Introduction: Around 10 million tons of coffee beans are consumed annually worldwide, resulting in the production of 6-8 million tons of spent coffee grounds (SCGs) [1,2]. Most of this waste is discarded in landfills, causing a threat to the environment [3]. Despite the brewing process, SCGs contain many valuable ingredients, such as lipids and antioxidants, which can be extracted as coffee oil and antioxidant extracts. Due to their antioxidant activity, those products are believed to have a positive effect on the skin and could find applications in the cosmetic industry. This study aimed to assess the feasibility of using these SCG-derived products as active ingredients in cosmetic emulsions.
Methods: O/W emulsions containing different concentrations of coffee oil and aqueous and ethanol antioxidant extracts were prepared by a hot-process emulsification technique. The antioxidant properties of the oil and antioxidant extracts after heating to emulsification temperature were measured via CUPRAC assay. The physical stability of emulsions was tested using the accelerated aging method. Emulsion cytotoxicity assessment was carried out on a 2D culture of keratinocytes from the HaCaT cell line. Cell viability was assessed using FDA/PI, MTT and resazurin assays.
Results: Heating coffee oil and antioxidant extracts did not lower their antioxidant activity. The addition of SCG-derived products to cosmetics did not affect their physical stability in an accelerated aging test. Emulsions containing different concentrations of coffee oil or antioxidant extract did not show a significant cytotoxic effect on HaCaT cells cultured in a monolayer.
Conclusion: Spent coffee grounds are a valuable source of antioxidants and coffee oil with potential use in the cosmetic industry. The studied
SCG-derived products could find application as active and base ingredients in cosmetic emulsions such as face or hand creams.