microbial fermented tea – a potential source of natural food preservatives

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  • Science and Technology, 453003 Xinxiang,

    industrial applications.

    Holzapfel, 1996). Although plants can provide a vast sourceof natural preservatives, many potential biological preserva-

    for innovative applications in the modern society.This article reveals the background information of micro-

    Trends in Food Science & Technresearch and development of these antimicrobial compounds

    from microbial fermentation of tea are discussed for potential

    nisin by lactic acid bacteria. Some potential and unexploredfood fermentation processes are certainly new possibilities* Corresponding author.

    0924-2244/$ - see front matter 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.tifs.2007.10.001d

    n

    tives are originated from traditional food fermentations. Themost well known example is probably the production oftation process with tea leaves as substrates. The antimicrobial

    components produced during the fermentation process have

    shown inhibitory effects against several food-borne and patho-

    genic bacteria. With the trend of increasing use of natural and

    biological preservatives in food products, natural antimicrobial

    agents from microbial fermented tea may offer an innovative

    and interesting measure for such applications. However,

    a breakthrough in this field can only be realised after several

    critical aspects are clarified and further studied. Only then,

    the application of these potential, novel and natural antimicro-

    bial substances from microbial fermented tea can be industri-

    alized. The present review describes some unique microbial

    fermentation of tea and the antimicrobial activities forme

    during the fermentation process. Moreover, future needs iHenan Province, ChinabFood and Bioprocess Engineering Group, WageningenUniversity and Research Centre, P.O. Box 8129, 6700

    EV, Wageningen, Netherlands (Tel.:D31 343 538103;

    fax: D31 343 538405; e-mail: yang.zhu@wur.nl)cChinese Tea Research Institute, Chinese Academy of

    Agricultural Sciences, 310008 Hangzhou, Zhejiang

    Province, China

    Antimicrobial activities of microbial fermented tea are much

    less known than its health beneficial properties. These anti-

    microbial activities are generated in natural microbial fermen-Microbial fermented

    tea e a potential

    source of natural

    food preservatives

    Haizhen Moa, Yang Zhub,* andZongmao Chenc

    aDepartment of Food Science, Henan Institute ofReview

    IntroductionTea is one of the most consumed beverages worldwide.

    In fact, there are mainly three different kinds of tea. In Chinaand many Southeast Asian countries, green tea is preferred.In Western countries and the rest of the world, the consump-tion of black tea is the highest. Another kind of tea is Kom-bucha, which is a sweet-sour tea beverage made actuallyfrom tea extract supplemented with sugar and fermentedwith yeast and acetic-acid bacteria. Fermentation processis necessary to produce black tea and Kombucha. Blacktea can be further subdivided into naturally oxidized tea(although the term of fermentation is often used), and micro-bial fermented tea. Fermentation process for producing mostblack teas is actually an oxidation process catalyzed byenzymes that are originally present in tea leaves (Fowler,Leheup, & Cordier, 1998). Because no microorganismsare involved in this kind of enzyme-oxidized black tea,the use of the term fermentation is obviously not completelycorrect. Microbial fermentation in the production of blacktea, however, is found to be carried out solely in certain Chi-nese tea assortments. Therefore, this kind of tea is littleknown outside China, whereas Kombucha is exceptionallywell known because of its increasing interests in the West.

    Recently, several microbial fermented teas got noticed inthe Western world, probably not only because of trade ex-pansions between China and the West, but also because ofseveral health beneficial claims associated with microbialfermented tea. A few studies reveal that extracts from mi-crobial fermented teas contain natural antimicrobial com-ponents that have inhibitive effect on several food-bornepathogen and spoilage bacteria (Greenwalt, Ledford, &Steinkraus, 1998; Mo, Xu, Yan, & Zhu, 2005; Sreeramulu,Zhu, & Knol, 2000; Sreeramulu, Zhu, & Knol, 2001;Steinkraus, Shapiro, Hotchkiss, & Mortlock, 1996).

    Application of natural antibacterial agents has been in-creasingly noticed as a novel trend in biological preserva-tion of foods in recent years (Schillinger, Geisen, &

    ology 19 (2008) 124e130bial fermented Puer tea and Fuzhuan brick-tea, as well as

  • fermented tea beverage Kombucha. The importance of theirantibacterial effects on several food-borne bacteria are givenin detail. Potential applications and research needs of thesemicrobial fermented teas are also critically discussed. Theantimicrobial effects of tea catechins or polyphenols havebeen intensively described previously elsewhere (An et al.,2004; Bandyopadhyay, Chatterjee, Dasgupta, Lourduraja,& Dastidar, 2005; Cushnie & Lamb, 2005; Friedman,Henika, Levin,Mandrell, &Kozukue, 2006; Hamilton-Miller,1995; Hirasawa & Takada, 2004; Kim, Ruengwilysup, &Fung, 2004; Si et al., 2006; Taguri, Tanaka, & Kouno, 2004;Yamamoto, Matsunaga, & Friedman, 2004; Yilmaz, 2006)and so this topic is not included here.

    Microbial fermentation and antimicrobial effect ofPuer tea, Fuzhuan brick-tea and Kombucha

    Both Puer tea and Fuzhuan brick-tea are microbial fer-mented black teas, whereas Kombucha is a fermented drink

    tea polyphenols in tea leaves come into contact with thetea polyphenol oxidases and then oxidized in the conse-quent fermentation process. During the Puer tea fermenta-tion process, fresh leaves are fixed by heat in a drum toinactivate polyphenol oxidases. The fixed leaves are thenrolled and partially dried. The partially dried leaves arepiled up in humid conditions (moisture content w40% at25e60 C) for a few weeks, during which the tea polyphe-nols are more intensively oxidized by the action of micro-organisms and environmental oxygen than in black teafermentation process, resulting in low concentrations oftea polyphenols and tea catechins (Liang, Zhang, & Lu,2005).

    Puer tea has not only a unique flavour but also severalhealth beneficial properties, such as suppressing fatty acidsynthase expression (Chiang et al., 2006), acting as an in-hibitor of lipid and nonlipid oxidative damage and alsoexhibiting metal-binding ability, reducing power, and scav-

    aluatio

    Press

    ion of

    ing

    tion o

    125H. Mo et al. / Trends in Food Science & Technology 19 (2008) 124e130of tea extract supplemented with sucrose and fermentedwith yeasts and acetic-acid bacteria. All three teas haveshown obvious antibacterial effects.

    Fermentation process and antimicrobialcharacteristics of Puer tea

    Puer tea is a unique Chinese microbial fermented tea ob-tained through indigenous tea fermentation where micro-organisms are involved in the manufacturing process. Aschematic description of Puer tea production is shown inFig. 1. This tea is different from common black tea that un-dergoes a natural oxidation process through enzymes orig-inally existing in tea leaves (Fowler et al., 1998). Theprocess of Puer tea manufacture is characterized by solid-state fermentation with natural flora as inoculums of whichthe fungus Aspergillus niger plays a key role (Mo et al.,2005; Xu, Yan, & Zhu, 2005). The processing of Puer teais quite different from that of black tea, although they areboth called fermented teas. During black tea processing,fresh tea leaves are rolled and cut before drying so that

    Wetting and cooling Ripening Ev

    Loose Puer tea productPasteurization

    DryingSteaming and pressing

    Collecting of fresh tea leaves Inactivat

    GradDrying Steaming treatment

    Fig. 1. Schematic descripenging effect for free radicals (Duh, Yen, Yen, Wang, &Chang, 2004; Jie et al., 2006). Kuo et al. (2005) reportedthat Puer tea and oolong tea can lower the levels of triglyc-eride more significantly than that of green tea and black tea,whereas Puer tea and green tea are more efficient thanoolong tea and black tea in lowering the level of totalcholesterol. Liang et al. (2005) reported that Puer tea sup-presses the genotoxicity induced by nitroarenes, lowers theatherogenic index and increases HDL (high density lipo-protein) e total cholesterol ratio. Rather recently, antimuta-genic and antimicrobial activities of Puer tea were alsoreported (Wu, et al., 2007). Although Puer tea has a historyof production and consumption for hundreds of years, fewstudies can be found on its microbiological properties,especially during the fermentation process.

    Mo et al. (2005) have done a microbiological analysis onsamples from the indigenously fermented Puer tea. Micro-bial counting and identification revealed that A. niger wasthe dominating microorganism during the fermentation.Antimicrobial activity of fermentation samples shows

    Inspection and packaging

    n and grading

    ed tea product Storage and ripening

    Inspection and packaging

    enzymes Dispersion of tea blocks

    Natural inoculation and fermentation

    f Puer tea manufacture.

  • inhibitory effect on several food-borne bacteria, includingspore-forming bacteria Bacillus cereus, Bacillus subtilis,Clostridium perfringens and Clostridium sporogenes. Theantimicrobial activity increases with the course of the fer-mentation. This implies that certain metabolites of A. nigergrowing on tea leaves have the feature of inhibiting certainfood-borne bacteria. As the fermentation process willdecrease the content of tea polyphenols and catechins, theincrease in antimicro