Comparative evaluation of maceration and ultrasonic-assisted extraction of phenolic compounds from fresh olives
Introduction
Olive (Olea europaea L., Oleaceae), an important woody oil crop, is widely distributed in many Mediterranean countries and southwest China [1], [2]. Olive oil obtained from olive fruits has generally acknowledged as an important role in human diet because of its health-promoting value [3], [4]. The fine characteristic and biological activity of olive oil are mainly due to the presence of components, such as the optimal balance among monounsaturated, polyunsaturated and saturated fatty acids, as well as to minor components, including polyphenol, phytosterol, chlorophyll and tocopherol [5]. Phenolic compounds, the secondary metabolites of plants, have shown a wide variety of biological properties, such as antioxidant, anti-inflammatory and antitumor activity [6], [7], [8].
Currently, the phenolic compounds of olives have attracted a great deal of attention due to healthy benefits to olive oil [9]. However, extract method is a limiting process as the first stage impacting the isolation of phenolic compounds from olives. Since maceration extraction (ME), a traditional method resulting in lower yield of phenolic compounds, is still a main method to extract phenolic compounds from olives. In recent years, several novel techniques, such as supercritical fluid extraction, enzymatic extraction, microwave-assisted extraction and ultrasonic-assisted extraction have been used for extraction of phenolic compounds from plants instead of conventional technique. Among these methods, UAE have become more and more popular because it is a simple and eco-friendly method. This method utilize acoustic cavitation to disrupt plant tissues and increase mass transfer, obtaining benefits like higher efficiency, shorter extraction time and less power consumption than the conventional extraction techniques [10], [11].
Response surface methodology (RSM) is a widely used statistical tool in optimizing any process when the independent parameters have combined effects [12]. The number of trials to evaluate the multiple variables and their interactions are reduced by using RSM. To the best of our knowledge, no research report exists on the optimization of UAE and ME for phenolic compounds from fresh olives and no investigation exists on the effects of different extraction methods of the major phenolic compounds and on the antioxidant activity. Therefore, this study was to optimize the methods of UAE and ME according to the maximum extraction yield of TPC. The major phenolic compounds of TPC were subsequently investigated using HPLC method. Moreover, the antioxidant activities of both extracts derived from olives were also estimated in vitro.
Section snippets
Materials and reagents
The olive fruits (Olea europaea L.) Picual cv. of yellow-green skin coloration were harvested at the second maturity in Xichang, Sichuan Province, China. The maturity stage was determined using a subjective evaluation of olive fruits epadermis and mesocarp colour according to Morelló et al. [13]. The fresh olives were stored at −80 °C. Before extraction processes, the olive pulp were separated from the kernel, grounded into fine powder with liquid nitrogen and then kept at −25 °C.
Gallic acid,
Optimization of UAE process
The design matrix and real values of BBD experiments to evaluate the effects of three variables including liquid-solid ratio (X1), extraction temperature (X2) and extraction time (X3) on the extraction yield of TPC are presented in Table 1. By applying multiple regression analysis on the experimental data, neglecting the non-significant terms (p > 0.05), the quadratic model for predicting the optimal point for UAE was:
The ANOVA
Conclusions
In this study, RSM was used to optimize the extraction process of phenolic compounds from olive fruits. The optimal conditions of UAE and ME were 22 mL/g, 47 °C and 30 min, yielding 7.01 mg/g, and 24 mL/g, 50 °C and 4.7 h, yielding 5.18 mg/g, respectively. The proposed UAE method gave the higher extraction yield with requiring less solvent, shorter time and lower temperature than ME method. Furthermore, from analysis of HPLC method, 14 phenolic compounds were found in both extracts and UAE offered
Acknowledgments
This work has been supported by the Science and Technology Support Project from Sichuan Provincial Science and Technology Department (2013NZ0047). Sincere thanks to Haoran Cheng, Shiling Feng, Shian Shen, Xuejing Jia and Kunfei Zhang for their supports in study process, and to anonymous reviewers for helpful suggestions.
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