Natural products as a powerful source of antioxidants

Synthetic antioxidants could be replaced by the valid bio-based alternatives. These renewable and low cost resources are available and offers a market opportunity for a green supply of raw materials for different industrial and health products. The aim of the present PhD project was to analyse the antioxidant activity of extracts obtained from different natural sources or microorganisms, in order to study their beneficial effects against oxidative stress injury and to characterize their chemical composition to obtain molecules to be used in food or cosmetic industry. Therefore, fruits and vegetables were considered a good starting point, as it is widely known that they are rich in molecules with antioxidant activity. As a first goal, the methanol extracts from two tomato varieties and from açai berries were analysed. These products are among the most consumed in Mediterranean and Brazilian diet, respectively. The beneficial effects of the extracts were demonstrated on a cell-based model in which oxidative stress was induced and the molecules responsible for the antioxidant activity were determined. Thereafter, to avoid the toxicity and high costs of solvent extractions, the attention was focused on extracts obtained without the need of solvents. In particular, the antioxidant activity of a water extract from the cladodes of Opuntia ficus-indica was analysed. The whole extract, as well as its active molecules, showed a good ability to protect human keratinocytes from UVA induced oxidative stress. Plants and their fruits are not the only source of antioxidants, as these are metabolites produced by microbes. From a biotechnological and economical point of view, the production of antioxidants by microorganisms is very convenient and provides an alternative to chemical synthesis. For this reason, two bacterial strains were used in different ways. In the first case, a lipophilic extract from Novosphingobium sp. PP1Y was obtained and tested, as the characterization of this recently isolated microorganism showed the presence of a great abundance of genes encoding for carotenoids. PP1Y extract was able to counteract oxidative stress in an in vitro system on cells as well as in an in vivo system on C. elegans. In the second case, the whole spore from the bacterium Bacillus subtilis was used as antioxidant. The results showed that incubation with spores induced the activation in the treated cells of Nrf-2 pathway, which induced the transcription of anti-stress response genes. Finally, a waste fraction from microalgae Chlorella sorokiniana Shihiraet Krauss was tested for its antioxidant activity. This fraction was discarded after starch purification (PhD project of Dr. Imma Gifuni). Therefore, in order to minimize the generation of waste, the recovery of high-value products was attempted. It was demonstrated that the cascade approach was a good strategy to produce starch and active antioxidants. In conclusion, in the present PhD thesis, different antioxidants from natural sources have been isolated and tested, and extracts from these sources showed an antioxidant power similar or higher than the isolated molecules. This opens the way to the use of the whole extract in food or cosmetic industries, avoiding the high costs for the purification of single compounds, in accordance with the increasing demand of natural products endowed with pro-healthy effects.