ABSTRACT Background Growing concerns regarding the safety and environmental impact of synthetic preservatives have increased interest in natural, plant‐derived alternatives for cosmetic formulations. Polyphenol‐rich botanical extracts are particularly attractive due to their combined antioxidant and antimicrobial properties. Aims This study aimed to develop and evaluate an ultrasound‐optimized polyphenol‐rich extract from a combination of Camellia sinensis (green tea) and Rosmarinus officinalis (rosemary) as a potential multifunctional preservative for cosmetic applications. Patients/Methods A 1:1 blend of green tea and rosemary was subjected to ultrasound‐assisted extraction (UAE) to maximize phenolic recovery. The extract was characterized by measuring total phenolic content and analyzing key phytochemical markers using HPLC‐DAD. Antioxidant activity was assessed using β‐carotene bleaching inhibition, while antimicrobial activity was evaluated against Staphylococcus aureus , Escherichia coli , Pseudomonas aeruginosa , and Candida albicans . Minimum inhibitory concentrations and time‐kill kinetics were determined. The extract was further incorporated into a model cosmetic emulsion to evaluate its preservative performance during storage. Results The optimized extract exhibited a high total phenolic content (152.8 ± 5.3 mg GAE/g) and higher yield compared with individual plant extracts. HPLC‐DAD confirmed the presence of catechin derivatives and carnosic acid, indicating a complementary phytochemical profile. Strong antioxidant activity was observed with β‐carotene inhibition of 78.4%. The extract demonstrated broad‐spectrum antimicrobial activity with minimum inhibitory concentrations ranging from 0.51 to 2.04 mg/mL. Time‐kill assays showed rapid microbial inactivation, and the cosmetic emulsion containing the extract maintained oxidative stability and microbial safety during storage. Conclusions The ultrasound‐optimized green tea–rosemary extract demonstrated significant antioxidant and antimicrobial activities and effectively enhanced the stability of a cosmetic formulation. These findings suggest that this natural extract could serve as a promising eco‐friendly preservative for clean‐label cosmetic products.
Singh et al. (Mon,) studied this question.