Umami free amino acids in edible green, red, and brown seaweeds from the Portuguese seashore

The fifth basic taste—umami—is based on hydrophilic monosodium L-glutamate (L-Glu), and, to a smaller extent, on L-aspartate (L-Asp), which can be found in free form in seaweeds. The umami taste can be elicited by the synergistic effect of 5′-nucleotides, guanosine-5′-monophosphate (GMP), and inosine-5′-monophosphate (IMP). In this work, twelve edible seaweeds, two green (Codium tomentosum, Ulva rigida), six red (Chondracanthus teedei var. lusitanicus, Chondrus crispus, Gracilaria gracilis, Grateloupia turuturu, Nemalion helminthoides, Osmundea pinnatifida), and four brown (Bifurcaria bifurcata, Fucus vesiculosus, Saccorhiza polyschides, Undaria pinnatifida), from the Portuguese seashore, were selected for the analysis of umami amino acids and 5′-nucleotides. To determine the concentrations of umami free compounds, L-Glu, L-Asp, GMP, and IMP, the usual procedure for the preparation of seaweed’s broth was carried out, and the resulting extracts were analyzed by HPLC-DAD. The effect of the seaweed’s pretreatment, oven-dried and lyophilized, was also studied. Results showed that all seaweed species contained free amino acids in broad range, whereas umami 5′-nucleotides were not detected. The lyophilized C.crispus and G. gracilis contained the highest amounts of free L-Glu (627 ± 109 mg (100 g)⁻¹ and 398 ± 67 mg (100 g)⁻¹, respectively) and L-Asp (520 ± 102 mg (100 g)⁻¹ and 270 ± 10 mg (100 g)⁻¹, respectively). Two-factor PCA explained quantitatively (90%) the variance of seaweed species based on umami L-Glu content after different drying techniques applied. The results indicate that lyophilization constitutes a superior procedure for increasing the umami potential in most of the selected seaweeds.