The protein content of seaweeds: a universal nitrogen-to-protein conversion factor of five

Abstract

A global drive to source additional and sustainable biomass for the production of protein has resulted in a renewed interest in the protein content of seaweeds. However, to determine accurately the potential of seaweeds as a source of protein requires reliable quantitative methods. This article systematically analysed the literature to assess the approaches and methods of protein determination and to provide an evidence-based conversion factor for nitrogen to protein that is specific to seaweeds. Almost 95 % of studies on seaweeds determined protein either by direct extraction procedures (42 % of all studies) or by applying an indirect nitrogen-to-protein conversion factor of 6.25 (52 % of all studies), with the latter as the most widely used method in the last 6 years. Meta-analysis of the true protein content, defined as the sum of the proteomic amino acids, demonstrated that direct extraction procedures underestimated protein content by 33 %, while the most commonly used indirect nitrogen-to-protein conversion factor of 6.25 over-estimated protein content by 43 %. We therefore determined whether a single nitrogen-to-protein conversion factor could be used for seaweeds and evaluated how robust this would be by analysing the variation in this factor for 103 species across 44 studies that span three phyla, multiple geographic regions and a range of nitrogen contents. An overall median nitrogen-to-protein conversion factor of 4.97 was established and an overall mean nitrogen-to-protein conversion factor of 4.76. We propose that the overall median value of 5 be used as the most accurate universal seaweed nitrogen-to-protein (SNP) conversion factor.

Seaweed as a protein source for mono-gastric livestock

“…We acknowledge this contradicts the accepted paradigm that many seaweeds have a high concentration of protein with high proportions of essential amino acids (Fleurence, 1999;Fleurence et al, 2012;Garcia-Vaquero & Hayes, 2015). However, protein concentration calculated for seaweeds are often overestimated by the use of the animal-based 6.25 N-toprotein conversion factor, and more accurately should be determined using a N-to-protein factor of 5.0 (Angell, Mata, de Nys, & Paul, 2016). In many instances the low concentration of protein is rarely identified when presenting amino acid profiles as a ratio to protein or TAA (Table 1).…”

Golden Tides: Problem or Golden Opportunity? The Valorisation of Sargassum from Beach Inundations

“…Brown seaweeds typically contain 3%-16% protein depending on the species and season [41,42]. The protein content of a biomass can be estimated from the nitrogen present by multiplying the N content by a factor (N factor).The N factor is based on the proteins present in the biomass.…”

“…Factors for common foods vary between 5.2 and 6.3 [40] and for algae 3.75-6.4 [44,48]. Overall N factors have been suggested for general use with algae of 5 [41], 4.78 [49], and 4.44 [44], and an average N factor for brown algae of 4.56 has been suggested in an extensive recent study by Angel et al [41]. Using this latest N factor of 4.56, a protein content of 18% can be calculated for S. natans.…”

Digestibility and pricing of Chlorella sorokiniana meal for use in tilapia feeds

“…range between 5.02 for those harvested in the log phase of growth (highest protein concentration) and 4.84 for those harvested in the phase of logarithmic growth decline -death phase (higher concentration of lipids) (Templeton and Laurens, 2015; Angell et al, 2016). When using the conversion factor of 5.00, suggested by Angell et al (2016), CP contents of the CSM drop from 69 % to 55 %, dry matter basis, yet a high protein content level. However, given that establishing a correlation between the CP levels of feed with protein levels of feces samples is rather challenging, values determined by the Kjeldahl method were herein conserved and used.…”