Freshwater microalgae may offer promise for aqua feed: Canadian team

A group of Canadian researchers working with the National Research Council (NRC) of Canada have been assessing the nutritional value and digestibility of several strains of freshwater microalgae for their potential as novel feed ingredients.

The work comes as part of the expansion of initial research into strains isolated in Western Canada for biodiesel production, said lead researcher Dr. Sean Tibbetts, associate researcher officer in nutrition with NRC's Aquatic and Crop Resource Development portfolio. “With my background in applied animal and fish nutrition research, ​it was a perfect fit for my lab to look at the nutritional side of these species for their potential use in animal and aquaculture feed,”​ he added.

The strains were selected through the NRC Algal Carbon Conversion (ACC) Flagship Strain Selection program as possibilities for industrial deployment to sites close to CO2 emitters, he told FeedNavigator. They are predominately freshwater chlorophytic (green) microalgae strains that appear to have potential for mass cultivation growth in in large land-based enclosed photobioreactors (PBRs) inland situations.

The strains were originally picked for rapid growth, lipid production and potential to be used in industrial biomitigation systems, said Tibbetts. They can be farmed using industrial waste streams.

“The overall goal of the NRC ACC program is to work with industry to demonstrate the technological and economic feasibility of industrial production of microalgae in a northern country like Canada,”​ he said.

Ongoing research details​

Previously, several strains were screened for in vitro digestibility and biochemical composition in the lab, said Tibbetts. The most promising can then be assessed in animal trials.

“The biggest problem with many microalgae, and especially chlorophytic [strains], is that even though they’re little ‘lunchboxes’ packed full of a great complement of essential nutrients – the availability in the digestive tract of monogastric animal, including fish, can be limited because of their rigid cellulosic cell walls,” ​he said. “Just because the nutrients are there doesn’t mean that the animal will be able to digest and metabolically utilize them.”​

One promising strain from previous trials has been selected for an ongoing, in-vivo study using the microalgae as a feed ingredient for Atlantic salmon, said Tibbetts. The team, which includes collaborators from the Center for Aquaculture Technologies Canada and EWOS Canada, is set to have results by the end of the year.

In that study, the group is looking at digestibility of the microalgae when included in the diet at different levels and in different forms, he said. Some of the algae used are a whole-cell intact meal while others have had their cell walls broken open using an industrially scalable, chemical-free form of downstream processing.

“In addition to finding out the effect on digestibility of ruptured and non-ruptured [microalgae], we will be able to determine what is the maximum dietary inclusion level that we can push these ingredients based on their digestibility,” ​he said. "It doesn’t make sense to continue with further feedings studies focused on growth performance, nutrient utilization efficiency, fish health and product composition if you haven’t addressed the first bottleneck to efficient nutrient utilization, which is digestibility.” ​

The information gained will give researchers a starting point for future research examining growth or health benefits from use of the feed material, he said.

In past research studies looking at the in-vitro digestibility of the microalgae strains with ruminant animals in collaboration with Dalhousie University and Agriculture and Agri-Food Canada, the group had a surprising result, he said.

A link between the inclusion of microalgae in cattle diets and a reduction in the methane produced by the cow has been noted by others, he said. But, it was thought that the long-chain polyunsaturated fatty acid content in the algae was the factor that dampened enteric methane production in the rumen.

“We expected the possibility to see a reduction in in-vitro methane production with the whole-cell algae that still had all its lipid in it, but we saw about a 50% methane reduction with the lipid-extracted microalgae,” ​he said. “If the lipid-extracted algae also significantly reduced digestibility, then this result might be easily explained, however, this was not the case and it even enhanced it in some cases. So there appears to be a methane abatement or anti-methanogenic effect here that doesn’t seem to be linked to the lipid content of the algae, but rather some other non-lipid components.”​

Exactly what caused the reduction seen in the trial is still unknown, and warrants additional investigation, he said.

Microalgae nutritional details​

“One of the things that we do when we look at potential novel sources of dietary ingredients, is to see where they might fit within the massive industrial commodity feed ingredient system, what would they compete against?” ​said Tibbets. “For these particular freshwater chlorophytic microalgae, they likely won’t directly compete against higher value products like fishmeal, but rather with other moderate protein alternatives derived from soy, canola, and corn protein.” ​

Unlike most marine algae, the freshwater chlorophytic strains being studied do not produce long-chain poly unsaturated fatty acids that can provide DHA and EPA to the diet, he said. They do contain amounts of the fatty acid alpha-linolenic acid, which provides a benefit beyond similar products used in animal feed like canola, soy, corn and wheat.

“The key is the essential amino acid profile, and that’s really exciting about these microalgae,”​ he said.

Depending on cultivation and when in the growth curve the microalgae are harvested – either during the exponential growth phase or the stationary phase – influences the levels of protein or hydrocarbons in the biomass, he said. But, the amino acid profile of the protein is attractive and consistent regardless of when it is harvested.

“When you compare microalgal protein to what’s on the market today, like soy, canola, corn and wheat protein, they are very good protein sources, [but] each tends to be deficient in specific essential amino acids, often lysine or methionine, so diets containing these ingredients typically need to be supplemented with purified amino acids, which is costly,” ​said Tibbetts.

Source: Algal Research​

Title: Biochemical characterization of microalgal biomass from freshwater species isolated in Alberta, Canada for animal feed applications​

DOI: doi:10.1016/j.algal.2014.11.011​

Authors: Sean M. Tibbetts, Crystal G. Whitney, Margaret J. MacPherson, Shabana Bhatti, Arjun H. Banskota, Roumiana Stefanova, Patrick J. McGinn