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J. Cosmet. Sci., 70, 137–147 (May/June 2019) 137 Microbiological Tests of Natural Limonene and the Compounds Obtained after Isomerization of Limonene in the Presence of Ti-SBA-15 Catalyst—α-Terpinene, γ-Terpinene, Terpinolene, and p-Cymene A GNIESZKA WRÓBLEWSKA, M. RETAJCZYK, D. KĄDZIOLKA, and A. MARKOWSKA-SZCZUPAK, Institute of Organic Chemical Technology, Faculty of Chemical Technology and Engineering, West Pomeranian University of Technology Szczecin, 70-322 Szczecin, Poland (A.W., M.R.) , Institute of Inorganic Chemical Technology and Environmental Engineering, Faculty of Chemical Technology and Engineering, West Pomeranian University of Technology Szczecin, 70-322 Szczecin, Poland (D.K., A.M.-S.) Acce pted for publication June 7, 2019. Synop sis The antimicrobial properties of natural limonene and the compounds obtained after isomerization of limonene (α-terpinene, γ-terpinene, terpinolene, and p-cymene) were studied. The following microorganisms were selected for the tests: Gram-negative bacteria Escherichia coli K12 (ACCT 25922), Gram-positive Staphylococcus epidermidis (ACCT 49461), yeast fungi Candida albicans, and fungi Trichophyton rubrum, Aspergillus niger, Penicillium commune, Trichoderma viride, and Cladosporium cladosporioides. During the studies, terpinolene showed the highest activity, and therefore, this compound was chosen for the preparation of therapeutic creams (content of terpinolene: 0.5 and 2 wt%). The obtained creams were active in the microbiological tests even at the lowest content of terpinolene. The mixture of products obtained after the isomerization of limonene also showed antimicrobial activity. Probably, in the future, this mixture of products can be used as a potential and relatively inexpensive ingredient in therapeutic and protective creams that can be applied for the relief of skin lesions and in the treatment of acne or atopic dermatitis. INTRODU CTION Essenti al oils containing terpene compounds can fi nd numerous applications in medicine. Studies conducted with the participation of terpenes isolated from various essential oils showed their bactericidal or bacteriostatic activity. This is connected with the high lipo- philicity of terpenes, thanks to which they easily penetrate the cell walls and membranes of various microorganisms, which in turn disrupts the integrity of these structures and Address all correspondence to Agnieszka Wróblewska at agnieszka.wroblewska@zut.edu.pl.