Elsevier

Process Biochemistry

Volume 110, November 2021, Pages 275-281
Process Biochemistry

Separation and microencapsulation of antibacterial compounds from wood vinegar

https://doi.org/10.1016/j.procbio.2021.08.020Get rights and content

Highlights

  • Specific antibacterial compounds in wood vinegar were identified and isolated.

  • Microencapsulation was prepared to protect the phenolic from environmental stress.

  • The phenolic microencapsulation remained significant antibacterial activity.

  • The microcapsules make core materials release gradually in environment.

Abstract

The major antibacterial components in wood vinegar was determined and novel microencapsulation of wood vinegar extract was successfully prepared to protect it from environmental stress. Three major fractions, including Fr.1 (mainly phenol and 2-methoxyphenol), Fr.2 (largely 2,6-dimethoxyphenol), and Fr.3 (mostly 3-methyl-1,2-cyclopentanedione), were extracted from wood vinegar by chromatography. Antibacterial activity was evaluated by serial dilution against eight pathogens, including an antibiotic-resistant strain. The minimum inhibition concentration were ranging in 1.56–12.50 μL/mL and 0.78–6.25 μL/mL, respectively, for Fr.1 and Fr.2, which shows that wood vinegar extract exhibits a broad antibacterial spectrum. To improve the stability of wood vinegar extract and make it easier to store, for the first time wood vinegar extract was encapsulated, alginate and chitosan were used as wall materials for the encapsulation using an ionic gelation method. The agar diffusion results showed that the microcapsules still exhibited excellent antibacterial action. The stability of the phenols in microcapsules was improved effectively and in vitro simulation digestion showed a more pronounced release in intestine. The application feasibility of wood vinegar extract was evident and real potential to produce natural antibacterial agents, with real possibility to be used in food and pharmaceutical industries.

Introduction

Wood vinegar (WV), also called pyroligneous acid, is a reddish-brown liquid obtained by condensation of volatile matters from high temperature slow pyrolysis of wood, branches, straw and other agricultural and forestry products. It can be used in various areas, such as in agriculture, food, medicine and so on [[1], [2], [3]]. WV contains a variety of organic compounds, and its composition and content vary with different raw materials [4,5], but no matter which kind of WV, organic acids and phenols account for the largest content and are used most widely. And both of them have significant antibacterial activity [6], but high content of organic acids will destroy the acid-base balance of the internal environment. Therefore, when WV is applied as food additive and medicine, the phenolic compounds which have significant antioxidant and antibacterial activities play an important role [7].

However, there are a number of phenolic compounds in WV, the main antibacterial components and their interactions are still unclear. Besides, the application of WV is limited by the fact that phenols and other active compounds are sensitive to environmental factors such as temperature, light, oxygen and so on [8,9]. And the smoky and pungent flavor of phenolic compounds may cause unpleasant smell of food and medicine [10]. The microcapsules can be used to increase the stability and availability of the core materials and to protect them from environmental stress [11,12]. And encapsulation can also be used for masking unpleasant odour [13]. Two natural polymers, alginate and chitosan, are reported to be non-toxic, biodegradable and biocompatible, and can be easily modified by physical or chemical methods [14,15]. They are widely used in encapsulation because of their ability to form gels in the presence of calcium cation [16]. It has been reported that the combination between alginate and chitosan to form microcapsules has been extensively applied in encapsulation of different bioactive [[17], [18], [19]], which contributed to the bioactive availability when applied as food-additive and pharmaceutical.

In the present work, the phenolic compounds were separated by the combination of extraction, regulation of pH and chromatography for their significant antibacterial activity. Broth dilution method was applied to study the interactions between phenolic compounds. To protect the bioactive phenols, microencapsulation with chitosan and alginate as wall materials was prepared. This is the first time that wood vinegar extract has been encapsulated, which makes it more stable in storage, cheaper in transportation and more convenient in application. And novel microcapsules still possess significant antibacterial activity, get the ability to release gradually in room condition and release selectively in vitro simulation digestion. This work identified the key antibacterial compounds in wood vinegar, and revealed the interaction of phenolic compounds in antibacterial aspects. The encapsulated wood vinegar extract is more conducive to be stored and transported, and can be used for food preservatives and antibacterial agents, which provides an important reference for the application of wood vinegar in food and pharmaceutical fields.

Section snippets

Chemicals and reagents

WV was obtained by high temperature slow pyrolysis from branches of Xylosma congesta (Lour.) Merr., which was a kind of evergreen tree in Northeast China. In addition, WV was prepared and provided by Musucheng Biotechnology Co., Ltd of Jilin. Ethyl acetate (AR grade) and n-hexane (AR grade) were purchased from Beijing Chemical Works (Beijing, China). Silica gel was purchased from Qingdao Kangyexin Medicinal Silicone Co., Ltd. (Qingdao, China). 2,6-dimethoxyphenol, phenol, 2-methoxyphenol,

Preparation and separation of wood vinegar extract (WVE)

The composition of WV, WVE, Fr.1, Fr.2 and Fr.3 were determined by GC–MS. Compounds were identified by their retention times and mass spectra. In WV, twenty-eight compounds above 0.50 % content were detectable, as shown in Table 1. The most abundant compounds were acids and derivatives (52.39 %), followed by phenols (24.74 %), ketones (12.35 %), aldehydes (2.69 %) and esters (2.18 %). In addition, some compounds with less than 0.50 % content were not listed, such as some nitrogenous compounds.

Conclusions

In this work, several kinds of bioactive compounds were extracted from wood vinegar. The antibacterial results show that the phenolic are key antibacterial components in wood vinegar, besides, there are synergism between the phenols. To improve the stability of the phenolic and make them easier to store, for the first time wood vinegar extract was encapsulated, alginate and chitosan were used as wall materials for the encapsulation using an ionic gelation method. After microencapsulation, the

CRediT authorship contribution statement

Xingyu Liu: Methodology, Investigation, Data curation, Writing - original draft. Rui Cui: Resources. Jingwei Shi: Supervision. Qian Jiang: Formal analysis. Junli Gao: Validation. Ziming Wang: Conceptualization, Writing - review & editing, Project administration. Xiaoyan Li: Project administration.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgments

This work was supported by the Fundamental Research Funds for the Central Universities [grant number 415010200045]; the Jilin Provincial Department of Education "Thirteenth Five-Year Plan" Science and Technology Research Planning Project [grant number #JJKH20201027KJ].

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