Abstract
Subcritical water extraction (SWE) technology has been used for the extraction of active compounds from different biomass materials with low process cost, mild operating conditions, short process times, and environmental sustainability. With the limited application of the technology to microalgal biomass, this work investigates parametrically the potential of subcritical water for high-yield extraction of biochemicals such as carbohydrates and proteins from microalgal biomass. The SWE process was optimized using central composite design (CCD) under varying process conditions of temperature (180–374°C), extraction time (1–20 min), biomass particulate size (38–250 μm), and microalgal biomass loading (5–40 wt.%). Chlorella vulgaris used in this study shows high volatile matter (83.5 wt.%) and carbon content (47.11 wt.%), giving advantage as a feedstock for biofuel production. The results showed maximum total carbohydrate content and protein yields of 14.2 g/100 g and 31.2 g/100 g, respectively, achieved under the process conditions of 277°C, 5% of microalgal biomass loading, and 5 min extraction time. Statistical analysis revealed that, of all the parameters investigated, temperature is the most critical during SWE of microalgal biomass for protein and carbohydrate production.
Highlights
Global energy demands continue to increase at a current annual consumption rate of about 500 Quadrillion Btu (QBtu)
Microalgal biomass is heavily researched as feedstock for the production of different types of biofuels as a result of its fast growth rate, nonedibility, and the capacity to accumulate high concentrations of biochemical compounds such as lipids and carbohydrates for biofuel synthesis [2]
The high volatile matter percentage of microalgal biomass is advantageous for biofuel production [24]
Summary
Global energy demands continue to increase at a current annual consumption rate of about 500 Quadrillion Btu (QBtu). Microalgal biomass is heavily researched as feedstock for the production of different types of biofuels as a result of its fast growth rate, nonedibility, and the capacity to accumulate high concentrations of biochemical compounds such as lipids and carbohydrates for biofuel synthesis [2] Microalgal primary metabolites, such as proteins, fatty acids, and carbohydrates, are produced intracellularly and entrapped within the cells; an effective extraction technology is required to release these biochemical products [3]. Andrich et al [11] compared the polyunsaturated fatty acids (PUFA) extraction yields of SFE and SE using Spirulina platensis and reported that SFE demonstrated a higher PUFA yield and fatty acid composition compared to SE Another promising technology for lipid extraction from microalgal biomass is via ultrasound. With increasing research interests in microalgal biotechnology through the development of value added products, along with the limited application of SWE on microalgal biomass, this work seeks to investigate the application of SWE for optimal extraction of biochemical compounds from Chlorella vulgaris
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