Thermal mud maturation: organic matter and biological activity

Synopsis Objective Many of the therapeutic and cosmetic treatments offered in spas are centred on mud therapy, to moisturize the skin and prevent skin ageing and rheumatic diseases. Thermal mud is a complex matrix composed of organic and inorganic elements which contribute to its functions. It is a natural product derived from the long mixing of clay and thermal water. During its maturation, organic substances are provided by the microalgae, which develop characteristic of the composition of thermal water. Methods The aim of this study was to identify methods for introducing objective parameters as a basis for characterizing thermal mud and assessing its efficacy. Samples of thermal mud were collected at the Saturnia spa, where there are several sulphureous pools. The maturation of the mud was evaluated by organic component determination using extractive methods and chromatographic analysis (HPLC, GC‐MS, SPME). We also studied the radical scavenging activity of mud samples at different stages of maturation, in a homogeneous phase, using several tests (DPPH, ORAC, ABTS). Results We identified several classes of compounds: saturated and unsaturated fatty acids, hydroxyl acids, dicarboxylic acids, ketoacids, alcohols and others. SPME analysis showed the presence of various hydrocarbons compounds (C11–C17) and long‐chain alcohols (C12–C16). Six or seven months seemed appropriate to complete the process of maturation, and the main effect of maturation time was the increase of lipids. Six‐month mud showed the highest activity. The hydrophilic extract was more active than the lipophilic extract. Conclusion The results indicate that maturation of thermal mud can be followed on the basis of the changes in its organic composition and antioxidant properties along the time. They also highlight the need to develop reference standards for thermal muds in relation to assess their use for therapeutic and cosmetic purposes. Résumé Objectif Beaucoup de traitements thérapeutiques et cosmétiques offerts dans les spas sont centrés sur la thérapie de boue, pour hydrater la peau et prévenir le vieillissement de la peau et les maladies rhumatismales. La boue thermale est une matrice complexe composée d’éléments organiques et inorganiques qui contribuent à ses fonctions. C'est un produit naturel dérivé du long mélange d'argile et de l'eau thermale. Au cours de sa maturation, des substances organiques sont fournies par les micro‐algues qui se développent, caractéristiques de la com