Page 410 - Biosystems Engineering

Extraction, Refining, and Stabilization of Edible Oils 387

Mix 10 g of fatty food with 50 mL water for 2 min and pour into a
distillation flask with 47.5 mL water. Add 2.5 mL of 4-N hydrochloric
acid to bring the pH to 1.5. Heat the flask with an electric mantle so
that the 50-mL distillate is collected in 10 min from the time boiling
commences. Pipette the 5-mL distillate into a glass-stoppered tube,
add 5 mL TBA reagent (0.2883 g/100 mL of 90 percent glacial acetic
acid), stopper, shake, and heat in boiling water for 35 min. Prepare a
blank similarly using 5-mL water with 5 mL of reagent. Then cool the
tubes in water for 10 min and measure the optical density (D) against
the blank at 538 μm using 1-cm cells. The TBA number (as mg malo-
naldehyde/kg sample) is 7.8D.
Measuring the Oxidation Stability of Fats Using the Rancimat Method
Oxidation processes that slowly take place in fats at ambient tempera-
ture are known as autoxidation. They start with the reaction of the
fatty acids. In multistage processes, this leads to a variety of decompo-
sition products such as peroxides, alcohols, aldehydes, and different
carboxylic acids. In the Rancimat method, the sample is exposed to a
particular high temperature (50 to 200°C), and the volatile oxidation
products are transferred to the measuring vessel by air stream and are
absorbed in the measuring water solution. When the conductivity of
the measuring solution is recorded continuously, an oxidation curve is
obtained whose point of inflection is known as induction time, which
provides characteristic values of the oxidation stability.

Apparatus Required (Rancimat Apparatus Attached to a Computer)—
Methods
1. Check initially that the Rancimat apparatus is attached to a
computer correctly and then switch both machines.
2. Sample vessel and measuring vessels should be cleaned, oth-
erwise reaction conditions are hampered.
3. Before starting measurement, program the required tempera-
ture and flow of air.
4. Place the weighed sample (approximately 2.0 to 2.5 g) and
cover the vessel with caps fitted with screws and tubes.
5. Place the measuring vessel containing 60 mL of distilled water
in the Rancimat apparatus (Fig. 13.5).
6. Attach the outlet tube of the sampling vessel in the measur-
ing vessel to absorb the oxidized products in water.
7. Place the exhaust tube of the measuring vessel in a hood
because oxidation products of are very irritating to the eyes.
8. After the required time as programmed on the computer, take
the induction result with the time from the computer.