Fermented functional foods based on probiotics and their biogenic metabolites Catherine Stanton 1,2 , R Paul Ross 1,2 , Gerald F Fitzgerald 1,3 and Douwe Van Sinderen 1,3 The claimed health benefits of fermented functional foods are expressed either directly through the interaction of ingested live microorganisms, bacteria or yeast with the host (probiotic effect) or indirectly as a result of ingestion of microbial metabolites produced during the fermentation process (biogenic effect). Although still far from fully understood, several probiotic mechanisms of action have been proposed, including competitive exclusion, competition for nutrients and/ or stimulation of an immune response. The biogenic properties of fermented functional foods result from the microbial production of bioactive metabolites such as certain vitamins, bioactive peptides, organic acids or fatty acids during fermentation. Addresses 1 Alimentary Pharmabiotic Centre, BioScience Institute, University College Cork, Co. Cork, Ireland, 2 Teagasc, Biotechnology Centre, Moorepark, Fermoy, Co. Cork, Ireland, 3 Department of Microbiology, University College Cork, Western Road, Co. Cork, Ireland Corresponding author: van Sinderen, Douwe (d.vansinderen@ucc.ie) Current Opinion in Biotechnology 2005, 16:198–203 This review comes from a themed issue on Food biotechnology Edited by Willem M de Vos Available online 3rd March 2005 0958-1669/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. DOI 10.1016/j.copbio.2005.02.008 Introduction Functional foods are foods that claim to promote human health over and above the provision of basic nutrition. The term functional foods, first proposed in Japan two decades ago and legally approved there in terms of Foods for Specified Health Use (FOSHU), is not cov- ered by a universally accepted definition. A relatively recently proposed working definition describes func- tional foods as ‘foods that can be satisfactorily demon- strated to affect beneficially one or more target functions in the body, beyond adequate nutritional effects, in a way relevant to an improved state of health and well- being and/or reduction of risk of disease’ [1]. It is important to emphasize, however, that at this time, functional foods are not covered by any specific legisla- tion in Europe [2]. Despite this, they have a significant and growing global market, with recent estimates indi- cating up to a $50 billion annual share [3]. The largest segment of this market in Europe, Japan and Australia comprises foods containing probiotics, prebiotics, and synbiotics. Probiotics are defined as ‘live microorgan- isms which when consumed in adequate numbers confer a health benefit on the host’ [4], with ongoing contro- versy as to whether cultures must be viable for efficacy in all cases. Prebiotics are nondigestible food ingredients that beneficially affect the host by stimulating growth and/or activity of one or a limited number of bacteria in the colon, thus improving host health [5]. The term synbiotic is used when referring to a product that uses a prebiotic and probiotic in combination [6]. Microorgan- isms might also indirectly impart health-promoting char- acteristics in food through the production of bioactive metabolites (referred to as biogenics) during fermenta- tion [7  ]. Given that fermented food products can contain probio- tics, prebiotics or both, it is not surprising that their consumption has long been associated with good health. Indeed, as far back as 76 AD the Roman historian Plinio advocated the use of fermented milks for treating gastro- intestinal infections. The French paediatrician Tissier proposed in the early 1900s that bifidobacteria could be effective in preventing infections in infants, as they were the predominant component of the intestinal microflora of breast-fed infants [8]. Development of the probiotic concept is attributed to Metchnikoff, who observed that the consumption of fermented milks could reverse putre- factive effects of the gut microflora [9]. This concept has matured, particularly over the past two decades, through sound scientific evidence based on placebo-controlled clinical trials showing that particular strains have asso- ciated health benefits. In addition, there is now con- siderable consumer awareness of the basis for ingesting such foods in relation to health promotion and disease prevention. The purpose of this review is to describe the challenges associated with the scientific and commercial develop- ment of fermented functional foods. The main benefits and challenges associated with the development of such products will be described first, followed by some examples of biogenic metabolite production and pro- spects for further developments in this exciting R&D area. Current Opinion in Biotechnology 2005, 16:198–203 www.sciencedirect.com