Studio dell'impatto della digestione sulle proprietà nutraceutiche di estratti di alga ricchi in polisaccaridi

Nowadays algae are going to be more and more a foodstuff of value because of their properties and their content in terms of proteins, fatty acids and sugars useful for human health.In the present study, extracts from Ascophyllum nodosum, a brown alga found in abundance off the West coast of Ireland coast were investigated in more detail for their potential prebiotic/growth reducing effects against lactic acid bacteria (LAB) and the opportunistic pathogens, Escherichia coli and Pseudomonas aeruginosa, and the possible effects of the digestive process on biological activity.A solution of the algal extract was subjected to a simulated, in vitro digestion experiment, using sequential treatment with specific enzymes at specific pH conditions in order to simulate the likely exposure to, and effects of, the human digestive process. The extract was first characterized, using different bioassays to quantify total sugars, reducing sugars and soluble phenolics present. The effects of the simulated digestion process on levels of each of these biomolecules types was evaluated using (bio)chemical assays. The results showed that later steps in the simulated digestion study appeared to modify or release carbohydrate but decreased the levels of soluble phenolics in the extract. The effects of filter-sterilized samples of the untreated algal extract, and samples of the extract from each sequential step of the simulated digestion study on the growth of some intestinal bacterial species, specifically strains of Lactobacilli, Bifidobacteria, Pseudomonas, and Escherchia coli were investigated in a microplate bioassay to assess effects on microbial growth. Species and strain specific differences in growth were observed between species of lactic acid bacteria (LAB), and between the LAB and other bacteria. For some LAB (e.g. L. fermentum), growth was better on the untreated and treated algal extract than on GOS, FOS or the optimum growth medium (MRS). However, with two L. acidophilus strains, prebiotic effects were reduced after the 2nd treatment step. In contrast, the treated extracts, especially those from the later steps were prebiotic for Bifidobacterium angulatum. Levels of L-lactic acid and ethanol were quantified in culture supernatants at the final growth timepoint for the LAB tested. Both metabolites were detected and results showed that L. fermentum produced mainly L-lactic acid (lower levels of ethanol). The algal extract inhibited the growth of E. coli by approx. 50%; however, some of this potency was lost for extracts from the later steps of the simulated digestion. Inter-strain differences were noted between four strains of P. aeruginosa tested (PA). Limited inhibition of the growth of strain PA10548 was observed in the presence of the filter sterilized algal extract, while in contrast, growth of strain PA01 was checked. Samples from the later digestion steps were potently inhibitory towards strain PA CF9029, but relieved inhibition of PA01. Potent anti-microbial properties had been noted previously for sterile, non-filtered preparations of the untreated extract. In this study, the effect of filter-sterilization on the potential antimicrobial potency of extract, alginate and fucoidan fractions from a related in-house algal extract, and commercial alginate and fucoidan on the growth of two Pseudomonas strains was tested and showed for the first time that filter-sterilization, especially through a 0.2 μm filter markedly reduced the growth in