Nutritional quality of some wild and cultivated seaweeds: Nutrient composition, total phenolic content and in vitro digestibility

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 included 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 digestible 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 following 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.