Yeast-cell-based microencapsulation of chlorogenic acid as a water-soluble antioxidant

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Abstract

The water-soluble antioxidant, chlorogenic acid, was successfully encapsulated in the low cost-high volume yeast cells for the first time, as characterized by FT-IR spectra and fluorescence micrograph of the yeast cells, chlorogenic acid and microcapsule.

The encapsulation efficiency (EE) of yeast cells could be enhanced significantly (P < 0.001) by the treatment of yeast cells with plasmolyser before encapsulation. Also, the release characteristics of the obtained yeast-encapsulated chlorogenic acid were evaluated, and its storage stability as a powder were investigated at 25 °C/75% relative humidity (RH), 25 °C/90% RH and 60 °C. It could be clearly demonstrated that no chemical changes had taken place during the encapsulation, and the yeast-encapsulated chlorogenic acid exhibited a good stability. This study would be helpful to promote the application of chlorogenic acid. The new yeast-cell-based encapsulation protocol may have some general interests for maintaining the stability of other water-soluble substances.

Introduction

There is a growing interest in using the so-called functional foods for preventing illness (Hilliam, 1996). Being due to their health benefits against chronic diseases including cardiovascular disease and certain types of cancers (Dillard and German, 2000, Doll, 1990, Hertog et al., 1997, Rimm et al., 1996), phytochemicals of antioxidant properties especially polyphenolics, have been extensively investigated (Kinsella et al., 1993, Scalbert and Williamson, 2000, Shahidi and Wanasundara, 1992). However, in many cases, the phenolics generally have the unpleasant tastes (Naczk et al., 1998, Vidal et al., 2004, Wu and Hwang, 2002) and unstable properties (Chang et al., 2006, Wang et al., 2006), thus their introductions to food engineering are challenging tasks.

Chlorogenic acid (CGA) is one of the most naturally existed phenolic compounds. Due to its ability to directly interact with reactive oxygen species (Kono et al., 1997), CGA has many beneficial properties (Challis and Bartlett, 1975, Chiang et al., 2003, Ina et al., 2004, Kim et al., 2005, Tsuchiya et al., 1996, Yoshimoto et al., 2002). Moreover, Zang, Cosma, Gardner, Castranova, and Vallyathan (2003) demonstrated that CGA is an effective radical dotOH scavenger.

However, the nature of the chemical configuration of its ortho-dihydroxyphenolics makes CGA be considered to undergo oxidation by gamma irradiation or other oxidation stress quickly to highly reactive electrophilic chlorogenoquinone. Additionally, it is easy to occur transesterification reaction during storage or processing (Villegas, Shimokawa, Okuyama, & Kojima, 1987). While Kono et al. (1997) reported that the antioxidant properties of CGA is attributed to its catechol structure of the phenyl ring, and the double bond conjugated with the catechol group may also serve as a site for free radical attack. Therefore, the stabilization of CGA is one of the most important concerns for its applications.

Microencapsulation techniques have been widely used in pharmaceutical, cosmetic, food industries, and so on (Gouin, 2004). However, it is a true challenge, using only food-grade wall materials, to prevent water-soluble core substances from change. The wall materials used usually are polymers or expensive lecithin (Dewettinck and Huyghebaert, 1999, Nii and Ishii, 2005, Schrooyen et al., 2001, Shahidi and Han, 1993).

A low cost-high volume microencapsulation process has been developed (Bishop et al., 1998, Nelson et al., 1991, Pannell, 1990) for the encapsulation of essential oil and flavour based on the light colour, bland taste, and availability in large volumes of yeast cells (Saccharomyces cerevisiae). Additionally, during the processing, no additives but only water, yeast and active are used. Thus, baker’s yeast (S. cerevisiae) has emerged as a convenient host for the development of a new kind of drug delivery system (Blanquet et al., 2005, Blanquet et al., 2001).

However, most of these technologies are focused on the encapsulation of essential oil and flavor. Serozym Laboratories (1973) has proved that yeast cells were able to absorb and retain water-soluble flavor compounds when pre-treated with a plasmolyser. In fact, yeast extracts have been commercially used both as savory food ingredients and a species in microbiological media (Sombutyanuchit, Suphantharika, & Verduyn, 2001) duo to the low cost.

To the best of our knowledge, there are no reports on the microencapsulation of CGA, thus, the objective of this study is to microencapsulate CGA in yeast, evaluate its characterizations by IR spectrum, fluorescence microscopy and in vitro CGA release, and test its stability as a powder at 25 °C/75% relative humidity (RH), 25 °C/90% RH and 60 °C.

Section snippets

Materials

Chlorogenic acid with purity of 35%, 85% or 98% was extracted and purified from Eucommia ulmoides. Chlorogenic acid standard was purchased from Sigma Ltd. Fresh yeast cells (S. cerivisiae) was cultured before used. All the chemicals used for HPLC analysis were HPLC grade and were purchased from Shanghai Chemical Reagent Factory (Shanghai, China). All the products for yeast culture media were from Dingguo biochemical Ltd. (Beijing, China) and other chemicals were analytical grade and supplied by

Effect of different chlorogenic acid purity on the EE

The EE of chlorogenic acid in yeast varied significantly (P < 0.001) with the purity of chlorogenic acid. The EE was only 5.2% when chlorogenic acid purity was 35%, it increased dramatically from 6.6% to 12.6% when chlorogenic acid purity changed from 85% to 98%. The exact reason is unclear at present, but according to Bishop et al. (1998), materials encapsulated in the yeast cell occurs by passive diffusion, the cell membrane appeared to be the major permeability barrier to the diffusion of

Conclusions

In summary, we have demonstrated the successful preparation of yeast-encapsulated water-soluble antioxidant, chlorogenic acid, as confirmed by the fluorescence micrographs and FT-IR spectra. Moreover, the same retention time and spectra between the standard and microcapsule suggested that no chemical changes had taken place during the encapsulation processing. The yeast encapsulated chlorogenic acid was highly stable under wet and thermal stresses, and the release profiles suggested that the

Acknowledgements

The authors are grateful to the Key Laboratory of Phytohormones of Hunan Province for the use of lyophilizer. The authors would also like to thank Professor Qingji Xie and Zeming Luo for the helpful advice and Mr. Xingrong Dong for the help of IR analysis.

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