Characterization of Algae Dietary Supplements Using Antioxidative Potential, Elemental Composition, and Stable Isotopes Approach

Jan Kejžar; Marta Jagodic Hudobivnik; Marijan Nečemer; Nives Ogrinc; Jasmina Masten Rutar; Nataša Poklar Ulrih

doi:10.3389/fnut.2020.618503

Characterization of Algae Dietary Supplements Using Antioxidative Potential, Elemental Composition, and Stable Isotopes Approach

Front Nutr. 2021 Feb 5:7:618503. doi: 10.3389/fnut.2020.618503. eCollection 2020.

Authors

Jan Kejžar¹, Marta Jagodic Hudobivnik², Marijan Nečemer³, Nives Ogrinc², Jasmina Masten Rutar², Nataša Poklar Ulrih¹

Affiliations

¹ Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
² Department of Environmental Sciences, Jožef Stefan Institute, Ljubljana, Slovenia.
³ Department of Low and Medium Energy Physics, Jožef Stefan Institute, Ljubljana, Slovenia.

Abstract

Dietary supplements based on algae, known for their nutritional value and bioactive properties, are popular products among consumers today. While commercial algal products are regarded safe by numerous studies, information about the production and origin of such products is scarce. In addition, dietary supplements are not as strictly regulated as food and medicinal drugs. We characterized different algal products (kelps: Laminariales, Spirulina spp., Chlorella spp., and Aphanizomenon flos-aquae), obtained on Slovenian market, based on their elemental composition (X-ray fluorescence, inductively coupled plasma-mass spectrometry), antioxidative potential [DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, total phenolic content], and stable isotope values [carbon (C), nitrogen (N), and sulfur (S); elemental analyzer isotope ratio mass spectrometry (EA-IRMS) method]. Antioxidative potential is consistent among products of the same type, with A. flos-aquae samples having 4.4 times higher antioxidative potential compared to Chlorella spp. and 2.7 times higher compared to Spirulina spp. Levels of toxic trace elements (arsenic, cadmium, mercury, and lead) are below the maximum allowed values and as such do not pose risk to consumers' health. Samples of Spirulina spp. have relatively high δ¹⁵N (7.4 ‰ ± 4.4‰) values, which indicate use of organic nitrogen sources in certain samples. Likewise, different elemental composition and isotopic ratios of stable elements (C, N, and S) for the samples with Spirulina spp. or Chlorella spp. are the consequence of using different nutrient sources and algae-growing techniques. Statistical analysis (principal component analysis) has confirmed that all tested A. flos-aquae samples originate from the same source, supposedly Klamath Lake (Oregon, USA). Hawaiian Spirulina pacifica can also be differentiated from all the other samples because of its characteristically high metal content (iron, manganese, zinc, cobalt, nickel, vanadium). Chlorella spp. and Spirulina spp. require further analyses with larger number of samples, as differentiation is not possible based on results of this study.

Keywords: Aphanizomenon flos-aquae; Chlorella; Spirulina; algae; antioxidative potential; elemental composition; stable isotopes; toxic elements.