Analytical Methods Accepted Manuscript
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Analytical Methods Accepted Manuscript This is an Accepted Manuscript, which has been through the Royal Society of Chemistry peer review process and has been accepted for publication. Accepted Manuscripts are published online shortly after acceptance, before technical editing, formatting and proof reading. Using this free service, authors can make their results available to the community, in citable form, before we publish the edited article. We will replace this Accepted Manuscript with the edited and formatted Advance Article as soon as it is available. You can find more information about Accepted Manuscripts in the Information for Authors. Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/methods Page 1 of 32 Analytical Methods 1 2 3 4 1 Characterization and authentication of four important edible oils 5 6 2 using free phytosterol profiles established by GC-GC–TOF/MS 7 8 a,b,g,i b,g,h c,d, i b,e,f,g,h, 9 3 Baocheng Xu , Liangxiao Zhang , Hua Wang *, Denglin Luo and Peiwu Li * 10 11 4 a College of Food Science and Engineering, Northwest A&F University, Yangling 712100, China 12 13 b 14 5 Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences, Wuhan 430062, China 15 16 6 c College of Enology, Northwest A&F University, Yangling, China 17 18 d 19 7 Shanxi Engineering Research Center for Viti-Viniculture, Yangling, China 20 21 e 8 Key Laboratory of Biology and Genetic Improvement of Oil Crops, Ministry of Agriculture, Wuhan, Manuscript 22 23 24 9 China 25 26 10 f Key Laboratory of Detection for Mycotoxins, Ministry of Agriculture, Wuhan, China 27 28 g 29 11 Laboratory of Risk Assessment for Oilseeds Products (Wuhan), Ministry of Agriculture, China 30 31 12 h Quality Inspection and Test Center for Oilseeds Products, Ministry of Agriculture, Wuhan, China Accepted 32 33 34 13 i School of Food and Bioengineering, Henan University of Science and Technology, Luoyang 471003, 35 36 14 China 37 38 39 15 40 Methods 41 16 * Corresponding authors. 42 43 44 17 College of Enology, Northwest A&F University, Yangling, China. Fax: ＋86 29 87091099; Tel: ＋ 45 46 18 86 29 87091994; E-mail: [email protected] (H. Wang) 47 48 49 19 Oil Crops Research Institute of Chinese Academy of Agriculture Science, Wuhan, China. Fax: ＋86 50 51 Analytical 20 27 86812862; Tel: ＋86 27 86812943; E-mail: [email protected] (P. Li) 52 53 54 55 56 57 58 59 60 1 Analytical Methods Page 2 of 32 1 2 3 4 21 Abstract 5 6 22 Adulteration of high-price edible oils has become a focus of attention and a tough problem in the 7 8 9 23 food trade and consumption all over the world. Therefore, there is a great demand for detecting oil 10 11 24 adulteration to protect interests and rights of customers and safeguard their health. In this study, 12 13 14 25 free phytosterol profiles of peanut, soybean, rapeseed, and sunflower seed oils were established by 15 16 26 SPE –multidimensional gas chromatography coupled with time-of-flight mass spectrometry 17 18 19 27 (GC-GC –TOF/MS) and employed to classify the four edible oils with the help of unsupervised 20 21 28 (principal component analysis and hierarchical clustering analysis) and supervised (random forests) Manuscript 22 23 24 29 multivariate statistical methods. The results indicated that free phytosterol profiles of edible oils 25 26 30 could help classify the four edible oils into four groups completely, and therefore could be taken 27 28 29 31 as important markers of the oils studied. Moreover, a simulated data test revealed that free 30 31 32 phytosterol profiles could also be used to detect peanut oil adulterated with 5% soybean oil, which Accepted 32 33 34 33 was simulated by the Monte Carlo method. 35 36 34 Keywords: Free phytosterol profiles; Adulteration identification; Edible oil; GC-GC–TOF/MS; 37 38 39 35 Chemometrics 40 Methods 41 36 42 43 44 45 46 47 48 49 50 51 Analytical 52 53 54 55 56 57 58 59 60 2 Page 3 of 32 Analytical Methods 1 2 3 4 37 Introduction 5 6 38 Vegetable oils play a vital role in human nutrition as the most important food in our daily life. 7 8 9 39 They provide energy and nutritional components including but not limited to essential fatty acids, 10 11 40 phytosterols, tocopherols, phenolic compounds, and vitamins 1, 2, as well as greatly affect flavor and 12 13 14 41 taste of food. In edible oil consumption in China, soybean oil possesses the largest market share, 15 16 42 followed by rapeseed, peanut, and sunflower seed oils3. However, due to the non-transgenic merit and 17 18 19 43 pleasant flavor, the market shares of peanut, rapeseed, and sunflower seed oils have been increasing 20 21 3 44 gradually though they are more expensive than soybean oil in China . As the same as olive oil in Manuscript 22 23 24 45 western countries, these high-price oils adulterated with lower-price oils including soybean oil as a 25 26 46 major adulterant, have become the biggest source of agricultural fraud in China and other developing 27 28 29 47 countries. Therefore, reliable detection of such adulterations is in great demand. 30 31 48 Adulteration of edible oils has been chronically practiced for many years. Besides economic fraud, Accepted 32 33 34 49 it sometimes causes potential harms or threats to the health of consumers 4. To ensure authenticity of 35 36 50 edible oils, a number of analytical methods have been established to detect and quantify these 37 38 39 51 adulterations. The most common methods are based upon detection and quantification of one or more 40 Methods 41 52 particular compounds, which are specific to adulterants and absent from authentic oils. Some previous 42 43 44 53 studies detected adulteration of a target oil by analyzing marker(s), such as detecting olive oil 45 46 5 54 adulterated with soybean, peanut, sunflower seed, corn, or sesame oil by the level of trilinolein (LLL) , 47 48 49 55 and using specific sesamol to detect sesame oil adulterated with other oils or fats 6. Although these 50 51 Analytical 56 methods are simple and reliable for routine detection, an obvious limitation is that not every oil/fat has 52 53 54 57 its own marker, so that they are not always effective for purity tests of all edible oils. Another option is 55 56 58 to directly analyze oils without sample pretreatment or with only organic solvent-based dilution. In this 57 58 59 60 3 Analytical Methods Page 4 of 32 1 2 3 7, 8 4 59 respect, a number of methods were proposed based on fluorescence spectroscopy , Raman 5 6 60 spectroscopy 9, 10 , Fourier transform near infrared spectroscopy 11, 12 , mid-infrared spectroscopy 13, 14 , 7 8 15 16, 17 18 9 61 nuclear magnetic resonance spectrometry , electronic nose , and differential scanning calorimetry , 10 11 62 as well as chemometric analysis methods such as linear discriminant analysis 11, 12 , multiple linear 12 13 14, 18 12, 17 15 7, 8 14 63 regression , principal component analysis , cluster analysis , partial least squares , and 15 16 64 artificial neural networks 16 . Since the optical and electrical signal based methods use the integrated 17 18 19 65 information of the whole sample but not quantitative information of some components, chemometric 20 21 66 analysis methods are necessary to identify adulteration. Multivariate analysis could provide a higher Manuscript 22 23 24 67 accuracy rate for adulteration identification. However, every coin has a flip side. An optimized 25 26 68 predictive model depends on the training samples, and is therefore hard to detect possible adulteration 27 28 29 69 out of the training set. As a compromise, metabolite profiles become promising for detection of oil 30 31 70 adulteration. Recently, some specific compounds in oil samples were taken as the target compounds, Accepted 32 33 34 71 including polar compounds 19 , triacylglycerols (TAGs)20, 21 , fatty acids 22, 23 , or volatile compounds 24 . In 35 36 72 the third strategy, chemometric methods were employed to select important markers and establish a 37 38 39 73 discriminative model for adulterated oils and pure oils. 40 Methods 41 74 As characteristic and potential nutrient components of vegetable oils, phytosterols make up the 42 43 44 75 largest proportion of the non-saponifiable fraction25 . They are a group of naturally occurring substances 45 46 26 76 derived from hydroxylated polycyclic isopentenoids . As in many other foods, sterols occur in edible 47 48 49 77 oils as free sterols and conjugated forms including steryl fatty acid esters, phenolic acid esters, steryl 50 51 Analytical 78 glycosides, and acylated steryl glycosides 27 . Generally, the analysis of plant sterols in edible oils is 52 53 54 79 mainly based on the determination of the amounts of free sterols and liberated ones from steryl fatty 55 56 80 acid esters after saponification 28, 29 , or determination of the total amounts after a combination of 57 58 59 60 4 Page 5 of 32 Analytical Methods 1 2 3 30 4 81 conjugated sterols of all types liberated by acidic and alkaline hydrolysis .