Fermented tea eyed as natural preservative source
benefits, could also offer an interesting source of food
preservatives, Chinese researchers report.
Extracts from microbially-fermented Puer tea and Fuzhuan brick-tea have the potential to inhibit several food-borne bacteria, including Bacillus cereus, Bacillus subtilis, Clostridium perfringens and Clostridium sporogenes .
"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," wrote lead author Haizhen Mo from Henan Institute of Science and Technology.
Before such a resource can be tapped however the researchers state that several critical aspects still need to be clarified before the tea extracts can be industrialised as alternatives to synthetic preservatives such as like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT) to slow down the oxidative deterioration of food.
Suspicion over chemical-derived synthetic preservatives has pushed food makers to source natural preservatives such as rosemary extract instead, and market analysts Global Information pitch the global food preservative market at €422.7bn ($575bn), reaching €522bn ($710bn) by 2008.
Among the challenges left include identification of the exact components in the tea responsible for the antimicrobial effects.
Indeed, Mo and co-authors ask whether it is the more well-known tea catechins or polyphenols or antimicrobial metabolites from the fermentation process not originally present in unfermented or green tea leaves that are responsible.
Another area in need of research is whether the antimicrobials could impact the flavour and nutritional aspects of the food products.
"These natural preservatives should be desirably colourless and tasteless so that they will not bring about any off flavour troubles," wrote the researchers.
"Ideally, these natural preservatives should not bring about any anti-nutritional effects," they added.
The process for fermentation also needs optimising, they said.
"[Both] Puer tea and Fuzhuan brick-tea… are produced through a solid state fermentation process, [and] standardisation and optimisation are necessary.
Solid-state fermentation is described as a process where no free water is present.
"A standardised fermentation process will not only ensure food safety but also the product quality.
"Furthermore, during the standardisation and optimisation of the process, more insight will be obtained for the metabolic mechanism of the fungi involved, how they produce antimicrobial metabolites and eventually an overproduction of these useful natural preservatives can be expected," they concluded.
The study was a collaboration with researchers from Wageningen University and Research Centre in the Netherlands and the Chinese Academy of Agricultural Sciences.
Source: Trends in Food Science & Technology (Elsevier) Published on-line ahead of print, doi: 10.1016/j.tifs.2007.10.001 "Microbial fermented tea - a potential source of natural food preservatives" Authors: H. Mo, Y. Zhu, Z. Chen
