Fatty acid profile, oxidative stability and toxicological safety of bayberry kernel oil
Introduction
Bayberry (Myrica rubra Sieb. et Zucc.), belonging to the family of Myricaceae, has a cultivation history of more than 2000 years in China (Chen et al., 2004). Bayberries are mainly cultivated in the southern side of the Yangtze River, where Zhejiang province is the major production area, with an annual yield of 350,000 tons (2010 data provided by Zhejiang Provincial Department of Agriculture). Bayberry fruit is very popular to the local people because of its enticing sweet/sour taste, exquisite flavor and attractive color. It is high in carbohydrates, organic acids, proteins, minerals, and vitamins (Chen et al., 2004). However, because bayberry is harvested ripe in the hot and wet seasons of mid-June to early July, it can only be kept fresh for 3 days at 20–22 °C or 9–12 days at 0–2 °C (Xi et al., 1994), and the taste and flavor deteriorate quickly. To reach a wider market, shelf-life is extended by processing the fruits into juice and wine. During processing, bayberry seeds, which account for >10% of the total fruit weight, are discarded as waste (Cheng et al., 2008). Each bayberry seed has one kernel, which is a potential source of edible oil since the oil content is very high at 62–68% of the kernel weight (Chen et al., 2005). Nine types of fatty acids have been previously reported in bayberry kernel oil (BKO), which consists of ∼85% unsaturated fatty acids (Chen et al., 2005). Intake of unsaturated fatty acids in human diet has the potential to reduce the risk of cardiovascular diseases, therefore, given its fatty acid profile bayberry kernel may have potential as a healthy edible oil source.
Conventional methods of extracting oil from fruit seeds include physical extraction by pressing, as well as chemical extraction using solvents, the efficiency of which can be increased by continuous solvent recycling as in Soxhlet method or by using microwave assisted extraction or superheated hexane extraction (Abbasi et al., 2008, Eikania et al., 2012). More recently, the applications of supercritical fluid extraction (SFE) for oils have increased. Supercritical CO2 (SC-CO2) is widely used for extracting heat-sensitive and high-value components from biomaterials. The advantages of using CO2 are its lack of toxicity, nonflammability, high availability, and low cost (Abbasi et al., 2008, Nodar et al., 2002). It has been reported that oils such as Hibiscus cannabinus L. seed oil (Chan and Ismail, 2009), Opuntia dillenii Haw. seed oil (Liu et al., 2009) and pomegranate seed oil (Liu et al., 2012) extracted by SC-CO2 maintain high antioxidant activity. SC-CO2 has previously been used to extract oil from bayberry kernel (Zhang et al., 2007, Xia et al., 2009), however, the effect of this technology on BKO quality, including fatty acid profile and storage stability has not been reported. The toxicological safety of bayberry kernel has been tentatively confirmed using an Institute of Cancer Research (ICR) rat model, in which the medium lethal dose was >20.0 g/kg body weight (Cheng, 2008). There is however no report on the mutagenicity and toxicity of the BKO. The acute oral toxicity test applied in the present work was also used for evaluation of other new oil sources, such as cashew seed oil (Konan et al., 2007) and pomegranate seed oil (Meerts et al., 2009). Therefore, the objective of this work was to investigate the effects of SC-CO2 extraction on the fatty acid compositions of BKO, and evaluate the oxidative stability and toxicological safety of the oil in order to determine the commercialization potential of BKO as a novel edible oil.
Section snippets
Materials and reagents
Bayberry fruits (cultivar Dongkui) were harvested on June 30, 2011 in an orchard in Taizhou city, Zhejiang province, transported to laboratory and used to separate the seeds on the same day. The seeds were squeezed out by a mini-juicer (Midea, Shunde, China) and dried at 50 °C overnight for further use. Five hundred grams of the kernels were taken out by cracking using a hammer from 1500 g of the seeds separated from 15 kg of fresh fruits. The kernels were dried at 50 °C for 6 h, sealed in a plastic
Effect of SC-CO2 extraction on the fatty acid profile of BKO
The gas chromatography of fatty acid profile of BKO was given in Fig. 1a. The chromatogram (Fig. 1a) identified seven fatty acids namely: palmitic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), punicic acid (C18:3) and arachidic acid (C20:0). Unlike the report of Chen et al. (2005), no myristic (C14:0) nor arachidic acid (C20:2) was found in our BKO. This may be attributed to different bayberry cultivars, since there are discrepancy in
Conclusion
Bayberry kernel oil (BKO) was extracted by SC-CO2 and Soxhlet methods. Oleic acid and linoleic acid were the major fatty acids in BKO either extracted by SC-CO2 or Soxhlet method. During the incubation test, the POV of the BKO extracted by Soxhlet were higher than those from SC-CO2 extraction, but both were all higher than those of lard and rapeseed oil, indicating BKO was more prone to oxidation. The acid value of the BKO either extracted by SC-CO2 or Soxhlet method was similar to those of
Conflict of Interest
The authors declare that there are no conflicts of interest.
Acknowledgments
This work was financially supported by the Program for Zhejiang Leading Team of S&T Innovation (No. 2010R50032), and Zhejiang Academy of Agricultural Sciences Innovation Capability Improvement Project (No. 2010R15Y01D02).
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