Characterization and Valorization of the Microalgal Co-Product Spirugrass®: Protein Profile, Iron Speciation, and Potential Use as a Supplement for Honeybees

Abstract

Microalgae are used as dietary supplements for humans and animals, due to their excellent nutritional profile. This research aims to characterize Spirugrass®, a co-product obtained after the extraction of phycocyanin from Limnospira platensis, and to evaluate whether a stabilization treatment involving high-pressure processing (HPP) affects its proteomic profile. The research also aims to evaluate the possible use of Spirugrass® as feed integration for honeybee health. Proteins were extracted and fractionated using size exclusion chromatography (SEC) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The iron content was measured using atomic absorption spectrometry (AAS). Samples of Spirugrass® were subjected to HPP at 600 MPa for five minutes and the effect on the integrity of the protein profile was analyzed. Finally, nine groups of 30 newly emerged honeybees were supplemented with Spirugrass® in a controlled laboratory experiment. SDS-PAGE and SEC enabled the assessment of the quality and integrity of the Spirugrass® proteome, which contains 80% of the proteins found in the algal biomass, including phycocyanin. The phycocyanin purity indices were 2.07 ± 0.14 and 0.72 ± 0.13 for the L. platensis and Spirugrass® extracts, respectively. Spirugrass® maintains a consistent iron content of 261 ± 15 μg/g dry weight, equivalent to 74% of the iron present in the algal biomass. In both L. platensis and Spirugrass®, iron was predominantly bound to high-molecular-mass proteins, including phycocyanin. Following HPP treatment, differences in the protein profiles were observed, which suggests partial protein degradation. Preliminary data obtained with honeybees are encouraging, as no mortality or adverse effects were observed and Spirugrass® can be considered a promising candidate as feed supplement. Overall, the presence of consistent levels of soluble proteins, as well as protein-bound iron, suggests that Spirugrass® could be used in animal nutrition.