Shelf-life prediction of edible cotton, peanut and soybean seed oils using an empirical model based on standard quality tests

Abstract

The purpose of the study was to determine the qualities of edible cotton, peanut and soybean seed oils, and predict their shelf stability using accelerated shelf-life testing method. Fatty acid profiles were determined by GC-MS as methyl esters and results revealed that the predominant fatty acid in edible soybean and cottonseed oils were linoleic acid 42.8 and 41.6%, respectively. While oleic acid (46.3%) was the major fatty acid in edible peanut oil. Peroxides formation was monitored for six successive weeks and data collected were used to model the deterioration mechanism. Accordingly, the model that best fitted the experimental data corresponds to a zero order kinetic model for all edible oil investigated. Arrhenius relation was applied to model the effect of temperature on the rate constant of peroxide formation. Combining the kinetic model identified and the rate constant model equation that could help to predict the shelf-life of oils studied at any temperature was developed. Based on this, the shelf-life of the domestic edible oils was determined at room temperature and amounts 36.9, 42.1 and 37.8 weeks for soybean, peanut and cottonseed oils; respectively.

Full text

FOOD SCIENCE & TECHNOLOGY | RESEARCH ARTICLE
Shelf-life prediction of edible cotton, peanut and
soybean seed oils using an empirical model
based on standard quality tests
Addisu Alemayhu
1
, Shimelis Admassu
2
*and Biniyam Tesfaye
3
Abstract: The purpose of the study was to determine the qualities of edible cotton,
peanut and soybean seed oils, and predict their shelf stability using the accelerated
shelf-life testing method. Fatty acid profiles were determined by GC-MS as methyl
esters and results revealed that the predominant fatty acid in edible soybean and
cottonseed oils were linoleic acid 42.8% and 41.6%, respectively. While oleic acid
(46.3%) was the major fatty acid in edible peanut oil. Peroxides formation was
monitored for six successive weeks and data collected were used to model the
deterioration mechanism. Accordingly, the model that best fitted the experimental
data corresponds to a zero order kinetic model for all edible oil investigated.
Arrhenius relation was applied to model the effect of temperature on the rate
constant of peroxide formation. Combining the kinetic model identified and the rate
constant model equation that could help to predict the shelf-life of oils studied at
any temperature was developed. Based on this, the shelf-life of the domestic edible
oils was determined at room temperature and amounts 36.9, 42.1 and 37.8 weeks
for soybean, peanut and cottonseed oils, respectively.
Subjects: Food Engineering; Food Laws & Regulations; Technology; Chemical Engineering;
Shimelis Admassu Emire
(Dr.Eng.)
ABOUT THE AUTHOR
Shimelis Admassu is a Professor (Associate) at
the Addis Ababa University, School of Chemical
and Bio-Engineering, Addis Ababa, Ethiopia. He
has Doctoral Degree in Food Process Engineering
and Bioprocess Technology from Asian Institute
of Technology, Bangkok, Thailand.
Dr.Eng. Shimelis has 86 Publications on Reputable
Journals. He supervised four PhD in food process
engineering, 106 MSc students in food engineer-
ing, food science and technology. His research
and contribution to knowledge focused on phy-
tochemicals nutraceutical foods and chilling
operation in biomaterials. Dr.Eng. Shimelis has
a great aspiration to work in the cutting-edge-
research areas of Agro-food and Bio-System
Engineering including Emerging Technologies,
Food Quality Assurance Management Systems
and Agro-based Industry Sector Development.
PUBLIC INTEREST STATEMENT
Prediction of shelf-life is a required aim in the
food manufacturing industry. The development
of an effective tool to predict edible oil shelf-life
is considered of utmost prominence in order to
protect consumers and to avoid the commer-
cialization of oils that do not comply with the
regulatory parameters for the commercial grade
stated on the label. Edible oil shelf life is one of
the significant quality markers, but yet not
renowned as a legal parameter in most food
safety and quality regulations and standards in
African context. This paper reports research into
the shelf-life of edible oils determined by ana-
lyzing the deterioration curves for the basic
quality tests. The proposed models are based on
common quality tests with predictable result
changes over time and influenced by different
aspects of edible oils. Thus, the developed model
equation could help to predict the shelf-life of
oils at any temperature.
Alemayhu et al., Cogent Food & Agriculture (2019), 5: 1622482
https://doi.org/10.1080/23311932.2019.1622482
© 2019 The Author(s). This open access article is distributed under a Creative Commons
Attribution (CC-BY) 4.0 license.
Received: 08 May 2019
Accepted: 18 May 2019
First Published: 24 May 2019
*Corresponding author: Shimelis
Admassu, Addis Ababa University,
Addis Ababa, Ethiopia
Email: shimelisemire@yahoo.com
Reviewing editor:
Fatih Yildiz, Food Engineering and
Biotechnology, Middle East
Technical University, Ankara Turkey
Additional information is available at
the end of the article
Page 1 of 18

Keywords: Consumers protection; shelf-life prediction; empirical model; quality
parameters; oxidation
1. Introduction
Manufactured oil products shelf-life defied as the length of time under normal storage condi-
tions within which no off-flavors or defects are developed and quality parameters are retained
within accepted limits for commercial category products. It is important to understand the
composition of food material and food products, and the changes that occur when they are
grown, harvested, stored, prepared, processed and eaten; so that foods can fulfill their basic
function (Mudambi, Rao, & Rajagopal, 2006). Food quality is the most important characteristics
that determine the consumer acceptability and willingness to purchase. The fact that foods are
diverse, complex and active system in which microbiological, enzymatic and physicochemical
reactions are simultaneously taking place, and make their age limited (Valentas, Rotstein, &
Singh, 1997). Consequently, foods are perishable by nature and food quality is always in
a dynamic state continuously moving to reduced levels until reaching the quality level that
discriminates products that are still acceptable for consumption from those that are no longer
acceptable. This quality level is generally defined as the acceptability limit beyond which the
product becomes unsuitable for consumption due to legal, nutritional, or sensory criticisms
(Kramer & Twigg, 1968).
Edible oils and fats are recognized as essential nutrients of our daily diet and contribute
significantly to the regulation of different body functions. Numerous physical and chemical para-
meters are used to assess their quality (Nielsen, 2003; Febrianto & Yang, 2011). Edible oil quality is
largely determined by physicochemical characteristics due to its nature and processing procedure,
and the environmental factor when it stays in the market shelf. However, these diverse groups of
organic substances are prone to oxidation. Autoxidation is the main cause of edible fats and oils
quality deterioration (Farhoosh, 2007). Oil shelf life is principally affected by its susceptibility to
autoxidation, which is determined in large part by its fatty acid composition (Broadbent & Pike,
2003; Merrill, Pike, Ogden, & Dunn, 2008). In the course of the autoxidation reaction, a series of
compounds are formed, causing off-flavors and rancidity, loss of nutritional value and finally
consumer rejection (Alonso, Campos, Salvador, & Frangipane, 2004). The reaction consists of
three main stages: initiation (involves abstraction of a hydrogen molecule from an unsaturated
fatty acid, forming an alkyl radical), propagation (begins when oxygen adds to the alkyl radical and
forming a high energy peroxyl radical, which can then abstract hydrogen from another molecule
and continues the oxidation cycle), and termination (occurs when two radical species combine,
forming a non-radical) (Nawar, 1996).
Even though proper care is taken during preparation, packaging, and storage of every food, they
are wholesome only for a certain period called shelf-life. The shelf life of a product begins from the
time the food is prepared or manufactured. The period is dependent on many factors including the
types of ingredients, manufacturing process, type of packaging and how the food is stored (NZFSA,
2005). So, shelf-life dating of foods is a mandatory requirement of all processed foods. It provides
a guide to consumer in food purchase. This requires a valid and reproducible shelf life study
(Kramer & Twigg, 1968). There are two test methods for conducting a shelf life study; direct
method and indirect method (New Zealand Food Safety Authority (NZFSA), 2005). The direct
method also known as real-time shelf life study involves storing the product under specific
conditions for a time longer than its expected shelf-life and checking it at regular intervals to
see when it begins to spoil. The two indirect methods allow for shelf life prediction without
conducting a full-length storage trial and are useful for products with a long shelf life. These are
predictive model: calculate shelf-life based on information from a database that predicts bacterial
growth under specific conditions, and accelerated shelf life study: which involves deliberately
increasing the rate, at which a product will spoil, usually by increasing the storage temperature
(Robertson, 2010). Prediction methods based on kinetic and/or mathematical approaches seem
Alemayhu et al., Cogent Food & Agriculture (2019), 5: 1622482
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Page 2 of 18

promising, but they usually require considerations over the likely temperature of storage, light
incidence, and packaging material to provide meaningful results (Gutiérrez & Fernández, 2002).
There were many reasons for the push to study the physicochemical characteristics and evalua-
tion of shelf-life of edible soybean, peanut and cottonseed oils produced in Ethiopia. They are
important in daily use as cooking, salad making and in various food processing industries. Quality
problem in finished products has been among the major challenges of the manufacturing sector in
Ethiopia as identified through industry level survey (AACCSA, 2014). Also, edible oil qualities
analysis and shelf life testing are an important part of the quality maintenance in the edible oil
industry for quality and safety reasons. Inappropriate labeling of the best before date and aging
are usually pointed out as the main reasons for failures that can lead to legal actions for
mislabeling and bad experiences for consumers (Moore, Spink, & Lipp, 2010). The development
of an effective tool to predict oils shelf-life is considered of paramount importance in order to
protect consumers and to avoid the commercialization of oils that do not comply with the
regulatory parameters for the commercial grade stated on the label.
Besides, nutritional and toxicological effectsof lipid oxidation in foods have attracted much interest
recently (Frankel, 1995; Blumenthal, 1996;FAO,2003). Oxidation reduces the essential fatty acid
content of edible oils. However, a more serious problem is associated with toxicological effects of
oxidation products. Since oxidative rancidity is a free radical chain reaction; lots of free radicals are
formed, which can pose a major threat to health by damaging the human body at the cellular level
(Holt, 2011). Excess free radicals can cause premature aging, heart disease, cancer, chronic fatigue
syndrome and a host of other conditions (Alonso et al., 2004; Greyt et al., 2000). The purpose of this
research was to achieve the accelerated shelf-life prediction of edible cotton, peanut and soybean
seeds oils using an empirical model and quality characterization of the produced oils in Ethiopia.
2. Materials and methods
2.1. Materials
The materials in the study were refined, bleached and deodorized (RBD) cotton, peanut and
soybean seed oils produced in Ethiopia. Have no antioxidant intentionally added. After collection,
they were kept at 4 °C until analyses commenced to control their deterioration.
2.2. Analysis of oil physical quality parameters
AOAC (1998) Official Method 920.212 was applied to determine the specific gravity of the edible oil
samples. The refractive index (RI) of oils samples was obtained by measuring the brix value at 20°
C using Refractometer (Model, E-line 90–44-806, Nova Analytical Company, 2008). Then, the
corresponding refractive reading was taken from Brix to refractive index conversion table. The
spectrophotometric method, AOCS (1998) Method Cc 13c-50 was applied to measure the color of
edible oils samples. Furthermore, gravimetric method, AOCS (1998) Method 3a-46 was applied to
determine the weight fraction of insoluble impurities in the edible oil samples.
2.3. Analysis of oil chemical quality parameters
Moisture content and volatile matter were analyzed by air oven method of AOAC (1998) Official
method 925.09. Hanus method was employed to determine the iodine value (IV) of edible oil
samples. AOAC (1998) Official method 920.160 was used to determine the saponification value
(SV) of the oil samples. AOAC (1998) Official method 933.08 which is ether extraction method was
used to quantify the percentage unsaponifiable matter in the oil samples. Non-aqueous titration
method was employed to analyze the acid value (AV) of the edible oil samples (FSSAI, 2012).
2.4. Fatty acids profile
The fatty acid compositions of edible oils were determined as methyl esters after trans-esterification
according to AOAC Official Methods 969.33 (AOAC, 1998). Analyses of fatty acids and fatty acids
methyl esters were carried out using a 7820A Network GC System equipped with an HP-5MS (30 m x
Alemayhu et al., Cogent Food & Agriculture (2019), 5: 1622482
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0.25 mm, 0.25 µm film thickness) capillary column and with a 5977E Network MSD mass spectro-
meter, operated in electron-impact ionization mode. GC-MS analyses were carried out in split mode
(split ratio 1:50), using helium as the carrier gas (1mL/min flow rate). The injector temperature was
fixed at 250°C. The sample volume injected was 1μl. The oven temperature was held at 150°C for 2
min and then programmed at 5°C/min to a final temperature of 280°C, where it was maintained for 5
min. It is known that individual fatty acids can be identified by GC because of their different retention
times. Major peaks were selected and using the systematic names and CAS no. of the major peaks,
their corresponding common names were identified from the literature. For comparative purpose,
area percentage was calculated considering only the peak area of selected major peaks.
2.5. Oxidative deterioration
Oxidative deterioration was measured by peroxide analysis. The widely used iodometric titration
method AOAC (1998) Official Method 965.33 was used to determine peroxide value (PV) of oil
samples in characterizing their oxidative deterioration.
2.6. Shelf-life prediction
The shelf life of oil was determined by using accelerated shelf life testing method. The behavior of
hydrogen peroxides formation was used to monitor the extent of oxidative deterioration in the oils
and predict their shelf-life (Hosseini, Ghorbani, Mahoonak, & Maghsoudlou, 2014). Accordingly,
edible oil samples were subjected to a preselected constant-elevated temperature (35, 45 and 55°
C) in acceleration/environmental chamber (model VC
3
4060/VC
3
7060) for six successive weeks to
speed up the deterioration kinetics. Then, the extent of oxidative deterioration was monitored by
chemical testing method (PV analysis) per week. Then, employing the fundamental kinetic princi-
ples and Arrhenius relation, data obtained were then modeled to obtain the parameters describ-
ing/predicting the oxidation kinetics and the shelf-life. Saguy and Karel (1980) on their study had
recommended a kinetic approach and the Arrhenius relationship for modeling the quality dete-
rioration during food processing, transportation and storage.
2.7. Experimental design and statistical data analysis
Design of experiment chosen for the study was a Randomized Complete Block Design. All deter-
minations were carried out in triplicates. Data collected were subjected to analysis of variance
applying the principles of one-way ANOVA to test levels of significant difference among the means.
The statistical software SPSS version 20 was employed for ANOVA while Microsoft office excel-2007
for regression analysis. Significant differences between the means were determined by Duncan’s
multiple range tests. P-values less than 0.05 level of probability were considered statistically
significant. The readings were reported in terms of mean ± Standard deviation (SD).
3. Results and discussion
3.1. Edible oils physical quality characteristics
The oil physical quality parameters analysis results obtained for edible oils considered are shown in
Table-1. The specific gravity of local edible oils was determined by using a specific gravity bottle at
a temperature of 20°C. For edible soybean oil determined specific gravity was amount 0.929 ± 0.02
while the specific gravity of peanut and cottonseed oils was 0.943 ± 0.01 and 0.922 ± 0.01,
respectively. There was no significant difference among the oils investigated. This could be
attributed to the similar fatty-acid composition, similar total solid content and similar moisture
content. The Ethiopian standard agency on the compulsory Ethiopian standard specified a specific
gravity amount ranging from 0.9090 to 0.913 for refined peanut oil and 0.918–0.926 for refined
cottonseed oil at 20°C, respectively (CES-16, 2014; CES-19, 2014). On the basis of this standard
values, the specific gravity result obtained in the study for edible peanut oil was above the upper
bound of the standard value. However, the specific gravity determined for edible cottonseed oil
was within the standard value range. On the other hand, the specific gravity of oils obtained in this
study was comparable to that reported by Gunstone (2008) for refined oil from soybean
(0.919–0.925), peanut oil (0.914–0.917) and cottonseed oil (0.918–0.926).
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The refractive index (RI) of local edible soybean, peanut and cottonseed oil samples were
measured at 20°C. As shown in Table-1 determined RI values were: 1.489 ± 0.00, 1.486 ± 0.00
and 1.486 ± 0.00 for edible soybean, peanut and cottonseed oils, respectively. There was no
significant difference between the RI of edible peanut and cottonseed oil. But, RI of edible soybean
oil was significantly different from the rest edible oils investigated. The RI of oils and fats is
sensitive to their composition. In fats, RI increases with an increasing chain length of fatty acids
in the triglycerides or with increasing unsaturation. A study by Ngassapa and Othman (2001) found
that oils of different types exhibited different RI. Besides, Gunstone (2002) stated RI is a parameter
that relates to molecular weight, fatty acid chain length, degree of unsaturation, and degree of
conjugation. This makes it an excellent spot test for uniformity of compositions of oils and fats
(Fakhri & Qadir, 2011). Based on this literature review, the higher RI value of soybean oil could be
attributed to the difference in composition and its higher degree of unsaturation. In the determi-
nation of IV, edible peanut and cottonseed oils had no significant difference but significantly lower
than the IV for soybean oil. This implies the degree of unsaturation in edible peanut and cotton-
seed oils lower; accordingly, lower RI value would expected and it was obtained.
Similar research conducted by Gunstone (2008) reported a RI range of 1.466–1.470 for soybean
oil, 1.460–1.465 for peanut oil and1.458–1.466 for cottonseed. The Ethiopian Standard Agency has
specified a RI range of 1.460–1.465 and 1.458–1.466 for both refined peanut and cottonseed oils,
respectively (Compulsory Ethiopian Standard CES-16, 2014; Compulsory Ethiopian Standard CES-
19, 2014). RI determined for oils analyzed in the study was not comparable to their corresponding
literature values. The percentage deviation was 1.37% and 1.34%, respectively.
Appearance is the manifestation of the nature of edible oils through visual attributes of which
the color is one. The color of the oil is one of the most important physical indicators for the
determination of oil quality (Kim et al., 2015). It is an important quality parameter of edible oil,
both in the refining process and marketplace. The color of edible soybean, peanut and cottonseed
oils were determined by spectrophotometric method and the results were summarized in Table 1.
as observed from the table there was a significant difference in photometric color index among the
oils investigated. Edible soybean oil had the lowest color index, while edible cottonseed oil had the
highest photometric color index.
Insoluble impurities analysis result for domestic edible oils are presented in Table 1. As indicated
in the table, percentage insoluble impurities amounting 0.001 ± 0.00, 0.004 ± 0.00 and 0.013 ± 0.00
were obtained for edible soybean, peanut and cottonseed oils, respectively. There was no signifi-
cant difference between the soybean and peanut oil. An exception was edible cottonseed oil that
contains a significantly higher amount of insoluble impurities than the other oils. The Compulsory
Ethiopian Standards indicate maximum insoluble impurities amounting 0.05% (w/w) for both
Table 1. Physical characteristics edible cotton, peanut and soybean seed oils manufactured in
Ethiopia
Quality parameter Edible oil type
Soybean Peanut Cottonseed
Specific gravity at
20/20°C
0.929 ± 0.01
a
0.943 ± 0.01
a
0.922 ± 0.01
a
RI at 20°C 1.489 ± 0.00
b
1.486 ± 0.00
a
1.486 ± 0.00
a
Color (photometric color
index)
5.262 ± 0.22
a
15.91 ± 0.02
b
216.316 ± 0.20
c
Insoluble impurities
% (w/w)
0.001 ± 0.00
a
0.004 ± 0.00
a
0.013 ± 0.00
b
a-c
All values are means ± SD; Means across a row with a different superscript differ significantly
at P< 0.05; Means across a row with the same superscript not differ significantly at P< 0.05.
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refined peanut and cottonseed oil (Compulsory Ethiopian Standard CES-16, 2014; Compulsory
Ethiopian Standard CES-19, 2014). Compared to the specified standard value, percentage insoluble
impurities determined for both edible peanut and cottonseed oils were below the permitted
maximum limit declared by Ethiopian Standard Agency.
3.2. Edible oils chemical quality characteristics
Low moisture content of the oil is advantageous in terms of storage stability since the lower the
moisture content, the better the storability and suitability to be preserved for a longer period
(Orhevba & Efomah, 2012). In the study, moisture content and volatile matters (MCVMs) of the
edible oils was determined 105°C and the results are shown in Table 2. Accordingly, percentage
MCVMs amounting: 0.210 ± 0.01, 0.219 ± 0.00 and 0.220 ± 0.01 %(w/w) were obtained in edible
soybean, peanut and cottonseed, respectively. There was no significant difference among the oils
investigated. As specified by Ethiopian standard agency on the Compulsory Ethiopian Standard, the
MCVMs of refined peanut and cottonseed oils is 0.2%(w/w) (Compulsory Ethiopian Standard CES-
16, 2014; Compulsory Ethiopian Standard CES-19, 2014). Thus, the MCVMs determined in the oils is
comparable to the values specified by the Ethiopian Standard Agency.
Peroxide value (PV) which is used as an indicator of deterioration of oils was found to be 1.299 ± 0.14
for edible soybean, while, 2.398 ± 0.00 and 3.396 ± 0.28 meqs of O
2
/kg of oil for edible peanut and
cottonseed oils, indicating that the oils are fresh. This is because, the PV is used as an indication of
quality and stability of oils and fats, and generally fresh oils usually have peroxide values well below
10meq/kg (Vidrih, Vidakovič, & Abramovič,2010). Of the three oils studied PV of edible soybean oil was
significantly lower than PV of peanut and cottonseed oil. Studies using soybean oil indicate that
peroxide levels ranging from 1.0 to 5.0 meq/kg signify low oxidation; 5.0–10.0 meq/kg signify moderate
oxidation; and 10.0meq/kg and above signify high levels of oxidation (AOCS, 1998). Accordingly,
determined PV of all oils investigated was between the ranges 1.0–5.0 meq/kg implying that low
oxidation had occurred in the oils studied. The result obtained for both edible oils in the study were in
agreement with the Ethiopian standard value (PV = 10 meq/kg) mentioned (Compulsory Ethiopian
Standard CES-16, 2014; Compulsory Ethiopian Standard CES-19, 2014).
As shown in Table 2that a PV value of 10meqs of O
2
/kg of oil, the upper limit for unrefined oils,
and a PV of 7meqs of O
2
/kg of oil, the upper limit for refined oils were not exceeded in the oil
samples investigated. In comparison, among the oils considered in the study, edible soya bean oil
Table 2. Chemical characteristics edible cotton, peanut and soybean seed oils manufactured in
Ethiopia
Quality parameter Edible oils
Soybean Peanut Cottonseed
Moisture content & volatile matters at
105°C % (w/w)
0.210 ± 0.01
a
0.219 ± 0.00
a
0.220 ± 0.01
a
Peroxide value
(meq. of O
2
/kg of oil)
1.299 ± 0.14
a
2.398 ± 0.00
b
3.396 ± 0.28
c
Iodine value
(g of I
2
absorbed/100g oil)
136.740 ± 2.03
b
97.536 ± 3.59
a
101.112 ± 3.45
a
Saponification value
(mg of KOH/g of oil)
210.345 ± 0.45
a
210.779 ± 0.45
a
208.411 ± 0.54
b
Unsaponifiable matters
[% (w/w)]
0.169 ± 0.04
a
0.069 ± 0.03
a
0.383 ± 0.03
b
Acid value
(mg of KOH per g of oil)
0.420 ± 0.00
a
0.630 ± 0.10
b
0.561 ± 0.00
a
a-c
All values are means ± SD; Means across a row with a different superscript differ significantly at P< 0.05; Means
across a row with the same superscript not differ significantly at P< 0.05.
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had on average a significantly lower PV amounting 1.299meqs of O
2
/kg of oil while edible cotton-
seed oil had a higher PV amounting 3.197meqs of O
2
/kg of oil. As compared to soybean oil, the rate
of higher peroxidation found in both peanut and cottonseed oils could be related to the kind of
treatment to which the oils were subjected, FFAs and degree of unsaturation on the fatty acids
that make up the oil. There was no significant difference between peanut and cottonseed oils.
Iodine value (IV) which gives the degree of unsaturation in oils was found to be 136.740 ± 2.03
g of iodine absorbed/100g of oil for edible soybean oil, 97.536 ± 3.59 g of iodine absorbed/100g of
oil for edible peanut oil and 101.112 ± 3.45 g of iodine absorbed/100g of oil for edible cottonseed
oil. The average IV determined for soybean oil was significantly higher than the other oils
investigated, suggesting that the unsaturated fatty acid content of soybean oil was high.
Because the IV is an index of unsaturation; the higher the IV, the more unsaturated fatty acid
are present in fat and/or oil (Fakhri & Qadir, 2011; Scrimgeour, 2005). There was no significant
difference between the IV of peanut and cottonseed oils; this implying that both oils had nearly
equal-unsaturated fatty acid content and degree of unsaturation.
A study by Ngassapa and Othman (2001) stated oxidative and chemical changes in oils during
storage are characterized by decrease in the total unsaturation of the oil. This could contribute to
the reduced IV of peanut and cottonseed oil. As seen in Table 2, differences in mean IV value
existed between the oils. This value classifies edible soybean and edible cottonseed oils as non-
drying whereas edible peanut oil as non-drying. Because Duel (1951) proposed that iodine value
above 100 g of iodine absorbed/100 g of oil makes an oil to be classified as drying while below 100
g of iodine absorbed/100g of oil as non-drying.
In the study, the Saponification values (SV) of the local edible oils were determined and is shown
in Table 2. It was found that 210.345 ± 0.45 mg of KOH/g of oil for edible soybean, 210.779 ±
0.45 mg of KOH/g of oil for edible peanut oil and 208.411 ± 0.54 mg of KOH/g of oil for edible
cottonseed oil. Even though there was no significant difference between soybean and peanut oils,
as compared to cottonseed oil, both oils had higher SV. The presence of high molecular weight
fatty acid and their longer chain could contribute to the higher SV of soybean and peanut oils while
the presence of low molecular weight fatty acid and their shorter chain attributed to the lower SV
of cottonseed oil. Because SV is an indication of the average molecular weight and hence
measures the average chain length of fatty acids which make up oil and/or fat (Ngassapa &
Othman, 2001; Scrimgeour, 2005).
All the samples had the highest SV value as compared to FAO & WHO (1993) standards. On the
Compulsory Ethiopia Standard, the SV specified for refined peanut and cottonseed oils amount
187–196, and 189-198 mg of KOH per g of oil, respectively (Compulsory Ethiopian Standard CES-16,
2014; Compulsory Ethiopian Standard CES-19, 2014). However, the SV of these oils determined in
this study was higher than the upper bound of the standard range. From previous studies the SV
values of edible oils amounts 189–195 g of KOH/g of oil for soybean oil, 187–196 g of KOH/g of oil
for peanut oil and 189–198 g of KOH/g of oil for cottonseed oil (Scrimgeour, 2005). Compared to
the literature values SV determined for the oils investigated in this work was higher.
Also, Table 2summarizes unsaponifiable matters of edible soybean, peanut and cottonseed oils
which were determined in this study. Accordingly, percentage unsaponifiable matters amounting
0.169 ± 0.03, 0.069 ± 0.03 and 0.383 ± 0.03% (w/w) was found in soybean, peanut and cottonseed
oils, respectively. There is no significant difference between soybean and peanut oils. The highest
value of unsaponifiable matters was found in edible cottonseed oil. A study by Shahidi (2005)
suggested that the content of unsaponifiable matters is varied in different oils depending on the
extent of oil refining.
Unsaponifiable matters in refined peanut and cottonseed oil is specified by Ethiopian Standard
Agency. The tolerable maximum unsaponifiable matters allowed in refined peanut and cottonseed
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amounts 0.8% and 1.5% (w/w), respectively (Compulsory Ethiopian Standard CES-16, 2014;
Compulsory Ethiopian Standard CES-19, 2014). Compared to these national standard values,
unsaponifiable matters determined for both oils were acceptable. In general, unsaponifiable
matters are resent in edible oils at less than 2% (Shahidi, 2005). Literatures showed that unsapo-
nifiable matters is about <1.5 for soybean, <1 for peanut oil and <2 for cottonseed oil (Belitz,
Grosch, & Schieberle, 2009; Scrimgeour, 2005). In view of this study, the unsaponifiable matters
determined for the oils investigated were comparable to literature values.
Acid value (AV) is a measure of the free fatty acids in edible oils; the higher the AV the higher the
free fatty acid which also means decreased oil quality (Tesfaye, Sahile, & Madhusudhan, 2015). The
AV of edible oils considered in this study is summarized in Table 2; amounts: 0.420 ± 0.00, 0.630 ±
0.10, and 0.561 ± 0.00 g of KOH per g of oil for edible soybean, peanut and cottonseed oils
respective. Among the oils studied, edible soybean and cottonseed oils nearly shows the same
AV or didn’t differ significantly. This could be due to either a similar refining technologies may have
applied in the respective oil company or low FFA content in raw materials prior to processing.
Edible peanut oil had a higher AV than the rest oils and significantly different. Natural variation in
moisture content and the variation in refining and deodorization process could attribute for the
significant difference.
Compulsory Ethiopia Standard specifies AV amounting 0.6 mg of KOH per g of oil for both edible
peanut and cottonseed oils, respectively (Compulsory Ethiopian Standard CES-16, 2014;
Compulsory Ethiopian Standard CES-19, 2014). The results obtained in the study were comparable
to the national standard value. According to the Codex Alimentarius Commission (1999), the
recommended maximum AV limits for refined plant oils is 0.3% and the limiting value for
unrefined oils is 3%. The investigation was revealed that the AV values of edible oils studied
were above the limiting value for refined oils (0.3%) as indicated in the Codex Alimentarius (1981)
Commission standard. Israel (2008) on his study stated that AV represents FFA content due to
enzymatic activity and is usually indicative of spoilage, and its maximum acceptable level is
4mgKOH/g of oil, below which the oil is acceptable for consumption. As compared to the study,
all edible oil samples had lower AV value.
The AV determination measures the amount of hydrolytic activity that has occurred in the oil. As
shown in Table 2determined AV value for edible peanut oil was significantly higher than for edible
soybean and cottonseed oil. This means that either the amount of hydrolytic activity that had
occurred in the edible peanut oil was higher than that had occurred in edible soybean and
cottonseed oils or the refining technology employed for FFAs removal in edible peanut oil factory
was not as effective as in edible soybean and cottonseed oils factory; in other way the edible oil
factories may differ in the refining technology applied to remove FFAs. Besides, the higher AV of
peanut oil might be due to the high FFAs content in the raw material prior to processing.
It is reported that oils with low free fatty acid (low AV) usually have high SV. As per the study’s
results, this was valid theory for edible soybean and cottonseed oil. As shown in Table 2,in
comparison to edible cottonseed oil, edible soybean oil had higher SV amounting 210.345 ±
0.451 mg of KOH/g of oil and lower AV which amounts 0.420 ± 0.0004 mg of KOH/g of oil while,
edible cottonseed oil had lower SV amounting 208.411 ± 0.538 mg of KOH/g of oil and had higher
AV which amounts 0.561 ± 0.0003 mg of KOH/g of oil. The same was true when peanut oil was
compared to edible cottonseed oil (or vice versa). However, the inverse relationship between AV
and SV was invalid when edible peanut oil compared to edible soybean oil (or vice versa).
3.3. Fatty acids profile
Determining the oils composition is important not only because of the fatty acid contents and the
pattern of glyceride distribution but also because the physical character and end-use performance
of oils are directly related to composition (O’Brien, 2009). Oils and fats are now characterized
mainly by their fatty acid composition. The GC-MS analysis results summarized in Tables 3
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qualitatively describes the fatty acids composition of edible soybean, peanut and cottonseed oils
(Figure 1). The fatty acid profile of the edible soybean oil was as follows: palmitic (15.489%),
linoleic (42.807%), oleic (37.668%), and margaric (4.035%). Determined fatty acid composition of
edible peanut oil includes Myristic (3.902%), Palmitoleic (2.506%), Pentadecanoic acid (22.464%),
Linoleic (13.139%), Oleic (46.252%), and Stearic (11.737%). The edible cottonseed oil fatty acid
profile was: Myristic (1.21%), Palmitic (29.52%), Linoleic (41.587%), Oleic (24.855%), and Stearic
(2.835%).
It is possible to observe that the higher percentage peak area was registered for the linoleic acid
42.807% and 41.587%, which is the most important fatty acid; essential fatty acid both in edible
soybean and cottonseed oils, respectively. Based on this, the predominant fatty acid both in edible
soybean and cottonseed oil were linoleic. In edible peanut oil, higher percentage peak area was
obtained for Oleic (46.252%); implying that being the major fatty acid in peanut oil. Forero, Ruiz,
and Giraldo (2012) on their study about the calculation of thermo-physical properties of oils and
triacylglycerols has found the fatty acid content of soybean oil which comprises: Palmitic (11.3%),
Oleic (23%), Linoleic (53.4%) and Linolenic (5.96%). As shown in Table 3for edible soybean oil, the
fatty acid profile determined was comparable to the literature.
The fatty acid profile provides information on oil nutritional quality. The content of fatty acids, as
well as the ratio between unsaturated and saturated fatty acids, is an important parameter for
determination of the nutritional value of certain oil. It is known that the excessive consumption of
saturated fatty acids is related to the increase of the plasmatic cholesterol and the obesity (Kostik,
Memeti, & Bauer, 2013). Saturated fatty acid content of edible soybean and cottonseed oil were
amount nearly half of the total fatty acids content (saturated and unsaturated fatty acids). However,
in edible peanut oil, the saturated fatty acid content was less than one-fourth of the total fatty acids
content. On the other hand, in respect of total percentage of essential fatty acids (linoleic), edible
soybean and cottonseed oils had comparable linoleic content and were superior to the amount in the
edible peanut oil.
Table 3. Typical fatty acid profile of edible cotton, peanut and soybean seed oils
Edible oil type Retention Time % peak area Systematic
Name
Common
Name
Soybean 18.917 15.489 Hexadecanoic acid Palmitic (16:0)
21.710 42.807 9, 12—Octadecadienoic
acid
Linoleic (18:2)
21.810 37.668 9—Octadecenoic acid Oleic (18:1)
22.260 4.035 Heptadecanoic Margaric (17:0)
Peanut 16.294 3.902 Tetradecanoate Myristic (14:0)
18.622 2.506 9—Hexadecenoic acid Palmitoleic (16:1)
18.906 22.464 Pentadecanoic acid —(15:1)
21.694 13.139 9, 12—Octadecadienoic
acid
Linoleic (18:2)
21.803 46.252 c-9—Octadecenoic acid Oleic (18:1)
22.239 11.737 Methyl stearate Stearic (18:0)
Cottonseed 12.678 1.21 Tetradacanoate Myristic (14:0)
14.938 29.52 Hexadecanoic acid Palmitic (16:0)
17.501 41.587 9, 12—Octadecadienoic
acid
Linoleic (18:2)
17.587 24.855 9—Octadecenoic acid Oleic (18:1)
18.004 2.835 Methyl stearate Stearic (18:0)
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3.4. Shelf-life prediction and kinetic analyses
Taking hydrogen peroxides formation into consideration, kinetic analyses were attempted to examine
deterioration behavior of edible soybean, peanut and cottonseed oils, and the effect on the shelf-life
the oils was also investigated from a quantitative viewpoint. Accordingly, it was proceeded to deter-
mine the parameters of the kinetic model and Arrhenius relation that fit better the experimental data.
Primarily, the apparent order of reaction for the formation of hydrogen peroxides was determined
through linear regression analysis. Figure 1shows the behavior of hydrogen peroxides formation of in
the edible soybean, peanut and cottonseed oils at 35°C, 45 °C and 55 °C, respectively.
AscouldbeobservedfromFigure2, during the early stages, i.e. initiation stage, lipid peroxidation
starts at a slow rate, in consequence, the level of hydrogen peroxides produced remains low until free
radicals formed. This can be theoretically interpreted as the reaction between the radical, formed during
the induction time, and the unsaturated fatty acid. Once the free radicals formation happened, as
observed in all the accelerated mode of oxidative deterioration of the edible oils, the reaction rates were
increased exponentially. A sudden increase observed in PV was related to the propagation stage of the
oils oxidation process. The graph of hydrogen peroxide formation at a temperature of 55°C for edible
soybean and cottonseed oils were declining nearly for the last two weeks. These different patterns of the
curves correspond to thermal decomposition of hydrogen peroxide into secondary oxidation products.
a)
b)
c)
Figure 1. Fatty acids chromato-
gram for a) soybean oil b) pea-
nut oil c) cottonseed oil.
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Most of the reactions responsible for food quality loss have been classified as zero, first and second
order (Cunha & Oliveira, 2000). These kinetic equations are specific for each food and for each
temperature studied (Steele, 2004). The model equation that represents the oxidative deterioration
of the edible oils studied was established based on the coefficients of linear regression (R
2
).
As shown in Figure 2, the experimental data for hydrogen peroxide formation in the edible
soybean, peanut and cottonseed oil verses time was plotted, including the corresponding values of
natural logarithm as well. For edible soybean oils studied at all acceleration temperature, the
coefficients of linear regression (R
2
) for zero order plot was more close to one than coefficients of
linear regression (R
2
) for first order plot. Similar relationships were also observed at 35, 45 and 55°
C for both edible peanut and cottonseed oils studied. Accordingly, the linear regression analysis
indicated that the kinetic model that best fitted the experimental data corresponds to a zero order
model for all edible oil investigated, since [PV] Vs time shows a good fit to linear equation. The
following Equation (1) represents the kinetic model which was identified for the oxidative dete-
rioration of edible soybean, peanut and cottonseed oils at every accelerated temperature studied.
PV ¼PVOkPVt(1)
Where: k
PV—
is the rate constant for hydroperoxides formation (meq. O
2
/kg-week),
t—is the reaction time and PV
O
represents the peroxide value at time zero of reaction.
Oxidation of edible oils is the most important reactions that cause deterioration of the quality of
the oil (Gonabad, Noghabi, & Niazmand, 2015; Eskin & Robinson, 2001). Taking the decaying linear
characteristics into consideration, coefficients of linear regression (R
2
) and the rate constant (k
PV
)
of the zero-order kinetic models for edible soybean, peanut and cottonseed oil at every accelerated
temperature studied was mentioned in Table 4. The reaction rate constant was determined for
each temperature from the slope of the line obtained from the zero order plot. The result
emphasizes the effects of temperature on the rate of hydrogen peroxide formation during the
lipid peroxidation of each edible oils studied. As could be seen in Table 4, the value of rate constant
became higher with an increase of the storage temperature, for all oils investigated.
(a).
(b).
(c).
y = 1.6443x + 1.5894
R² = 0.973
y = 0.3102x + 0.7678
R² = 0.8832
0
5
10
15
02468
PV (meq O2/kg of oil)
Time (in weeks)
PV &lnPV vs Time @ 35OC
y = 12.777x - 2.27
R² = 0.9912
y = 0.5896x + 1.3055
R² = 0.8352
-20
0
20
40
60
80
100
02468
PV (meq O2/kg of oil
Time (in weeks
PV &lnPV vs Time @ 45OC
y = 61.579x - 12.088
R² = 0.9561
y = 0.7961x + 1.9651
R² = 0.7566
-100
0
100
200
300
400
02468
PV (meq O2/kg of oil
Time (in weeks
PV & lnPV vs Time @ 55OC
y = 1.3238x + 1.7823
R² = 0.9879
y = 0.2532x + 0.8692
R² = 0.9853
0
5
10
15
02468
PV (meq O2/kg of oil)
Time (in weeks
PV &lnPV vs Time @ 350C
y = 6.5634x + 0.4201
R² = 0.9878
y = 0.4416x + 1.3524
R² = 0.9203
0
10
20
30
40
50
02468
PV (meq O2/kg of oil
Time (in weeks
PV &lnPV vs Time @ 450C
y = 43.619x - 8.8599
R² = 0.9901
y = 0.6573x + 2.2336
R² = 0.7732
-100
0
100
200
300
02468
PV (meq O2/kg of oil
Time (in weeks
PV &lnPV vs Time @ 550C
y = 1.3748x + 3.0006
R² = 0.9932
y = 0.2064x + 1.2625
R² = 0.9891
0
5
10
15
02468
PV (meq O2/kg of oil )
Time (in week)
PV &lnPV vs Time @ 350C
y = 11.508x - 2.5621
R² = 0.9777
y = 0.5063x + 1.5282
R² = 0.9456
-20
0
20
40
60
80
02468
PV (meq O2/kg of oil )
Time (in week)
PV & lnPV vs Time @ 450C
y = 59.859x - 9.1252
R² = 0.9525
y = 0.6821x + 2.4487
R² = 0.797
-100
0
100
200
300
400
02468
PV (meq O2/kg of oil
Time (in week
PV & lnPV vs Time @ 550C
Figure 2. Hydrogen peroxides
formation profile in edible (a)
soybean, (b) peanut and (c)
cottonseed oils at 35°C, 45°C
and 55°C.
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Temperature is the main environmental factors that influence the rate of quality loss (Tan, Man,
Selamat, & Yusoff, 2001). This fact was confirmed by the development of Arrhenius model. From data
of kinetic model of zero order, Arrhenius plot was drawn, ln(k
PV
)Vs1/Tfor all local edible oils
considered in the study to determine the entity of dependency between the oxidative reaction
constant and temperature. Figure 3shows the Arrhenius plot for edible soybean, peanut and cotton-
seed oils; respectively. For these calculations, it was taken into account the values of the rate constant
of formation of hydrogen peroxides (k
PV
) that were obtained from kinetic models of zero order at each
accelerated temperatures tested. Because with the results obtained at 35°C, 45°C and 55°C, it is
possible to extrapolate the rate constant value and shelf-life of oil at any other temperature.
A coefficient of linear regression (R
2
) value close to one indicates that the Arrhenius model is
applicableto experimental data obtained (Piedrahita, Penaloza, Cogollo, & Rojano, 2015). In the linear
form Arrhenius model (lnk = lnk
A
-E
A
/R(1/T)), the coefficient—E
A
/R represents the slope of Arrhenius
plot while lnk
A
represents the intercept. Having the values of these variables could help to develop the
rate constant equation by substituting the corresponding values into the Arrhenius equation (k=k
A
exp
(-E/RT)). Accordingly, the following rate constant equations were developed for the oxidative dete-
rioration of edible soybean (Equation-2), peanut (Equation-3) and cottonseed (Equation-4) oils. With
these equations, the oxidative deterioration rate constant could be predicted at any temperature for
the corresponding edible oils.
kfor edible soybean oilðÞ
¼e60:1018350 1
T
ðÞ½ (2)
kfor edible peanut oilðÞ
¼e57:5317643 1
T
ðÞ½ (3)
kfor edible cottonseed oilðÞ
¼e62:4019116 1
T
ðÞ½ (4)
Where: k—rate constant and T—temperature in Kelvin (K).
The Zero-order reaction was already the identified kinetic model equation (Equation-1) for
oxidative deterioration of edible soybean, peanut and cottonseed oil. Substituting the rate con-
stant model equation developed (Equation-2, Equation-3 and Equation-4) into the kinetic model
equation, Equation-1 and rewriting for time, the following general shelf-life prediction models were
developed for edible soybean (Equation-2), peanut (Equation-6) and cottonseed (Equation-7) oils.
These shelf-life equations could help to predict the shelf-life of the corresponding edible oils at any
temperature.
Table 4. Kinetic parameters of hydrogen peroxides formation in edible cotton, peanut and
soybean seed oils
Edible oil type Temperature (°C) Linear correlation
coefficient (R
2
)
Rate constants k
PV
(meq. O
2
/kg-week)
Soybean oil 35 0.973 1.644
45 0.991 12.77
55 0.956 61.57
Peanut oil 35 0.987 1.323
45 0.987 6.563
55 0.990 43.61
Cottonseed oil 35 0.993 1.374
45 0.977 11.50
55 0.952 59.85
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ts for edible soybean oilðÞ
¼PVOPV
e60:1018350 1
T
ðÞ½ (5)
ts for edible peanut oilðÞ
¼PVOPV
e57:5317643 1
T
ðÞ½ (6)
ts for edible cottonseed oilðÞ
¼PVOPV
e62:4019116 1
T
ðÞ½ (7)
Where: t
s
—shelf-life, PV—Peroxide Value of oil at the end of shelf-life, PV
O
—Initial Peroxides
Value, and T—Temperature in K.
(a)
(b)
(c)
y = -18350x + 60.101
R² = 0.9966
0
1
2
3
4
5
0.003 0.0031 0.0032 0.0033
ln(kPV) (meq. Oxygen/Kg-
week
Risprocal of temperature (1/T) in K
Arrhenius plot for edible soybean oil
y = -17663x + 57.532
R² = 0.9956
0
0.5
1
1.5
2
2.5
3
3.5
4
0.003 0.0031 0.0032 0.0033
ln(kPV) (meq. Oxygen/Kg-week)
Risprocal of temperature (1/T) in K
Arrhenius plot for edible peanu oil
y = -19116x + 62.40
R² = 0.997
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0.003 0.0031 0.0032 0.0033
ln(kPV) (meq. Oxygen/Kg-week
Risprocal of temperature (1/T) in K
Arrhenius plot for edible cottonseed oil
Figure 3. Effect of temperature
on the rate constant of hydro-
gen peroxides formation in
edible (a) soybean (b) peanut
(c) cottonseed oils.
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The concentration of hydrogen peroxides in edible fats and oils has been regulated by legislation.
As indicated in the Compulsory Ethiopia Standard for edible peanut and cottonseed oils, the
agency declared a maximum PV of 10meq oxygen/kg both in edible peanut and cottonseed oils
(Compulsory Ethiopian Standard CES-16, 2014; Compulsory Ethiopian Standard CES-19, 2014). For
this reason and as general rule, this value was set as the limit to predict the shelf-life of the edible
soybean, peanut and cottonseed oils at 25°C. for Arrhenius plot a value coefficient of linear
regression (R
2
) close to one indicates that Arrhenius model is applicable to experimental data
obtained, and that the activation energy (E
A
) remains constant within the range of accelerated
temperatures studied (Singh, 1994; Piedrahita et al., 2015). Based on this background and employ-
ing the predictive models developed, the rate constant (k
PV25
) and shelf-life of edible oils investi-
gated were predicted at ambient temperature (25°C) and the result is summarized in Table 5.
Besides, activation energy (E
A
) and temperature acceleration factor (Q
10
), for oxidative deteriora-
tion of edible soybean, peanut and cottonseed oils were also calculated and mentioned in Table 5.
As revealed in Table 5the calculated activation energy amounts 152.569, 146.857, and 158.938 kJ/
mol.K for edible soybean, peanut and cottonseed oils, respectively. According to the Arrhenius
principle, oil with a high E
A
value oxidizes faster at high temperatures, while oil with a low E
A
value
oxidizes faster at low temperatures (Saldana & Monteagudo, 2013). Based on this, edible soybean oil
had the highest oxidation rate compared to edible peanut and cottonseed oil. This could be attributed
to the highest degree of unsaturation. From the analysis, edible soybean oil had the highest value
136.740 ± 2.031grams iodine absorbed/100g oil followed by edible cottonseed oil having IV amount-
ing 101.112 ± 3.454grams iodine absorbed/100g oil and edible peanut with IV of 97.536 ± 3.592
grams’iodine absorbed/100g oil. Also the values of the E
A
were in a reasonable order, i.e. E
A
of edible
peanut oil< E
A
of edible cottonseed oil < E
A
edible of soybean oil. Souza, Santos, Conceica, Silva, and
Prasad (2004) was investigated the oxidation kinetics of sunflower oil in the temperature range of
380–550°C and determined the kinetic parameters using four different methods, for the study
temperature range of 380–480, on average calculated E
A
was amount 293.923 kJmol
−1
. Activation
energy values obtained at 25°C for all edible oils considered in this study were much lower than the
value determined for sunflower oil.
The presence of double bonds increases the oxidation rate and would increase the reaction rate
constant (Campo, Zhao, Suidan, Venosa, & Sorial, 2007). The predicted k
PV25
°
C
values for the oxidative
deterioration of all edible oils studied are presented in Table 5. It was amounts 0.235, 0.181 and 0.179
week
−1
for edible soybean, peanut and cottonseed oils, respectively. The higher reaction rate constant
belongs to edible soybean oil; it could be attributed to a higher percentage of polyunsaturated fatty
acids in the oil in comparison with edible peanut and cottonseed oils. A study by Tan et al. (2001)on
the evaluation of oxidative stability of vegetable oils by isothermal differential scanning Calorimeter;
they determined the rate constant at four different temperatures for soybean and peanut oils. At 110°
C, the corresponding rate constants were amounts 0.804 and 0.784 week
−1
respectively. Rate constant
values obtained at room temperature (25°C) for all edible oils investigated were much lower than
these literature values.
Table 5. Parameters of Arrhenius model for the formation of hydrogen peroxides in edible
cotton, peanut and soybean seed oils
Edible oil
type
R
2
E
A
(kJ/mol) k
PV25
°
C
(week
−1
)
Shelf-life
(week)
Q
10
Soybean oil 0.996 152.569 0.235 36.953 7.369
Peanut oil 0.995 146.857 0.181 42.115 6.838
Cottonseed oil 0.997 158.938 0.179 37.816 8.010
Where: R
2
- linear regression coefficient, E
A—
activation energy in kJ/mol, k
PV25
°
C
—rate constant for hydrogen peroxide
formation at 25°C, and Q
10—
temperature acceleration factor.
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The predicted shelf-life at room temperature (25°C) for all edible oils investigated is shown in
Table 5; it was amounts: 36.953, 42.115 and 37.816weeks for edible soybean, peanut and
cottonseed oils, respectively. Compared to soybean and cottonseed oil, peanut oil has longer
shelf-life. The shelf-life of properly refined edible oils is typically 12–18 months at ambient
temperature (Farhoosh, 2007).Ascomparedtotheliterature,theshelf-lifeofedibleoils
determined in this research was lower. Studies using soybean oil indicate that peroxide levels
ranging from 1.0 to 5.0 meq/kg signify low oxidation; 5.0–10.0 meq/kg signify moderate
oxidation; and 10.0meq/kg and above signify high levels of oxidation (AOCS, 1998). The PV of
edible oils determined fall within the moderate oxidation range. This could attribute to lower
the shelf-life of all edible oils studied.
The magnitude of the temperature effect on the rate of oxidative deterioration of edible
soybean, peanut and cottonseed oils was evidenced by Q
10
values. The effect of temperature on
the reaction rate of oil oxidation is expressed by a number called Q
10
. This number is determined
as the ratio of the reaction rate constant at temperatures with 10°C differences (Taoukis, Labuza, &
Saguy, 1997). As shown in Table 5,Q
10
value for edible soybean, peanut and cottonseed oils were
7.369, 6.838 and 8.010, respectively. In general, a higher Q
10
number implies that a smaller
temperature change is needed to induce a certain change in the rate of lipid peroxidation
(Farhoosh, Niazmand, Reazaei, & Sarabi, 2008). Based on this, the rate of hydrogen peroxide
formation in edible peanut oil was slower than in edible soybean and cottonseed oils. Farhoosh
et al. (2008) determined this number for refined canola, soybean, sunflower, and corn oils contain-
ing antioxidants as 13.2, 18.2, 15.2, 10.2 and 2.08, respectively. Low Q
10
value of oils investigated
as compared to the mentioned oils could be attributed to fatty acid composition.
4. Conclusions
Various physicochemical characteristics of local edible soybean, peanut and cottonseed oils
were studied. Except for SV and specific gravity, the result obtained for the rest quality
parameters considered were within the standard range indicated by Ethiopia Standard
Agency. It can be concluded that the edible oils have acceptable quality parameters. Fatty
acid profile analysis showed that the predominant fatty acid in edible soybean and cotton-
seed oils was linoleic acid 42.807% and 41.587%, respectively. While oleic acid (46.252%) was
major fatty acid in edible peanut oil. Therefore, local edible soybean, peanut and cottonseed
oils are an excellent source of omega-6, linoleic acid (essential; fatty acid) and omega-9, oleic
acid. For all oils investigated, the kinetic model established was identical implying that, edible
soybean, peanut and cottonseed oils have a similar mechanism of oxidative deterioration
(peroxide formation). Relative to edible soybean and cottonseed oils, the shelf-life of edible
peanut oil was better. Thus, edible peanut oil has longer hypothetical stability and is more
suitable for frying.
Funding
The authors received no direct funding for this research.
Competing Interests
The authors declares no competing interests.
Author details
Addisu Alemayhu
1
E-mail: addis991@gmail.com
Shimelis Admassu
2
E-mail: shimelisemire@yahoo.com
E-mail: shimelis.admassu@aait.edu.et
Biniyam Tesfaye
3
E-mail: biniyamer@gmail.com
1
Department of Food Process Engineering and Post-harvest
Technology, Ambo University, Ambo, Ethiopia.
2
School of Chemical Bio-engineering, Food Process
Engineering Stream, Addis Ababa University, Addis
Ababa, Ethiopia.
3
Ethiopian Public Health Institute, Food Science and
Nutrition Research Directorate, Addis Ababa, Ethiopia.
Declaration of interest
The authors declare no conflict of interest. The authors
have no competing interests to declare.
Citation information
Cite this article as: Shelf-life prediction of edible cotton,
peanut and soybean seed oils using an empirical model
based on standard quality tests, Addisu Alemayhu,
Shimelis Admassu & Biniyam Tesfaye, Cogent Food &
Agriculture (2019), 5: 1622482.
Correction
This article has been republished with minor changes.
These changes do not impact the academic content of
the article.
Alemayhu et al., Cogent Food & Agriculture (2019), 5: 1622482
https://doi.org/10.1080/23311932.2019.1622482
Page 15 of 18

References
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