Table 2.

Published definitions of postbiotics (adapted from [12], CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/, accessed on 22 February 2022)).

Definition	Microbial Cells/Cell Components Included?	Metabolites Included in the Absence of Cells/Cell Components?	Scope Limited to Substances Produced by a Probiotic?	Health Benefit Required?	Is In Situ Production of ‘Postbiotic’ Sufficient?
Any factor resulting from the metabolic activity of a probiotic or any released molecule capable of conferring beneficial effects to the host in a direct or indirect way [10]	No	Yes	Yes	No	Yes
Soluble factors (products or metabolic byproducts), secreted by live bacteria, or released after bacterial lysis, such as enzymes, peptides, teichoic acids, peptidoglycan-derived muropeptides, polysaccharides, cell surface proteins, and organic acids [13]	No	Yes	No	No	Yes
Compounds produced by microorganisms released from food components or microbial constituents, including non-viable cells that, when administered in adequate amounts, promote health and well-being [14]	Yes (not required)	Yes	No	Yes	No
Non-viable metabolites produced by probiotics that exert biological effects on the hosts [15]	No	Yes	Yes	No *	Yes
Non-viable bacterial products or metabolic byproducts from probiotic microorganisms that have positive effects on the host or microbiota [16]	No	Yes	Yes	No **	Yes
Functional bioactive compounds, generated in a matrix during fermentation, which may be used to promote health [17]	No	Yes	No	Yes	No
Preparation of inanimate microorganisms and/or their components that confers a health benefit on the host [1]	Yes (required)	No	No	Yes	No

* Biological, but not health effects, stipulated. ** A health benefit is not specifically stipulated.