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

Abstract

BACKGROUNDChlorella 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.RESULTSIn 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.CONCLUSIONThe 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.

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

“…Dai et al studied the influence of ionic strength on the stability of emulsions and reported that the bridging mechanism is not electrostatically driven and is rather due to Van der Waals interactions. 14,17 Knudsen et al, 31 similarly, reported an increase in the viscosity of emulsions stabilized by heat-induced ⊎-lactoglobulin aggregates as a result of stronger interactions between adsorbed molecules at the oilwater interface due to the presence of aggregates with higher surface hydrophobicity. Aside from bridging, entanglement may also play a role.…”

“…[14][15][16][17] Results from investigations of the behavior of moderately concentrated oil-in-water emulsion (with 10% w/w of a mediumchain triglycerides oil) stabilized by the microalgae insoluble protein fraction after hydrolyzing with 0.5 mol L -1 HCl at 85°C for 4 h (Hydrolysates 85) showed that emulsions were stable in terms of droplet size (at around 15 μm) after 14 days of storage, even when subjected to harsh environmental conditions such as an extreme pH (2)(3)(4)(5)(6)(7)(8)(9) or high salt concentrations (NaCl concentration 0-500 mmol L -1 or CaCl 2 concentration 0-50 mmol L -1 ), and no coalescence was observed. 14,17 However, visual and microscopic assessments revealed pronounced emulsion flocculation. In emulsions with low oil droplet concentrations, flocculation caused emulsion instability by accelerating gravitational separation due to the larger effective droplet size compared with individual emulsion droplets.…”