Simultaneous Determination of Acrylamide, Caffeic Acid, and Caffeine in Commercial Coffee Capsules Using a Rapid and Validated HPLC-DAD Approach

Abstract

Background: Coffee capsules are increasingly consumed worldwide and represent a complex source of bioactive compounds, notably caffeine (stimulant), caffeic acid (antioxidant), and acrylamide (toxicant). Aims: The objectives of this investigation were twofold: (i) assess total phenolic content (TPC), antioxidant capacity, pH, and browning index, across seven commercial capsule products (comprising six Algerian brands widely consumed locally and one European comparator with undisclosed blend/roast); and (ii) to develop and validate an HPLC – Diode Array Detection (DAD) procedure for the simultaneous determination of caffeine, caffeic acid, and acrylamide , serving as joint indicators of product quality and safety. Methods: The TPC was determined employing the Folin–Ciocalteu method, while antioxidant activity was assessed by the DPPH radical scavenging assay. The simultaneous quantification of caffeine, caffeic acid, and acrylamide were performed by a validated HPLC – DAD procedure in accordance with International Council for Harmonization (ICH) guidelines. Results: The resulting coffee brews exhibited pH values ranging from 5.64 to 6.25 and browning indices between 0.280 and 0.482, reflecting roasting differences. Despite a modest TPC (0.9 to 2 mg GAE/g), the antioxidant activity was high, (up to 95.3% inhibition DPPH). Caffeine was consistently detected (0.05 – 0.33 mg/25 mL), confirming its stimulant role. Caffeic acid was present in lower concentrations (0.001 – 0.14 mg/25 mL), contributed to the antioxidant potential. In contrast, acrylamide was detected in all analyzed samples ranging from 4.75 to 28.15 µg/25 mL). On a dry coffee basis, these concentrations correspond to 458 – 4023 µg/kg. A majority of the capsules yielded levels that exceed the European Commission’s benchmark of 400 µg/kg for roasted coffee, thereby underscoring consumer-relevant exposure level and raising toxicological concern. Conclusions: Coffee capsule brews demonstrated notable antioxidant capacity despite modest TPC, with caffeine ubiquitous and caffeic acid detectable. The presence of acrylamide was confirmed in all samples at levels that warrant monitoring. The validated HPLC–DAD workflow enables the simultaneous determination of these markers and offers a robust basis for integrated quality control and risk assessment in encapsulated coffee products.