Determination of thermally deteriorated oil re-used as adulterants in sunflower oil using Fourier transform infrared spectroscopy

doi:10.21203/rs.3.rs-2505418/v1

Download PDF

Research Article

Determination of thermally deteriorated oil re-used as adulterants in sunflower oil using Fourier transform infrared spectroscopy

https://doi.org/10.21203/rs.3.rs-2505418/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Sunflower oil (SFO) is preferably chosen for frying because it gets soaked less and is very light. Nevertheless, there is a possibility that SFO is adulterated with thermally deteriorated oil re-used such as the leftover oil after the frying process of meat with breadcrumbs (TDO A) and potatoes (TDO B). It may be very harmful to our health and the environment, requiring a fast and reliable screening test for such adulterants. In this study, Fourier transform infrared spectroscopy based on the attenuated total reflectance (ATR-FITR) sampling technique was studied for the direct determination of TDOA and TDO B as adulterants in SFO-TDO binary mixtures. Our proposed quantification methods were based on the simple linear regression analysis of IR spectral intensity (peak height or peak area) at the wavenumber 1746 cm ^− 1 on adulterant concentration 0 ÷ 10% (v/v) (R² > 0.990). They proved to be accurate (% recovery in the range of 98.0 ÷ 101.1%), precise (RSD < 2.7%) and technically simple (total analysis time of 5–10 min).

sunflower oil

adulteration

thermally deteriorated oil

infrared spectroscopy

frying process

peak height

peak area

screening test

“Edible oils” (also known as “cooking oils”) is the term specifically ascribed to a group of plant, animal, or synthetic fatty liquids employed in food preparation such as frying, baking and flavoring (salad dressings and bread dips). They are, in fact, an important component of the human diet as they are rich in liposoluble vitamins such as A, D, E and K, among which vitamin E having antioxidant properties can devour free radicals blamed for carcinogenesis and aging (Ying et al 2020). The composition of edible oils is such that triacylglycerides (composed of different fatty acids) account for about 96% of their mass. The susceptibility to oxidative processes can render fatty acids, free and/or bound to glycerol degraded into volatile and non-volatile compounds in edible oils. Thus, a great number of studies have been dedicated to monitoring the quality of such products after processing until use by the consumer (Bunaciu et al 2020).

The sunflower (Helianthus annuus L.) is a large annual forb of the Asteraceae family cultivated in many countries in the world for its edible oil and seeds (Raß et al 2008; Rauf et al 2017). Typically, the yield for oilseed sunflower and sunflower oil (SFO) is 68.40-74.35 bushels per acre (or 2.3–2.5 t/ha) and 1026–1227 pounds/acre (or 1.15–1.37 t/ha), respectively (Oleksii 2022). SFO has high amounts of unsaturated fatty acids, of which 70% is linoleic acid. It was reported that the domestic consumption of sunflower seed oil in 27 EU countries reached 5,063,000 metric tons (Shahbandeh 2022). Thus, there is a possibility that sunflower oil could be used as an adulterant (Downey and McIntyre 2002) or be adulterated with reused frying oil (as investigated for other edible vegetable oils (e.g. Zhang et al 2012) given the fact that repeatedly heating edible oils at high temperature is common practice during cooking. Kumar et al. pointed out in a review that the consumption of repeatedly heated oils and inhalation of cooking fume may cause a high incidence of genotoxicity, mutagenicity, tumorigenicity and other types of cancers (Kumar et al 2019).

In the literature, Fourier Transform Infrared Spectroscopy (FTIR) has been successfully exploited for studying the oxidation of edible oils (Russin et al 2004; Rohman et al 2011; Guillén and Cabo 1999; Guillén and Cabo 2000) and the effect of heating processing on edible oil quality (Tena et al 2009; Poiana et al 2013; Innawong et al 2004). Recently, our research group has also demonstrated the applicability of FTIR spectroscopy for monitoring the oxidation process of lard during heating (Bunaciu et al 2021; Bunaciu et al 2022a) and determining the adulteration of some edible oils with paraffin oil (Bunaciu et al 2022b). With this study, we aim at further emphasizing the suitability and applicability of FTIR spectroscopy for a fast, cost-effective and reliable determination of the adulteration of sunflower oil with thermally degraded oil (TDO) obtained during the frying process of meat with breadcrumbs (TDO A) and potatoes (TDO B).

Samples

Sunflower oil (SFO) was purchased in 1-L PET bottles from a local supermarket under the brand name “Spornic” (Prutul SA; produced in Galați district, Romania). Based on the manufacturer’s label claim, it contains at least 75% of Omega-9 meaning that there is about 7 g of saturated fatty acids, about 71 g of monounsaturated fatty acids, 14 g of polyunsaturated fatty acids enriched with 40.43 mg of vitamin E per 100 ml of sunflower oil. The adulterants, in this study, were heated oils reused after the frying process of meat with breadcrumbs (TDO A) and potatoes (TDO B) at the restaurant “Pikandy Pizza & Grill” (Romania, Bragadiru – Ilfov district).

All the samples were prepared in our laboratory by mixing fresh commercial SFO with the stock solution of one adulterant (either TDO A or TDO B) to have the concentration range under study of TDO 0 ÷ 1 % (v/v). These mixtures were manually shaken for homogenization before analysis.

Measurement Procedure

FTIR spectra were acquired with a PerkinElmer FTIR spectrometer equipped with an ATR sampling station, a detector of deuterated triglycine sulfate and a beam splitter of potassium bromide. For measurement, a small drop (~ 10 µL) of edible oil mixture was pipetted on the top of the ATR baseplate, which was kept at 30°C. The spectra were then recorded in the range of 650–4,000 cm^− 1 as absorbance values at each data point and were subtracted by air background air signal; the interferograms of 32 single scans were co-added at a resolution of 4 cm^− 1. The collection time for each sample’s spectrum was approximately 2 minutes. After every scan, a new background spectrum was taken. Spectrum software version 5.01 (Perkin Elmer Co., Beaconsfield, Bucks, UK) and spectrum software version 10.5.1.581 (Perkin Elmer Inc., Boston, MA, USA) were used for spectral acquisition and processing, respectively. The ATR base was carefully cleaned in situ by scrubbing with hexane and then ethanol, and dried with soft tissue prior to the next measurement. Unless stated otherwise, each sample was measured in triplicate to get the average spectrum for quantitative purpose.

Nowadays, deep frying in which food is submerged in edible oil at 176.7 ÷ 190.6°C is one of the common cooking methods (FreshFry 2022) because it can enhance the sensorial properties including crispy texture, golden brown color, and of course fried flavor. It is known that forced oxidation of edible oil could occur even at a moderate temperature (∼ 58°C) (Russin et al 2004). It is obvious that the two oil adulterants, in our study, definitely contain thermally degraded products. It may be evidenced by the growth of the absorption band and/or band shift as the oxidative processes take place. To quantify adulterant(s) in SFO mixtures, we thus search for infrared spectral characteristics to reliably indicate the presence of TDO A and TDO B. Herein, our quantification method for TDOs in SFO mixtures was proposed using simple linear regression analysis. It means that IR signal intensity (peak height or peak area) at a specific wavenumber between TDO-SFO mixtures and pure SFO was regressed on the percentage of either adulterant. The proposed method was validated in terms of linearity, accuracy, precision, specificity, limit of detection and limit of quantification (Michael et al 2002).

Figure 1 displays the FTIR spectra of representative samples for sunflower oil (SFO) and two adulterants (TDO A and TDO B) under study. For the sake of better visualization, they are all scaled vertically.

In the first spectral region, 3600-3200cm^− 1, the peak at around 3472 cm^− 1 is assigned to the ROOH absorption band (Russin et al 2004). In the second spectral region, 3000-2800cm^− 1, there are peaks due to the asymmetric and symmetric stretching vibration of the aliphatic CH₂ functional group observed at around 2921 and 2852 cm^− 1 (Guillén and Cabo, 2000). It is interesting to note that the oils with a high proportion of linolenic or linoleic acyl groups show higher frequency data for the peak characteristic for a cis-double bond (Guillén and Cabo, 1999) at around 3005 cm^− 1 than those with a high proportion of oleic acyl groups. Upon thermal oxidation, these peaks of TDOs exhibit only a slight increase in intensity (at around 3472 cm^− 1) or a significant increase in intensity (at around 2921 and 2852 cm^− 1). However, they are not used for the quantification of TDOs in SFO-TDO binary mixtures since there is no marked difference in their intensity when a spectral comparison is done for pure SFO and TDOs samples.

In contrast, in our study, the band at 1746 cm^− 1 was used to quantify TDOs in SFO mixtures. The peak area for the band at 1746 cm^− 1, was calculated using 1800 cm^− 1 and 1682.84 cm^− 1 as points on the baseline. This peak is due to the ester carbonyl functional group of the triglycerides (Guillén and Cabo, 2000), and it shows a significant increase in intensity as well as absorption band widening for TDOs. This is in agreement with our previous findings (Bunaciu et al., 2022a). Table 1 displays the IR spectral data obtained for the band around 1746 cm^− 1 used for the first quantification method. In Fig. 2A and B are presented the ATR – FTIR spectra for SFO-TDO binary mixtures. Statistical evaluation of the calibration curves for the measurements performed at 1743.60 cm^− 1 for either adulterant was summarized in Table 2, together with LOD and LOQ values calculated based on the parameters (standard deviation of the residuals and regression slope) of the best-fitting lines. The coefficient of determination (R²) for all the methods is greater than 0.990, suggesting a strong association between two variables (i.e., IR signal intensity (peak height or peak area) as the dependent variable, Y, and percentage of adulterant in SFO-TDO binary mixtures as the independent variable, X). It is noteworthy that the quantification methods based on IR peak area are more sensitive than those based on IR peak height as evidenced by their higher values of the regression slope. The accuracy and precision of all the methods were also accessed by the quantification of TDOs as adulterants in the range of 3.5 ÷ 7.5% (v/v). Basically, the presence of TDOs in laboratory-made SFO-TDO binary mixtures is invisible to the naked eye at this concentration range. The results displayed in Table 3 show that all the methods are precise (RSD < 2.7%) and accurate (percent recovery in the range of 98.0 ÷ 101.1%). It is reasonably acceptable; in other words, the quantification of TDOs in SFO-TDO binary mixtures is considered to be specific (no significant influence of sample matrix existed). In comparison with chromatographic methods reported for identifying edible oil adulterants (Priyankar et al 2005; Chia-Ding et al 2017; Changrui et al 2019), our proposed methods proved to be more suitable as a reliable screening test for SFO adulterants because they are time-saving (the quantification could be performed in only about 5–10 minutes, taking into account from sample preparation to data acquisition) and cost-effective (solvent-free analysis and no sophisticated equipment requirement).

Table 1

Spectral data (peak height and peak area) of the band around 1746 cm^− 1
TDO (%)	TDO A		TDO B
TDO (%)	Peak Height	Peak Area	Peak Height	Peak Area
0	1.16	28.14	1.159	27.2
1	1.177	28.53	1.172	27.5
2	1.19	28.92	1.18	27.73
3	1.2034	29.31	1.1898	27.97
4	1.2161	29.71	1.195	28.21
5	1.2288	30.01	1.2086	28.44
6	1.2415	30.49	1.22	28.68
7	1.2543	30.88	1.2275	28.92
8	1.267	31.27	1.237	29.15
9	1.28	31.66	1.2465	29.39
10	1.294	32.06	1.258	29.63

Table 2

Statistical evaluation of the regression analysis, LOD and LOQ values of the proposed quantification methods
Parameter	TDO A		TDO B
	Peak measurements
	Area	Height	Area	Height
Slope (a)	0.3917	0.0131	0.2394	0.0097
Intercept (b)	28.13	1.1629	27.24	1.1601
Coefficient of determination (R²)	0.9995	0.9991	0.9995	0.9974
Standard error of the slope (S_a)	26.5×10^–4	1.18×10^–4	16.0×10^–4	1.65×10^–4
Standard error of the intercept (S_b)	156.8×10^–4	6.95×10^–4	94.5×10^–4	9.76×10^–4
Standard deviation of the residuals (S_y.x)	278.1×10^–4	12.3×10^–4	168.0×10^–4	17.3×10^–4
LOD = 3.3 × S_y.x/a (%)	0.23	0.31	0.23	0.59
LOQ = 10 × S_y.x/a (%)	0.71	0.94	0.70	1.79

Table 3

Quantitative determination of TDOs in SFO-TDO binary mixtures
	Found (%) (mean ± SD, n = 5)
Taken (%)	peak area method		peak high method
Taken (%)	TDO A	TDO B	TDO A	TDO B
3.50	3.46 ± 0.01	3.43±0.05	3.52 ± 0.09	3.55± 0.06
5.50	5.52 ± 0.03	5.49± 0.04	5.49 ± 0.02	5.51± 0.04
7.50	7.57 ± 0.10	7.59± 0.12	7.57 ± 0.03	7.58± 0.06

It was concluded that ATR-FTIR spectroscopy is a very useful technique for the direct determination of thermally deteriorated oil re-used as SFO adulterants, TDO A and TDO B. In this study, the quantification of TDOs in SFO-TDO binary mixtures was done using the simple linear regression models describing the relationship between IR spectral intensity (peak height or peak area) at the wavenumber 1746 cm^− 1 and adulterant concentration. According to the validation data, our proposed quantification methods could serve as a screening test in the routine analysis of SFO adulteration with TDOs because it is labor-saving (easy to perform and quick), accurate, precise and specific.

FUNDING

No funding was received for this study.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

AUTHOR CONTRIBUTION

Andrei A. Bunaciu contributed to conceptualization, methodology, sampling and sample analysis, and writing the original draft. Vu D. Hoang and Hassan Y. Aboul-Enein- contributed to data curation, supervision and writing - reviewing and editing.

COMPETING INTERESTS.

Andrei A. Bunaciu declares no conflict of interest.

Vu Dang Hoang declares no conflict of interest.

Hassan Y. Aboul-Enein declares no conflict of interest.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

Not applicable.

HUMAN AND ANIMAL RIGHTS

No animals/humans were used for studies that are the

basis of this research.

CONSENT FOR PUBLICATION

Not applicable.

PERMISSION AND/OR CREDIT FOR REPRODUCED IMAGES

Non-applicable

Bunaciu AA, Aboul-Enein HY, Hoang VD (2020) Chap. 7 – Edible oil analysis. In: Bunaciu AA, Aboul-Enein HY, VD Hoang (Eds) Vibrational Spectroscopy Application in Biomedical, Pharmaceutical and Food Sciences. Elsevier Inc., pp 167–187. https://doi.org/10.1016/B978-0-12-818827-9.00009-3
Bunaciu AA, Fleschin S, Aboul-Enein HY (2021) FTIR spectroscopy used for study the thermal degradation of lard. Egypt Pharm J 20:166–172.
Bunaciu AA, Fleschin S, Aboul-Enein HY (2022a) Detection of sunflower oils adulteration by ATR–FTIR spectra. Chem Pap 76:5333–5339
Bunaciu AA, Fleschin S, Aboul-Enein HY (2022b). Determination of some edible oils adulteration with paraffin oil using infrared spectroscopy. Pharmacia 69(3):827–832
Changrui X, Xiangyu Y, Xueyou W, Xiaolong S, Jian Y, Wenjing Y (2019) Chemometric classification and quantification of sesame oil adulterated with other vegetable oils based on fatty acids composition by gas chromatography. LWT 108:437–445
Chia-Ding L, Guan-Jhih P, Yueh T, Mei-Hua C, Su-Hsiang T, Ya-Min K, King-Fu L, Yu-Mei C, Ming-Kung Y, Hwei-Fang C (2017) Using phytosterol as a target compound to identify edible animal fats adulterated with cooked oil. Food Control 79:10–16
Downey G, McIntyre P (2002) Detecting and quantifying sunflower oil adulteration in extra virgin oil from the Eastern Mediterranean by visible and near-infrared spectroscopy. J Agric Food Chem 50(20):5520–5525
FreshFry LLC (2022) The perfect frying oil temp for common cooking oils https://freshfry.me/blogs/news/the-perfect-frying-oil-temp-for-common-cooking-oils Accessed 18 October 2022
Guillén MD, Cabo N (1999) Usefulness of the frequency data of the Fourier Transform Infrared Spectra to evaluate the degree of oxidation of edible oils. J Agric Food Chem 47:709–719
Guillén MD, Cabo N (2000) Some of the most significant changes in the Fourier transform infrared spectra of edible oils under oxidative conditions. J Sci Food Agric 80:2028–2036
Innawong B, Mallikarjunan P, Irudayaraj J, Marcy JE (2004) The determination of frying oil quality using Fourier transform infrared attenuated total reflectance. Lebensmittel-Wissenschaft und-Technologie 37(1):23–28.
Kumar G, Kumeshini S, Baojun X (2019) Impact of consumption of repeatedly heated cooking oils on the incidence of various cancers- A critical review. Crit Rev Food Sci Nutr 59(3):488–505
Michael T, Stephen LRE, Roger W (2002) Harmonized guidelines for single laboratory validation of methods of analysis (IUPAC Technical Report). Pure Appl Chem 74(5):835–855
Oleksii O (2022) What is the sunflower yield? https://farming.org.ua/Sunflower%20yield%20per%20acre,%20sunflower%20yield%20per%20hectare.html Accessed 18 October 2022
Poiana MA, Mousdis GA, Georgiou CA, Alexa E, Moigradean D, Cocan I (2013) Detection of thermal processing impact on olive and sunflower oil quality by FTIR spectroscopy. J Agroaliment Processes Technol 19(1):48–56.
Priyankar G, Krishna RMM, Sashidhar RB (2005) Quantitative evaluation of sanguinarine as an index of argemone oil adulteration in edible mustard oil by high performance thin layer chromatography. Food Chem 91(4):757–764
Raß M, Schein C, Matthäus B (2008) Virgin sunflower oil. Eur J Lipid Sci Technol 110: 618–624
Rauf S, Jamil N, Tariq SA, Khan M, Kausar M, Kaya Y (2017) Progress in modification of sunflower oil to expand its industrial value. J Sci Food Agric 97:1997–2006
Rohman A, Che Man YB, Ismail A, Hashim P (2011) Monitoring the oxidative stability of virgin coconut oil during oven test using chemical indexes and FTIR spectroscopy. Int Food Res J 18:303–310.
Russin TA, van de Voort FR, Sedman J (2004) Rapid determination of oxidative stability of edible oils by FTIR spectroscopy using disposable IR cards. J Am Oil Chem Soc 81:111–116
Shahbandeh M (2022) Leading countries of sunflower seed oil consumption worldwide 2021. https://www.statista.com/statistics/1199454/domestic-consumption-of-sunflowerseed-oil-worldwide-by-country/ Accessed 18 October 2022
Tena N, Aparicio R, García-González DL (2009) Thermal deterioration of virgin olive oil monitored by ATR-FTIR analysis of trans content. J Agric Food Chem 57(21):9997–10003.
Ying Z, Weiwei Z, Yong L, Baohong Z, Dangquan Z (2020) Edible plant oil: Global status, health issues, and perspectives. Front Plant Sci Sec. Crop and Product Physiology https://doi.org/10.3389/fpls.2020.01315
Zhang Q, Liu C, Sun Z, Hu X, Shen Q, Wu J (2012) Authentication of edible vegetable oils adulterated with used frying oil by Fourier Transform Infrared Spectroscopy. Food Chem 132(1):1607–1613.

No competing interests reported.

Download PDF

Version 1

posted

You are reading this latest preprint version

Determination of thermally deteriorated oil re-used as adulterants in sunflower oil using Fourier transform infrared spectroscopy

Status:

Version 1

Abstract

Figures

Introduction

Materials And Methods

Samples

Measurement Procedure

Results And Discussion

Conclusions

Declarations

References

Additional Declarations

Status:

Version 1