Interest in probiotics is invariably traced back to Elie Metchnikoff’s studies about the potential
benefits of fermented milks in human nutrition, in the beginning of the twentieth century. The word
probiotic itself was introduced much later. There has been some controversy regarding the
operational definition of probiotics (e.g. kind of microorganisms, whether they have to be alive or
not), but widely accepted is the definition as a preparation of live microorganisms which, when
administered in adequate amount, have beneficial effects on the health of the person or animal
(Hamilton et al., 2003).