Spirulina (Arthrospira platensis) protein-rich extract as a natural emulsifier for oil-in-water emulsions: optimization through a sequential experimental design strategy

Spirulina (Arthrospira platensis) proteins have been proven to present emulsifying properties. In this work, a Spirulina protein-rich extract obtained by ultrasound extraction (SpE) was tested to stabilize oil-in-water (O/W) emulsions. For this purpose, a sequential experimental design strategy (Fractional Factorial Design (FFD) 24–1 followed by a Central Composite Rotatable Design (CCRD) 22)) was applied. The effect of four variables, SpE concentration, O/W weight ratio, pH and storage time, on emulsions’ zeta potential and number-mean droplet diameter was considered for the FFD 24–1, indicating SpE concentration and storage time as the relevant variables for the CCRD 22. According to zeta potential and number-mean droplet diameter evaluation, for the studied SpE concentration range (2–5 wt%), quite stable emulsions were obtained along the tested 30-days period. Even so, for 5%, visual inspection revealed extract segregation after 20-days. The optimal solution comprised 4 wt% of SpE, for an O/W weight ratio of 30/70 and a pH of 7.0 (number-mean droplet diameter of 55.66 nm and zeta potential of -43.83 mV). Overall, SpE has proven to be an excellent emulsifier, offering the potential to substitute animal-based proteins and synthetic emulsifiers. In addition, no signs of contamination by microorganisms were observed, suggesting that the SpE may also act as an antimicrobial agent.CIMO (Centro de Investigação de Montanha, Portugal) (UIDB/00690/2020), LSRE-LCM (Laboratory of Separation and Reaction Engineering – Laboratory of Catalysis and Materials, Portugal) (UIDB/50020/2020; UIDP/50020/2020), and ALiCE (Associate Laboratory in Chemical Engineering, Portugal) (LA/P/0045/2020), funded by national funds through Fundação para Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior (FCT/MCTES) (PIDDAC). National funding by Fundação para a Ciência e a Tecnologia (FCT) (Portugal), P.I., through the institutional scientific employment program contract with A. Santamaria-Echart, L. Barros, and A. Fernandes. FCT for the PhD research grant of Samara Cristina da Silva (SFRH/BD/148281/2019) and Giovana Colucci (2021. 05215. BD).info:eu-repo/semantics/publishedVersio

Spirulina (Artrhospira platensis) protein extract: techno-functional properties and potential application as a natural emulsifier

Microalgae are valuable sources of proteins (20-70%) and have emerged as great alternatives to animal-based proteins (e.g., whey protein, egg yolk)1. This work aimed to obtain a microalga protein extract (SpE) from Artrhospira platensis (Spirulina) and evaluate its techno-functional properties and emulsion formation capability. The SpE was obtained by ultrasound and conventional mechanical stirring under an alkaline medium (pH 9.0) followed by acid precipitation (pH 3.0)2. In addition, the SpE techno-functional (protein solubility; oil and water absorption capacities) and structural properties (FTIR analysis) were investigated. Moreover, an emulsion (oil/water ratio (30/70); pH 7.0; SpE concentration (3.5%)) was prepared according to two sequential steps: i) high-shear homogenization (UltraTurrax; 11,000 rpm; 3 min) and ii) high-pressure homogenization (100MPa; 6 cycles)3. Then, it was analysed by optical microscopy, zeta potential and particle size. The SpE (66.6%±0.31 protein) presented the lowest solubility at pH 3.0 and the highest at pH 8.0. The protein extract showed higher absorption capacity in oil (21.7±0.10 g oil/ g SPE) than in water (10.3±0.50 g water/ g SPE). From the FTIR analysis (Figure 1a), the SpE showed two peaks at 1635 cm-1 and 1535 cm-1 (red circle in Figure 1a) attributed to the presence of characteristic protein groups, amide I and amide II, respectively. The oil-in-water emulsion (ESp) presented a light blue-green colour due to the presence of SpE (Figure 1a) and remained stable for 30 days (Figure 1b). The SpE presented a zeta potential of -47.20 mV and a particle size of 330 nm (D50, volume distribution) on the 30th storage day. Small and spherical droplets were observed, evidencing the particle size and stability over the storage time (Figure 1c). Thus, the SpE showed the ability to form emulsions with stability for up to 30 days, being a great alternative to replace animal-based and synthetic emulsifiers.CIMO (UIDB/00690/2020), and AL LSRE-LCM (UIDB/50020/2020) funded by FCT/MCTES (PIDDAC). National funding by FCT, P.I., through the institutional scientific employment program-contract for L. Barros, A. Fernandes, A. Santamaria, and Y. Manrique contracts. G. Colucci thanks project GreenHealth for her contract. A4F, SA – Algae for Future (www.a4f.pt) for supplying the studied microalga. FCT for the Research grant (SFRH/BD/148281/2019) of Samara Cristina da Silva.info:eu-repo/semantics/publishedVersio