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Study on the thermal degradation of palm olein and the effects of trace metals
Author
Feng, Shulan
Supervisor
Chu, Chit Kay
Abstract
Palm olein is used for the study of thermal degradation of edible oil during frying. The free fatty acids, peroxide value, total polar contents, uv/vis absorption coefficient, viscosity and percentage linoleic acid content are investigated for two sets of experiments to mimic batch and continuous frying. These parameters are determined for oil heated in utensils made of copper, iron, aluminum, stainless steel and glass. It is found that at low temperature, the metals act as promoters of degradation reactions, such as oxidation, transformation, and polymerization. At higher temperatures, these catalytic properties of the metals are not so pronounced, in fact, copper seems to show antioxidant properties. Atomic absorption spectrophotometry shows that copper has higher solubility than iron or aluminum in heated palm olein; attributed to the passivity of metal oxides formed. A similar study has been carried out using the oxidised form of the metal in the oil (as metal palmitate). Although the degradation trend is quite similar for both the elemental metals and corresponding oxidized metals, the latter shows that the degradation processes are more dependent on the concentrations of the metal salt introduced. A correlation study between the total polar content with other parameters is made for the frying of prawn crackers (keropok) in palm olien. Using a value of 25% total polar compound as the upper limit for frying palm olein to be discarded, the corresponding free fatty acid (0.35%), peroxide value (0.55M/kg), linoleic acid content (below 15%) and viscosity (29.2cp) are established. It is also concluded that continuous is more economical than batch frying of keropok using palm olein, a loading of 1.4kg keropok per kg against 1.2kg keropok per kg oil. Also, the continuous frying process produced more crispy keropok with less oil uptake, than keropok produced by the batch frying process.
Date Issued
2000
Call Number
TP684.P3 Fen
Date Submitted
2000