Formation and Stability of Emulsions Prepared with a Water-Soluble Extract from the Microalga Chlorella protothecoides

Microalgae Proteins as Sustainable Ingredients in Novel Foods: Recent Developments and Challenges

Microalgae are receiving increased attention in the food sector as a sustainable ingredient due to their high protein content and nutritional value. They contain up to 70% proteins with the presence of all 20 essential amino acids, thus fulfilling human dietary requirements. Microalgae are considered sustainable and environmentally friendly compared to traditional protein sources as they require less land and a reduced amount of water for cultivation. Although microalgae's potential in nutritional quality and functional properties is well documented, no reviews have considered an in-depth analysis of the pros and cons of their addition to foods. The present work discusses recent findings on microalgae with respect to their protein content and nutritional quality, placing a special focus on formulated food products containing microalgae proteins. Several challenges are encountered in the production, processing, and commercialization of foods containing microalgae proteins. Solutions presented in recent studies highlight the future research and directions necessary to provide solutions for consumer acceptability of microalgae proteins and derived products.

Microalgal Proteins and Bioactives for Food, Feed, and Other Applications

Microalgae are a known source of proteins, prebiotics, lipids, small molecules, anti-oxidants and bioactives with health benefits that can be harnessed for the development of functional foods, feeds, cosmeceuticals and pharmaceuticals. This review collates information on the supply, processing costs, target markets and value of microalgae, as well as microalgal proteins, lipids, vitamins and minerals. It discusses the potential impact that microalgae could have on global food and feed supply and highlights gaps that exist with regards to the use of microalgal proteins and ingredients as foods and supplements.

Behavior of concentrated emulsions prepared by acid-hydrolyzed insoluble microalgae proteins from Chlorella protothecoides

BACKGROUND

Microalgae are a promising alternative source to meet the increasing global demand for protein. The insoluble microalgae protein fraction that makes up over half of the protein composition of the biomass has shown potential to serve as a functional emulsifier after acidic hydrolysis. However, creaming was observed due to the flocculation of emulsion droplets, suggesting a preferable use in concentrated emulsions.

RESULTS

In this study, we examined the emulsifying behavior of the untreated insoluble microalgae protein fraction and two of its hydrolysates obtained in 0.5 mol L^-1 HCl for 4 h at 65 °C (Hydrolysates 65) or 85 °C (Hydrolysates 85), at a concentration of 3% (w/w), and elevated levels of oil (50-70%). The results showed an increase in droplet size and apparent viscosity with increasing oil content in the emulsions. The emulsions made with Hydrolysates 85 had the smallest droplet size and the highest apparent viscosity. The gravitational separation was hindered when oil content was increased. The Hydrolysates 85 stabilized emulsions had a gel-like structure and were stable against coalescence or creaming during a 7 day storage test.

CONCLUSION

The results suggest that the thermal acid-treated fraction Hydrolysates 85 may, in particular, be a good emulsifier to formulate concentrated emulsion-based foods with oil content over 50%, such as mayonnaise, salad dressings, or dips. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Alternative Protein Sources as Technofunctional Food Ingredients

Proteins obtained from alternative sources such as plants, microorganisms, and insects have attracted considerable interest in the formulation of new food products that have a lower environmental footprint and offer means to feed a growing world population. In contrast to many established proteins, and protein fractions for which a substantial amount of knowledge has accumulated over the years, much less information is available on these emerging proteins. This article reviews the current state of knowledge on alternative proteins and their sources, highlighting gaps that currently pose obstacles to their more widespread application in the food industry. The compositional, structural, and functional properties of alternative proteins from various sources, including plants, algae, fungi, and insects, are critically reviewed. In particular, we focus on the factors associated with the creation of protein-rich functional ingredients from alternative sources. The various protein fractions in these sources are described as well as their behavior under different environmental conditions (e.g., pH, ionic strength, and temperature). The extraction approaches available to produce functional protein ingredients from these alternative sources are introduced as well as challenges associated with designing large-scale commercial processes. The key technofunctional properties of alternative proteins, such as solubility, interfacial activity, emulsification, foaming, and gelation properties, are introduced. In particular, we focus on the formation of isotropic and anisotropic structures suitablefor creating meat and dairy product analogs using various structuring techniques. Finally, selected studies on consumer acceptance and sustainability of alternative protein products are considered.

Effect of Arthrospira platensis microalgae protein purification on emulsification mechanism and efficiency

In light of environmental concerns and changing consumer demands, efforts are increasing to replace frequently used animal-based emulsifiers. We demonstrate the interfacial network formation and emulsifying potential of Arthrospira platensis protein extracts and hypothesize a mechanistic change upon progressing purification. A microalgae suspension of A. platensis powder in phosphate buffer solution (pH 7, 0.1 M) was homogenized and insoluble components separated by centrifugation. Proteins were precipitated at the identified isoelectric point at pH 3.5 and diafiltrated. In interfacial shear rheology measurements, the build-up of an interfacial viscoelastic network was faster and final network strength increased with the degree of purification. It is suggested that isolated A. platensis proteins rapidly form an interconnected protein layer while coextracted surfactants impede protein adsorption for crude and soluble extracts. Emulsions with 20 vol % medium chain triglycerides (MCT) oil could be formed with all extracts of different degrees of purification. Normalized by protein concentration, smaller droplets could be stabilized with the isolated fractions. For potential applications in food, pharma and cosmetic product categories, the enhanced functionality has to be balanced against the loss in biomass while purifying microalgae proteins or other alternative single cell proteins.

Extraction, Properties, and Applications of Bioactive Compounds Obtained from Microalgae

With the increase in the global population, getting new sources of food is essential. One of the solutions can be found in the oceans due to algae. Microalgae are aquatic photosynthetic organisms used mainly due to their variety of bioactive compounds. The consumption of microalgae has been carried out for centuries and is recommended by organizations, such as OMS and FAO, due to its nutritional value and its properties. Based on the existing literature, there is substantial evidence of the nutritional quality of the algae as well as their functional elements. However, much quantification is still necessary, as well as studying possible adverse effects. The present review describes the compounds of alimentary interest present in these algae as well as different extraction techniques assisted by different energetic mechanisms (such as heat, supercritical-fluid, microwave, ultrasound, enzymes, electric field, high hydrostatic pressure, among others). The most challenging and crucial issues are reducing microalgae growth cost and optimizing extraction techniques. This review aimed a better understanding of the uses of microalgae for new researches in nutrition. Since the use of microalgae is still a field in which there is much to discover, it is likely that more benefits will be found in its consumption.

Ionic strength and pH stability of oil-in-water emulsions prepared with acid-hydrolyzed insoluble proteins from Chlorella protothecoides

BACKGROUND

Chlorella protothecoides is one of the most widely commercialized and studied microalgae species. Recent research reported improved emulsifying properties of the insoluble protein fraction from C. protothecoides after thermal-acid treatment.

RESULTS

In this research, we studied the influence of ionic strength (sodium chloride 50-500 mmol L^-1 or calcium chloride 5-50 m mol L^-1 ) and pH (2-9) on the stability of oil-in-water emulsions prepared by 3% (w/w) of the untreated insoluble microalgae protein fraction or hydrolysates obtained after treatment with hydrochloric acid at 65 °C (Hydrolysates 65) or 85 °C (Hydrolysates 85) for 4 h. The emulsions were prepared by mixing 10% (w/w) oil and homogenized at 68.9 MPa. The ionic strength and pH were, subsequently, adjusted. The mean particle diameter of emulsions remained constant despite extensive variations in ionic strength or pH. Emulsion droplets stabilized by Hydrolysates 85 were stable against coalescence at all ionic strengths or pH values tested.

CONCLUSION

The results indicate a high potential to use acid-hydrolyzed insoluble microalgae protein fractions for the formulation of various emulsion-based food systems. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Sensory properties of aqueous dispersions of protein-rich extracts from Chlorella protothecoides at neutral and acidic pH

BACKGROUND

Water-soluble proteins extracted from the heterotrophically cultivated microalga Chlorella protothecoides have been shown to have a good solubility over a broad pH range, which makes them a promising candidate for beverage formulations. This study investigated the sensory properties of dispersions of a protein-rich extract from C. protothecoides at neutral and pH 3.

RESULTS

Sensory acceptance tests of the pure extract revealed an overall low acceptance at pH 7 without sucrose addition. Sensory acceptance was significantly (P ≤ 0.05) increased by lowering the pH to 3 with citric acid, and the addition of 50 g kg^-1 sucrose. Here, overall positive sensory acceptance ratings were achieved up to a protein extract concentration of 40 g kg^-1 . Basic taste evaluations showed only low bitterness scores and no significant (P > 0.05) increase in bitterness with decreasing pH.

CONCLUSION

It is suggested that protein-rich extracts from C. protothecoides have promising sensory properties in beverage formulations. © 2019 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Towards the Properties of Different Biomass-Derived Proteins via Various Extraction Methods

This study selected three representative protein-rich biomass-brewer's spent grain (BSG), pasture grass (PG), and cyanobacteria (Arthrospira platensis; AP) for protein extraction with different extraction methods (alkaline treatment, aqueous extraction, and subcritical water extraction). The yield, purity, molecular weight, oil-water interfacial tension, and thermal stability of the obtained proteins derived from different biomass and extraction methods were comprehensively characterized and compared. In the view of protein yield and purity, alkaline treatment was found optimal for BSG (21.4 and 60.2 wt.%, respectively) and AP (55.5 and 68.8 wt.%, respectively). With the decreased oil-water interfacial tension, the proteins from all biomass showed the potential to be emulsifier. BSG and AP protein obtained with chemical treatment presented excellent thermal stability. As a novel method, subcritical water extraction is promising in recovering protein from all three biomass with the comparable yield and purity as alkaline treatment. Furthermore, the hydrolyzed protein with lower molecular weight by subcritical water could promote its functions of foaming and emulsifying.