Nutritional quality of some wild and cultivated seaweeds: Nutrient composition, total phenolic content and in vitro digestibility Sean M. Tibbetts 1 & Joyce E. Milley 1 & Santosh P. Lall 1 Received: 8 December 2015 /Accepted: 24 April 2016 # Her Majesty the Queen in Right of Canada 2016 Abstract Nutrient composition, total phenolic content (TPC) and in vitro protein digestibility (IVPD) of wild and cultivated seaweeds were determined. Seaweeds had a high range of protein (7–31 % of dry weight (DW)), lipid (3–13 % DW), carbohydrate (32–60 % DW), ash (9–45 % DW) and energy (10–18 MJ kg -1 DW). Seaweeds had favourable amino acid (AA) profiles with moderate (0.77–0.86) to high (0.93–1.07) essential AA indices. Major minerals and trace elements in- cluded calcium (0.1–1.1 % DW), magnesium (0.2–0.8 % DW), phosphorous (0.1–0.6 % DW), potassium (2.1–4.6 % DW), sodium (1.1–3.9 % DW), sulphur (0.4–6.5 % DW), copper (1–21 mg kg -1 DW), iron (26–945 mg kg -1 DW), manganese (3–191 mg kg -1 DW) and zinc (28–74 mg kg -1 DW). Red seaweeds contained low TPC (4–5 mg gallic acid equivalents (GAE) g -1 DW) whereas most brown seaweeds contained moderate (11–18 mg GAE g -1 DW) to high levels (47–59 mg GAE g -1 DW). IVPD was mid-range (82–87 %) for Saccharina latissima, Palmaria palmata (W), Palmaria palmata (M-S), Chondrus crispus, Meristotheca papulosa and Sarcodiotheca gaudichaudii and lower (79 %) for Ascophyllum nodosum, Fucus vesiculosus and Alaria esculenta. Despite relatively good AA profiles, estimated di- gestible protein (DP) levels for seaweeds were generally low (<15 % DW) with exception of moderate levels (16–24 % DW) for P. palmata (W), P. palmata (M-S) and S. gaudichaudii. A highly significant inverse correlation (r = -0.81, R 2 = 0.83, P < 0.001) was found between TPC and IVPD of seaweeds (IVPD = 89.198 × TPC -0.035 ). The fol- lowing species-specific nitrogen-to-protein conversion factors were determined: P. palmata (W), 6.28; P. palmata (M-S), 4.54; C. crispus, 4.85; S. gaudichaudii, 5.55. Keywords Seaweeds . Composition . Amino acids . Minerals . In vitro digestibility . Total phenolic content Introduction Seaweeds are potential sources of dietary nutrients and bioactive compounds (MacArtain et al. 2007; Harnedy and FitzGerald 2011; Holdt and Kraan 2011). They are being harvested or cul- tured at industrial scale for direct food consumption, production of functional polysaccharides for the food, beverage, pharmaceu- tical, materials manufacturing and cosmetics industries, agricul- tural fertilizers and fine chemicals, and new uses are beginning to emerge (Venugopal 2009; Holdt and Kraan 2011; Rebours et al. 2014; Hafting et al. 2015). Current global production of sea- weeds exceeds 24 million tonnes worth an estimated US$6.4 billion, of which >94 % is farmed (FAO 2014; Hafting et al. 2015). Most (99 %) of this production is dominated by a rela- tively small number of species, namely Japanese kelps (Saccharina and Laminaria spp.), Eucheuma spp., Gracilaria spp., nori (Pyropia and Porphyra spp.) and wakame (Undaria pinnatifida). Although consumption of seaweeds is most often associated with their trace minerals and prebiotic functions linked to polysaccharides (Sweeney et al. 2011; Kadam et al. 2015), it is possible that some species, under certain conditions, may also possess significant levels of other essential digestible nutrients and calories (MacArtain et al. 2007; Harnedy and FitzGerald 2011). Seaweeds contain high levels of fermentable carbohy- drates (e.g., mannitol and laminarin) and offer good potential as a next-generation feedstock for bioethanol production (Roesijadi * Sean M. Tibbetts Sean.Tibbetts@nrc-cnrc.gc.ca 1 National Research Council of Canada, Aquatic and Crop Resource Development, 1411 Oxford Street, Halifax, Nova Scotia B3H 3Z1, Canada J Appl Phycol DOI 10.1007/s10811-016-0863-y