Spent coffee as a new source of bioaccessible and bioactive compounds with antimutagenic and antimicrobial activity

Abstract

Spent coffee is the main by‐product of the coffee brew preparation and a promising source of bioactive compounds. The aim of this work was to evaluate the main bioactive compounds of spent coffee extracts, their bioaccessibility, as well as their antimutagenic and antimicrobial activity. Previously, the extraction method of antioxidant compounds was improved by applying defatting and lyophilisation. The phenolics and caffeine content of Arabica filter and Robusta espresso spent coffee was measured by HPLC‐DAD‐MS, and the total content of phenolic compounds (free and bound) was assessed after applying three treatments (alkaline, acid, saline). A total of 36 free chlorogenic acids (CGA) were identified and quantified showing that Arabica and Robusta spent coffee extracts have 329 and 345 μmol of free CGA /g, respectively. Furthermore, bound compounds were estimated as half of the total phenolic content, due to presence of phenolics linked to macromolecules like melanoidins, mainly by non‐covalent interactions. The majority of CGAs of spent coffee extracts remain bioaccessible after an in vitro simulated gastroduodenal digestion (89‐92%), being the major compounds ‐ caffeoylquinic (CQAs) and feruloylquinic (FQAs) acids‐ those with a low degradation, whereas lactones were partially degraded. However, CGAs showed very limited absorption and transport (1% initial dose) across the Caco‐2 human cell monolayer (intestinal epithelium). Therefore, in vivo studies are required to assess bioavailability of spent coffee bioactive compounds. Spent coffee extracts exhibited strong protection activity against indirect acting mutagen (up to 92%), whereas the protection against a direct acting mutagen was 12‐35% (Ames Test), being phenolics with a caffeic acid highly effective. The growth inhibition of common food‐borne pathogen and food spoilage microorganisms by coffee extracts was also studied. Spent coffee extracts showed antimicrobial activity, mainly against Gram‐positive bacteria (Staphylococcus aureus, Listeria monocytogenes) and yeast (Candida albicans). In conclusion, all the results support the idea that spent coffee is an accessible, sustainable, and major source of bioactive compounds with potential health benefits in order to be applied as ingredients of functional foods.