Effects of extraction method on the prebiotic potential of Ascophylum nodosum extracts

Seaweed-derived bioactive compounds exhibit various beneficial activities in humans and animals. A factor influencing their concentrations, and subsequent bioactivity, is the extraction method. Our aim was to evaluate the in vitro prebiotic potential of three differently-extracted Ascophylum nodosum samples. The samples were produced using either solid-liquid extraction with water (AN-W), or ethanol (AN-EtOH) as solvent or high pressure-assisted extraction with water as solvent (AN-HPW). All extracts were two-fold diluted from 2 mg/ml to 0.25 mg/ml. Lactobacillus plantarum (LP), L. reuteri (LR) and Bifidobacterium thermophilum (BT) were used at 106 -107 colony-forming unit(CFU)/ml. Each concentration of each extract and controls (0 mg/ml) were incubated for 18 h at 37 °C aerobically or anaerobically (BT). Final bacterial concentrations were determined by spread plating. All experiments were carried out in triplicate with technical replicates. All data were logarithmically transformed and analysed using PROC GLM (SAS 9.4). AN-HPW increased BT (≤0.9 LogCFU/ml, P<0.05) at all concentrations and LR and LP (0.2 LogCFU/ml, P<0.05) at 2 mg/ml and 1mg/ml, respectively. AN-W increased BT (≤0.6 LogCFU/ml, P<0.05) at 1-2mg/ml, but decreased both lactobacilli; LP ≤0.7 LogCFU/ml and LR ≤5.4 LogCFU/ml at all concentrations (P<0.05). AN-EtOH increased LP (≤0.7 LogCFU/ml, P<0.05), but reduced LR (≤5.7 LogCFU/ml, P<0.05) at all concentrations and BT (≤4 LogCFU/ml, P<0.05) at 1-2 mg/ml. In conclusion, the extraction method influenced the prebiotic potential of the A. nodosum extracts in vitro with AN-HPW being the most promising.