Although their inclusion as a specific ingredient in finished foods is a relatively recent phenomenon, prebiotics are commonly found in a variety of well-established functional foods. The following article examines how prebiotics work and presents evidence of their efficacy as ingredients. There is strong evidence that the market for prebiotics is growing and new techniques are rapidly being developed that test the interaction between these functional ingredients and gut microorganisms.
By Dr Wang Y
Prebiotics are defined as “selectively fermented ingredients that allow specific changes, both in the composition and/or activity of the gastrointestinal microbiota that confers benefits upon host well-being and health.” Thus, the basic criteria for selection of prebiotics are as follows: beneficial health effects to the host, hydrolysis and fermentation by colonic microflora, selective stimulation of growth of one or more bacteria, and resistance to digestion. With the rapid development of modern food science and technology, now is a particularly important moment in the evolution of prebiotic research.
Prebiotics and human gut flora
Gut flora consist of microorganisms that live in the digestive tracts of humans. Compared with other regions of the gastrointestinal tract, the human large intestine is a complex, heavily populated and diverse microbial ecosystem. The impact of the microbial community of the gut on host physiology and pathology has been studied and the data obtained indicates that the gastrointestinal microflora has important and specific functions. Indeed, gut flora is essential for normal anatomical and physiological development of the intestinal mucosa and provides non-immunological protection against infection. In addition, gut flora stimulates maturation and balancing of the immune system at birth and then stimulates and primes the immune system throughout life. Furthermore, gut flora facilitates a wide variety of metabolic functions in the host. In comparison to probiotics, which introduce exogenous microorganisms into the gut flora, prebiotics aim to stimulate the growth of one or a limited number of the potentially health-promoting indigenous microorganisms. This mode of action modulates the host’s natural ecosystem and so improves human health. With the demand for better quality food, there has been considerable interest in introducing prebiotics as food ingredients in order to increase the numbers of health-promoting indigenous microorganisms in the human gut flora, speciafically, Bifidobacterium and Lactobacillus spp.
Application of prebiotics as food ingredients
Prebiotics are frequently used as ingredients in functional foods [Table 1]. The functional food industry’s perception of the importance of gut microbiology in human health and nutrition has led to a major increase in prebiotic and prebiotic-based products. At the present time, some naturally occurring and synthetic substances are classified as prebiotics, i.e.disaccharides (such as lactulose and lactitol), oligosaccharides (such as fructo-oligosaccharides, soybean oligosaccharides, xylo-oligosaccharides and trans-galacto-oligosaccharides) and polysaccharides (such as inulin and resistant starches). The majority of these prebiotics are produced on an industrial scale from synthetic lactose, the extraction/hydrolysis of soy beans and extracts from plants. Recent analysis from Frost & Sullivan (http://www.food.frost.com) on the European Human Food and Beverage Prebiotics Market, found that the prebiotic products generated revenues of €295.5 million in 2008, equivalent to 91,905 tonnes. The market is expected to reach € 766.9 million in 2015, with overall volumes of 204,895 tonnes and a compound annual growth rate of 14 per cent.
As the health benefits of prebiotics become established, prebiotic ingredients are being made available in almost every product imaginable. Today, prebiotic-containing foods are commonly found and consumed all around the world, especially in Japan, Europe and the US. New prebiotics are being continuously developed as our understanding of the interactions between prebiotics and gut flora (especially Bifidobacterium and Lactobacillus spp) increases. However, as with any food component, the question of product safety still needs to be considered and further clinical research is essential.
Future perspectives
A variety of models have been developed to stimulate and quantify the gut fermentation of prebiotics. Prebiotic effect is determined at intervals by removing samples and assessing growth through microbiological culture techniques. However, there are still some problems, it remains unclear whether the interactions observed between prebiotics and a limited number of the potentially health-promoting microorganisms are representative of a common interaction between prebiotics and human gut flora. In fact, there are still 20-40% unculturable microorganisms that we have no data for. Molecular-based microbiological techniques have been developed which should facilitate future research on the interaction between prebiotics and
gut microorganisms.
Acknowledgements:
This study was supported by the foundation of Zhejiang Provincial Scientific Program (No. 2009C32018) and Science Fund for Young Scholars of Zhejiang Gongshang University, China (No. Q 09-20).
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The author
Dr Yanbo Wang
Key Laboratory of Food Safety of Zhejiang Province
Food Quality & Safety Department
Zhejiang Gongshang University
Hangzhou 310035, China
Email: wangyb@mail.zjgsu.edu.cn
