Abstract
The current work reports protein extraction from Spirulina platensis cyanobacterial biomass in order to simultaneously generate a potential co-product and a biofuel feedstock with reduced nitrogen content. S. platensis cells were subjected to cell disruption by high pressure homogenization and subsequent protein isolation by solubilisation at alkaline pH followed by precipitation at acidic pH. Response surface methodology (RSM) was used to optimize the process parameters - pH, extraction (solubilisation/precipitation) time and biomass concentration for obtaining maximum protein yield. The optimized process conditions were found to be pH 11.38, solubilisation time of 35 min and biomass concentration of 3.6 % (w/w) solids for the solubilisation step, and pH 4.01 and precipitation time of 60 min for the precipitation step. At the optimized conditions, a high protein yield of 60.7 % (w/w) was obtained. The protein isolate (co-product) had a higher protein content (80.6 % (w/w)), lower ash (1.9 % (w/w)) and mineral content and was enriched in essential amino acids, the nutritious γ-lenolenic acid and other high-value unsaturated fatty acids compared to the original biomass. The residual biomass obtained after protein extraction had lower nitrogen content and higher total non-protein content than the original biomass. The loss of about 50 % of the total lipids from this fraction did not impact its composition significantly owing to the low lipid content of S.platensis (8.03 %).
Highlights
The concept of biorefinery which proposes the integration of biofuel production processes with the extraction of co-product(s) such as proteins, pigments, and other high-value compounds is the path forward to improve the sustainability and economic feasibility of microalgal processing technologies
Protein Isolation Optimization Comparison of Different Pretreatments The results indicated that both high-pressure homogenization and ultrasonication resulted in a higher protein recovery in the supernatant compared to control (Figure S2 in Supplementary Material)
An α-hydroxy fatty acid (2-OH-C17:0) was detected in low levels in the protein isolate, but not in the residual biomass. These results clearly indicated that the protein isolate was enriched in polyunsaturated fatty acids while the residual biomass was enriched in saturated fatty acids
Summary
The concept of biorefinery which proposes the integration of biofuel production processes with the extraction of co-product(s) such as proteins, pigments, and other high-value compounds is the path forward to improve the sustainability and economic feasibility of microalgal processing technologies. The high protein (and nitrogen) content of algal feedstock is a major limitation to whole biomass to biofuel conversion processes such as hydrothermal liquefaction (HTL) and anaerobic digestion (AD). High-protein feedstocks result in high nitrogen content in the fuel produced from HTL and Optimization of protein extraction from Spirulina platensis ammonia toxicity in AD (Chen et al, 2008; López Barreiro et al, 2013). Nitrogen removal through protein extraction could potentially improve the feedstock composition for biofuel applications, while generating a useful co-product. Autoclaving was reported as an effective pretreatment to improve lipid extraction from microalgae (Prabakaran and Ravindran, 2011)
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