267 

 

Journal homepage: www.fia.usv.ro/fiajournal 
Journal of Faculty of Food Engineering,  

Ştefan cel Mare University of Suceava, Romania  

Volume XIX, Issue 4 - 2020, pag. 267 - 274 

 

 

 

EFFECT OF ROSEMARY EXTRACT ON THERMAL STABILITY 

OF SUNFLOWER OIL 

 

*Artan GASHI
1 
, Mila ARAPCHESKA

1
, Fatos REXHEPI

2
 

1
Faculty of Biotechnical Sciences, “St. Kliment Ohridski“University,  

Bitola, Republic of North Macedonia 
2
Department of Technology, University of Mitrovica “Isa Boletini” Ukshin Kovaqica, Mitrovica, 

40000, Kosovo 
agashi02@hotmail.com 

*Corresponding author 

Received 22nd September 2020, accepted 29th December 2020 

 
 
 

Abstract: The purpose of this study was to evaluate the effect of rosemary extract (Rosemarinus 
officinalis L.) on thermal stability of sunflower oil. Samples of sunflower oil and sunflower oil 
containing 0.1% rosemary extract were subjected to three successive cycles of thermal heating at 
burning point for 8 hours, followed by cooling at room temperaturefor16 hours. After each cycle, 
samples of oils were taken for analysis ofdensity, viscosity and FTIR spectroscopy measurements. 
Analyzed parameters were used as indicators of structural changes in analyzed samples of oils. 
According obtained results the addition of rosemary extract in sunflower oil effectively protect its 

triglyceride structure and level of unsaturation during thermal heating and increase its thermal 
stability. Performed FTIR spectroscopy has indicated the role of rosemary extract as a natural 
protective agent. Samples of sunflower oil with rosemary extract have shown improved thermal 

stability compared with pure sunflower oil. 
 
Keywords:sunflower oil, thermal stability, rosemary extract, natural antioxidants,FTIR spectroscopy 

 

 

 

 

1. Introduction 

 

Vegetable oils, especially cold pressed are 

an essential component of a healthy diet. 

Polyunsaturated fatty acids contained in 

vegetable oils are important substances 

from physiological and nutritional points 

of view. Despite their health benefits, they 

can also be considered as a reason of 

instability of oils during the technological 

processes of their production, thermal 

heating, during cooking or during the 

storage [1]. Double bounds present in 

chemical structure in edible oils make 

them prone to oxidative reactions, which 

are major cause of deterioration of oils 

during the period of heating. Thermal 

heating processes may compromise oil`s 

stability, causing modifications in the 

chemical structure and organoleptic 

properties. Moreover, these processes 

result in the formation of secondary, 

potentially toxic compounds [2-4]. 

Diets in developed countries contain 

substantial quantities of oils subjected to 

different processing and heating treatments 

[5]. High temperature treatment such as 

deep frying oil is one of the most common 

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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XIX, Issue 4 – 2020 

Artan GASHI, Mila ARAPCHESKA, Fatos REXHEPI, Effect of Rosemary Extract on Thermal Stability of Sunflower Oil, 
Food and Environment Safety, Volume XIX, Issue 4 – 2020, pag. 267 - 274 

268 

 

food processing methods used worldwide. 

The quality parameters of the edible oils 

such as: taste, texture, shelf life and 

nutritional composition are affected as a 

result of complex chemical reactions i.e. 

oxidation, hydrolysis, and polymerization, 

which are occurred during the high 

temperature heating process [6]. 

Heating in the presence of air cause 

oxidative and thermal degradations in 

polyunsaturated triacylglycerolsin the oils, 

and induce the formation of polar 

compounds and polymers [5]. 

The changes linked to the process of 

heating itself, depends of: temperature, 

duration of heating, type of heating 

(continuous or discontinuous), type of used 

oil, its initial quality, unsaturation level, 

antioxidant content and presence of 

additives, etc. [7, 8]. 

Lipid oxidation occurring in food products 

is responsible for rancid odors and flavors 

of the products, and leads to consequent 

decrease in their nutritional value and 

safety, and is one of the major concerns in 

food technology. The problem of ensuring 

a high quality of lipids and lipid-containing 

products and prolonging their storage time 

is directly associated with their optimum 

stabilization by addition of suitable 

antioxidants. This is very important from 

aspect of human health protection, and also 

it is economically important [9, 10]. 

Due to their ability to protect foods 

containing oils and fats, antioxidants play 

an important role in food processing [2]. 

They are added to food in order to retard, 

reduce or prevent oxidative deterioration. 

In food industry it is not unusual the use of 

synthetic antioxidants. However, the 

utilization of some of them has been 

questioned because of their toxicity [11]. 

According to recent literature data there 

concerns about the safety and health risks 

associated with the use of some of 

synthetic antioxidants. For this reason, the 

use of herbs and spices to inhibit the 

development of oxidative reactions in food 

systems and improve the oxidative stability 

of food has recently become popular. 

Plants, including herbs and spices, are 

known to have many phytochemicals that 

could be potential sources of natural 

antioxidants, which can retard oxidative 

rancidity via the following pathways: 

capturing of free radicals, 

decomposing/deoxidizing peroxides, and 

scavenging oxygen [9,12, 13]. 

Мany species of the Lamiaceae family 

have strong antioxidant capacity. 

Rosemary (Rosmarinus officinalis L.) 

extract has potentanti oxidant activity and 

it is widely used in the food industry. Its 

antioxidant activity has been associated 

with the presence of several phenolic 

compounds: diterpenes, triterpenes, 

carnosic acid, carnosol, rosmarinic acid, 

rosmanol,rosmariquinone, rosmaridiphenol 

and flavonoids [14-16]. 

The effects of high temperatures on 

vegetable oils with high contents of 

unsaturated fatty acids, especially 

polyunsaturated fatty acids are major 

concern both for product quality and for 

human health. In the diet, sunflower oil is 

widely used, and it is a valuable source of 

essential linoleic acid [17]. It is one of the 

most important vegetable oils employed 

for deep-frying. Because of higher content 

of unsaturated fatty acids, especially 

polyunsaturated fatty acids, sunflower oil 

is more susceptible to oxidation. The 

purpose of this study was to evaluate the 

effect of rosemary extract on thermal 

stability of sunflower oil. 

 

 

2. Matherials and methods 

 

2.1. Samples 
Sunflower oil was purchased from local 

market in Kosovo. According to the 

manufacturer`s specifications, the oil was 

free from antioxidants. The samples were 

prepared as: sunflower oil (control) and 

sunflower oil with 0.1% rosemary extract. 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XIX, Issue 4 – 2020 

Artan GASHI, Mila ARAPCHESKA, Fatos REXHEPI, Effect of Rosemary Extract on Thermal Stability of Sunflower Oil, 
Food and Environment Safety, Volume XIX, Issue 4 – 2020, pag. 267 - 274 

269 

 

The samples were subjected to three 

successive cycles of thermal heating at 

burning point for 8 hours, followed by 

cooling at room temperature for 16 hours. 

After each cycle, samples of oils were 

taken for analysis of density, viscosity and 

fourier transform infrared (FTIR) 

spectroscopy measurements. Analyzed 

parameters were used as indicators of 

structural changes in analyzed samples of 

oils. 

 

2.2. Chemicals 

Folin Ciocalteu reagent, DPPH (2, 2-

diphenyl-1-picrylhydrazyl), gallic acid and 

sodium carbonate were purchased from 

Sigma – Aldrich. Gallic acid stock solution 

in ethanol (1 mg/ml) was prepared and 

used for the preparation of working 

standard solutions necessary for creation of 

calibration curve. 

 

2.3. Characterisation of rosemary 

extract 
Rosemary extract was obtained from 

rosemary (Rosemarinus officinalis L.) 

leaves by steam distillation. 

 

Determination of total phenolic content of 

rosemary extract - The total phenolic 

content in the rosemary extract was 

determined using Folin–Ciocalteu reagent 

[16]. A volume of 1 ml of rosemary extract 

solution, prepared in ethanol at a 

concentration of 0.1 mg/ml, was mixed 

with 7.5 ml Folin–Ciocalteu reagent 

diluted 10 times. The mixture was left 5 

min at room temperature before mixing 

with 7.5 ml of 60 mg/ml of aqueous 

sodium bicarbonate (Na2CO3) solution. 

The prepared mixture was placed at room 

temperature at darkness for 2 h. The 

absorbance of the sample was measured at 

725 nm using spectrophotometer (Jasco V-

630). The concentration was determined 

using gallic acid as reference and the result 

is expressed as mg of gallic acid 

equivalents per gram extract (mg GAE/g). 

 

Antioxidant activity of rosemary extract–

The antioxidant activity of rosemary 

extract was determined using DPPH (2, 2-

diphenyl-1-picrylhydrazyl). For this 

purpose, 0.3 mL aliquot of rosemary 

extract was mixed with freshly prepared 

1.5 mL of DPPH solution in ethanol (0.1 

mmol/L). The solution was stored at 25 °C 

for 30 min at dark and then the absorbance 

was measured at 517 nm by UV-VIS 

spectrophotometer. The control was 

conducted in the same manner, except that 

distilled water was used instead of sample 

(rosemary extract). The IC50 is the 

concentration of an antioxidant that is 

required to inhibit 50% of the initial DPPH 

radicals under given experimental 

conditions. The DPPH scavenging capacity 

assay value was calculated according to the 

formula (1): 

 

IC50 % = [1 – (Asamples / Acontrol)] × 100   (1) 

 

2.4. Density and Viscosity 

Measurements 

After each cycle of thermal heating, 

samples of oils (with and without rosemary 

extract) were taken for analysis of 

viscosity and density. Density of oil 

samples was measured by pycnometer 

using 10 ml of sample at 25°C, and 

viscosity was measured using Ostwald 

viscometer (ASTM D445 England). 

 

2.5. FTIR Measurements 

An IRAfinity-1 Shimadzu Fourier 

transform infrared (FTIR) 

spectrophotometer equipped with a 

DLATGS (deuterated L-alanine triglycene 

sulfate) detector and calcium fluoride CaF2 

as transparent window, managed by the IR 

software was used to acquire FTIR spectra 

of analyzed samples of sunflower oil (with 

and without rosemary extract). Samples for 

analysis were taken after each cycle of 

thermal heating. Spectra were recorded in 

the spectral region from 4000 to 1000 cm-1 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XIX, Issue 4 – 2020 

Artan GASHI, Mila ARAPCHESKA, Fatos REXHEPI, Effect of Rosemary Extract on Thermal Stability of Sunflower Oil, 
Food and Environment Safety, Volume XIX, Issue 4 – 2020, pag. 267 - 274 

270 

 

with a resolution of 4 cm-1. FTIR spectral 

bands were assigned to specific vibrations 

based on literature data and software 

spectral library. 

 

 

3. Results and discussion 

 

In recent years, natural antioxidants from 

plant origin have attracted considerable 

attention due to their beneficial functional 

and nutritional effects including 

antioxidant activity. Since ancient times, 

herbs have been used not just for food 

flavorings, but also for its medicinal 

antiseptical, and preservative properties. 

Preservative effects of herbal extracts 

suggest the presence of antimicrobial and 

antioxidant constituents in their 

composition [18, 19]. 

In this study, rosemary extract was 

obtained by steam distillation from 

Rosemarinus officinalis L. leaves. The 

physicochemical properties of the obtained 

extract are presented in Table 1. The 

density of the exract was 0.87 (g/cm3), and 

viscosity 67±2 mP. The Folin-Ciocalteu 

assay was used for determination of the 

total phenolic content, which in the 

analysed rosemary extract was 21.6±0.5 

mg GAE/g. The antioxidant activity is 

defined as capacity of antioxidants to 

protect a biological system against the 

harmful effects of oxidative processes. The 

antioxidant activity of analysed extract was 

76±2.5%. 

Physicochemical characterization of 

rosemary extract indicates high content of 

polyphenols compounds as well as high 

antioxidant activity of analyzed extract, 

and obtained results are in accordance with 

the literature data [20]. 

 

 
Table 1. 

Physicochemical parameters of rosemary extract 
 

Physicochemical parameters  Rosemary extract 

Density (g/cm3) 0.87 

Viscosity (mP) 67±2 

Polyphenols (mg GAE/g) 21.6±0.5 

Antioxidant activity (%) 76±2.5 

 

Effect of rosemary extract on thermal 

stability of sunflower oil was studied 

through analysis of density, viscosity, and 

FTIR measurements. Analyzed parameters 

were used as indicators of structural 

changes in analyzed samples of oils during 

their thermal heating. Comparative 

analysis of parameters between samples of 

two types of oil, sunflower oil (SFO) and 

sunflower oil with rosemary extract (SFO 

+ RE) was done. 

Density changes during the heating of 

sunflower oil samples with and without 

rosemary extract are presented in Figure 1. 

Differences are very clear between the 

samples. During the heating of oil several 

reactions are occurred. These reactions 

lead to decomposition of natural 

constituents into oxidative and non-

oxidative degradation products that can 

polimerize, which later results with density 

increase [21]. 

The viscosity changes of analyzed samples 

of oil during the thermal heating are 

presented in Figure 2. According obtained 

results during the first heating cycle, 

decrease of viscosity was noted in both 

type of oil (SFO and SFO + RE). This 

should be due to the weakening of the 

intermolecular forces between oil 

components which lead to the oil 

degradation. In the second and third 

heating cycles an increase of viscosity 

values was noted. 

 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XIX, Issue 4 – 2020 

Artan GASHI, Mila ARAPCHESKA, Fatos REXHEPI, Effect of Rosemary Extract on Thermal Stability of Sunflower Oil, 
Food and Environment Safety, Volume XIX, Issue 4 – 2020, pag. 267 - 274 

271 

 

 

 
Fig. 1. Density changes in sunflower oil (SFO) and sunflower oil with 0.1% rosemary extract (SFO + RE) 

during the thermal heating 

 

 

 

 

 
Fig.2. Viscosity changes in sunflower oil (SFO) and sunflower oil with 0.1% rosemary extract (SFO + RE) 

during the thermal heating 

 

 

According literature data high temperature 

process such as frying produces 

compounds (polymers) with high 

molecular weight. Polymerization products 

decrease the stability of frying oils and can 

be used to measure oil fry life [22]. 

 

Results of this study indicate that the 

increase of oil viscosity is a consequence 

of increased amount of polymerization 

compounds. The changes in density and 

visosity values are more rapidly in the pure 

sunflower oil (SFO) compared with 

mixture (SFO + RE) (Figure 1 and Figure 

2), this is probably due to the effect of 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XIX, Issue 4 – 2020 

Artan GASHI, Mila ARAPCHESKA, Fatos REXHEPI, Effect of Rosemary Extract on Thermal Stability of Sunflower Oil, 
Food and Environment Safety, Volume XIX, Issue 4 – 2020, pag. 267 - 274 

272 

 

polyphenols content and antioxidative 

activity of rosemary extract on higher 

thermal stability of the mixture oil. 

Another procedurе used in this study for 

evaluation of chemical changes in analysed 

samples of oils (SFO and SFO+RE) during 

the thermal heating was FTIR 

spectroscopy. The characteristic functional 

group used in this research and their 

wavenumbers are presented in Table 2. 

FTIR spectral bands were assigned to 

specific vibrations based on software 

spectral library and literature data [23, 24]. 

 
 

Table 2. 

FTIR absorbance bands and their characteristic functional groups 
 

Wavenumbers 

cm-1 
Characteristic group and mode of vibration 

3008 =C–H Stretching symmetric vibration of the cis double bonds  

2925 −CH(CH2) Asymmetric stretching vibration of the aliphatic CH2 group 

2854 −CH(CH2) Symmetric stretching vibration of the aliphatic CH2 group  
 

1745 −C = O Stretching vibration of ester carbonyl functional groups of triglycerides 

 

 

FTIR characterization of analysed samples 

of oils during the first heating cycle is 

presented in Figure 3. Obtained FTIR 

spectra peaks are common for the majority 

of vegetable oils. Intesity of peak at 

3007cm-1 can be interpreted by the 

unsaturation level. Analysis of FTIR 

spectra based on carbonyl group at 

1745cm-1 indicate triglycerides as mayor 

compounds in anlysed oil`s samples. 

 

 

 

 
Fig. 3. FTIR Spectra of sunflower oil and sunflower oil with 0.1% rosemary extract after 8 hours of 

thermal heating 

 

 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XIX, Issue 4 – 2020 

Artan GASHI, Mila ARAPCHESKA, Fatos REXHEPI, Effect of Rosemary Extract on Thermal Stability of Sunflower Oil, 
Food and Environment Safety, Volume XIX, Issue 4 – 2020, pag. 267 - 274 

273 

 

 
Fig. 4. Intesity ratio at 3008/2854 cm-1 during the thermal heating of sunflower oil (SFO) and sunflower oil 

with 0.1% rosemary extract (SFO + RE) 
 

 

In this study as an indicator for the 

chemical changes in analysed samples of 

oil during thermal heating the intensity 

ratio of selected peaks is used (Figure 4). 

Oxidative reactions, are major cause of 

deterioration of vegetable oils during the 

period of heating. Usually as a result of 

oxidation, double bonds are converted in 

single. The decreasy of ratio intensity 

3008/2854 cm-1 means conversion of 

double bonds in single. According 

obtained results rapid decrease of ratio 

3008/2854 cm-1 was noted in sunflower oil, 

especially during the first heating cycle, 

which was not the case for sunflower oil 

with rosemary extract (the decrease was 

more slowly). 

 

4. Conclusion 

 

The results obtained in the present study 

showed that the rosemary extract is a 

promising source of natural antioxidants 

for vegetable oils. It can protect the oils 

against oxidative processes, even at high 

temperatures. According obtanied results 

rosemary extract was more effective in 

delaying the oxidation of sunflower oil.  

Samples of sunflower oil with rosemary 

extract have shown improved thermal 

stability compared with pure sunflower oil. 

In general rosemary extract in sunflower 

oil effectively protect its triglyceride 

structure and level of unsaturation (with 

minor structural changes). 

FTIR Spectroscopy used in this study was 

proved to be suitable method for the 

analysis of structural changes vegetable oil 

during heating. This methodology brings 

advantages over conventional laboratory 

procedures and allows rapid, specific, non-

invasive analyses independent of number 

of chemicals and without requirement of 

special sample preparation. 

 

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Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XIX, Issue 4 – 2020 

Artan GASHI, Mila ARAPCHESKA, Fatos REXHEPI, Effect of Rosemary Extract on Thermal Stability of Sunflower Oil, 
Food and Environment Safety, Volume XIX, Issue 4 – 2020, pag. 267 - 274 

274 

 

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