Variation in biochemical constituents and master elements in common seaweeds from Alexandria Coast, Egypt, with special reference to their antioxidant activity and potential food uses: prospective equations Mona M. Ismail & Gehan M. El Zokm & Abeer A. M. El-Sayed Received: 7 April 2017 /Accepted: 15 November 2017 # Springer International Publishing AG, part of Springer Nature 2017 Abstract Biochemical constituents and master elements (Pb, Cr, Cd, Fe, Cu, Zn, Hg, B, Al, SO 4 2− , Na, K, Li, Ca, Mg, and F) were investigated in six different seaweed species from Abu Qir Bay in the Egyptian Mediterranean Sea coast. The moisture level ranged from 30.26% in Corallina mediterranea to 77.57% in Padina boryana. On dry weight basis, the ash contents varied from 25.53% in Jania rubens to 88.84% in Sargassum wightii . The protein contents fluctuated from 8.26% in S. wightii to 28.01% in J. rubens. Enteromorpha linza showed the highest lipids (4.66%) and carbohydrate contents (78.95 %), whereas C. mediterranea had the lowest lipid (0.5%), and carbohydrate contents (38.12%). Chlorophylls and carotenoid contents varied among the species. Total antioxidant capacity of the tested green seaweeds had the highest activities followed by brown and red seaweeds which had a similar trend of phenol and tannins contents. High reducing power was observed in all tested seaweeds extract except Ulva lactuca. Brown species had the highest amount of elements followed by red and green seaweeds. Notably, SO 4 2− recorded the highest level in the tested green species (108.05 mg/g dry weight (DW)). The Ca/Mg and K/Na ratios reflected highly significant differ- ence between seaweed species. This study keeps an eye on 29 parameters and by applying stepwise multiple regres- sion analysis, prospective equations have been set to describe the interactions between these parameters inside seaweeds. Accordingly, the tested seaweeds can be recom- mended as a source of healthy food with suitable ion quotient and estimated daily intake values. Keywords Seaweeds . Biochemical . Antioxidant . Master elements . Ion quotient . Estimated daily intake Introduction Seaweeds are marine multicellular macroscopic algae and renewable resources. They are defined as non-vascular plants which form primary producers in the ocean and follow the kingdom BProtista^ not BPlanta.^ They are classified into three broad groups based on pigmentation, anatomy, morphology, and biochemical composition as brown (Phaeophyta), red (Rhodophyta), and green sea- weeds (Chlorophyta) (Manivannan et al. 2009). Seaweeds have a wide diversity in biochemical com- position which is related to physiological and biochemi- cal characteristics (Holdt and Kraan 2011). There are more than 15,000 primary and secondary metabolites that were produced during different metabolic pathways of seaweeds with various applications (Grosso et al. 2011). Generally, the nutritional properties of seaweeds are usually determined according to biochemical composi- tion such as proteins, carbohydrates, lipids, and ash content (McDermid and Stuercke 2003). The seaweed proteins are highly variable (10–47% DW) with high proportions of essential amino acids, about 50% carbo- hydrates, and 1–3% lipids (García-Casal et al. 2007). Environ Monit Assess (2017) 189:648 https://doi.org/10.1007/s10661-017-6366-8 M. M. Ismail (*) : G. M. El Zokm : A. A. M. El-Sayed Marine Environmental Division, National Institute of Oceanography and Fisheries, Alexandria 21556, Egypt e-mail: mona_es5@yahoo.com e-mail: mm.esmail@niof.sci.eg