J. Cosmet. Sci., 65, 147–159 (May/June 2014) 147 Method for screening sunscreen cream formulations by determination of in vitro SPF and PA values using UV transmission spectroscopy and texture profi le analysis WATCHAREE KHUNKITTI, PANITTA SATTHANAKUL, NETI WARANUCH, TASANA PITAKSUTEEPONG, and PICHET KITIKHUN, Faculty of Pharmaceutical Sciences, Khon Kaen University, Khon Kaen 40002, Thailand (W.E., P.S.), and Cosmetics and Natural Products Research Center, Faculty of Pharmaceutical Science, Naresuan University, Phitsanulok 65000 (N.W., T.P., P.K.), Thailand. Accepted for publication April 21, 2014. Synopsis Formulation of sunscreen products to obtain high values of sun protection factor (SPF) and protection from ultraviolet A (PA) is challenging work for cosmetic chemists. This study aimed to study factors affecting SPF and PA values using ultraviolet transmission spectroscopy as well as texture profi les of sunscreen formulations using 23 factorial designs. Results demonstrate that the correlation coeffi cient between the labeled SPF values of counter-brand sunscreen products and the in vitro SPF values was 0.901. In vitro SPF determination showed that the combination effect of phase volume ratio (PVR) and xanthan gum caused a signifi cant increase to the SPF values of the formulations, whereas the interaction effect between PVR and stearic acid signifi cantly decreased the SPF value. In addition, there was the interaction effect between xanthan gum and stearic acid leading to signifi cant reduction of hardness, compressibility, and pH, but signifi cantly increasing the adhe- siveness. All tested factors did not signifi cantly affect the cohesiveness of tested formulations. In conclusion, apart from sunscreen agents, the other ingredients also affected the SPF and PA values. The calculated SPF values range from 21 to 60. However, a selected formulation needs to be confi rmed by the standard method of testing. In addition, the physical, chemical, and biological stability shelf life and sensory evaluation of all formulations need to be evaluated. INTRODUCTION It is generally known that ideal sunscreen products should be able to protect skin from damage from ultraviolet (UV) radiation (290–400 nm). Long-term exposure to UVB (290–320 nm) and UVA (320–400 nm) may cause sunburn, immunosuppression, and skin cancer (1–3). The effi cacy of sunscreen products may be indicated by numerical rat- ing of sun protection factor (SPF) and UV-A protection (PA). Several attempts have been made to develop in vitro SPF testing methods (1,4–11), but there is no offi cially recognized Address all correspondence to Watcharee Khunkitti at watkhu@kku.ac.th.
JOURNAL OF COSMETIC SCIENCE 148 method due to the limitation of measurement techniques (12). In 2011, Cosmetics Eu- rope, formerly known as COLIPA, provided guidelines for an in vitro method for the de- termination of the UVA protection factor and critical wavelength values for sunscreen products using PMMA plates (polymethylmethacrylate) as a substrate for applying the tested sunscreen product (13,14). However, in the case of having limitation on the assess- ment of SPF and PA values using the standard guidelines, in vitro preliminary screening of processing variables in an earlier stage of sunscreen formulations such as sun protection effi cacy using UV spectrophotometer appears to be practical. Moreover, the physical properties measurements, texture profi les, and stability studies should be simple, rapid, and reproducible, and provide important information before proceeding to the in vivo test, which is very expensive, time-consuming, and prone to having risks related to UV ex- posure of human volunteers. In addition, the relationship between the product texture measurement and sensory skin perception may be useful to predict consumer responses. In this study, although in vitro SPF testing methods demonstrated that the in vitro SPF values underestimated the in vivo SPF values, using a linear regression equation for the relationship between labeled SPF value and calculated SPF by UV transmission spectros- copy appears to be simple and directly proportional to the in vivo SPF values (15). More- over, texture analysis may also be used for product characterization and stability evaluation. Many studies have demonstrated that there is a relationship between sensory and instru- mental texture profi les in some aspects of food and cosmetic emulsions (16–20). As a re- sult, a correlation between physical measurements and certain sensory attributes of the semi-solid products can be useful for a fast in-line screening study. The aim of this study was to investigate factors affecting SPF and PA values of sunscreen formulations and their texture profi les. The SPF and PA values of the formulation were carried out using UV transmission spectroscopy. MATERIALS AND METHODS MATERIALS Titanium dioxide (and) diethylhexyl carbonate (and) polyglyceryl-6 polyhydroxystearate was a gift from Evonic, Bangkok, Thailand. C12-15 Alkyl benzoate (and) dipropylene glycol dibenzoate (and) PPG-15 stearyl ether benzoate and other ingredients at cosmetic grade were purchased from Numsieng, Bangkok, Thailand. Two standard sunscreen products, which were the standard homosalate sunscreen (8%) with the mean SPF value of 4.47 and the high standard SPF value of 15, were prepared according to the recom- mendation of theUnited States Food and Drug Administration (FDA) (21) and COLIPA (22), respectively. The international counter-brand sunscreen products were purchased from a drug store. METHODS Factorial design experiments. Sunscreen formulations were prepared based on 23 factorial designs. The following three factors were investigated: (i) oil to water phase volume ratio (PVR), concentrations of (ii) Xanthan gum, and (iii) stearic acid. Their levels are shown
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