Physical, chemical, and antioxidant stability studies of a topical formulation containing pot marigold (Calendula officinalis L.) flowers extract

Abstract

Pot marigold flower extract (Calendula officinalis L.) has pharmacological properties due to the presence of various bioactive compounds. It is known that the extract has antioxidant, anti-inflammatory, antitumor, antibacterial, antifungal, antiviral, antimutagenic, antidermatitis properties, etc. The aim of this study was to improve the quality of the selected topical formulation by adding the ethanolic extract of pot marigold flower, as well as to monitor its stability. The topical formulation was water-in-oil emulsion prepared using the hot/hot emulsification process with an oil phase consisting of Vaseline, lanolin, and almond oil. The extract, prepared by ultrasound-assisted extraction, had an antioxidants content of 3.512 g gallic acid equivalent per 100 g-1 of dry weight and the half-maximal inhibitory concentration of 0.14 mg mL-1 determined by the DPPH assay. Chemical stability studies have shown that daylight has no significant effect on the stability of antioxidants in the extract, while an increase in temperature leads to their degradation. The shelf-life of the extract is about 8 months at 4 °C and 3 months at 22 °C (room temperature). The prepared uncategorized topical formulations containing 1% and 2% (w/w) pot marigold extract were stable at different temperatures during the storage. The uncategorized formulations showed antioxidant activity, but the activity of the extract in the formulations decreased with increasing storage temperature. Pot marigold flower extract and the developed uncategorized formulations showed an inhibitory effect on Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae), as well as on Candida albicans. The uncategorized formulations with this activity can be used in the treatment of skin infection.