| dc.description.abstract | Industrial exploitation of cultivated microalgae as protein feedstock has gained interest in recent years as a promising driver for the Norwegian bioeconomy. However, robust microalgal cell wall structures may lead to inefficient, unsafe and otherwise unsustainable protein extraction. Thus, cell wall disruption is a critical step governing protein recovery and functionality. Conventional cell wall disruption methods pose environmental/health risks and may result in protein denaturation, limited extraction yield and high energy consumption. Therefore, innovative, sustainable, safe & cost-effective disruption strategies that enhance protein recovery and functionality, while preventing excessive downstream purification and quality loss, are desirable.
The bioactivity and functionality of Chlorella sorokiniana were assessed by measuring the antioxidant activity and anti-glycation properties. The experimental methods included superoxide dismutase (SOD) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays. Additionally, angiotensin-converting enzyme (ACE) was performed to assess the function of inhibition blood pressure elevation. In addition, albumin, elastin, and collagen glycation assays were conducted.
In this MSc thesis, the potential of innovative strategies for cell wall disruption of C. sorokiniana was studied towards enhanced protein recovery and functionality. Particularly, the effect of plasma activated water (PAW) at different pH (acidic, PAW / basic, PAW-pH12) and temperature (40, 55 and 65 °C) and with different thermal history (autoclaved, PAWau) was assessed alone or in combination with sonication (US) (68 kHz at 500 W or 68 + 170 kHz at 1000 W; 65 °C, 60 min) or high-pressure processing (HPP) (600 MPa, 15 min, room temperature). The protein content after cell wall disruption and protein extraction (tap water at pH 12 and 15 °C for 60 min) was measured in supernatants and pellets using Lowry-based assays.
The assays SOD, ACE, DPPH resulted in 80%, approximately 100%, and 20% inhibition ratio, respectively. Thus, the results indicate that C. sorokiniana exhibits high antioxidant activity, particularly in relation to SOD assay, and ACE assay exhibited high ability to inhibit blood pressure elevation. The albumin, elastin, and collagen glycation assays did not yield any statistically significant results, indicating that no levels of glycation inhibition were detected in the C. sorokiniana sample.
The cell wall disruption with PAW at pH 12 and 65 °C (Sup1 and Sup2) resulted in a significantly higher protein concentration as compared to other solvents, temperatures, and untreated sample (UN-1). The pH of the PAW and the autoclaving resulted in no significant change in the pH. Furthermore, the highest protein concentration among the Sup1 was observed at 65 °C, while in the case of Sup2, the highest protein concentration, on average, was observed at 55 °C. Cell wall disruption (PAW or PAW-pH12) in combination with US or HPP did not result in a significantly higher protein yield as compared to the respective non-sonicated or non-pressurised treatments.
This study has demonstrated the potential of PAW (acidic (2.3) and basic (12.0) pH) combined with mild temperature to effectively disrupt the cell wall of C. sorokiniana towards enhanced protein recovery. Future work is needed to fully explore the potential of PAW, both independently and in combination with other cell wall disruption methods, in order to enhance protein bioactivity and functionality. | |