J. Cosmet. Sci., 68, 147–157 (March/April 2017) 147 Commercial plant extracts may act as antioxidants or pro-oxidants in cosmetic emulsions based on argan oil PAULINA MALINOWSKA, ANNA GLISZCZYŃSKA-ŚWIGLO, and HENRYK SZYMUSIAK, Faculty of Commodity Science, Poznań University of Economics and Business, 61-875 Poznań, Poland Accepted for publication March 10, 2017. Synopsis Cosmetic emulsions containing plant extracts should be tested in a range of temperatures from 5°C to 40°C to be sure that they will be stable during general use by consumers and that plant extracts used as antioxidants do not accelerate oxidative degradation of their oil base. The oxidative stability of argan oil-in-water emulsions containing 1% and 5% commercial acerola, willow, and rose extracts [or 0.01% butylhydroxytoluene (BHT)], stored at 5°C and 20°C for 6 months and at 40°C for 4 weeks, was monitored by the determination of peroxide content. The antioxidant or pro-oxidant activities of extracts or BHT in emulsions were expressed as the protection factor (PF) and inhibition of peroxide formation (Ip). At the end of storage, 5% willow, 0.01% BHT, 1% willow, and 5% acerola were the most protective for emulsions stored at 5°C. At 20°C, the most effective was 0.01% BHT, 5% rose, and 5% acerola. At 40°C, inhibition of peroxide formation calculated for 1% rose, 5% acerola, and 0.01 % BHT was similar. Altogether, the results show that some plant extracts, depending on storage conditions, may act as pro-oxidants, whereas the others can be applied as natural antioxidants instead of synthetic BHT. INTRODUCTION Cosmetic products containing plant compounds have recently become very popular, as the consumers prefer cosmetics without synthetic preservatives, antioxidants, perfumes, and dyes. Therefore, cosmetic producers very often use plant extracts rich in polyphenols which exert multidirectional activities (1). Plant polyphenols with high antioxidant activity may prolong the stability of cosmetic products and replace synthetic antioxidants such as butyl- hydroxyanizole (BHA) and butylhydroxytoluene (BHT), which are suspected of causing the exanthemas and allergic contact dermatitis (2,3). Moreover, plant polyphenols infl uence physiology of skin demonstrating particular activities such as sealing of capillary vessels, induction or inhibition of some enzymes in the skin, antiphlogistic, antiallergic, UV- protective, antimycotic, antibacterial, antiviral, and estrogen-like properties (4–7). In cosmetic industry, producers suggest the application of plant extracts at much higher concentrations (1–5%) than those recommended in food industry (0.001–0.1%). Food antioxidants are the most often effective at low concentrations and may show pro-oxidative Address all correspondence to Anna Gliszczyńska-Świglo at anna.gliszczynska-swiglo@ue.poznan.pl.

JOURNAL OF COSMETIC SCIENCE 148 activity at higher concentrations (8,9). In contrast to low concentrations, higher concen- trations of antioxidants in cosmetic emulsions show different activities, and as a conse- quence, they may improve the appearance of the skin. There is limited information in literature (10–12) about application of plant extracts as antioxidants at higher concentrations (1–5%) recommended by their producers. Our pre- vious studies concerning the effect of plant extracts with healing properties such as acerola fruit (Malpighia punicifolia L.), rose buds (Rosa canina L.), and willow bark (Salix alba L.) on the oxidative stability of cosmetic emulsions based on different oils (13,14) revealed that these extracts may act as antioxidants or pro-oxidants depending not only on the concentration of extract or storage conditions but also on the type of oil. Therefore, we decided to analyze these extracts in emulsion based on argan oil. Argan oil obtained from Argania spinosa L. seeds is eaten raw in southwest of Morocco and it is also used in tradi- tional medicine. It is a rich source of unsaturated fatty acids and it has anti-allergic, anti- infl ammatory, and UV-protective activities so it is applied in cosmetics for dry, mature, sensitive, and allergic skin. Moreover, it improves acne-prone skin condition, moistur- izes, smoothes, revitalizes, and fi rms the skin, as well as protects it against the dryness and soothes irritations. It also strengthens hair and nails. Therefore, it is used as an ingre- dient in many kinds of cosmetics, e.g., massage and skin care oils, face, body and hair care cosmetics, such as creams, lotions, and milks (15). Extracts from acerola, willow, and rose are applied in many cosmetics and exhibit stronger or weaker antioxidant activity. It was reported that acerola fruit extract has antioxidant activity measured with the use of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) assays, superoxide anion radical scavenging activity, and reducing power (16,17). Ethanolic willow bark extracts were found to have antioxi- dant activity in DPPH (18) and β-carotene/linoleic acid bleaching (19) assays. There are less scientifi c reports indicating the antioxidant activity of rose bud extracts (20), litera- ture provides more data concerning properties of rosehip (21–23) and rose leaves extracts (24). The antioxidant activities of these three extracts were confi rmed in our previous study with the use of DPPH, Trolox Equivalent Antioxidant Capacity (TEAC), and Ferric Reducing Antioxidant Power (FRAP) tests (13). Therefore, in the present study, the effect of 1% and 5% acerola, willow, and rose ready- to-use commercial extracts on the oxidative stability of oil-in-water (o/w) cosmetic emul- sions based on argan oil stored in different conditions was evaluated. MATERIALS AND METHODS CHEMICALS BHT was purchased from Merck (Darmstadt, Germany). Phenochem preservative (mixture of parabens in 2-phenoxyethanol) was from Custom Ingredients (New Braunfels, TX). Polyoxyethylene (20) sorbitan monolaurate (Tween 20) was from Fluka (Buchs, Switzerland). COMMERCIAL PLANT EXTRACTS Ready-to-use commercial plant extracts, acerola fruit (M. punicifolia L.) hydroglycolic extract, rose buds (R. canina L.) glycolic extract, and willow bark (S. alba L.) glycolic extract