Antioxidant and prebiotic functions of aqueous extracts of three common culinary Lamiaceae herbs

Background Lamiaceae herbs are a large family of chiefly annual or perennial herbs which are grown all over the world. The common lamiaceae herbs include rosemary, thyme, basil, mint, oregano, sage, lavender, perilla and savory. Aqueous extract and essential oils of this group of herbs are known to have been used both in the past and present for therapeutic purposes. The therapeutic effects of lamiaceae herbs are due to their phytochemical content which is dominated by the phenolic compounds [8, 12]. Probiotics can be either non-pathogenic normal gastrointestinal bacteria found in the microflora of healthy individuals or bacterial preparations that have been clinically proven to impart beneficial clinical effects on the health of hosts when already present or consumed. Lactobacillus and Bifidobacteria cultures are the main strains used as probiotics in pharmaceuticals and foods. Although probiotic bacteria can survive transit in the gastrointestinal tract, they do not colonise and grow during shorter or after prolonged feeding periods [7,11]. Consequently, there is a need for complementary means to promote/maintain growth in the colon. Prebiotics are dietary factors specifically intended to promote/stimulate the growth of probiotic bacteria [4]. The most common prebiotic compound used is known to promote the growth of probiotic bacteria is the non-digestible oligosaccharide inulin [6,10]. Bello et al. (2001) have demonstrated that the use of fructo-oligosaccharides (FOS) resulted in enhanced growth of Eubacterium biform and Clostridium perfringens. However, the disadvantage of the use of carbohydrate type prebiotics is that they also promote the growth of non-probiotic bacteria. Hence there is search for non-carbohydrate sources of prebiotic compounds. Some studies reported the prebiotic functions of products with high phenolic compound content. For instance, Goto et al (1998) found that the administration of 300 mg of catechin per day to 15 subjects over a 3-week period significantly increased faecal levels of lactobacilli and bifidobacteria with a significant decrease in levels of Enterobacteriaceae, Bacteroidaceae and Eubacteria. Furthermore, Ishihara et al (2001) evaluated and reported the inhibition of pathogenic bacteria by green tea while encouraging and maintaining intestinal microflora balance in calves by high faecal counts of Bifidobacterium species and Lactobacillus species. Hence from these studies, catechin which is the main phenolic component of tea has been implicated as an alternative prebiotic compound. However, to our knowledge, no work has been carried out on the prebiotic function of herb extracts in relation to their different phenolic content