Photostability of Phenolic Compounds from Propolis in Micellar Media

MARIA FLORENCIA FANGIO; DALILA ORALLO; NAYLA LORES; MARIA SANDRA CHURIO

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

International Union of Photobiology

Propolis is a mixture of substances collected by honey bees (Apis mellifera L) from various vegetal sources such as tree exudates. Among more than 200 different compounds that can be found in propolis, phenolic and flavonoids are particularly distinguished by their antioxidant and antimicrobiological properties.[1] Gallic acid (3,4,5-trihydroxybenzoic acid) is one of the natural components of propolis. Previous studies have demonstrated their antioxidant and bactericidal capacities, and that photoirradiation induces the enhancement of the antimicrobial activity [2]. With the purpose of gaining a deeper understanding of the effect of photoirradiation on the activity of gallic acid, we explore in this work the photodegradation of the phenolic molecule in simple organized media as models of biological environments such as that found in propolis. The study was carried out in direct micelles and in homogenoeus aqueous soluction at neutral pH regulated by Trizma buffer. The micelles were prepared alternatively with anionic (sodium dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium chloride, CTAC).surfactants. Steady state irradiation of the samples in the UV range was achieved by a 400 W HPA lamp. The decay in gallic acid concentration was followed by the absorption at 260 nm. The photodecomposition yield in 0.1 M SDS solution was similar to that observed for the homogeneous solution, but larger than that one showed in 0.1 M CTAC micelles. The results can be rationalized by considering the acidity constants for gallic acid (pKa1 = 4.16 and pKa2= 8.55), and the fact that dissociated organic acids show higher reactivity under UV than the neutral compounds.[3-4] However, in the presence of cationic CTAC micelles, the attractive interactions of gallate anions with the positive surfactant heads may favour the compound entering the micellar phase and enhancing its photoreactivity. These results are relevant in order to chacterized the system in which the potential antimicrobial activity of gallic acid against Paenibacillus larvae, a causative agent of American Foulbrood (AFB), a severe disease that affects larvae of the honeybees, is being tested.