Optimization, identification and application techniques of functional proteins production from microalgae

• Main Authors: Yu-ChengLai, 賴昱成
• Other Authors: I-Son Ng
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/jq9jht

碩士 === 國立成功大學 === 化學工程學系 === 107 === Microalgae are high-quality carbonic circular materials. Due to their great carbon-fixing capacity, growth of microalgae makes a considerable contribution to the global greenhouse gas reduction. Moreover, microalgae contain many high-value products, such as pigments, unsaturated fatty acids and functional algal proteins, which have the potential for high-value utilization. However, the biggest challenge for commercialization is the high production cost. Therefore, it is necessary to establish low-cost biomass production techniques of microalgae and high-value technology for microalgal biomass. Microalga is one of the most promising sustainable feedstock as it uptakes waste to convert to large range of sectors: food, feed, fertilizers, nutraceuticals, cosmetics, chemicals, energy, etc. via a circular economy concept, which becomes research hotspot in recent years. According to the abundance of protein content and a variety of essential amino acids in microalgae, they are considered as the major sources of protein supplement. Therefore, a series of discussions on the functional proteins production from native algal strains were examined in this study. In this study, six indigenous algal strains, Synechococcus elongatus PCC7002, Chlamydomonas reinhardtii CC-400, Chlorella variabilis, Chlorella vulgaris ESP-31, Chlorella vulgaris FSP-E and Chlorella sorokiniana were selected. Two kinds of protein-rich microalgae, Chlorella vulgaris FSP-E (CV) and Chlorella sorokiniana (CS), were screened as promising sources for algal proteins due to their high protein productivity. Procedure for optimization of functional proteins production was further carried out. As a result of growth regulation of CV and CS, the optimal CO2 concentration for the growth of both microalgae was 5% (v/v) by adjusting the CO2 concentration from 2% to 17%. The optimal nitrogen source for CV and CS were 12 mM of NaNO3 and NH4Cl by adjusting the nitrogen concentration from 2 mM to 72 mM, respectively. Regulating trace iron element can effectively stimulate the growth of microalgae. With the addition of 12 mg/L ammonium iron (III) citrate, the biomass concentration (4.08 g/L and 4.24 g/L), biomass productivity (583.0 mg/L/d and 606.3 mg/L/d) and protein concentration (793.3 mg/L and 812.8 mg/L) of CV and CS were obtained, representing a 4.86 fold and 2.77 fold increase, respectively, in protein productivity of CV and CS (113.3 mg/L/d and 116.1 mg/L/d). Next, semi-batch cultivation strategy was employed to successively increase protein content of CV and CS at the medium replacement ratio of 80%, achieving the biomass concentration of 4.56 g/L and 4.75 g/L, protein concentration of 794.2 mg/L and 852.2 mg/L and protein content of 394.8 mg/g DCW and 424.4 mg/g DCW for CV and CS, respectively. The obtained microalgal proteins consist of 40% essential amino acids, participating in energy conservation in Calvin cycle. In terms of activity characteristics analysis, the CV and CS proteins possess prebiotic activities as they enhanced the growth of Lactobacillus rhamnosus ZY by 48% and 74%, respectively. Moreover, the CV and CS proteins have high antibacterial activities against predominant pathogens. The diameter of inhibition zones for microalgal proteins with six kinds of pathogen strains, such as Aeromonas hydrophila, Bacillus cereus, Escherichia coli, Pseudomonas putida, Rhodococcus erythropolis and Staphylococcus aureus, varied from 1.30 cm to 1.60 cm. The CV and CS proteins, respectively, also possess high hydroxyl free radical scavenging rate of 51.7% and 54.9%, which have commercial IC50 values of 10.3 g/L and 6.6 g/L.