Food Chemistry

14.6 References 669

Table 14.28.Indicators of refined oils and fats

Refining step Indicator Remarks

Bleaching
(cf.14.4.1.4)

a. Fatty acids

with conjugated

triene systems

Determination of “b”

is more reliable than

the UV measurement

of “a”

b. Disterylether

(> 0 .5mg/kg)

Deodorization
(cf. 14.4.1.5)

a. Dimeric and

oligomeric tria-

cylglycerides

Unlike “a”, the indi-

cators “b” appear

even on relatively

gentle deodorization

b. Position and

substitution iso-

mers of linoleic

acids

longed frying, and it decreases in the presence
of decomposition products. When it falls below
170 ◦C, the fat is considered to be spoiled. At
this point, the amount of fatty acids which are in-
soluble in petroleum ether exceeds 0.7%. How-
ever, this petroleum ether method is not repro-
ducible. Fat separation by column chromatogra-
phy is more reliable. The heated fat or oil is sep-
arated into a polar and a nonpolar fraction using
silicic acid as an adsorbent. The value of 0.7% ox-
idized petroleum ether-insoluble fat corresponds,
in this chromatographic separation, to 73% non-
polar and 27% polar fractions.

14.5.3.4 Refining

The addition of a refined oil to natural plant oil
is detected by the determination of substances
which can be formed during bleaching and de-
odorization (cf. Table 14.28).

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