Page 69 - rise 2017

Identification of Non-Halal Recycled Cooking Oils Using Differential Scanning Calorimetry
(DSC) combined with Principal Component Analysis (PCA)

1, c
1, d
1, b
1, a
Mualim, M. S. , Nur Azira, T. , Muhamad Shirwan, A. S. and Nurrulhidayah, A. F.

1 International Institute for Halal Research and Training (INHART), Level 3, KICT Building,
International Islamic University Malaysia (IIUM), Jalan Gombak, 53100, Selangor, Malaysia

a b c
aziratukiran@iium.edu.my, mualim.salleh@gmail.com, shirwansany@iium.edu.my,
d nurrulhidayah@iium.edu.my

Abstract
Recycled cooking oil was used to save costs. The practice is worrying as recycled cooking oil taken
from non-halal food premises should not be used by halal food premises. Therefore, an appropriate
method should be developed in order to monitor the halal status of these cooking oils. Means of
identifying recycled cooking oils (palm oil) that have been used for frying pork were investigated in
this study. Pork and chicken were fried in palm oil heated up to 180oC. The cooking oil that has been
used for frying pork (P) and chicken (C) containing 0.5-50% v/v of mixture of P and C were analyzed
for thermal profile using differential scanning calorimetry (DSC) combined with Principal Component
Analysis (PCA). The method used was able to identify cooking oils that have been used for frying
pork in different percentage of mixture. The simple approach employing DSC and PCA reported in
this paper may provide a useful tool for monitoring the halal status of recycled cooking oils.
Keywords: Pork, Chicken, Recycled Cooking oil, Differential Scanning Calorimetry (DSC),
Principal Component Analysis (PCA).

Introduction
People have been frying their food as one of the methods of food processing since a long time ago.
The method is often used because it is easy to handle and not time-consuming while able to produce
palatable fried products. Despite that, there are many harmful effects produced during frying the food,
such as polymers, trans configuration, etc. [1]. The fried oil is often reused to avoid wastage. The
more times the fried oil is reused, the more harmful the effects will be. Most of the times, these used
fried oil is reprocessed in the factory to be sold back cheaply to stalls and restaurants. The real
problem comes when the reprocessed cooking oil might be used for frying pork from non-muslim
restaurants. This is a major problem for Muslims because pork is prohibited to be consumed in Islam.
Therefore, the establishments of methods to detect pork derivative in the recycled cooking oil may be
useful. Due to the advancement of technology, there have been several methods to authenticate the
adulteration of cooking oil either recycled or pure form such as Fourier transform infrared (FTIR)
spectroscopy [3-5], gas chromatography-mass spectrometry (GC-MS) [6], mid-infrared (M-IR)
spectroscopy [7], micro-UV spectrophotometer [8], proton transfer reaction mass spectrometry (PTR-
MS) [9], optothermal window (OW) assay [10], hydrogen-1 nuclear magnetic resonance (1H NMR)
[11], carbon isotope analysis [12,13], Raman spectroscopy [14], and synchronous front-face
fluorescence spectroscopy [15].
Nevertheless, thermal analysis has been the choice of method to analyze oils for decades.
Differential scanning calorimetry (DSC) has gained remarkable popularity in thermal studies of foods
and their components following the development of instrumentation of sufficient sensitivity. DSC is
simple, rapid and able to supply both thermodynamic (heat capacity, enthalpy and entropy) and
kinetic data (reaction rate and activation energy) on examining the physical state and properties of
liquid in food [16]. In this study, palm oil was used as the cooking oil. There have been several
studies involving adulteration of palm oil using DSC method, including lard adulteration [17] and
tropical oils adulteration [18]. Nonetheless, there are also many other studies involving edible cooking
oils using DSC, including canola oil [19], sesame oil [20], seed oil [21], sunflower oil [22], olive oil
[23–26], and virgin coconut oil [27].
However, DSC application as a sole technique is often not definitive as some thermal
transitions are very weak, making evaluation troublesome. Thus, the aim of this study was to identify
recycled cooking oils (palm oil) that have been used for frying pork by using combination method of