**2.6 Postbiotics**

The term postbiotics refers to metabolites and cell-free supernatants (CFS) and also soluble factors such as metabolic bioproducts secreted by live microbes [80]. Metabiotics refers to the structural constituents of probiotic bacteria and/or their metabolites and/ or specific signaling molecules that can improve physiological functions of the body and regulatory or metabolic reactions related with gut microbiota [85, 86].

Postbiotics are found in fermented food (kefir, sauerkraut, yogurt, certain pickles, etc.) and inside the human body. They are mainly represented by organic acids (i.e., short-chain fatty acids (SCFA)), tryptophan (Trp), and bacteriocins and present direct benefits due to their action on the host cells and indirect benefits related to the stimulation of proliferation of beneficial gut bacterial strains and inhibition of harmful microbial strains. They may have different properties depending on their type; the most important benefit is related to their anti-inflammatory and antioxidant effects.
