Chemical Characterization of Mediterranean Macroalgae With a Focus on Antioxidant Molecules Through the Use of Liquid Chromatographic Techniques

Seaweeds represent an excellent vegetable protein resource capable of supporting the objectives of the sustainable blue economy. Today, attention toward algae is growing, due to their applications, both in biofuel production and as an alternative source of healthy food and nutraceuticals. The objective of this work was to valorize marine macroalgae coming from the Mediterranean area in order to be able to expand their potential use in the nutraceutical and pharmaceutical industries, maintaining the circularity of financial and biological resources. Micronutrients with higher antioxidant activity were determined in 10 samples, specifically four red algae, four brown algae, and two green algae. In particular, vitamin C was analyzed using a reversed phase (RP)-HPLC system coupled to photodiode array (PDA) detection, following extraction with an acidified aqueous solution. Vitamin E analysis was performed using a normal-phase HPLC system, following extraction with n-hexane and taking advantage of the high selectivity and sensitivity of fluorescence detector. Vitamin B12 was extracted with an acidified solution of methanol and water and analyzed by RP-HPLC system coupled to PDA and MS, the latter operated under selected ion monitoring mode to increase instrumental sensitivity and selectivity. Finally, carotenoids and pigments were extracted with an acetone/methanol solvent mixture and analyzed by RP-HPLC system coupled to PDA and MS to exploit the complementarity between MS and UV spectra for identification purposes. Overall, the validated HPLC methods confirmed the presence of vitamin E in all the samples analyzed, with highest levels obtained in two brown algae, namely, Undaria pinnatifida (1.54 ± 0.08 mg/kg) and Himanthalia elongata (0.93 ± 0.02 mg/kg), whereas vitamins C and B12 were detected only in two macroalgae species, including the widely consumed Porphyra sp., commercially known as Nori. Finally, carotenoids were mainly determined in the largely consumed U. pinnatifida sample, commercially known as Wakame.