Effect of frying oils’ fatty acid profile on quality, free radical and volatiles over deep-frying process: A comparative study using chemometrics

Accepted Manuscript Effect of frying oils’ fatty acid profile on quality, free radical and volatiles over deepfrying process: A comparative study using chemometrics Ying Liu, Jinwei Li, Yajun Cheng, Yuanfa Liu PII:

S0023-6438(18)30983-6

DOI:

https://doi.org/10.1016/j.lwt.2018.11.033

Reference:

YFSTL 7597

To appear in:

LWT - Food Science and Technology

Received Date: 29 October 2018 Revised Date:

5 November 2018

Accepted Date: 10 November 2018

Please cite this article as: Liu, Y., Li, J., Cheng, Y., Liu, Y., Effect of frying oils’ fatty acid profile on quality, free radical and volatiles over deep-frying process: A comparative study using chemometrics, LWT - Food Science and Technology (2018), doi: https://doi.org/10.1016/j.lwt.2018.11.033. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Effect of frying oils’ fatty acid profile on quality, free radical and volatiles over

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deep-frying process: A comparative study using chemometrics

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Ying Liu, Jinwei Li, Yajun Cheng, Yuanfa Liu*

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School of Food Science and Technology, Synergetic Innovation Center of Food Safety

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and Nutrition, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province

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214122, People’s Republic of China

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*Corresponding author: Yuanfa Liu

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aPhone: 0510-85876799; Fax: 0510-85876799; E-mail: [email protected]

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ACCEPTED MANUSCRIPT ABSTRACT: The effects of frying oils’ fatty acid profile on quality, free radical and

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volatiles over deep-frying process were investigated, using oils with different fatty

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acid composition. Results showed oxidative stability of frying sunflower oil (SO)

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were higher than that of frying palm oil (PO). Meanwhile, free radicals in frying oils

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increased over frying time, and amounts of free radicals in SO were higher than those

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in PO. Our further analysis on fatty acid composition showed oleic and linoleic acid

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decreased significantly with the increasing frying time, indicating unsaturated fatty

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acid of oils degraded under frying process, while no significant change of saturated

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fatty acids was observed. Results of volatiles indicated that totals of 27 main volatile

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compounds were found in both frying oils but their content distributed differently in

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two oils. Chemometrics analysis showed that (E,E)-2,4-octadienal, (E)-2-decenal,

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2-undecenal, 1-heptanol, 1-octanol, 2-undecanol, 3-hepten-2-one, 1-undecanol,

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octanoic acid, nonanoic acid, octane, dodecane and tetradecane was highly correlated

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with AV, POV, p-AV, PCs and free radical in frying PO, while (E)-2-hexenal,

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1-nonen-3-ol, 2-dodecanol,3-methyl-3-buten-2-one, 4-methyl-2-hexanone, pentanoic

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acid and nonadecane was highly correlated with quality indices in frying SO,

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indicating these volatiles may be proposed as potential indicators for evaluating lipid

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oxidation of corresponding frying oil.

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Keywords: Fatty acid composition, Deep-frying oil, Quality, Free radical, Volatile

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1. Introduction Deep-frying is one of the most prevalent processes for food preparation at a high

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temperature about 180 °C. Even though frying process provides fried products

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pleasant flavor, golden color, good taste, and crispy texture (Bou, Navas, Tres &

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Guardiola, 2012; Juániz, Zocco, Mouro, Cid & Peña, 2016; Lim, Jeong, Oh & Lee,

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2017), oil and substance are continuously exposed to atmospheric oxygen and

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moisture in food during frying process, resulting in many reactions including

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oxidation, hydrolysis, isomerization and polymerization. Therefore, adverse changes

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in the sensory, physicochemical and nutritional aspects of food and oil over frying

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period occur (Esposto et al., 2015; Urbančič, Kolar, Dimitrijević, Demšar & Vidrih,

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2014).

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Lipid thermal oxidation occurs through a chain reaction mechanism of free radicals

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and associates with a series of reactions (Farmer, Koch & Sutton, 1943; Marmesat,

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Velasco & Dobarganes, 2008), which not only produces peroxides, free radicals,

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oxidized volatile products and other small molecular substances, but also decreases

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the quality of fat and oil-containing food. Besides, these oxidative products may also

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exert negative effects human health (Feldstein et al., 2010; Kanazawa, Sawa, Akaike

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& Maeda, 2002). Conventional methods such as determination of acid value (AV),

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peroxide value (POV), p-anisidine value (p-AV), polar compounds (PCs) and trans

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fatty acids (Cho, Kim, Khurana, Li & Jun, 2011) have been developed to evaluate the

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oxidative status of oil. Lipid oxidation is also accompanied by changes in the volatile

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profiles. The volatile characteristics could indicate the effective information for

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assessing the quality of oil and fat during frying (Zhang, Saleh, Chen & Shen, 2012).

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The modern gas chromatography-tandem mass spectrometry (GC-MS/MS) technique,

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as a sensitive analytical technique for volatile compounds (Xu et al., 2014), was

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ACCEPTED MANUSCRIPT applied for analysis of oxidized volatile products. In addition, lipid oxidation process

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involves free radical chain reactions. Electron paramagnetic resonance (EPR), also

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known as electron spin resonance (ESR), as a spectroscopic technique for highly

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specific detection and quantification of free radicals produced by lipid oxidation in

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food matrices (Chen, Wang, Cao & Liu, 2017; Liu, Wang, Cao & Liu, 2017; Pingret et

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al., 2012), was used to detect changes of free radicals during frying process.

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Oxidative susceptibility of lipids is correlated with their fatty acid composition,

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especially degree of unsaturation of lipids. As it is well known, oils containing higher

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proportions unsaturated fatty acids are easier to be oxidized (Kamal-Eldin, 2006;

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Sathianathan, Kannapiran, Govindan & Periasamy, 2014). Previous study showed that

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the oxidation rates of stearic, oleic, linoleic and linolenic acid were 1: 100: 1200:

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2500 (Mistry & Min, 1992). Palm oil and sunflower oil, as most widely used

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vegetable oils, contain high levels of saturated fatty acids and unsaturated fatty acids,

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respectively. The content of saturated fatty acids in palm oil reaches up to about half

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of total fatty acids (Mba, Dumont & Ngadi, 2015), while sunflower oil is rich in

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unsaturated fatty acids containing approximately 40% to 70% linoleic acid (Meydani

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et al., 1991). Therefore, more attention should be paid to lipid oxidation in frying oils

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with different fatty acid compositions.

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A few studies focused on the effects of frying on the physical, chemical and sensory

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quality of vegetable oils (Casal et al., 2010; Debnath, Rastogi, Gopala Krishna &

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Lokesh, 2012), but there is little information on the volatile profile characteristics of

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oils during frying process. Our present study was to compare the effects of fatty acids

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profile on quality, free radical and volatiles over deep-frying process. Palm oil and

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sunflower oil were selected as frying media. In addition, the correlation of the

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amounts of volatiles with conventional physicochemical indices and free radicals 4

ACCEPTED MANUSCRIPT were discussed using chemometrics in order to find possible markers of freshness or

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spoilage and to provide a more comprehensive understanding of lipid oxidation.

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Meanwhile, we hoped the potential markers identified for evaluating oxidative degree

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of vegetable oils with different fatty acid composition could be found.

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2. Materials and methods

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2.1. Chemicals and oils

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Methyl heneicosanoate (C21:0) and 37 component FAME mix analytical standards

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(C4-C24) were supplied by Supelco (Bellefonte, PA, USA). Standards of n-alkanes

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(C8–C40) and 2-octanol were purchased from Sigma-Aldrich Co. (St. Louis, MO,

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USA). Hexane (99% purity) and 5,5-Dimethyl-1-pyrroline N-oxide (DMPO, 99%

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purity) were purchased from J & K Chemical Technology (Shanghai, China). DMPO

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was further purified with activated carbon and stored at -80 °C in darkness before use.

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Boron trifluoride, methanol and all other chemical reagents were of analytical grade

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and were obtained from Sinopharm Chemical Reagent Company (Shanghai, China).

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Palm oil and sunflower oil were purchased from Wilmar International Ltd (Shanghai, China).

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2.2. Preparation of frying oils

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5 L of palm oil (PO) and sunflower oil (SO) was placed in a 10 L stainless deep

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fryer (24 × 30 × 14 cm) with temperature control, and then the oil was heated to and

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kept at 180 ± 5 °C. Four Drumsticks (120 g ± 10 g) were fried for 10 min after the

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temperature of oil reached 180 ± 5 °C in every 30 min. The frying procedure was held

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constantly for 4 continuous days (10 h per day). Deep-fried oil (50 mL) was collected

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at 0, 5, 10, 15, 20, 25, 30, 35 and 40 h of frying. All the oil samples were kept at

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-20 °C in darkness before analysis.

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2.3. Quality parameter

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Quality properties including AV, POV, p-AV, PCs were measured according to the

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AOCS Official Method Cd 3d-63, Cd 8b-90, Cd 18-90 and Cd 20-91, respectively

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(AOCS, 2011).

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2.4. Fatty acid composition and free radical level Fatty acid composition of frying oil samples was determined following the method

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reported by Liu et al. (2018). Free radical measurement was performed based on our

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previously published paper (Liu, Wang, Cao & Liu, 2017). Detailed information was

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all presented in the Supplementary material of this manuscript.

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2.5. Volatile compounds analysis

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The volatile compounds of frying oils were determined according to the method

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reported by Liu et al. (2017) (Liu, Wang, Cao & Liu, 2017). Detailed information was

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all presented in the supplementary material of this manuscript.

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2.6. Statistical analysis

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Analytical determinations were performed in triplicate and results were presented

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as means ± standard deviations (SD). Statistical comparisons were performed by

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one-way ANOVA combined with Duncan’s multiple-range test at the 5 % significance

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level using the SPSS statistical package (Version 19.0, SPSS Inc., Chicago, Illinois,

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USA). Chemometrics including principal component analysis (PCA) and hierarchical

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cluster analysis (HCA) were used to analyze the obtained data.

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3. Results and discussion

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3.1. Quality parameter

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As shown in Fig. 1, quality properties including AV, POV, p-AV, PCs of the test

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frying oils were quite different. Although the significant general increase in AV, p-AV,

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POV and PCs of both oils was observed with the increase of frying time, vegetable

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oils with the high proportion of unsaturated fatty acids are prone to oxidized during 6

ACCEPTED MANUSCRIPT the thermal oxidation process, thus lead to the increasing contents of free fatty acids,

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peroxides, polar compounds and so on, which were the main reasons responsible for

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the higher AV, POV, p-AV and PCs of the frying SO than those of frying PO. Similar

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results have been reported in previous studies (Li, Li, Wang, Cao & Liu, 2017; Liu,

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Wang, Cao & Liu, 2017; Velasco, Andersen & Skibsted, 2004). For POV, the content

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of hydroperoxides in frying SO was consistently higher than that in PO, and POV of

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both oils increased during frying process. While there is a sudden decrease of POV at

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40 h and 35 h of PO and SO, respectively, which might be because hydroperoxides are

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unstable and could decompose to small molecules, decay rate is higher than formation

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rate when the content of hydroperoxides is relatively high, leading to the POV

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fluctuates (Nayak, Dash, Rayaguru & Krishnan, 2016).

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3.2. Fatty acid composition

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The fatty acid composition of frying palm and SO is shown in Table 1. It could be

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seen from Table 1 that palmitic acid and oleic acid were the main fatty acids of frying

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PO samples, with the content of 47.62 ± 0.54–49.60 ± 1.06 g/100g and 25.28 ± 0.24–

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34.85 ± 0.64 g/100g, respectively. Nevertheless, the relative high content of oleic and

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linoleic acid was found in frying SO. The frying SO samples were rich in unsaturated

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fatty acids (UFAs), and the sum of oleic and linoleic acid accounted for more than 60%

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of the total fatty acids. Considering the overall fatty acid compositions, frying PO and

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SO followed the order: SFA > MUFA > PUFA and PUFA > MUFA > SFA,

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respectively. From the results, it could be found that the content saturated fatty acids

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C16:0, C18:0 and C20:0 in both frying oils changed slightly. While the degradation of

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unsaturated fatty acids increased with the increase of frying time. Besides, the

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degradation of UFAs in frying PO increased aggressively when the frying time

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ranging from 30 to 40 h, while it slightly increased with the frying time from 0 to 10 h.

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ACCEPTED MANUSCRIPT The content of PUFAs in frying SO decreased significantly from 30 to 40 h of frying

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time. These results were quite similar to the most predominant unsaturated fatty acid

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of frying oils. The content of C18:1 in frying PO decreased gradually from 20 to 40 h

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of frying period, while content of C18:2 and C18:3 decreased slightly with the

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prolonged frying time. The content of C18:1 and C18:2 in frying SO showed a

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gradual decrease during frying process. No significant decrease was observed in

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C18:3 content. Notably, the content of trans oleic acid in both frying oils increased

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significantly with the increase of frying time, while no significant increase of trans

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linoleic acid content was found in both oils.

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3.3. Amount of spin adducts

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Lipid oxidation occurs during deep-frying process and involves free radical chain

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reactions which could generate free radicals. Free radicals produced by lipid oxidation

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are not likely to be detected because of their short-lived nature. Therefore, DMPO, as

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a powerful spin trap for trapping carbon-centered and oxygen-centered radicals, was

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used to form stable and detectable spin adducts in frying oils. Total amounts of spin

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adducts in frying palm and SO are shown in Table 2. At the initial stage of detection,

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the amount of spin adducts in fresh palm and SO was 0.96 ± 0.004 and 1.22 ± 0.03,

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respectively. As the frying time increased, the content of total radical adducts in both

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frying palm and SO increased, and the spin adduct content of SO was higher than that

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of PO, possibly because vegetable oils with high unsaturation degree were prone to be

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oxidize to generate free radicals. In the first 10 h of deep-frying process, amount of

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spin adducts in frying PO slightly increased, then a significant increase of spin adduct

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content from 15 h to the end of frying period was obtained. While the amount of spin

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adducts in frying SO increased significantly as the frying time prolonged. The

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significantly increasing content of spin adducts indicated that lipid oxidation rate

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increased gradually and formation rate of spin adducts was higher than decay rate at

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the initial detection period. As displayed in Table 2, change of spin adduct content in frying oils was monitored

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within 32 min at 2 min intervals. Results showed the low amount of spin adducts

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existed in the first 8 min and 10 min of detection in palm and SO, respectively, then

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the content of spin adducts increased peaking at 22 min and 28 min, respectively,

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during which the formation rate of the radical adducts was higher than the decay rate.

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After that, spin adduct amount decreased because that higher level of spin adducts

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leads to higher decay rates, which thus cause the decrease of spin adduct content. The

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decreasing trend of spin adducts indicated that the silence of signal intensities

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appeared owing to the newly formed free radicals in frying system react with spin

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adducts. After peaking at the maximum value, the amount of spin adducts decreased

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slightly and kept in a certain level, indicating formation and decay rate of the spin

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adducts was kept in balance. Amount of spin adducts within 36-minute monitoring

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varied depending on the type of vegetable oils.

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3.4. Volatile compound profiles

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Changes of volatile compounds identified and quantified in frying oils are shown in

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Table 3. A total of 40 and 37 main volatile compounds were detected in frying palm

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and SO, respectively. These components could be divided into six groups: aldehydes,

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ketones, alcohols, acids, alkanes and furan. Most of these compounds detected have

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been identified previously in frying oils (Boskou, Salta, Chiou, Troullidou &

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Andrikopoulos, 2006; Vichi, Guadayol, Caixach, Lópeztamame & Buxaderas, 2007;

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Zhu, Wang & Shoemaker, 2016). Aldehydes were the major components of frying

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vegetable oils, followed by alcohols, alkanes, acids and ketones. While the amount of

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furan was minor among volatiles.

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ACCEPTED MANUSCRIPT In total, 16 and 15 aldehydes were identified in frying palm and SO, respectively.

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The content of all the aldehydes increased linearly with the frying time. Among them,

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the content of octanal, nonanal, decanal, (E)-2-decenal and 2-undecenal in frying PO

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was far higher than those in frying SO, while the content of hexanal, 2,4-decadienal

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and (E,E)-2,4-decadienal in frying PO was obviously lower than those in frying SO.

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This is because oleic acid in PO was higher than that in SO, and octanal, nonanal,

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decanal, (E)-2-decenal and 2-undecenal were produced by homolytic cleavages on the

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alkoxyl intermediate group of oleate hydroperoxides. In contrast, linoleic acid in PO

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was lower than that in SO, and hexanal, 2,4-decadienal and (E,E)-2,4-decadienal were

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generated from homolytic cleavages on the alkoxyl intermediate group of linoleate

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hydroperoxides (Frankel, 2005). Besides, heptanal, (E,E)-2,4-octadienal and

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2,4-nonadienal were only found in frying PO samples, while (E,E)-2,4-nonadienal

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only existed in frying SO.

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Alcohols are usually generated by the degradation of unsaturated fatty acids (Zhang,

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Li, Luo & Chen, 2010). A total of 7 and 6 alcohols were detected in frying palm and

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SO, respectively. The amounts of alcohols in both frying oils increased in the process

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of deep frying. Among these alcohols, 1-octen-3-ol was the most abundant in both

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frying oils and increased linearly with the prolonged frying time. The content of

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1-octen-3-ol in 50 h-fried palm and SO samples were 8 times and 2 times higher than

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that in fresh palm and SO samples PO, respectively. Besides, 1-octanol was only

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found in PO samples. It has been reported 1-octen-3-ol and 1-octanol were generated

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by the degradation of C8 compounds during heat treatment (Picardi & Issenberg,

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1973). The content of 1-pentanol existing in both frying oils was similar. And

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1-octen-3-ol, 1-octanol, and 1-pentanol were widely found in oxidized samples and

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frying oils (Picardi & Issenberg, 1973; Romano et al., 2013).

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ACCEPTED MANUSCRIPT A total of 6 and 7 ketones were identified in frying palm and SO, respectively.

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Ketones are derived from the enzymatic degradation of polyunsaturated fatty acids

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(PUFAs), amino acid degradation or Maillard reaction (Fratini, Lois, Pazos, Parisi &

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Medina, 2012). The content of ketones increased in the process of deep frying.

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Among all ketones, 6-methyl-5-hepten-2-one, 4-methyl-2-hexanone, 3-nonen-2-one

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and 4-mthyl-3-heptanone existed in both frying oils whose amounts varied in frying

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palm and SO. Besides, 1-hexen-3-one and 3-hepten-2-one were only found in frying

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PO. 3-Hexen-2-one, 3-methyl-3-buten-2-one and 2,4-heptanedione were the most

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abundant which only existed in frying SO.

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After thermal oxidation, several aliphatic acids appeared, which were possibly

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formed by further oxidation of their corresponding aldehydes (Morales, Rios &

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Aparicio, 1997). Four types of acids were identified. Hexanoic, pentanoic and

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nonanoic acid were the common acids in both frying oils. The content of pentanoic

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and nonanoic acid in frying PO was higher than those in frying SO, while hexanoic

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acid showed the opposite result. The content of pentanoic and nonanoic acid in 50

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h-fried PO samples were 1.6 times and 1.4 times higher than that in 50 h-fried SO

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samples, respectively, while hexanoic acid in 50 h-fried PO samples was 2.4 times

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lower than that in 50 h-fried SO samples. Additionally, octanoic acid and heptanoic

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acid was only found in frying palm and SO, respectively.

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Though considered unimportant contributors to flavor because of high odor

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threshold values (Liu et al., 2011), alkanes were significantly presented in frying oil

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samples. There were six and four alkanes identified in frying palm and SO,

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respectively. Among these alkanes, the highest amount of undecane (528.79±18.55

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µg/kg) and the lowest amount of decane (14.93±0.99 µg/kg) were found in frying PO

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samples, while frying SO samples contained the highest amount of nonadecane 11

ACCEPTED MANUSCRIPT (28.34±1.50 µg/kg) which was only found in 50 h-fried samples. Content of most

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alkanes showed a trend of fluctuation and no significant change was found. Notably,

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the content of undecane in frying PO samples increased significantly with the frying

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time. The result indicated homolytic cleavage on C-C linkage of palmitic acid could

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lead to the formation of volatile compounds. The main furan detected in both frying

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oils was 2-pentyl-furan which is one of oxidized products of linoleic acid rather than

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Maillard reaction products. 2-Pentyl-furan offers undesirable reversion flavor and

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exists widely in thermally oxidized oils (Lee, Kim, Chang & Lee, 2007; Min et al.,

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2011). The content of 2- pentyl-furan in both frying oils presented a growth trend with

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the increasing frying time which was 2.7 times higher in 50 h-fried SO samples than

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in 50 h-fried PO samples.

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3.5. Principal component analysis (PCA) and hierarchical cluster analysis (HCA)

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PCA is a mathematical procedure used to identify patterns in data set and then

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expresses them in a reduced-dimension plot to highlight similarities and differences

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(Franciscojosé, José, Ramón, Jesús & Rosario, 2010). In this study, PCA was applied

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to obtain a better understanding between physicochemical, free radical and volatile

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profiles changes of frying oils. Fig. 2 shows the loadings plots after PCA of the

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different variables of frying PO and SO by the two first principal components (PC1

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and PC2). As shown in Fig. 2A, PC1 and PC2 accounted for 88.76% and 6.18% of

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total variability, respectively. AV, POV, PAV, PCs, Transoleic and Freeradicals were

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stretched more to the positive side of PC1. Positive loadings on PC1 also located

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volatile compounds including Ald1, Ald2, Ald4, Ald5, Ald6, Ald7, Ald8, Ald9, Ald10,

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Ald11, Ald12, Ald13, Ald14, Ald15, Ald16, Alc2, Alc3, Alc4, Alc5, Alc6, Alc7, Ket3,

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Ket5, Ket6, Aci3, Aci4, Alk1 and Furan with loading from 0.96 to 1.0. Whereas PC1

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negatively contributed by Oleic, Linoleic, MUFAs and PUFAs. PC2 was mainly

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ACCEPTED MANUSCRIPT correlated to Alk4 and Alk5. As exhibited in Fig. 2B, the first two principal

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components took into account 92.57% of the total variations (PC1=84.08% and

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PC2=8.49%). PC1 was positively contributed by AV, POV, PAV, PCs, Transoleic and

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Freeradicals, Ald1, Ald2, Ald3, Ald4, Ald5, Ald6, Ald7, Ald8, Ald9, Ald10, Ald12,

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Ald14, Ald15, Alc2, Alc3, Alc4, Alc5, Ket4, Ket5, Ket7 and Furan, whereas

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negatively contributed by Oleic, Linoleic, MUFAs and PUFAs. PC2 was mainly

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correlated to Translinoleic, Ket3, Alk4 and Aci2. The results observed suggested that

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oleic acid, linoleic acid, MUFAs and PUFAs could reflect the characteristics of fresh

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PO and SO, and characteristics of oxidized PO and SO samples may be well reflected

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by AV, POV, p-AV, PCs, trans oleic acid, free radicals, hexanal, heptanal, octanal,

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(E)-2-heptenal, (E,E)-2,6-nonadienal, nonanal, (E)-2-octenal, decanal, (E)-2-nonenal,

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2,4-decadienal,

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4-methyl-3-heptanone and 2-pentyl-furan. Besides, the most influential features on

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PC1 of frying PO also included (E,E)-2,4-octadienal, 2,4-nonadienal, (E)-2-decenal,

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2-undecenal, 1-heptanol, 1-octanol, 2-undecanol, 1-undecanol, 3-hepten-2-one,

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octanoic acid, nonanoic acid, octane, dodecane, tetradecane, while regarding frying

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SO,

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3-methyl-3-buten-2-one, translinoleic, 4-methyl-2-hexanone, pentanoic acid and

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nonadecane had positive loadings. This indicated that different vegetable oil could be

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clearly differentiated by PCA based on the volatile profiles. Moreover, different frying

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oil samples were grouped closely and displayed similar volatile characteristics which

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were derived from oxidation of corresponding fatty acids.

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1-pentanol,

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(E,E)-2,4-decadienal,

(E,E)-2,4-nonadienal,

1-nonen-3-ol,

3-nonen-2-one,

2-dodecanol,

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(E)-2-hexenal,

1-octen-3-ol,

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HCA is a basic method used to investigate the data in which the natural groupings

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of samples were characterized by the values of measured features. HCA was applied

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for specifying the differences of volatile compounds among fried samples with 13

ACCEPTED MANUSCRIPT different frying time. Fig. 3 displays the resulting dendrogram of volatiles in frying

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PO and SO samples with different frying time. As shown in Fig. 3A, three clusters

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were identified, indicating that there were noteworthy differences among PO samples

329

of different frying period. The first cluster was the fresh and 5 h-fried oil samples. The

330

frying PO samples fried for 10-30 h were located in the second cluster while oil

331

samples fried for 35 h and 40 h were detected as the third cluster. According to Fig.

332

3A, the bottom right of the figure was much brighter than any other part of the graph,

333

which indicated that frying PO samples possessed much higher contents of aldehydes,

334

especially

335

((E)-2-decenal) and Ald16 ((E,E)-2,4-decadienal). However, fresh and 5 h-fried oil

336

samples contained lower amounts of these typical flavor components of oxidized oil,

337

which could explain why the area of first cluster was much darker than that of other

338

clusters. As shown in Fig. 3B, the results revealed a clear clustering tendency of

339

frying SO samples composed of three clusters. The fresh SO was arranged in the first

340

cluster, the frying SO samples fried for 5-25 h were classified as the second cluster

341

with similar properties, and frying SO fried for 30-40 h were detected as the third

342

cluster. The bottom right of the figure which was much brighter indicated that frying

343

SO samples possessed much higher contents of aldehydes, especially Ald1 (hexanal),

344

Ald5 ((E)-2-heptenal), Ald7 (nonanal), Ald14 (2,4-decadienal) and Ald15

345

((E,E)-2,4-decadienal). However, the area of first cluster was much darker because

346

fresh SO samples contained lower amounts of flavor components of oxidized oil. The

347

result observed by cluster analysis was in consistent with that analyzed by PCA.

348

4. Conclusion

(octanal),

Ald5

((E)-2-heptenal),

Ald7

(nonanal),

Ald13

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Ald4

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349

The physicochemical (AV, POV, p-AV, PCs), fatty acid composition, free radical

350

and volatile profiles changes of PO and SO during frying process for 40 h were 14

ACCEPTED MANUSCRIPT studied. Results showed that AV, POV, p-AV and content of PCs and free radical in oil

352

samples increased in the process of deep frying, which were much higher in frying SO

353

than in frying PO. Our further analysis on fatty acid composition showed unsaturated

354

fatty acids decreased with the increasing frying time, and no significant change of

355

saturated fatty acids was observed in both frying oils. Results of volatiles suggested

356

that main volatile compounds in PO and SO were generated from oxidation of oleic

357

acid and linoleic acid. It is of interest to explore and compare the volatile

358

characteristic of vegetable oils with different fatty acid composition. PCA and HCA

359

results demonstrated that 16 common volatiles were highly correlated to

360

physicochemical indices for evaluating lipid oxidation of frying oils. Besides,

361

chemometrics analysis also showed apparent distinctions of volatile markers between

362

frying PO and SO, and the results observed in this study proved that the variety of

363

fatty acid composition of oils were important tissue in terms of the volatile marker for

364

evaluating lipid oxidation of corresponding frying oil.

365

Conflict of interest

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The authors declare no competing financial interest. Acknowledgements

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This work was supported by the Natural Science Foundation of China (31671786),

369

the Research Fund of National 13th Five-Year Plan of China (2016YFD0401404),

370

Northern Jiangsu province science and technology projects (BN2016137), the

371

Fundamental Research Funds for the Central Universities (JUSRP51501), and

372

Postgraduate Research & Practice Innovation Program of Jiangsu Province

373

(KYCX18_1755).

374

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ACCEPTED MANUSCRIPT TABLE AND FIGURE CAPTIONS

509

Table 1

510

Fatty acid composition of frying oils at different frying periods

511

Table 2

512

Content of free radical spin adducts of frying oils detected in 32 min at different

513

frying periods

514

Table 3

515

Main volatile compounds of frying oils at different frying periods

516

Fig.1

517

Quality characteristics of frying oils including acid value (A), peroxide value (B),

518

p-anisidine value (C), and polar compounds (D) at different frying periods.

519

Fig. 2

520

Bi-plot principal component analysis (PCA) for all physicochemical, free radical,

521

fatty acids and volatile profiles of frying palm (A) and sunflower (B) oil.

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Fig. 3

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Hierarchical clustering analysis (HCA) of frying palm (A) and sunflower (B) oil

524

based on volatile components concentration.

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ACCEPTED MANUSCRIPT

Table 1 Fatty acid composition of frying oils at different frying periods composition (g/100g)

Frying time (h) 0

5 a

10

15

20

47.62±0.54

a

25

4.36±0.07b

C18:0

4.73±0.16a

4.71±0.23ab

4.70±0.19ab

4.52±0.14ab

4.64±0.16ab

4.61±0.07ab

i

h

g

f

e

d

C18:1

34.85±0.64a

34.09±0.42ab

33.05±0.26b

31.47±0.54c

C18:2(T)

0.11±0.002a

0.11±0.002a

0.11±0.006a

0.10±0.005a

C18:2

5.80±0.20a

5.58±0.21a

5.46±0.35a

4.83±0.10b

C18:3(n-3)

0.08±0.002a

0.08±0.001a

0.08±0.001a

C20:0

0.32±0.004a

0.32±0.003ab

0.31±0.004ab

∑SFAs

56.48±1.22a

56.29±0.94a

54.97±0.45a

∑MUFAs

35.11±0.64a

34.35±0.42ab

33.33±0.26b

∑PUFAs

5.99±0.21a

5.77±0.21a

5.64±0.36a

7.98±0.24bc

7.69±0.14abc

0.08±0.001

0.10±0.001

0.12±0.002

48.85±0.69a

4.43±0.05ab

4.64±0.06ab

b

0.20±0.004a

49.39±1.41

0.16±0.001

29.68±0.64d

28.12±0.42e

25.28±0.24f

0.10±0.003ab

0.10±0.004ab

0.10±0.001ab

0.09±0.003b

0.09±0.001b

4.48±0.14bc

4.24±0.14c

4.02±0.24c

3.50±0.21d

3.39±0.21d

0.06±0.001b

0.06±0.001b

0.04±0.001c

0.04±0.001c

0.04±0.001c

NDd

0.29±0.005c

0.30±0.003b

0.31±0.003ab

0.29±0.002c

0.31±0.006ab

0.31±0.004ab

54.33±0.68a

55.66±1.21a

55.25±0.95a

55.33±0.59a

56.01±1.36a

55.73±0.75a

31.74±0.54c

32.00±0.49c

31.07±0.78cd

30.02±0.64d

28.47±0.42e

25.67±0.24f

5.00±0.09b

4.63±0.14bc

4.38±0.14c

4.16±0.24c

3.63±0.21d

3.48±0.21d

7.69±0.28abc

7.73±0.14abc

C18:0

4.12±0.05

a

8.22±0.23c

C18:1(T)

0.04±0.002i

0.06±0.001h

0.07±0.001g

0.09±0.002f

0.12±0.006e

0.14±0.004d

C18:1

21.32±0.78a

20.66±0.71ab

19.53±0.99bc

19.11±0.71bc

18.15±0.71c

C18:2(T)

0.06±0.002ab

0.07±0.002a

0.07±0.001a

0.07±0.001a

C18:2

60.98±1.23a

59.70±1.27ab

58.38±1.34bc

C18:3(n-3)

0.09±0.002a

0.07±0.004b

C20:0

0.30±0.004a

∑SFAs

14.07±0.27ab

∑MUFAs

21.63±0.78a

∑PUFAs

61.13±1.23a

TE D

7.41±0.21a

0.19±0.004b

0.22±0.007a

16.23±0.71d

15.69±0.71de

14.05±0.71ef

13.46±0.60f

0.06±0.001ab

0.05±0.002d

0.05±0.001cd

0.05±0.004d

0.07±0.002ab

56.00±1.33cd

53.87±0.51de

51.83±1.14ef

50.30±0.42f

46.15±1.00g

43.26±1.18h

0.07±0.001b

0.07±0.004b

0.07±0.002b

0.05±0.002c

0.05±0.004c

0.04±0.003c

0.04±0.001c

0.25±0.004bc

0.25±0.002bc

0.26±0.004b

0.25±0.002bc

0.23±0.004d

0.26±0.005b

0.24±0.004cd

0.27±0.004b

14.39±0.10a

13.61±0.10bc

14.55±0.37a

14.07±0.23ab

12.84±0.44d

13.33±0.17cd

13.37±0.42cd

13.64±0.29bc

20.95±0.71ab

19.83±0.99bc

19.49±0.70bc

18.50±0.71c

16.57±0.71d

16.08±0.71de

14.44±0.71ef

13.91±0.59f

59.84±1.27ab

58.52±1.34bc

56.13±1.32cd

54.00±0.51de

51.92±1.14ef

50.41±0.42f

46.24±0.99g

43.37±1.18h

EP

AC C

3.62±0.07

3.30±0.21

d

7.37±0.28a 0.15±0.006c

3.65±0.14

bcd

7.58±0.21ab

3.73±0.14bc

3.68±0.14

bcd

8.12±0.16c

cd

3.77±0.15

bc

c

40 a

30.71±0.78cd

C16:0

b

0.14±0.002

a

31.71±0.49c

SC

0.07±0.001

M AN U

0.06±0.001

35

48.70±0.66

oil

0.04±0.001

48.06±1.02

30

a

49.60±1.06

C18:1(T)

48.85±1.37

a

C16:0

oil

48.04±0.26

a

Palm

Sunflower

49.34±0.71

a

RI PT

Fatty acid

3.61±0.21

bcd

3.39±0.12

Data within the same row with different letters are significantly different at P < 0.05. ND, not detected. SFAs, saturated fatty acids. MUFAs, monounsaturated fatty acids. PUFAs,

ACCEPTED MANUSCRIPT

AC C

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polyunsaturated fatty acids.

ACCEPTED MANUSCRIPT

Table 2 Content of free radical spin adducts of frying oils detected in 32 min at different frying periods time(min)

0

5 h

20

25

30

4.19±0.03a

1.18±0.03h

1.51±0.02g

1.66±0.06f

1.92±0.03e

2.42±0.04d

2.65±0.08c

3.66±0.05b

4.25±0.07a

6

1.17±0.04h

1.35±0.06g

1.55±0.06f

1.70±0.04e

1.97±0.05d

2.67±0.04c

2.67±0.08c

3.76±0.05b

4.26±0.05a

8

1.72±0.06f

1.98±0.04e

2.05±0.08e

2.07±0.05e

2.27±0.03d

2.97±0.05c

3.00±0.06c

4.56±0.05b

4.70±0.05a

10

2.10±0.05g

2.41±0.05f

2.55±0.07f

2.76±0.10e

2.78±0.11d

3.07±0.06c

3.38±0.04c

5.06±0.05b

5.32±0.04a

12

2.55±0.07

g

f

e

e

de

d

c

b

6.37±0.11a

14

3.13±0.06h

3.49±0.02g

4.00±0.09f

3.95±0.08ef

4.10±0.05de

4.21±0.08d

4.49±0.03c

6.37±0.05b

6.57±0.05a

16

3.43±0.05g

3.73±0.04f

4.34±0.08e

4.57±0.05d

4.61±0.02d

4.66±0.04d

4.89±0.05b

6.79±0.01c

6.99±0.09a

18

3.99±0.04h

4.19±0.04g

4.92±0.03f

5.07±0.06e

5.26±0.04d

5.55±0.06c

5.82±0.04b

7.57±0.04a

7.65±0.05a

20

4.75±0.08h

4.60±0.02g

5.56±0.04f

5.34±0.04e

5.85±0.07d

5.96±0.03cd

6.06±0.06c

7.75±0.03b

8.07±0.05a

22

5.36±0.06g

5.42±0.04g

6.07±0.05f

6.28±0.03e

6.37±0.04e

6.84±0.05d

7.28±0.03c

8.07±0.06b

8.69±0.05a

24

5.25±0.07i

5.34±0.06h

5.89±0.02g

6.04±0.05f

6.35±0.04e

6.57±0.04d

6.88±0.03c

7.80±0.01b

8.47±0.04a

26

5.04±0.06i

5.28±0.03h

5.76±0.04g

5.87±0.05f

6.08±0.03e

6.39±0.02d

6.81±0.02c

7.63±0.06b

8.29±0.01a

28

4.70±0.03i

5.07±0.05h

5.50±0.01g

5.70±0.01f

5.89±0.02e

6.34±0.06d

6.61±0.03c

7.67±0.04b

8.01±0.04a

30

4.88±0.06g

4.98±0.04g

5.57±0.05f

5.67±0.05f

5.85±0.08e

6.26±0.05d

6.55±0.04c

7.46±0.03b

8.00±0.08a

32

4.65±0.08

h

g

f

f

e

d

c

b

7.71±0.02a

Sunflower

2

1.22±0.03i

1.73±0.03h

oil

4

1.35±0.06i

1.95±0.07h

(×1012)

6

1.38±0.02i

8

M AN U

TE D

5.44±0.05

SC

1.010.03i

5.46±0.03

5.77±0.10

3.59±0.05

6.08±0.02

3.88±0.03

6.47±0.04

3.35±0.07

40 b

4

3.45±0.06

2.57±0.05

35 c

(×1012)

4.86±0.05

2.35±0.07

d

0.96±0.004

3.30±0.15

1.83±0.04

e

2

3.30±0.02

1.51±0.03

f

Palm oil

3.01±0.10

1.36±0.04

15 g

EP

1.04±0.06

10 h

RI PT

Frying time(h)

Detection

5.77±0.05

7.57±0.04

2.32±0.02f

2.85±0.07e

3.49±0.02d

5.01±0.03c

6.00±0.03b

8.13±0.11a

2.22±0.11g

2.47±0.05f

2.91±0.03e

3.63±0.10d

5.17±0.09c

6.15±0.14b

8.21±0.13a

2.01±0.03h

2.30±0.14g

2.50±0.05f

3.07±0.08e

3.68±0.04d

5.24±0.07c

6.30±0.12b

8.30±0.13a

1.47±0.08h

2.09±0.12g

2.44±0.14f

2.57±0.05f

3.13±0.04e

3.89±0.12d

5.36±0.06c

6.35±0.07b

8.32±0.10a

10

1.87±0.05h

2.29±0.11g

2.40±0.02g

2.78±0.06f

3.59±0.08e

4.05±.07d

5.51±0.03c

6.30±0.01b

8.36±0.06a

12

2.60±0.06g

2.64±0.07g

2.73±0.08g

3.13±0.16f

3.89±0.03e

4.30±0.08d

5.99±0.07c

6.59±0.07b

8.68±0.05a

14

2.78±0.04g

2.79±0.01g

2.87±0.09g

3.43±0.08f

4.00±0.01e

4.68±0.06d

6.07±0.06c

6.77±0.05b

9.01±0.06a

AC C

2.07±0.09g

16

2.98±0.09g

3.04±0.07g

3.12±0.03g

4.03±0.10f

4.53±0.05e

4.88±0.03d

6.20±0.12c

6.86±0.06b

9.20±0.08a

18

3.30±0.06h

3.68±0.04g

3.75±0.08g

4.23±0.03f

4.55±0.07e

5.09±0.06d

6.38±0.04c

7.10±0.08b

9.40±0.03a

20

4.47±0.04f

4.52±0.07f

4.56±0.06f

4.60±0.05ef

4.72±0.04e

5.29±0.09d

6.54±0.08c

7.39±0.06b

9.46±0.04a

22

5.01±0.04

f

ef

ef

ef

e

d

c

b

9.83±0.05a

24

5.29±0.01g

5.40±0.06fg

5.49±0.07f

6.00±0.03e

5.92±0.09de

6.16±0.05d

6.81±0.07c

7.62±0.10b

10.33±0.12a

26

5.37±0.05h

5.64±0.04g

5.78±0.02g

6.18±0.08f

RI PT

ACCEPTED MANUSCRIPT

6.35±0.08e

6.57±0.05d

7.11±0.13c

7.15±0.10b

10.96±0.06a

28

5.60±0.03g

5.77±0.05f

5.56±0.06f

6.60±0.05e

6.81±0.03d

6.86±0.06d

7.39±0.06c

7.89±0.04b

11.62±0.04a

30

5.37±0.08g

5.67±0.06g

5.46±0.04f

6.38±0.08e

6.51±0.03de

6.67±0.02d

7.30±0.03c

7.81±0.03b

11.14±0.16a

32

5.27±0.08f

5.48±0.07f

5.34±0.03f

6.20±0.14e

6.57±0.04d

6.80±0.03cd

7.06±0.06c

7.65±0.08b

10.90±0.22a

AC C

EP

TE D

Data within the same row with different letters are significantly different at P < 0.05.

5.24±0.03

5.22±0.06

5.87±0.05

SC

5.19±0.09

M AN U

5.09±0.07

6.74±0.05

7.52±0.09

ACCEPTED MANUSCRIPT

Table 3 Main volatile compounds of frying oils at different frying periods 0

5

10

15

20

Palm oil Aldehydes Hexanal

84.901±4.92i h

167.32±4.37h

172.62±7.19

f

390.30±16.77f

43.78±2.18

(E)-2-Hexenal

27.39±1.49g

31.00±1.88g

41.89±2.04f

49.50±0.96e

Octanal

121.21±6.36g

197.72±4.95f

438.40±20.51e

534.90±15.56d

(E)-2-Heptenal

176.42±14.85g

408.12±29.70f

718.04±23.23e

19.33±1.41h

23.95±1.41g

32.73±2.12f

686.12±37.48g

1708.46±91.92f

2249.05±149.20e

92.66±4.24h

217.18±13.44g

336.17±19.80f

210.27±10.61g

211.10±7.07g

267.31±14.14f

(E)-2-Nonenal

65.71±2.83i

107.24±4.24h

(E,E)-2,4-Octadienal

10.15±0.42h g

243.42±5.64

e

30

521.29±12.51d 272.78±4.60

d

35

619.22±15.54c 301.97±13.50

c

40

882.84±9.07b 446.83±12.17

b

975.46±14.18a 483.08±9.41a

55.84±4.95d

70.95±3.54c

83.08±3.54b

128.10±3.54a

630.64±13.44c

681.85±14.14c

739.40±27.58b

1093.71±127.99a

1141.13±77.78a

760.56±36.77de

789.32±21.21d

808.80±26.87d

1017.67±44.55c

1517.24±105.36b

1697.93±92.63a

34.17±2.12f

44.44±1.41e

50.69±2.12d

55.48±2.83c

62.55±2.83b

78.95±2.12a

2539.57±86.97d

2759.07±134.35c

2866.47±155.56c

4118.77±164.76b

4254.46±184.55b

5011.74±192.33a

352.31±12.73f

376.50±16.26e

423.59±15.56d

542.41±15.56c

647.11±30.41b

735.62±42.43a

295.39±12.02e

298.94±16.26de

317.97±14.85d

381.13±21.21c

435.27±14.85b

557.75±32.53a

174.58±5.66g

200.22±7.07f

213.39±12.02e

228.98±7.07d

252.09±11.31c

362.30±12.02b

394.70±12.02a

12.71±0.71g

13.68±0.92g

17.92±0.71f

19.39±0.72e

22.44±1.41d

29.70±1.45c

33.56±1.54b

39.53±1.43a

f

e

d

d

d

c

b

16.32±0.78

33.16±1.63

44.64±1.06

45.70±1.48

46.50±1.13

67.33±2.59

70.38±2.26

101.13±3.54a

11.42±0.71

(E)-2-Decenal

99.44±4.24h

314.43±15.56g

566.77±23.33f

878.38±19.80e

876.78±25.46e

1122.89±54.45d

1293.10±41.01c

1822.46±86.97b

1922.55±78.49a

2-Undecenal

58.43±4.25h

152.58±15.56g

310.86±23.65f

491.22±19.85e

494.56±25.34e

585.73±54.22d

655.70±41.86c

789.60±86.45b

1023.44±76.46a

2,4-Decadienal

36.39±1.44i

148.60±15.23h

160.70±21.21g

172.40±19.34f

193.12±25.30e

288.69±53.22d

308.05±40.12c

356.50±80.45b

423.59±74.56a

149.17±1.87h

489.54±7.34g

565.61±10.32f

588.85±19.45f

667.37±21.94e

784.32±24.56d

1009.31±33.29c

1036.70±30.21b

1118.84±56.23a

NDh

16.99±0.77g

22.55±1.01f

27.52±0.70e

33.16±1.95d

33.63±1.54d

39.73±1.51c

41.74±1.54b

44.25±1.95a

1-Pentanol

8.01±0.21g

30.57±1.12f

87.92±3.03e

89.29±3.03e

90.74±2.52e

107.74±2.34d

182.20±4.71c

207.10±4.70b

239.46±5.07a

1-Octen-3-ol

38.55±0.81h

89.25±2.26g

134.21±4.72f

141.56±4.12ef

145.21±6.14de

151.00±4.71d

197.90±6.82c

281.03±8.40b

314.32±13.21a

NDg

NDg

140.99±5.95f

155.42±6.43e

160.30±4.70e

173.19±6.54d

287.05±8.58c

299.66±12.58b

313.61±17.06a

(E,E)-2,4-Decadienal Alcohols 2-Butyl-1-octanol

1-Heptanol

AC C

2,4-Nonadienal

EP

Decanal

419.68±27.51e

M AN U

(E)-2-Octenal

25

54.57±6.36d

TE D

Nonanal

240.94±6.38

e

Heptanal

(E,E)-2,6-Nonadienal

72.44±2.99

356.56±11.60g

g

SC

(µg/kg)

RI PT

Frying time(h)

Volatile compound

ACCEPTED MANUSCRIPT

108.19±3.87h

124.76±4.98g

190.92±7.75f

213.15±10.89e

226.77±7.52d

243.23±7.05c

405.31±8.32b

453.05±15.15a

2-Undecanol

39.33±1.12i

42.43±2.14h

52.48±1.77g

56.05±2.44f

60.78±1.91e

63.36±2.98d

69.05±2.29c

75.52±2.93b

89.16±3.86a

1-Undecanol

67.48±2.88g

84.37±2.71f

99.53±5.78e

110.40±4.05d

111.64±3.26d

121.38±5.55c

124.22±5.63c

145.64±5.96b

162.60±7.17a

6-Methyl-5-hepten-2-one

NDh

11.55±0.47g

19.50±0.81f

22.68±0.99e

26.47±1.39d

30.85±1.17c

33.31±1.72b

34.37±1.34b

37.08±1.78a

4-Methyl-2-hexanone

NDc

NDc

NDc

NDc

NDc

NDc

NDc

36.36±1.46b

43.21±1.54a

3-Nonen-2-one

NDh

20.95±0.74g

24.24±0.98f

26.26±1.36e

28.28±1.05d

34.57±1.90c

42.93±2.09b

44.08±1.99b

53.41±1.68a

1-Hexen-3-one

NDe

NDe

NDe

9.08±0.30d

14.75±0.88c

15.18±0.44c

15.39±0.50c

16.12±0.33b

16.79±0.63a

3-Hepten-2-one

NDh

20.55±0.80g

27.96±0.66f

33.37±1.52e

41.33±1.56d

47.56±1.60c

52.76±1.94b

53.92±2.70b

61.35±2.35a

4-Methyl-3-heptanone

NDf

16.28±0.97e

16.64±0.92e

27.66±1.65d

30.88±1.64c

32.54±1.54c

40.63±2.55b

50.70±3.02a

52.19±2.46a

Pentanoic acid

NDg

NDg

57.53±1.24f

119.18±3.72e

168.90±6.16d

176.78±9.13c

186.09±8.30b

192.67±8.82ab

198.78±7.56a

Hexanoic acid

NDh

5.29±0.21h

33.23±1.85g

51.44±2.52f

74.77±3.57e

81.43±4.09d

130.49±5.71c

200.82±6.36b

297.85±12.04a

f

e

d

Acids

h

h

g

SC

M AN U

Ketones

RI PT

NDi

1-Octanol

10.91±0.39

Nonanoic acid

NDh

NDh

11.02±0.26g

30.81±1.46e

34.10±2.01d

38.90±1.75c

68.13±3.74b

74.73±3.85b

79.13±3.80a

Octane

NDf

NDf

NDf

153.31±3.77e

155.98±6.43e

217.62±7.63d

278.01±9.27c

330.68±11.79b

430.31±14.10a

Decane

NDi

19.11±0.81h

30.20±1.22g

25.96±0.46f

12.83±0.68e

24.23±1.58d

21.21±1.39c

22.79±1.22b

14.93±0.99a

Undecane

181.34±7.07h

222.29±8.42g

240.79±8.69f

265.60±11.10e

315.83±15.65d

329.58±12.63d

432.38±14.85c

501.45±15.25b

528.79±18.55a

Dodecane

46.67±1.88g

66.16±2.58f

169.74±10.46b

167.36±10.06b

158.56±5.95c

224.55±8.94a

228.15±13.71a

93.44±4.69e

108.54±7.54d

Tetradecane

NDh

41.81±1.76g

58.62±2.60f

84.81±4.75c

68.35±3.63e

112.28±7.14a

100.32±5.50b

66.02±3.94e

78.64±4.67d

Nonadecane

NDe

NDe

NDe

18.08±1.20b

12.32±0.47d

19.70±1.64a

16.22±1.41c

16.68±1.06c

12.38±0.66d

73.03±3.83g

122.66±6.11f

143.36±6.96e

171.24±8.34d

189.87±10.23c

217.86±10.48b

221.42±8.48b

302.65±12.90a

Aldehydes

EP

AC C

Sunflower oil

21.67±1.06h

TE D

ND

2-Pentyl-furan

22.91±0.74

27.24±1.83

33.33±1.40

36.75±1.86a

ND

Furan

16.73±1.00

b

Octanoic acid

Alkanes

13.12±0.48

c

ACCEPTED MANUSCRIPT

343.07±12.50g

353.82±11.57g

364.57±13.05g

654.30±30.90f

720.90±26.25e

994.79±34.58d

1114.62±57.26c

1284.73±89.48b

1489.73±98.17a

Heptanal

60.19±3.13g

69.55±3.63g

66.98±4.25g

113.59±6.51f

142.52±7.83e

186.71±12.19d

198.42±12.53c

213.04±11.55b

248.28±16.11a

(E)-2-Hexenal

106.72±4.34f

114.25±6.63f

138.23±8.33e

143.02±6.33e

147.86±6.23e

172.10±9.25c

187.44±9.76b

204.95±10.60a

f

f

f

e

Octanal

107.84±4.94

109.73±3.38

111.56±4.57

144.62±8.59

RI PT

Hexanal

168.42±11.42

d

160.19±8.27d

218.23±13.85

c

223.47±11.35

c

234.78±14.48

b

303.69±13.23a

1683.56±69.60ef

1797.44±58.13e

2113.66±127.89d

2133.85±119.21d

2651.78±164.68c

2864.59±141.92b

2951.14±149.27b

3105.86±143.56a

21.90±0.80i

32.40±1.50h

37.17±1.25g

52.71±2.72f

58.80±2.50e

62.14±3.18d

69.69±2.47c

80.96±3.27b

86.98±3.47a

Nonanal

664.50±31.03e

742.83±31.80de

802.66±34.08d

1067.99±68.38c

1255.24±71.71b

1315.25±64.77b

1306.73±96.59b

1492.24±102.95a

1574.58±99.33a

(E)-2-Octenal

185.44±8.34h

281.74±17.53g

300.33±14.13g

528.27±40.66f

617.40±22.85e

740.20±42.08d

826.09±39.65b

844.65±45.59c

1157.68±92.25a

Decanal

217.70±11.97g

258.98±15.05f

267.74±13.16f

274.89±13.30f

300.66±16.01e

327.25±19.52d

346.70±21.56c

394.39±19.71b

426.09±22.13a

(E)-2-Nonenal

67.91±3.67h

87.35±5.51g

97.30±4.00g

155.55±10.03f

167.64±10.32e

182.87±9.23d

202.60±10.11c

216.09±12.21b

247.14±15.43a

(E)-2-Decenal

75.06±3.85g

111.11±6.74f

131.31±7.04e

233.32±11.13d

288.64±14.56c

290.98±13.48c

313.89±14.64b

316.11±17.74b

338.51±20.04a

(E,E)-2,4-Nonadienal

19.54±0.97f

25.69±1.41e

27.34±1.06e

56.05±2.41d

67.95±3.23c

100.73±6.19b

104.85±4.95b

113.39±5.88a

115.71±7.59a

2-Undecenal

54.22±2.51f

187.44±11.00b

187.36±12.44b

195.36±8.23b

205.58±11.65a

c

c

371.30±14.60

83.87±3.73d f

477.50±21.97

M AN U

72.84±3.53e g

159.89±9.11c

e

763.65±23.58

d

805.99±35.44

813.86±32.51

854.84±56.65

b

1012.67±43.45

a

207.22±9.76a 1044.71±73.45a

258.84±11.28

(E,E)-2,4-Decadienal

813.07±41.61g

1140.68±73.89f

1545.08±82.84e

2629.31±134.31d

2648.23±118.32d

2721.15±135.19d

2907.51±213.52c

3374.38±248.96b

3646.54±202.36a

NDe

NDe

NDe

24.31±1.37d

25.52±1.35d

27.42±1.53c

27.57±1.39c

33.89±2.03b

43.01±2.36a

63.64±3.10f

64.23±2.70f

66.00±3.14f

133.74±7.02e

142.24±7.59e

160.17±7.76d

186.71±8.70c

266.64±10.96b

295.77±18.24a

1-Octen-3-ol

353.36±15.27g

385.17±18.14f

393.92±15.93f

529.55±24.18e

557.22±32.20de

583.93±25.98d

615.26±29.61c

651.50±39.68b

795.82±42.96a

1-Nonen-3-ol

NDi

9.88±0.47h

14.05±0.69g

17.53±0.96f

19.65±0.97e

22.79±1.34d

25.67±1.42c

29.23±1.48b

31.54±1.83a

2-Dodecanol

40.32±1.65g

42.43±1.70g

52.51±3.49f

53.85±2.34f

58.34±2.63e

61.56±3.15d

69.78±3.16c

88.80±3.75b

98.45±3.93a

1-Undecanol

67.74±2.98g

77.03±3.81f

79.08±4.98ef

84.65±3.42e

95.63±4.50d

98.53±4.50d

111.03±7.58c

150.70±7.43b

162.38±10.63a

6-Methyl-5-hepten-2-one

NDe

NDe

31.45±1.72d

34.08±1.68c

35.95±2.12c

40.32±1.93b

44.43±2.96a

45.67±2.32a

46.68±2.35a

3-Hexen-2-one

NDg

17.59±0.99f

17.91±0.74f

20.36±1.29f

47.59±3.18e

81.34±4.27d

123.16±6.68c

144.12±6.60b

218.06±15.00a

4-Methyl-2-hexanone

NDb

NDb

NDb

NDb

NDb

NDb

NDb

NDb

14.06±0.71a

2-Butyl-1-octanol 1-Pentanol

Ketones

AC C

Alcohols

TE D

2,4-Decadienal

EP

(E,E)-2,6-Nonadienal

SC

1621.67±79.66f

(E)-2-Heptenal

ACCEPTED MANUSCRIPT

28.65±1.51g

36.23±2.21f

42.00±2.35e

66.49±4.30d

67.35±3.97d

72.97±3.88c

75.05±3.78c

86.54±4.33b

94.53±5.71a

3-Methyl-3-buten-2-one

94.73±4.64f

108.60±6.17e

114.83±5.09de

119.35±6.93cd

121.38±7.01cd

126.45±5.82d

136.31±6.87b

144.88±7.70a

147.40±7.15a

2,4-Heptanedione

14.97±0.89h

39.49±1.63g

156.55±8.63f

177.50±9.99e

189.79±7.74d

210.42±8.75c

227.83±10.75b

244.85±11.87a

h

g

4-Methyl-3-heptanone

22.19±1.04

35.93±1.94

49.04±2.13

f

60.50±2.92

e

Acids

RI PT

3-Nonen-2-one

72.73±4.08

d

198.24±8.18d 74.09±3.82

cd

77.90±3.76

c

90.05±4.94

b

109.32±6.77a

71.22±2.51f

82.33±4.23f

120.60±5.87e

300.14±14.83d

313.05±20.37cd

321.10±15.37c

331.74±18.46c

352.89±16.02b

711.87±34.40a

Pentanoic acid

NDf

NDf

NDf

NDf

9.18±0.32e

17.66±1.09d

27.66±1.40c

37.10±1.85b

120.60±7.17a

Heptanoic acid

NDc

NDc

NDc

NDc

NDc

NDc

NDc

16.86±0.73b

26.37±1.46a

Nonanoic acid

NDe

NDe

NDe

NDe

NDe

21.30±0.88d

51.73±1.82c

54.64±3.25b

57.65±2.96a

365.37±15.60g

314.07±20.52h

395.79±15.88ef

490.66±20.03b

429.77±18.99d

623.15±37.29a

457.50±20.17c

402.79±20.12e

377.45±17.64fg

Tetradecane

46.60±2.29e

51.52±2.34d

51.94±2.69d

84.35±5.04b

70.48±3.53c

96.00±4.27a

84.93±4.17b

89.03±4.31b

87.29±4.18b

Hexadecane

NDe

NDe

NDe

185.55±12.12b

171.61±7.97c

267.03±11.38a

172.64±10.83c

NDe

138.80±8.23d

Nonadecane

b

b

b

ND

ND

ND

149.83±5.34f

155.83±7.63f

171.78±8.95f

Furan 2-Pentyl-furan

b

ND

ND

ND

ND

ND

28.34±1.50a

270.53±11.37e

339.62±15.80d

357.42±16.77d

421.91±24.88c

479.00±27.80b

820.43±39.60a

TE D

Undecane

M AN U

Alkanes

EP

Data within the same row with different letters are significantly different at P < 0.05. ND, not detected.

AC C

SC

Hexanoic acid

b

b

b

b

ACCEPTED MANUSCRIPT (B) 2.0

(A) 2.0

Sunflower oil Palm oil

Sunflower oil Palm oil 1.5

1.0

0.5

1.0

0.5

0.0

0.0 0

5

10

15

20

25

30

35

0

40

5

10

15

20

25

30

35

40

Frying time (h)

Frying time (h)

(D) 25

(C) 100

Sunflower oil Palm oil

SC

Sunflower oil Palm oil 20

50

15

M AN U

Polar compounds (%)

75

P-anisidine value

RI PT

Peroxide value (meq/kg)

Acid value (mg/g)

1.5

10

25

5

0 0

5

10

15

20

25

30

Frying time (h)

35

40

0

5

10

15

20

25

30

35

40

Frying time (h)

TE D

Fig. 1. Quality characteristics of frying oils including acid value (A), peroxide value (B),

AC C

EP

p-anisidine value (C), and polar compounds (D) at different frying periods.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Fig. 2. Bi-plot principal component analysis (PCA) for all physicochemical, free radical, fatty acids and volatile profiles of frying palm (A) and sunflower (B) oil.

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

(A)

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

(B)

Fig. 3. Hierarchical clustering analysis (HCA) of frying palm (A) and sunflower (B) oil based on volatile components concentration.

ACCEPTED MANUSCRIPT Application of EPR with DMPO as spin trap in thermal oxidation of frying oils. Volatiles of frying palm and sunflower oil were formed by oxidation of fatty acids. Potential volatile indicators for evaluating oxidation differed in different oils.

RI PT

Chemometrics analysis was used for finding volatile markers for quality

AC C

EP

TE D

M AN U

SC

evaluation.