The effect of different drying methods and carrier addition on the antimicrobial activity of prunus domestica and ribes nigrum extracts on different bacterial strains

Abstract

The consumption of fruit juices (in the form of powder) is increasing worldwide due to their nutritive and health promoting characteristics. Some of the active molecules that are suspected to be adding to the nutritive value are phenolic compounds which are secondary metabolites found in most plant extracts and have proven to possess several functions ranging from defensive mechanisms in plants to anti-cancer and antibacterial effects. One drawback in juice production is that some of the methods used may negatively affect the phenolic content of the extracts obtained. In this study we investigated the effect of three drying methods (freeze drying, vacuum drying and spray drying) and the effect of adding different carriers on the antibacterial activity of Prunus domestica and Ribes nigrum. Furthermore, we checked for synergism between pectin and the dried Prunus domestica powders. Results showed that freeze drying, vacuum drying at 40°C and spray drying maintained the highest concentrations of phenolic compounds. Whereas vacuum drying at 60°C and 80°C had lower phenolic concentrations although different patterns were sometimes observed. The addition of maltodextrin decreased the phenolic content drastically in all extracts. This also led to the decrease in the antibacterial activity against different bacterial strains (S. aureus, P. aeruginosa, E. coli and A. baumannii). When different carriers were added to spray dried Ribes nigrum, inulin showed to be the best in terms of antibacterial activity, it was followed by maltodextrin, starch and Arabic gum. Pectin and Prunus domestica extracts had synergistic antibacterial activity in the absence of maltodextrin. This implies that depectinization and the addition of maltodextrin as a carrier may be actually reducing the value of these fruits.