Recent advances in the extraction of bioactive compounds with subcritical water: A review

https://doi.org/10.1016/j.tifs.2019.11.018Get rights and content

Highlights

  • Fundamental principles of subcritical water extraction (SWE) are introduced.

  • The advantages and disadvantages of SWE are discussed.

  • Bioactive compounds obtained with SWE are also mentioned.

Abstract

Background

Because of the important role of bioactive compounds in functional foods and health care, more and more attention has been paid to the active components extracted by green extraction methods. However, how to ensure the extraction yield and biological activity during the extraction process is an urgent problem to be solved. Subcritical water extraction (SWE) is a promising engineering method, which provides an environmentally friendly technology for extracting various bioactive compounds from natural products. Especially, under high temperature and high pressure, subcritical water can change the polarity and dielectric constant of solvents, thus contributing to a better extraction process, improving the mass transfer efficiency of the extracts and maintaining its biological activities, which has a high application prospect.

Scope and approach

This review provided an update overview on the fundamental principles and bioactive compounds extraction with subcritical water. This will contribute to deepen the understanding of SWE and provide theoretical basis and reference value for further improving the application of subcritical water.

Key founds and conclusions

It is expected that this green and efficient extraction technology will be increasingly applied in the extraction of more bioactive ingredients in the near future. In addition, future research should consider combining SWE with other physical extraction techniques to ensure the retention of the biological ingredients better. These active compounds with SWE have great potential in health care medicine and functional foods. Meanwhile, future researches should focus on consumer acceptability, safety, legal aspects, and commercial availability of health products.

Introduction

Natural active ingredients play an important role in life activities. More and more studies focus on these active ingredients (Chan, Ngoh, & Yusoff, 2012; Chien & Norman, 2009; Kai, Michela, Antonio, & Annamaria, 2015; Levac, Rivard, & Missiuna, 2012; Rojas-Graü, Soliva-Fortuny, & Martín-Belloso, 2009; Wen, Zhang, Zhang, et al., 2019; Zhang, Wen, Zhang, et al., 2019; Zhang, Zhu, & Jiang, 2014). Different active ingredients have different biological effects and were widely used in the manufacture of functional foods and the treatment of human diseases (Kroyer, 2004; Liu, 2017; Zhang, Zhang, Wen, et al., 2019). The discovery and extraction of biological ingredients have important practical significance for the development of human society. Therefore, obtaining bioactive substances with suitable extraction methods from natural products is a frontier topic in food and pharmaceutical industries (Joana Gil-Chávez et al., 2013).

At present, a wide variety of biologically active ingredients are separated from all sorts of natural products, such as animals (Seinen et al., 1977), plants (Rios & Recio, 2005), fungi (Zjawiony, 2004), and microorganisms (Georgiou, Lin, & Sharma, 1992), among others. In order to better characterize and quantify the active compounds, it is very important to choose an effective and appropriate extraction method. There are many factors which can influence the extraction process, including the matrix properties, solvent, temperature, pressure, time applied, and ratio of solvent to matrix (Hernández, Lobo, & González, 2009). In recent years, the active compounds have been extracted by using various extraction methods, including Soxhlet extraction, impregnation method, and hot water extraction (Kimbaris et al., 2006; Trochimczuk, Kabay, Arda, & Streat, 2004; Zhao et al., 2010). However, these methods have a number of obvious disadvantages. For example, Soxhlet extraction may cause a large amount of waste of organic reagent, and the extraction efficiency is low. These shortcomings limit the application of this method in industrial amplification (Armenta, Esteve-Turrillas, Garrigues, & de la Guardia, 2017). The disadvantages of the impregnation method are that the extraction time is long, and the extraction efficiency is low. Besides, the extracts with this method is prone to mold, and it is necessary to add a preservative. In addition, the volume of the extracts is large, and then a concentration step is required. For hot water extraction, low extraction rate is still one of the defects. Apart from this, the temperature of hot water extraction is high, and there is also a risk of denaturation of heat sensitive compounds (Chi et al., 2018). Based on above situation, a variety of mature innovative extraction techniques have been developed for the extraction of highly active compounds from natural products, including subcritical water extraction (SWE) (Zhang, Chen, et al., 2019; Zhang, Wen, Duan, et al., 2019; Zhang, Wen, Gu, et al., 2019; Zhang, Wen, Li, et al., 2019; Zhang, Wen, Qin, et al., 2018; Zhang, Wen, Zhang, et al., 2018), supercritical fluid extraction (SFU) (Clifford & Williams, 2000; McHugh & Krukonis, 2013; Reverchon & De Marco, 2006), ultrasound-assisted extraction (UAE) (Wen, Zhang, Yao, et al., 2018; Wen, Zhang, Zhang, et al., 2018; Wen, Zhang, Zhou, et al., 2019; Wen, Zhang, Zhou, et al., 2018), microwave-assisted extraction (MAE) (Kaufmann & Christen, 2002; Lopez-Avila, Young, & Beckert, 1994; Mandal, Mohan, & Hemalatha, 2007), ultrahigh pressure-assisted extraction (UPE) (Prasad et al., 2009; Prasad et al., 2010), pulsed electric field extraction (PEF) (Corrales, Toepfl, Butz, Knorr, & Tauscher, 2008; Fincan, DeVito, & Dejmek, 2004), among others. Especially, SWE has captured more and more attention due to its safety, efficiency, and environment protection. Large amounts of bioactive ingredients such as polysaccharides, proteins, antioxidants, and polyphenols (Herrero, Cifuentes, & Ibañez, 2006; Zakaria & Kamal, 2016) were extracted by using subcritical water. In addition, subcritical water has a modification effect on the molecular structure, which is beneficial with improving its biological activities of active ingredients (Getachew & Chun, 2017). As an environmentally-friendly and efficient extraction technology, SWE technology has shown potential value for application in multiple extraction fields.

Based on these, this review concluded the recent progress in the application of SWE to the extraction of various bioactive constituents in the food and pharmaceutical industrials. The first section highlighted the properties of subcritical water, including its principles, mechanism, influencing factors, and devices. The second section discussed the extraction of various biologically active constituents by using subcritical water. It is expected that all these results could contribute to the application of SWE in the related industries.

Section snippets

Changes in properties of water

In general, water has three states including solid, liquid, and gas. Water is a highly polar solvent at room temperature and atmospheric pressure, and has a high dielectric constant (ε) because of its extensive hydrogen bonding structure (Teo, Tan, Yong, Hew, & Ong, 2010). Therefore, researchers didn't regard water as an effective extraction solvent for extracting non-polar or organic compounds. The nature of water is very different from other solvents, as it is the lightest in the gas state,

Polysaccharides

Polysaccharides have a variety of biological activities, including immunological activity (Chen & Huang, 2018; Luo, Dong, et al., 2018), anti-tumor activity (Liu, Zhang, & Meng, 2018; Mao et al., 2019), and antioxidant activity (Ballesteros, Teixeira, & Mussatto, 2017; Wang, et al., 2016), among others. It is worth noting that many studies have focused on extracting polysaccharides by using subcritical water in recent years (Table 2). For example, our previous work has extracted polysaccharides

Conclusion and future trends

In conclusion, the bioactive compounds from natural products with SWE are preferred for use in the food and pharmaceutical industries, and its biological activity and stability can be maintained during the extraction process. The use of SWE to extract compounds from natural products provides an even better method, especially in environmental protection. In addition, subcritical water can greatly improve heat and mass transfer efficiency during extraction, which can increase extraction yield,

Acknowledgement

This work was funded by National Key R & D Program, China (2016YFD0400303); Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (KYCX17_1799).

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    Jixian Zhang and Chaoting Wen contributed equally to this work and should be regarded as co-first authors.

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