Natural flavourings from green chemistry for foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 264

identical to either hydro-distillation or to conventional solvent extraction. In the
extraction of hops, black pepper and capsicums, for example, it has been
demonstrated that recovery of the key molecules responsible for fl avour, bitterness
and heat is much greater when supercritical carbon dioxide is used compared
to conventional solvents (Hubert and Vitzthum 1978). This has led to the extrac-
tion of hops now being carried out almost exclusively using liquid or super-
critical carbon dioxide (Zeković 2007). The ability to vary solubility as a result of
changing temperature and pressure can also be used to produce products with
specifi c composition. For example, extraction of black pepper and ginger can
be carried out in such a way that fractions rich in essential oils or the heat prin-
ciples can be produced (Norac Technologies 1992; Nguyen et al. 1998). This
can be achieved either by total extraction at high pressure and temperature
followed by reduction in pressure in sequential separators, or by sequential
increase in temperature and pressure as shown in Table 12.3. In a commercial
operation, the option of extraction at a single pressure with multiple separators to
recover fractions is the preferred route as this is operationally simpler and more
cost-effective.
Both black and white pepper can be fractionated with supercritical CO 2 to
separate the heat/pungent (piperine) and aroma (essential oil) components. As
shown in Table 12.4, separation of these two components can be achieved in two
fractions and, with careful control of extraction conditions, heavy fractions can be
produced containing 50-80% piperine and less than 1.5 ml essential oil per 100g
(Nguyen et al. 1998). This separation allows formulation of oleoresins to meet
any combination of aroma and pungency rather than the fi xed ratio that would be
obtained by traditional solvent extraction.

Table 12.3 Resin fractionation using temperature and pressure

Process Pressure

(mPa)

Temperature
(K)

Product

￿ ￿ ￿ ￿ ￿

Sequential
pressure steps

Extraction 12 313 Light fraction - volatile

oil

Extraction 30 333 Middle fraction - resins

and lipids

Extraction 40 353 Heavy fraction - heavy

resin

Sequential
pressure
reduction

Extraction
Separator 1

50
25

353
338

Total extract
Heavy fraction - heavy
resin

Separator 2 12 333 Middle fraction - resins

and lipids

Separator 3 3 391 Light fraction -

volatile oil