The aim of this study was to determine the antioxidative activity of propolis from ecologically clean parts of Dalmatia.
Phenol concentration in ethanolic propolis extracts was determined by Folin-Ciocalteu reagent using gallic acid as the standard. Flavonoid phenolic compounds were analyzed after precipitation with formaldehyde. The residual non-flavonoid phenolics were also determined by Folin-Ciocalteu method. By determining the change of peroxide number (PN), of tiobarbiture acid reactive species (TBARS), and of DPPH-radical activity, antioxidative efficiency of propolis was tested and compared with well known and widely used synthetic antioxidants. Values of PN and TBARS were determined at 60 degrees C in samples of trigyceride substrate (lard) without and with the addition of antioxidants. Compared was the efficiency of three antioxidants: propolis (alcoholic extract), vitamin E, and (+)-catechin in a concentration of 1%. PN was monitored during 50 days. By the method of Sedlacek, TBARS were measured during 30 days. Antioxidative activity of propolis extract was also measured in terms of hydrogen donating ability using stable radical alpha,alpha-diphenyl-beta-picril hidrazyl (DPPH*) and compared with commercial synthetic antioxidants of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and (+)-cathecin. Inhibition degree of DPPH* was calculated by the formula of Yen and Duh.
Total phenol content, expressed as gallic acid, in propolis extracts varied from 75.2 to 90.2 g/kg propolis. The proportion of flavonoids in total phenols ranged from 62% to 65%. Values of TBARS were not increased only in samples with added propolis. The inhibition of DPPH-radical by propolis extracts ranged from 93% to 96%, by catechin 95%, by BHT 49%, and by BHA 64%. Compared to BHT and BHA, propolis extracts showed greater reducing activity against DPPH-radical.
The chemical composition of propolis, and thus its biological activity depend on the plant from which it has been collected, and on the macro- and microclimatic conditions. Many compounds in propolis exert antioxidative activity. A belief was expressed that the biological activity of propolis is very probably based mostly on its antioxidative efficiency. Dalmatian propolis showed high efficiency in the prevention of oxidative processes. This could be explained by the high proportion of polyphenol constituents, especially flavonoids. A very low and equal degree of increase of PN, as a measure of oxidative processes, was noticed in the samples of triglyceride substrate with the addition of propolis and (+)-catechin. The greatest rise of TBARS was measured in the samples of pure lard. There was no increase of TBARS only in the samples with added propolis. Propolis and (+)-catechin showed great efficiency in the inhibition of DPPH-radical, greater than BHT and BHA, which are widely used in food industry.
The results indicate that Dalmatian propolis could be an efficient protective agent against oxidative processes in food. The high antioxidative activity of propolis, its natural origin, and present knowledge about its biological properties, make it a very promising nutritional additive for human diet.