oxidation products are removed by adsorptive effect of the bleaching earth. Then, the
mixture of oil and bleaching agent is filtered through a standard plate and frame press
for separation. The clear oil obtained is bleached oil and is very much lighter in color
than the neutralized oil. The oil charge is dehydrated under vacuum to avoid any
further deterioration due to oxygen. In this operation, the colored pigments in oil are
adsorbed by certain bleaching agents under specific conditions. Used bleaching
material is called spent earth. Spent bleaching earth contains some entrained oil, as
much as 30–50%. The spent bleaching earth is removed in pressure filters and blown
with steam to reduce its oil content to about 20%. It is possible to reduce the oil
content to about 1% if the cake removed from the filter is extracted with a solvent.
2.4 Hardening
The aim of hardening is to raise the melting point of the oil for use in shortening or
margarine manufacture by the addition of hydrogen to unsaturated oil molecules
over a nickel catalyst. The degree of hardening is determined by the temperature,
pressure, and quantity of hydrogen gas added to the reaction. The catalyst is filtered
out of the oil after the reaction is complete. No significant wastewater is generated by
hydrogenation.
2.5 Deodorization
The final step in refining fats and oils is deodorization. The oil after bleaching is
practically pure, but it contains small amounts of original odoriferous matter and also
the chemicals used during neutralization process. The filtered oil is channeled into
the deodorizer for the deacidification and deodorization treatment. Deodorization is
mainly aimed to remove compounds responsible for undesirable odors and flavors,
such as residual free fatty acids (especially low-molecular-weight fatty acids),
aldehydes, ketones, and alcohols from crude degummed and/or alkali refined edible
oils and fats after bleaching. This process utilizes a combination of high-temperature
heating about 200
C, under vacuum (2–4 mmHg), and direct steam injection of
about 2.5–4.0% by weight of oil [10]. The volatile materials are evaporated off with
some carrier (commonly direct steam). This oil is then cooled and clarified through a
filter press to get sparkling oil. The purpose of deodorization is to make oil bland and
tasteless. During this process, FFA in the form of fatty acid distillate is removed as
refining waste, at the upper section of deodorizer. Apart from FFA, carotenoid
pigments and primary and secondary oxidation products are also being removed as
they may contribute to off-flavors.
332
D. Kaya and Y.-T. Hung
mixture of oil and bleaching agent is filtered through a standard plate and frame press
for separation. The clear oil obtained is bleached oil and is very much lighter in color
than the neutralized oil. The oil charge is dehydrated under vacuum to avoid any
further deterioration due to oxygen. In this operation, the colored pigments in oil are
adsorbed by certain bleaching agents under specific conditions. Used bleaching
material is called spent earth. Spent bleaching earth contains some entrained oil, as
much as 30–50%. The spent bleaching earth is removed in pressure filters and blown
with steam to reduce its oil content to about 20%. It is possible to reduce the oil
content to about 1% if the cake removed from the filter is extracted with a solvent.
2.4 Hardening
The aim of hardening is to raise the melting point of the oil for use in shortening or
margarine manufacture by the addition of hydrogen to unsaturated oil molecules
over a nickel catalyst. The degree of hardening is determined by the temperature,
pressure, and quantity of hydrogen gas added to the reaction. The catalyst is filtered
out of the oil after the reaction is complete. No significant wastewater is generated by
hydrogenation.
2.5 Deodorization
The final step in refining fats and oils is deodorization. The oil after bleaching is
practically pure, but it contains small amounts of original odoriferous matter and also
the chemicals used during neutralization process. The filtered oil is channeled into
the deodorizer for the deacidification and deodorization treatment. Deodorization is
mainly aimed to remove compounds responsible for undesirable odors and flavors,
such as residual free fatty acids (especially low-molecular-weight fatty acids),
aldehydes, ketones, and alcohols from crude degummed and/or alkali refined edible
oils and fats after bleaching. This process utilizes a combination of high-temperature
heating about 200
C, under vacuum (2–4 mmHg), and direct steam injection of
about 2.5–4.0% by weight of oil [10]. The volatile materials are evaporated off with
some carrier (commonly direct steam). This oil is then cooled and clarified through a
filter press to get sparkling oil. The purpose of deodorization is to make oil bland and
tasteless. During this process, FFA in the form of fatty acid distillate is removed as
refining waste, at the upper section of deodorizer. Apart from FFA, carotenoid
pigments and primary and secondary oxidation products are also being removed as
they may contribute to off-flavors.
332
D. Kaya and Y.-T. Hung