Seaweed may offer promise as novel protein source

In the first of our two articles on his work into protein alternatives, Marinus van Krimpen, who is an animal nutrition researcher at Wageningen Livestock Research, tell us about investigations into seaweed as a partial replacement for soy in pig and poultry diets. 

“Seaweed as a new protein source is very topical subject at the moment in the Netherlands, it is attracting a lot of attention here, with the Dutch government allocating €5m worth of funds to a project that is looking to exploit the nutritional value of seaweed for both feed and food sectors,”​ he told us. 

The Dutch government is willing to stimulate seaweed cultivation, which, currently, is limited, he said.

The authorities have estimated there is scope for up to 400 square km of seaweed fields off the Dutch north coast by 2050. They are looking at combining such cultivation with offshore wind energy generation to make it more economical, but some commentators have questioned​​ the likely profitability of such ventures.  

Wageningen researchers are heavily involved in this seaweed nutrition initiative, which officially got underway last week.

Inherent challenges​

“On the livestock side, we want to discover how we can select and cultivate seaweed species with a high protein content. We will see if the addition of higher amounts of nitrogen in the water, for example, will increase the protein levels,”​ said van Krimpen.

Seasonal fluctuations can affect seaweed growth, and determining the optimal time to harvest is critical. “If you harvest too early, you can get higher fiber than protein content.”​

However, there are a lot of things the team still has to determine, he said, in particular how to extract the protein, to separate it from the other nutrients. The polysaccharide cell wall makes ionic interactions with the attached proteins, making efficient extraction difficult.

The team is also conscious of the restrictions involved in using seaweed in animal nutrition given its high quantity of sodium and potassium. Heavy metals have to be taken into account as well. 

“We will run digestibility trials, we are focusing our efforts on piglets and poultry,”​ he said. 

Economic value ​

He argues that while the economic value of seaweed is low, greater exploitation of its components that are known to stimulate gut health and immunity could change its value proposition.

In a 2016 paper​​, Van den Burg et al (including van Krimpen), estimated the cost benefit of using seaweed to partially replace other protein raw materials in animal feed, citing the total amount of soy used in the Netherlands for feed in 2010 to 2011 as 2,353,000 metric tons.

“We calculated the economic value of several ‘intact’ (not refined) seaweed species by use of a feed optimization program. This program allows the calculation of the economic value for feed applications. Based on the characterization of the seaweeds, the program analyses which current ingredients can be removed from the feed-mix and calculates total value of​ those ingredients.​ ​

“The expressed value of seaweeds thus represents the avoided costs for other feed ingredients. The economic value was expressed as the price (metric ton of dry product, 94% DM) which resulted in a 5% addition of seaweed into a grower pig diet. Based on these assumptions, the economic value was US $61.60/metric ton DM for Saccharina latissima, US$168.22/metric ton DM for Palmaria palmate and US$67.29/metric ton DM for Ulva lactuca.”​ ​

Promising protein source​

In another 2016 study​​, Bikker et al concluded that seaweed may be a valuable source of protein for animal feed.

The authors documented a protein extraction method for the green seaweed Ulva lactuca​. 

They described how the sugars in the biomass were solubilized by hot water treatment followed by enzymatic hydrolysis and centrifugation resulting in a sugar-rich hydrolysate containing glucose, rhamnose and xylose, and a protein-enriched (343 g kg−1 in DM) extracted fraction.

“This extracted fraction was characterized for use in animal feed, as compared to U. lactuca biomass. Based on the content of essential amino acids and the in vitro N (85 %) and organic matter (90 %) digestibility, the extracted fraction seems a promising protein source in diets for monogastric animals with improved characteristics as compared to the intact U. lactuca,”​ they said.