Process for preparing an algal powder containing a reduced content of proteins, and bioplastic composition formulated from such a powder

A process for preparing an algal powder, comprising the successive steps of:

• (a) harvesting algae;
• (b) culturing the algae in conditions favoring the biosynthesis of starch, said culturing comprising setting up the algae in a tank and culturing for four to six weeks in a seawater culture medium without supplying fertilizers, and without supplying nitrogen;
• (c) depigmenting the algae in the presence of ethanol;
• (d) reducing by at least 75% the amount of intrinsic proteins of the depigmented algae by enzymatic hydrolysis of the intrinsic proteins, the reducing step (d) comprising:
• (d1) macerating over night the depigmented algae in water, filtering the macerated algae to generate a first algal residue, and recovery of the first algal residue,
• (d2) mixing the recovered first algae residue with a sodium hydroxide solution to produce a mixed algae, filtering the mixed algae to generate a second algal residue, and recovery of the second algal residue,
• (d3) mixing the recovered second algae residue and Bacillus licheniformis as a source of one or more proteases to hydrolyze the intrinsic proteins, then
• (d4) separating a hydrolysate enriched in peptides and/or amino acids from the hydrolyzed second algal residue to generate a third algal residue, and recovery of the third algae residue;
• (e) destructuring the cell walls of the recovered third algal residue by mixing the third algae residue with a chelating agent and water, heating the mixture to a temperature of between 80° C. and 100° C., to generate a fourth algal residue, then cooling and concentrating the fourth algal residue by elimination of water;
• (f) adding starch to the concentrated fourth algal residue to form a dispersion of the starch and the concentrated fourth algal residue,
• (g) drying an algal material derived from the dispersion, and
• (h) reducing the dried material of the step (g) to give powder or granules, thereby obtaining the algal powder.