Emulsion carrier formulations for natural plant extracts : development and stability testing

Abstract

South African-grown plants and their possible skin care benefits are increasingly gaining interest. For skin care applications, stable carrier formulations must be developed to incorporate extracts of these plants. Many cosmetic cream and sunscreen formulations are emulsions. The success of these formulations depends on their efficacy, stability and sensory characteristics. The main objective of this investigation was to develop stable carrier formulations to incorporate four ethanolic plant extracts for topical skin applications. These plant extracts are referred to using the codes HO, BS, PM, and LSSJ. All four plant extracts were ethanol/water extracts and are therefore water soluble. In an emulsion formulation it is expected that the plant extract will report to the water phase. The Department of Plant and Soil Sciences from the University of Pretoria hypothesised and tested the activity of these plants and found strong evidence of anti-acne, anti-cancer and SPF boosting properties. Development of the carrier formulations involved conducting sensory evaluations and preliminary stability testing on placebo formulations. The best performing formulations were selected and these formulations, in their placebo form and containing 10 % (by mass) of the respective plant extract, underwent long term stability testing. During this testing, formulations were stored under temperature conditions of 4 °C, 25 °C, and 40 °C. The stability of the formulations was tested using three techniques. These were (a)

coalescence analysis which involved determining the rates of coalescence and shelf-lives, (b) microscopy which allowed visual observation of the change in droplet size, and (c) cycle testing which involved exposing samples to two extreme temperatures and evaluating pH, droplet size and response to centrifugation. Two lotion formulations were developed in this investigation and were referred to as “Formulation A” and “Formulation B”. The sunscreen formulation developed was referred to as “Formulation C”. Different carrier formulation types were considered including gels, body milks, creams and lotions. Formulation A - a light lotion formulation - showed excellent sensory appeal. It also showed satisfactory long-term stability in its placebo form and with the addition of the HO and LSSJ plant extract where the minimum shelf lives exceeded 1 year under normal storage conditions and 6 months under accelerated conditions. During the development of Formulation B only locally produced ingredients were used in an attempt to reduce production cost. In the sensory evaluation, formulations were compared to a commercially available lotion. Preliminary stability evaluations of this formulation considered the effect of the plant extract dosage. The best performing formulation was selected by considering its sensory performance as well as its preliminary stability. Formulation C was chosen based on its long-term stability. It was based on Formulation A and showed good long-term stability and resistance to harsh temperatures during cycle testing. A titanium dioxide dispersion was used as the UV filter in this sunscreen. Formulation A was suggested for the addition of the HO plant extracts whereas Formulation B showed good stability in the presence of the LSSJ plant extract. The PM plant extract did not perform well in the lotion formulations. It was suggested that a gel

formulation should be considered for this plant extract. Formulation C showed good stability with the addition of the BS plant extract. SPF testing showed slight SPF boosting capability of the BS plant extract. Formulations developed in this study will be sent for efficacy testing. With the efficacy of the formulations containing the plant extracts quantified, these formulations can be introduced into the commercial marked for possible cosmetic and pharmaceutical applications. outh African-grown plants and their possible skin care benefits are increasingly gaining interest. For skin care applications, stable carrier formulations must be developed to incorporate extracts of these plants. Many cosmetic cream and sunscreen formulations are emulsions. The success of these formulations depends on their efficacy, stability and sensory characteristics. The main objective of this investigation was to develop stable carrier formulations to incorporate four ethanolic plant extracts for topical skin applications. These plant extracts are referred to using the codes HO, BS, PM, and LSSJ. All four plant extracts were ethanol/water extracts and are therefore water soluble. In an emulsion formulation it is expected that the plant extract will report to the water phase. The Department of Plant and Soil Sciences from the University of Pretoria hypothesised and tested the activity of these plants and found strong evidence of anti-acne, anti-cancer and SPF boosting properties. Development of the carrier formulations involved conducting sensory evaluations and preliminary stability testing on placebo formulations. The best performing formulations were selected and these formulations, in their placebo form and containing 10 % (by mass) of the respective plant extract, underwent long term stability testing. During this testing, formulations were stored under temperature conditions of 4 °C, 25 °C, and 40 °C. The stability of the formulations was tested using three techniques. These were (a)

coalescence analysis which involved determining the rates of coalescence and shelf-lives, (b) microscopy which allowed visual observation of the change in droplet size, and (c) cycle testing which involved exposing samples to two extreme temperatures and evaluating pH, droplet size and response to centrifugation. Two lotion formulations were developed in this investigation and were referred to as “Formulation A” and “Formulation B”. The sunscreen formulation developed was referred to as “Formulation C”. Different carrier formulation types were considered including gels, body milks, creams and lotions. Formulation A - a light lotion formulation - showed excellent sensory appeal. It also showed satisfactory long-term stability in its placebo form and with the addition of the HO and LSSJ plant extract where the minimum shelf lives exceeded 1 year under normal storage conditions and 6 months under accelerated conditions. During the development of Formulation B only locally produced ingredients were used in an attempt to reduce production cost. In the sensory evaluation, formulations were compared to a commercially available lotion. Preliminary stability evaluations of this formulation considered the effect of the plant extract dosage. The best performing formulation was selected by considering its sensory performance as well as its preliminary stability. Formulation C was chosen based on its long-term stability. It was based on Formulation A and showed good long-term stability and resistance to harsh temperatures during cycle testing. A titanium dioxide dispersion was used as the UV filter in this sunscreen. Formulation A was suggested for the addition of the HO plant extracts whereas Formulation B showed good stability in the presence of the LSSJ plant extract. The PM plant extract did not perform well in the lotion formulations. It was suggested that a gel

formulation should be considered for this plant extract. Formulation C showed good stability with the addition of the BS plant extract. SPF testing showed slight SPF boosting capability of the BS plant extract. Formulations developed in this study will be sent for efficacy testing. With the efficacy of the formulations containing the plant extracts quantified, these formulations can be introduced into the commercial marked for possible cosmetic and pharmaceutical applications.