Deodorizing

Deodorisation is a vacuum-steam distillation process of an oil at an elevated temperature, during which FFA and small amounts of odoriferous materials are removed to obtain a bland and odorless oil.

Small quantities of volatile components, responsible for tastes and odors are removed, leaving a neutral, odorless product suitable for the manufacture of bland shortening or delicately flavored margarine.

Deodorisation process has four main objectives:

(1) Stripping of volatile components such as FFA (in the case of physical refining), valuable minor components (tocopherols, sterols etc.) and contaminants (pesticides, light polycyclic aromatic hydrocarbons etc.)

(2) Actual deodorisation by removal of different off-flavors

(3) Thermal destruction of pigments (so-called heat bleaching) and peroxides

(4) Rendering of the oil, by means of some chemical change, as more flavor-stable during its shelf life.

Deodorisation increases the oil’s flavor and oxidative stability by nearly complete removal of FFA and other volatile odor and flavor materials, by partial removal of tocopherols, and by thermal destruction of peroxides. The thermal treatment that is a necessary part of the Deodorisation process also heat bleaches the oil by destruction of the carotenoids that are unstable at Deodorisation temperature.

Deodorisation is actually a stripping process in which a given amount of a stripping agent (usually steam) is passed for a given period of time through hot oil at a low pressure. Hence, it is mainly a physical process in which various volatile components are removed. However, since it is usually carried out at high temperature (> 200°C), some chemical, thermal effects may take place as well.

As the temperature of a liquid mixture is raised, those components of the mixture with the lowest boiling points (and hence highest volatility) evaporate first, leaving behind the less volatile compounds with the higher boiling points. By reducing the pressure of the system the temperature at which the evaporation of the more volatile components occurs can be reduced, although the order in which the components of the mixture distill does not change.

An efficient removal of these volatile substances depends mainly upon their vapor pressure and their concentration in the oil. The vapor pressure for a given constituent is a function of the temperature and increases with increasing temperature (See Fig below).The lower the vapor pressure, the lower the volatility, and the more difficult it is to remove the constituent from the oil. The use of an inert (non-reacting) stripping agent effectively enhances the vaporization of the volatile components.

Summary of Component Removal During Deodorisation

Physical Removal

FFA: reduced to below 1%*
Odor compounds (aldehydes and ketones): reduced to acceptable levels
Tocopherols: partially removed
Sterols: partially removed
Methyl/ethyl esters: almost completely removed
Antioxidants (BHA, BHT): completely removed
Pesticides: partially removed
Polycyclic aromatic hydrocarbons: partially removed
Monoglycerides: partially removed

Chemical Reaction

Oxidized fatty acids: partially decomposed
Carotene: partially decomposed
Hydroperoxides: partially decomposed
Soaps: completely decomposed
Unsaturated fatty acids: some cis/trans isomerization

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