1. Introduction
The evergreen shrub Camellia oleifera Abel., belonging to Camellia genus of Theaceae family, is a unique woody edible oil species widely distributed in southern China (Gao et al., 2020).Camelliaseed oil, known as the “oriental olive oil” (Cheng et al., 2018; Ma et al., 2011), contains abundant unsaturated fatty acids, among which the total amount of oleic acid and linoleic acid is over 85% (Wei et al., 2015; Yang et al., 2016; Zhu et al., 2019). The edible value ofCamellia seed oil is high, for it also contains various nutritional ingredients such as polyphenols, sterols and tocopherols (Wu et al., 2018; Ye et al., 2014; Zhou et al., 2019). Meanwhile, its bioactive properties, e.g., anti-inflammatory, anti-oxidant activity and anti-obesity (Fattahi-far et al., 2006; Guan et al., 2011; Wang et al., 2019), rendering Camellia seed oil a great application potential in cosmetic and medicinal field (Chaikul et al., 2017). Recommended by FAO as high quality edible oil (Zhou et al., 2019),Camelliaseed oil is now in great demand for people have higher requirements for health, and thus the corresponding industry has a promising prospect in the future.
Cold pressing and solvent extraction are the most commonly used industrial methods in oil extraction process (Yang et al., 2019). Over refinement could be avoided by cold pressing via cutting down the high temperature pretreatment ofCamelliaseed, the decolorization and deodorization of crude oil (Moslavac et al., 2014). Thus the quality of cold pressing oil is guaranteed by reducing the loss of bioactive compound which is sensitive to heat and also by reducing the formation of benzopyrene and glycidyl ester at high temperature (Qi et al., 2015; Wei et al., 2015; Wu et al., 2012). Organic solvent extraction method has obvious defects such as solvent residue, and environmental pollution. This method is still in use especially in the treatment of pressed seed cake for the economic reason (Shao et al., 2015). In comparison, cold pressed oil showed stronger antioxidant and antimicrobial activities than oil extracted by organic solvent (Zhou et al., 2014). Supercritical CO2extraction (SCCE) has been widely applied as a green technology. It is superior to traditional technology as it is non‐toxic, fast and high efficient. Besides that, its critical temperature and critical pressure (T c = 304.2 K, P c = 7.38 MPa) are moderate to reach (Duan et al., 2013). The oil quality extracted by SCCE is superior both in higher bioactive constituents content such as squalene and sterols, and also better physicochemical characteristics like lighter color, stronger aroma, lower acid value (AV) and peroxide value (POV) (Shao et al., 2015). The oil quality differs obviously when extracted by different processes, and this implies that developing a proper methodology to distinguish oil from different sources appears to be meaningful.
In the PRC National Standard (GBT11765-2018), to classifyCamellia seed oil by quality, the physicochemical parameters and the corresponding analytical procedures, are defined listed in Table 1. Conventional analytical techniques such as HPCL and GC-MS have certain drawbacks, e.g., expensive instruments, complex sample pretreatment and consuming more time (Aparicio et al., 2013; Semenov et al., 2019). In recent years, electronic tongue (e-tongue) technique, as an analytical technique mimicking the human senses of taste, owing to its simple, rapid and precise characters, has been widely explored in food, cosmetic and pharmaceutical industries (Sliwinska et al., 2014). Many qualitative and/or quantitative applications of e-tongue for olive oils have been reported successfully. Quality parameters such as peroxide, anisidine values and total tocopherols (Semenov et al., 2019), carotenoid (Semenov et al., 2019), oxidative stability and polyphenols (Rodrigues et al., 2019) were correlated and assessed using e-tongue system combined with chemometrics. Studies of classification of the olive oil base on quality (Tahri et al., 2018; Veloso et al., 2018), discrimination of adulterate olive oil (Harzalli et al., 2018; Oliveri et al., 2009), olive oil shelf-life estimation (Buratti et al., 2018; Rodrigues et al., 2017) and olive oil sensory assessment (Rodrigues et al., 2019; Rodrigues et al., 2018) were also well achieved indicating broad application of e-tongue in oil characterization. ForCamellia oil, chemometrics combined with electronic nose was found effective to discriminate the geographical origins (Peng et al., 2020). Methods of FTIR (Han et al., 2020) or NIR (Chu et al., 2017) spectroscopy combined with chemometrics was developed to identifyCamellia oil adulteration with rapeseed oil or vegetable oil. To the best of our knowledge, discrimination of Camellia seed oils produced by different processes has not been reported.
The aim of the present work was to evaluate the versatility of e-tongue for the characterization of Camellia seed oils (pressed, extracted with organic solvent and scCO2) and simulation of peroxide value (POV) and acid value (AV) associated with sensory assessment. For this, chemometric quantitative approach (multiple linear regression models) is applied to establish predictive multivariate models.