as
hexane or by absorption using an in-line trap. Using hexane would be undesirable
from a green chemistry perspective and the cost of solid absorbents would be
prohibitive on an industrial scale. Where the yield of essential oil is relatively
high, physical separation or the use of a small re-boiler should be a practical and
economic solution. The greenest option would be to use the aromatic extract
directly and for some applications, such as clear beverages, this could provide a
unique and soluble preparation.
Extraction of essential oils from a wide range of aromatic plants and herbs
including foliage, seeds, roots and fl owers has been demonstrated using subcritical
water and high recovery of the oils has been demonstrated. The optimum pressure,
temperature and fl ow rate varies according to raw material but generally falls in
the range 120-150°C and 2-5 MPa. As examples of this application, the essential
oil from marjoram leaf ( Thymus mastichina ) (Jimenez-Carmona et al. 1999) and
coriander seed ( Coriandrum sativum ) (Saim et al. 2008) was extracted using

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