Page 44 - FoodFocusThailand No.143_February 2018

SMART PRODUCTION

about −48 °C. Above this temperature, a certain amount of crystallization is visible but the correspond-ing
peaks are small. In contrast, the refined walnut oil crystallizes at lower temperatures and the DSC curve
shows several more pronounced peaks. As already mentioned, the crystallization behavior of a vegetable
oil depends mainly on its chemical composition. Vegetable oils and fats contain fatty acids with mostly
even numbers of carbon atoms and chain lengths of 4 to 24 carbon atoms. Quantitatively, fatty acids
with chain lengths of 14 to 18 carbon atoms predominate. In general, oils composed mainly of
saturated fatty acid triglycerides crystallize at relatively high temperatures, whereas oils with
unsaturated fatty acid triglycerides crystallize at relatively low temperatures. Depending on the
proportions of fatty acid triglycerides present in the oils, several crystallization peaks appear in the
DSC curve. Usually the curve exhibits one pronounced crystallization peak (as a rule at about −50 °C,
−35 °C or 10 °C) and one or more smaller peaks. This is also true for the refined oils (see Figure 4).
Compared with native oils, crystallization occurs here at slightly lower temperatures.

Conclusions
Vegetable oils exhibit characteristic crystallization behavior that is strongly influenced by the
composition of the oil. The crystallization behavior can easily be studied by DSC methods. The
resulting measurement curves are used to identify unknown native and refined vegetable oils and
to monitor and control refining processes. DSC is therefore an extremely useful technique for the
quality assurance of vegetable oils.

Figure 1. DSC curve of
coldpressed soya oil. The Figure 3. DSC curves
exothermic peaks arise of different cold-pressed
through the crystallization of (native) oils.
different triglycerides in the
soya oil.

Figure 4. DSC curves of
different refined oils.

Figure 2. Comparison of the DSC
curves of coldpressed and refined
walnut oil. The exothermic peaks
aredue to the crystallization of
different triglycerides in the walnut
oil.

ข้อมูลเพิ่มเติม/Additional Information
1 DSC822e Differential Scanning Calorimetry by Mettler-Toledo
2 IntraCooler by Mettler-Toledo

44 FOOD FOCUS THAILAND FEB 2018