Interactions between plant bioactive food ingredients and intestinal flora: Effects on human health

Gut is the site of active fermentation of non-digestible dietary components (dietary fibre and prebiotics) as well as bioconversion and absorption of plant-derived phenolics. These compounds have an important role in gut fermentation by influencing the composition of microflora and fermentation metabolites, and consequently by contributing to both local and systemic effects in humans. Possibilities to enhance viability and promote growth of probiotic bacteria by non-digestible food components have been a subject to extensive scientific interest in the last ten years. Gut bacteria are known to degrade and ferment dietary fibre, producing metabolites, especially short-chain fatty acids. They also mediate a number of important consequences through their further metabolism in the liver. Current research is at quick steps increasing our understanding about the interactions between gut microbes and bioactive dietary phenolics. Absorption and metabolism of phenolic compounds occurs along the digestive tract. Those compounds not absorbed or converted earlier enter the colon, and may be converted to metabolites concomitantly with carbohydrate fermentation. All the colonic metabolites can have effects on the epithelium at the site of conversion, and also affect the colonic flora locally. When absorbed the metabolites are found in plasma and urine and can have systemic health effects. The health effects of phenolic compounds have been studied extensively, but those of the metabolites are poorly known. As strong antimicrobial agents the phenolics might also have unpredictable effects on the composition of the intestinal flora.