antioxidant activity of rambutan

79 Pages·2012·2.45 MB·English

ANTIOXIDANT ACTIVITY OF
RAMBUTAN (NEPHELIUM
LAPPACEUM) PEEL EXTRACTS IN
SOYBEAN OIL DURING
ACCELERATED STORAGE AND
FRYING

Number of words: 20.392

Minh Viet Thao Nguyen
0150047

Promotor: Prof. dr. ir. Katleen Raes

Master’s Dissertation submitted to Ghent University in partial fulfilment of the requirements for the
degree of Master of Science in Food Technology

Academic Year: 2016 - 2017
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Universiteitsbibliotheek Gent, 2021.
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Preface

The completion of this thesis has required the help and support of numerous people. First of
all, I would like to express my gratitude towards Prof. dr. ir. Katleen Raes for all of her help
and constructive advice throughout my research. Secondly, I would like to thank my
supervisor – Nhat Minh Phuong Nguyen for her valuable experience in laboratory, for
detailed explanation and for her enthusiastic guidance. I have learned so much from them.
I would also like to thank members the Laboratory of Food Microbiology and Biotechnology
(UGent, Campus Kortrijk) for all of their help and support.
Finally, I would like to thank my parents, who supported me with infinite love and
understanding, my dearest friends and my boyfriend for their support and encouragement. I
feel extraordinarily blessed to have such a network of wonderful people in my life. Thank you
all for believing in me and helping me reach my goals.
Table of contents
Abstract ................................................................................................................................................ 1
1. INTRODUCTION ....................................................................................................................... 2
2. LITERATURE REVIEW ............................................................................................................ 4
2.1. Lipid oxidation ...................................................................................................................... 4
2.1.1 Overview ........................................................................................................................ 4
2.1.2 Mechanism of lipid oxidation ........................................................................................ 4
2.1.2.1 Autoxidation .......................................................................................................................... 4
2.1.2.2 Photosensitized oxidation ...................................................................................................... 6
2.1.3 Lipid oxidation decomposition products ....................................................................... 7
2.1.4 Factors influencing oxidative stability ........................................................................... 8
2.1.4.1 Fatty acid composition ........................................................................................................... 8
2.1.4.2 Temperature ........................................................................................................................... 9
2.1.4.3 Light ..................................................................................................................................... 11
2.1.4.4 Impact of storage on lipid oxidation .................................................................................... 11
2.1.4.5 Minor compounds ................................................................................................................ 11
2.1.4.6 Enzymes ............................................................................................................................... 12
2.2. Antioxidants: control of lipid oxidation .............................................................................. 12
2.3.1 Overview ...................................................................................................................... 12
2.3.2 Classification and mechanism ...................................................................................... 13
2.3.2.1 Primary antioxidants ............................................................................................................ 13
2.3.2.2 Secondary antioxidants ........................................................................................................ 13
2.3.3 Natural antioxidants ..................................................................................................... 16
2.3.4 Impact of high heat treatment on antioxidants ............................................................. 19
2.3. Rambutan peel, a natural source of antioxidants................................................................. 20
2.3.1. Overview ...................................................................................................................... 20
2.3.2. Cultivation and processing of rambutan in Southeast Asia ......................................... 21
2.3.3. Phenolic compounds in rambutan peel ........................................................................ 23
2.4. Soybean oil .......................................................................................................................... 24
2.4.1. Introduction .................................................................................................................. 24
2.4.2. Composition of soybean oil ......................................................................................... 26
2.4.3. Factors influencing oxidative stability, evaluation and control ................................... 27
3. MATERIALS AND METHODS ............................................................................................... 29
3.1. Materials .............................................................................................................................. 29
3.1.1. Reagents ....................................................................................................................... 29
3.1.2. Rambutan peel ............................................................................................................. 29
3.1.3. Soybean oil................................................................................................................... 29
3.1.4. Potato ........................................................................................................................... 30
3.2. Methods ............................................................................................................................... 30
3.2.1. Preparation of rambutan peel extract ........................................................................... 30
3.2.2. Experiments ................................................................................................................. 31
3.2.2.1. Accelerated storage conditions ........................................................................................ 31
3.2.2.2. Heating test ...................................................................................................................... 32
3.2.2.3. Frying process: Application on deep frying with potatoes .............................................. 32
3.2.3. Analysis of oil and potato ............................................................................................ 32
3.2.3.1. Conjugated dienes and trienes .......................................................................................... 32
3.2.3.2. Determination of peroxide value (PV) ............................................................................. 33
3.2.3.3. Para-anisidine value (p-AnV) .......................................................................................... 33
3.2.3.4. Determination of total phenolic content (TPC) ................................................................ 34
3.2.3.5. Determination of malondialdehyde (MDA) in oil............................................................ 34
3.2.3.6. Determination of malondialdehyde in fried potatoes ....................................................... 35
3.2.3.7. Color measurement .......................................................................................................... 36
3.2.4. Statistical analysis ........................................................................................................ 37
4. RESULT AND DISCUSSION .................................................................................................. 38
4.1. Accelerated storage conditions............................................................................................ 38
4.1.1. Color of oils ..................................................................................................................... 38
4.1.2. Conjugated dienes and trienes ......................................................................................... 40
4.1.3. Peroxide value (PV)......................................................................................................... 40
4.1.4. p-anisidine value (p-AnV) ............................................................................................... 44
4.2. Heating test .......................................................................................................................... 49
4.3. Frying process ..................................................................................................................... 52
4.3.1. Conjugated dienes and trienes ..................................................................................... 53
4.3.2. Peroxide value (PV) ..................................................................................................... 53
4.3.3. Para-anisidine value (p-AnV) ...................................................................................... 54
4.3.4. Malondialdehyde (MDA) in oil ................................................................................... 56
4.3.5. Color of potatoes .......................................................................................................... 57
4.3.6. Color measurement ...................................................................................................... 59
4.3.7. Malondialdehyde (MDA) in potato ............................................................................. 62
5. CONCLUSIONS AND PROSPECTS ....................................................................................... 65
References .......................................................................................................................................... 67
List of abbreviations
BHA butylated hydroxyanisole
BHT butylated hydroxytoluene
CD conjugated dienes
CT conjugated trienes
DHHDP dehexahydroxydiphenoyl
FC Folin–Ciocalteu
GAE gallic acid equivalents
HHDP exahydroxydiphenoyl
KI potassium iodine
MDA malondialdehyde
p-AnV para-anisidine
PC phosphatidylcholine
PI phosphatidylinositols
PV peroxide value
RP rambutan peel
Sen photosensitizers
TAG triacylglycerols
TBA thiobarbituric acid
TBHQ tert-butylhydroquinone
TCA trichloroacetic acid
TEP tetraethoxypropane
TPC total phenolic content
Abstract
Rambutan peel is a by-product which has been proven to possess a high amount of phenolic
compounds, and antioxidant potential. The antioxidant efficacy of rambutan peel extract in
stabilization of soybean oil under different conditions i.e. storage, frying with (frying test) and
without food matrix – potatoes (heating test) conditions was investigated.
To evaluate the antioxidant effect of rambutan peel on the oxidative stabilization of soybean oil
during 160 days of storage periods under different storage conditions (dark/light, 4 and 30˚C),
conjugated dienes (CD), conjugated trienes (CT), peroxide value (PV), p-anisidine (p-AnV) and
total phenolic content (TPC) of oils were analyzed for every 20-day interval. The changes in the
PV, p-AnV and TPC of oils indicate that rambutan peel extract seemingly exhibit antioxidant
potentials in soybean oil during storage. However, phenolic compounds in rambutan peel extract
are not stable in light condition compared to TBHQ.
The results from peroxide value (PV), p-anisidine (p-AnV), of soybean oils under frying with
and without potatoes illustrate that both TBHQ and rambutan peel extract have no effect on
retardation of oil oxidation. However, the results from malondialdehyde (MDA) levels of oil
samples and fried potatoes indicate that rambutan peel extract can prevent the formation of MDA
– a secondary oxidation product. Besides this, the tremendous decrease in TPC of 100ppm
TBHQ and 1000ppm RP treatments under heating condition indicate that both TBHQ and
phenolic compounds in rambutan peel are not heat stable. The fluctuation of CD and CT
parameters in all tests shows that they are not reliable to evaluate the oxidation level of soybean
oil in this study.
The most attractive appearance of fried potatoes was obtained from rambutan peel extract (apart
from batch 1). The results from color measurement showed that both rambutan peel extract and
TBHQ treatments had insignificant effect on the total color attributes of fried potatoes compared
to the control.
The overall results suggest that rambutan peel can be considered as a promising source of
antioxidants for retardation of the lipid oxidation, especially in vegetable oils.

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1. INTRODUCTION
Vegetable oils are well-known as the ideal cooking medium due to a high amount of
polyunsaturated fatty acids which are known for their cholesterol lowering effect. However,
these fatty acids are more prone to be oxidized compared to animal fats which contain
mainly saturated fatty acids (Ruxton, Reed et al. 2004). Lipid oxidation is a serious issue in
food science, causing off-flavors, and decreasing nutritional quality and safety. Oxidation
can be prevented by means of methods such as vacuum packaging, modified atmosphere
packaging, and freezing. Yet, the utilization of antioxidants seems to be the most preferable
way due to its effectiveness, convenience, and economy (Naz, Siddiqi et al. 2005). Synthetic
antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and
tert-butylhydroquinone (TBHQ) are applied to retard the oxidative degradation. However,
synthetic antioxidants are known to have the potential mutagenicity and other health
problems (Sehwag and Das 2013). The carcinogenic effect of synthetic antioxidants was
reported by Ito, Hirose et al. (1986). Also, synthetic antioxidants, may cause liver
enlargement and interfere with the liver enzyme system (Martin and Gilbert 1968). These
reasons induce the search for their replacement with natural antioxidants.
In recent decades, much attention has been paid to phenolic compounds due to their multiple
biological effects such as inhibition of low-density protein oxidation, reducing the heart
disease risks, anticarcinogenic properties and antioxidant activity (Williams and Elliot 1997,
Miyake, Murakami et al. 1999). Phenolic compounds work as antioxidants to scavenge
reactive oxygen species and to chelate metals (Khatun, Eguchi et al. 2006). Top sources
containing phenolic compounds are fruits and vegetables (Dimitrios 2006). Spices, herbs
and their extracts have been proved to demonstrated strong antioxidant activities (Sehwag
and Das 2013). Recently, worldwide emerging great sources of natural antioxidants are
agricultural by-products which are peels and seeds. Some studies have reported the
effectiveness of by-product extracts in stabilization of vegetable oils. For instance, the strong
effectiveness of potato peel extract as a natural antioxidant in soybean oil during storage was
evaluated by Habib and Shah (2004). Pomegranate peel extracts also exhibited the
antioxidant activity in stabilization of sunflower oil under accelerated conditions (Iqbal,
Haleem et al. 2008). Shaker (2006) reported that red grape seed and peel extracts can
prevent oxidation in sunflower oil. Besides, many published studies which focus on the
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evaluation and exploitation of waste products such as citrus peels and pomace, apple
pomace, grape seeds and pomace, carrot pulp waste, mango seed kernel, and others were
summarized by (Dimitrios 2006, Maisuthisakul 2009).
Rambutan (Nephelium lappaceum L.) is a tropical fruit which is a member of the family
Sapindaceae. Rambutan is popular in South-East Asia such as Vietnam, Philippines,
Indonesia, Thailand, Burma, Sri Lanka and India (Tindall 1994). This kind of fruit can be
consumed in fresh or as processed fruit. During processing, a huge amount of peels is
discarded. Rambutan peels have been proven to be a rich source of phenolic compounds
with great antioxidant activity, low pro-oxidant and non-toxic capacity (Okonogi, Duangrat
et al. 2007, Palanisamy, Cheng et al. 2008, Thitilertdecha, Teerawutgulrag et al. 2010). The
effect of rambutan peel extract on stabilizing sunflower oils during 24 days of storage at
60oC was reported by Mei, Ismail et al. (2014). However, the effect of the rambutan peel
extract as a rich source of antioxidants in oils under different storage conditions (light –
dark, low – high temperature) as well as under frying condition with food matrix the has not
yet been reported.
Within this framework, the objective of this thesis is to investigate antioxidant activity of
rambutan peel extract in soybean oil under different storage conditions i.e. dark – 4°C, dark
– 30°C and light – 30°C. Furthermore, the effectiveness of rambutan peel towards oxidative
stability of soybean oil under frying conditions without and with a food matrix (e.g.
potatoes) was assessed in this thesis.

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