Postbiotics are preparations containing inactivated microbial cells or their components with health benefits, while postbiotic metabolites are purified microbial compounds alone. Since your work involves extracellular metabolites without whole cells, they should be classified as postbiotic metabolites.

Can you suggest a reference paper for this ?

Microbiologically generated postbiotics would function via metabolites. Only in the rare case of nonviable bacterial cells functioning physically would postbiotic efficacy not be based on metabolites.