# Analysis of Seaweeds from South West England as a Biorefinery Feedstock
## 3 Results and Discussion
### Macronutrients--Carbohydrate and Protein  
Many types of useful carbohydrates such as laminarin, cellulose, starch, alginate, fucoidan, agar and carrageenan are found in seaweed. Agar, alginate and carrageenan are all used within the food industry as thickening agents within food [10] and are currently the most commercially significant products from seaweed after direct consumption as food [5]. Crucially, they are all produced in single product-based industrial processes, rather than in the biorefinery approach explored herein. Beyond the food ingredients industry, seaweed biomass with high carbohydrate content can be used for production of biofuels by anaerobic digestion and fermentation converting the sugars to ethanol or butanol. Seaweeds were initially assessed for the total carbohydrate content using a traditional phenol-sulphuric acid method in which polysaccharides are broken down to monosaccharides, dehydrated to furfurals and reacted with phenol to produce a measurable colour.  
Although the method detects almost all carbohydrates, the sensitivity varies depending on the type of sugars present [6] since the absorptivity of the different carbohydrates varies somewhat.  
Thus, unless a sample is known to contain only one carbohydrate, the results must be expressed arbitrarily in terms of one carbohydrate (in this instance we used glucose). We found this method to be very unreliable due to the variations in carbohydrate structures found in seaweeds and, as such, we instead estimated the total carbohydrate content based on the protein, lipid and ash values (Table 4).  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multicolumn{5}{c}{**Component \% of Dry Biomass**} \\ \hline  & **C** & **N** & **Protein** & **Ash** & **Carbohydrate** \\ \hline _U. lactuca_ & 30.8 & 1.09 & 5.45 & 22.7 & 71.8 \\ _S. aeruginosa_ & 20.3 & 1.06 & 8.01 & 46.4 & 45.6 \\ _P. rotunda_ & 31.0 & 3.53 & 17.65 & 29.6 & 52.7 \\ _L. articulata_ & 20.2 & 2.75 & 13.77 & 50.1 & 36.2 \\ _A. devoinensis_ & 31.8 & 1.87 & 9.37 & 24.2 & 66.4 \\ _P. palmata_ & 38.3 & 2.5 & 12.50 & 21.4 & 66.1 \\ _R. conferoides_ & 26.2 & 2.51 & 12.54 & 45.8 & 41.6 \\ _D. carnosa_ & 36.3 & 2.91 & 14.55 & 18.2 & 67.2 \\ _S. muticum_ & 34.5 & 1.39 & 4.64 & 26.4 & 69.0 \\ _H. elongata_ & 35.8 & 1.13 & 5.65 & 24.6 & 69.7 \\ _F. serratus_ & 39.3 & 1.8 & 8.98 & 21.5 & 69.5 \\ _L. digitata_ & 34.2 & 1.37 & 6.87 & 27.8 & 65.3 \\ _S. latissima_ & 36.2 & 1.21 & 6.03 & 20.9 & 73.0 \\ _C. peregrina_ & 13.8 & 0.58 & 2.48 & 85.3 & 12.2 \\ _P. latifolia_ & 28.8 & 1.15 & 5.73 & 43.8 & 50.5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Carbon (C), nitrogen (N), protein, carbohydrate and ash content of seaweeds from South West England.  
Nine of the seaweeds tested had an estimated carbohydrate content of over 60%, with the highest observed in _Saccharina latissima_ (73.0%).  
_Colomenia peregrina_ had the highest ash content and was particularly mineral rich resulting in a much lower carbohydrate content (estimated at 12.2%).  
The CHN analysis was used to calculate the protein content of the seaweeds. As well as protein being an important part of a healthy diet, nitrogen is an important component needed for plant growth; seaweeds with a high nitrogen content work well as sustainable sources of nitrogen for fertilisers [32]. With the exception of _Fucus serratus_, the highest concentrations of nitrogen/protein were observed in the Rhodophyta ranging from 9.37-17.65% of the total dry biomass. All of the seaweeds, however, have a nitrogen content that can make them suitable as a feed stock for the sustainable production of agricultural fertilisers.