Food Chemistry

14.4 Processing of Fats and Oils 655

lized in marine oil fractionation, e. g., in the pro-
duction of vitamin A concentrates.

14.4.1.4 Bleaching

In order to remove the plant pigments (chloro-
phyll, carotenoids) and autoxidation products, the
fat or oil is stirred for 30 min in the presence of
Al-silicates (bleaching orFuller’searth) in a vac-
uum at 90◦C. The silicate has to be activated prior
to use – a suspension in water is treated with hy-
drochloric acid, followed by thorough washing
with water, then drying. The amount of silicate
used is 0.5–2% of the fat (oil) weight. It is often
used together with 0.1–0.4% activated charcoal.
The bleached oil is removed from the adsorbent
by filtration. The oil retained by the absorbent
can be recovered by hexane extraction and recy-
cled into the refining process. The residual alkali
soaps, gums, part of the unsaponifiable matter and
the heavy metal ions are also removed during the
bleaching process.
After bleaching, some oils or fats which contain
polyunsaturated fatty acids show an increase in
absorbance at 270 nm. This is due to decomposi-
tion of hydroperoxides, formed by autoxidation,
into oxo-dienes (I) and fatty acids with three dou-
ble bonds (II):

(14.4)

Table 14.14.Removal of chloro pigments in the refin-

ing of rapeseed oil (values in mg/kg)

Amounts after

Raw oil Deacidifi- Bleach- Deodori-

cation ing zation

Chlorophyll A 2.62 0. 89 0 .028 0. 007

Chlorophyll B 2.92 0. 08 0 .059 0. 023

Pheophytin A 35. 631. 50 .235 0. 108

Pheophytin B 4.99 6. 85 0 .071 0. 036

Sum 46. 139. 30 .393 0. 174

Fig. 14.5.Oxidation of soybean oil on exposure

to room light (according to Usukiet al., 1984).

(1), (2), (3), and (4) contain 39, 233, 425, and

623 μg/kg respectively of the mixture chloro-

phyll A/chlorophyll B/pheophytin A/pheophytin B

(1:3:10:3)

As shown in Table 14.14 with rapeseed oil, most

of the chlorophylls and their degradation prod-

ucts are removed during bleaching. However, the

rest, which is in the range of 70–1200 μg/kg in re-

fined plant oils, could still accelerate photooxida-

tion (Fig. 14.5). As a result of their high stability

on exposure to light, the pheophytins are stronger

photooxidants than the chlorophylls. As shown

in Table 14.14, the pheophytins are the predom-

inanting pigments.

14.4.1.5 Deodorization

Deodorization is essentially vacuum steam dis-

tillation (190–230◦C, 0.5–10 mbar). The volatile

compounds, together with undesirable odorants

present in the fat or oil, are separated in this re-