Effect of upstream processing on nutritional value of post-extraction algal residue for beef cattle

Post-extraction algal residue (PEAR), a co-product from extracting algal oil for conversion to biofuel, has the potential to be marketed as livestock feed. However, the algal biofuel industry has not yet adopted standardized processing practices, which potentially causes nutrient fluctuations in the coproduct, PEAR. Our objective was to determine the effect of various upstream processing methods on the nutritional value of PEAR for beef cattle production. To meet this objective, a batch of Nannochloris oculata was subjected to different methods of harvesting, drying, preparation for oil extraction, and oil extraction, yielding ten unique samples for nutritional analysis. Crude protein and lipid content of samples ranged 19–36 and 2–10 per cent, respectively, demonstrating wide macronutrient variation in accordance with different upstream processing methods. All PEAR contained S concentrations (>0.81%) which may limit the inclusion rate in beef cattle rations. For harvesting methods, flocculation increased Fe and Al >289% relative to centrifuged PEAR. Flocculated and centrifuged PEAR had Ca: P of 18: 1 and 9: 1, respectively, which would present additional formulation challenges. Flocculation decreased S and Na concentrations by 37 and 77%, respectively, relative to centrifuged PEAR; however, both minerals remained present in quantities, which would impact the their level of inclusion in rations. Reducing mineral and increasing protein concentrations in PEAR will increase its value and utilization in beef cattle production, ultimately enhancing the success and viability of algal biofuel production. Mineral imbalances in PEAR can be partially attributed to upstream processing methods that are avoidable or manageable, underlining the need for upstream algal biofuel processers to be aware of the downstream (co-product) impacts of their practices.