Phytochemical and microbiological stability of spent espresso coffee grounds in capsules

- Spent coffee grounds (SCGs) in capsules showed a high amount of antioxidants.
- Bioactive compounds of SCG were well preserved within a month of storage.
- SCG was microbiologically stable for 15 days.
- SCG in capsules can be re-used within 15 days as a source of bioactive compounds.

Wet spent coffee grounds (SCGs) from espresso capsules, a post-consumer organic solid residue produced worldwide, were analysed to determine their chemical and microbiological stability during storage. In particular, the changes in the total phenolic content and antioxidant capacity (based on two free radical scavenging assays and one oxygen radical absorbance assay) were determined on espresso SCG stored in capsules for up to one month at room temperature in a container open to the air. Phenolic compounds were also identified and quantified using high performance liquid chromatography coupled with diode array and mass detectors. Microbiological analysis was performed in parallel on the same stored SCG to determine the total counts and quantify the main microbial groups present during the storage. The total phenolic content, antioxidant capacity and the most important bioactive compounds, such as the total caffeoylquinic acids, were significantly stable during storage for up to one month, while overall microbial stability was observed for up to two weeks of storage. Overall, the recovery of espresso coffee capsules within 15 days could guarantee the maintenance of microbiological stability as well as the content of valuable antioxidant compounds.