Elsevier

Journal of Chromatography B

Volume 1104, 1 January 2019, Pages 157-167
Journal of Chromatography B

Rapid and direct determination of fatty acids and glycerides profiles in Schisandra chinensis oil by using UPLC-Q/TOF-MSE

https://doi.org/10.1016/j.jchromb.2018.11.022Get rights and content

Highlights

  • Systematic information was provided for fatty acids and glycerides in the S. chinensis oil.

  • UPLC-Q/TOF-MSE is a powerful method for the analysis of glycerides in the S. chinensis oils.

  • All of the calibration equations of the compounds had good linear relationships (R2>0.99).

  • A total of seventeen FFAs, six DAGs and 20 TAGs were directly determined in S. chinensis oils.

  • L-L-L, O-L-L and O-L-O were the most abundant triglycerides in S. chinensis oil.

Abstract

Fatty acids and glycerides are globally accepted quality and nutrition indicators of oils. Schisandra chinensis (S. chinensis) is a good functional oil source, with an oil content of 10–50% (dry weight). In this study, the UPLC-Q/TOF-MSE technique was developed to profile FFA and glycerides in the S. chinensis oils directly. The results showed that all of the 36 FFA calibration equations of the mixture standard had good linear relationships (R2 > 0.99). The limit of detection for the tested compounds ranged from 0.0001 to 0.0200 μg/mL, while the limit of quantification ranged from 0.0005 to 0.1300 μg/mL. In total, seventeen FFAs, six diglycerides and 20 triglycerides were identified. Linoleic, oleic, stearic and palmitic acids were the most abundant FFAs in the S. chinensis oils. It was also found that S. chinensis oil is rich in the L-L, L-L-L, O-L-L and O-L-O glycerides. These results will be helpful for the use of this technique in physicochemical evaluation and for further application development.

Introduction

Glycerides are main constituents of plant oils and fats [1]. Recent studies revealed that dietary triglycerides (TAGs) may affect the metabolism of lipids in humans [2,3]. Additionally, the physiochemical and nutritional features of plant oils mainly depend on its TAGs content. TAGs are also used in quality control and nutritional indication of oils. Moreover, it was reported that oils rich in diglycerides (DAGs) can reduce the plasma TAG levels, body weight, waist circumference, visceral and subcutaneous fat, and offer other health benefits [4,5]. Fatty acids (FFAs) are a relatively small fraction of lipids that are present in food and oils and play a significant rule in the quality control and biological functions of food [6,7]. It is well known that FFAs are generated as the hydrolysis products of TAGs during fabrication and storage [8]. Meanwhile, glycerides in oils are derived from the esterification of the FFA chains with a glycerol unit. The biological and physical properties of a glyceride are strongly affected by its FFA chains (length, position and distribution) [9]. Therefore, oils are complex mixtures of several organic compounds including FFAs (saturated, unsaturated) and glycerides (di-, tri- and mono-). Their contents reflect the stability and quality of plants oils, indicating the quality of the oil refining process and storage under various conditions.

Schisandra chinensis (Turcz.) Baill. is a dioecious perennial plant and is well known in ancient and modern Chinese pharmacopoeia. It has been used to treat various disorders, including kidney infections, mental problems, asthma, diabetes, cough, thirst and insomnia [10]. The fruits are also used as a medicinal food and potential source of nutrients because they contain various bioactive metabolites such as lignans, polysaccharides, essential oil, polyphenols, and vitamins [11,12]. In addition to containing the abovementioned bioactive metabolites, S. chinensis oil is one of the most important components of S. chinensis fruits. Its content is 10–50% dry weight of S. chinensis [10,11]. The oil of S. chinensis may be used as medicine, but there have been few studies examining the possible medicinal application of this oil. It is well known that TAGs and FFA are the major source of oils and play an important role in food industry. For these reasons, the composition of FFA and glycerides in the S. chinensis oil were chosen for further exploration and analysis in this study.

To date, many analytical techniques have been developed for the analysis of FFAs and glycerides. It is well known that GC has been widely applied in the analysis of FFAs (derivatization or esterification) in the past few years [13,14]. However, separation of FFAs with the derivatization or esterification pre-treatment is time-consuming and complicated. Therefore, rapid and direct FFA analysis has become increasingly popular. For example, the FFAs can be directly determined in edible oils, fish lipids and other food samples without pre-treatment by various mass spectrometry techniques (SFC-QQQ-MS, UHPSFC and HPLC/ESI-Q-TOF-MS) [10,[15], [16], [17]]. For glycerides, due to their numerous isomers and structure (various FFA chains, different position, lengths), the coupling of ion mobility spectrometry with mass spectrometry has been shown to be a very powerful analytical technique [18,19]. It has been applied in the identification of the structures and regioisomers of glycerides [12,20], and determination of the glyceride profiles of food samples [[21], [22], [23]]. Among the different analytical techniques, the UPLC-Q/TOF used in the independent mass data acquisition mode (MSE) was chosen for the analysis of the lipid profiles in two S. chinensis oils. In the MSE mode, there are two alternative scan functions. The first scan function provides the full mass information of the precursor ion at the low collision energy (MSE-L). The second scan mode using a high collision energy (MSE-H) collects the fragment ion information based on all of the ions acquired in the first scan. Thus, the information regarding the precursor ions and fragment ions can be acquired in a single run [[24], [25], [26]]. Meanwhile, the current developments and modifications of this analytical technique resulted in better separations with higher resolution, increased sensitivity, and faster analysis. Therefore, the problems involved in complex lipid separation and characterization can be solved [23,27,28]. Importantly, comprehensive analysis of FFAs and glycerides of S. chinensis oil by UPLC-Q/TOF-MSE has not been reported to date.

Therefore, the aim of our study was to develop an efficient, sensitive, and selective UPLC-Q/TOF-MSE method for simultaneous determination of FFAs and glycerides directly in the S. chinensis oil by modifying the analytical conditions. It was expected that the results of this study would be helpful for the further quality evaluation and practical application of S. chinensis oil.

Section snippets

Standards and reagents

The mixed FFA standards were purchased from Shanghai ZZBIO Co., Ltd. (Shanghai, China). The specific constituents of each component were presented in Table 1. The glyceride standard of 1,2,3‑tri (9Z, 12Z-octadecadienyl)‑glycerol (> 99%, GC) was purchased from ANPEL Laboratory Technologies Inc. (Shanghai, China).

Formic acid, n‑hexane, and chloroform were supplied by the Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Methanol, acetonitrile and isooctane (HPLC, grade) were obtained from

Calibration and evaluation of the FFA standards by UPLC-Q/TOF-MSE

FFAs are weakly polar compounds. To achieve good FFA separation, the detection conditions (column, modifier, column temperature, back pressure, flow rate) were optimized manually. The parameters or operation were modified slightly under the permission of equipment, based on the elution efficiency, resolution and analytical repeatability. The specific information for the FFAs in the mixed standard and in the S. chinensis oils was acquired in the negative ion mode. Fifteen concentrations were

Conclusion

In this study, characterization of the FFAs and glycerides profiles in S. chinensis oil was performed by UPLC-Q/TOF-MSE for the first time. It was found that linoleic acid (C 18:2) and stearic acid (C 18:0) are the most abundant FFA components (>50%) in the S. chinensis oils. For glycerides, we detected approximately six kinds of DAGs and 20 kinds of TAGs. L-L was the most abundant DAG, with the content of 13.37 ± 1.21 and 16.20 ± 1.34 mg/g in UAE-Oil and SFE-Oil, respectively. The top three

Conflict of interest

The authors declare that there is no conflict of interests regarding this paper publication.

Acknowledgment

This work was supported by the National Natural Science Foundation of China (Nos. 31471668 and 31671958), and Shanghai Jiao Tong University Agri-X Fund (No. Agri-X2015007).

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