A wide bibliographic review exploring the global development of algae protein in the food industry and emphasizing its potential in association with animal protein or as substitute for animal protein in foods has been performed. It highlighted the current utilization of both entire algae biomass and algae protein concentrates for incorporation into new food matrices.
The experimental study therefore focused on the use of Spirulina biomass alone and in mixture with pea protein, with and without fat, to produce instant powders by spray drying to be used as potential milk analogues. Spray drying is widely used in the food industry but it is energy intensive and must be used to eliminate the last traces of water in liquids with the highest possible dry matter content while remaining suitable for pumping and spraying.
A methodology for the production initial liquid feeds with a high dry matter content has been established and the particle size distribution, rheological behavior and physical stability for the different formulations were characterized.
Feeds (10 %w dry matter), with and without fat (sunflower and coconut oil, 2.5 %w), containing Spirulina had a shear-thinning behavior, with a high viscosity and the rheological characteristics of both weak gel and liquid. This was attributed to the polysaccharide content of the biomass, and contributed to the very good physical stability of the suspension. The addition of pea protein was found to be interesting in decreasing the feed viscosity but led to a lower stability. Results also showed that long-chain unsaturated sunflower oil is easier to emulsify by protein while short-chain saturated coconut oil prefers emulsification by surfactants. Furthermore, solids fractions of algae biomass remaining in the emulsion acted as space meteorite encompassing the oil droplets and ensuring a good physical stability of the emulsion.
Under the conditions studied, atomized powders were obtained at laboratory and pilot scales with satisfactory water activity (< 0.3) but the process yield varied between formulations and scales. Generally, it was better at pilot scale and without fat. Coconut oil-based powders had smaller particle sizes than sunflower oil-based powders, but in all cases, due to their small size inherent to the process scale (median particle diameter < 25 μm), the powders were cohesive with low fluidity. However, compared to skimmed milk and pea protein powders alone, Spirulina-based powders were slightly better. They also have the best wettability and allow the initial particle size distribution of the emulsion to be recovered after rehydration. Despite a slight impact of the spray drying conditions and scale, one of the main drawbacks of using Spirulina biomass is the dark green color of the resulting powders. The addition of pea protein is interesting to slightly increase the whiteness of the powder.
The digestion of the spray-dried powders was studied using the classic INFOGEST method for static in vitro simulation of gastrointestinal food digestion. Compared to the digestion of raw products a significant reduction in size could be observed, even though powders of same formula from different drying scales have different digestion profiles.
As a conclusion, conditions were found to produce Spirulina-based liquid feeds with physical properties compatible with spray drying for the obtaining of powders with satisfying stability and reconstitution properties. Interestingly, we found that spray drying could provide a more pleasant aroma of algae-based powder compared to the initial liquid form. This unexpected finding could facilitate the development of algae-based food. From both the powder and process point of view Spirulina biomass and pea protein are therefore proven as promising candidates for creating alternative milk analog powders, but the sensory and functional aspects must be further considered.
