Protein and amino acid digestibility of 15N Spirulina in rats

Abstract

Purpose Spirulina is often used as dietary supplement for its protein content and quality. However, in vivo data on protein digestibility are lacking. This study aims to determine nitrogen and amino acid digestibility in rats. A secondary objective was to test the effect of sonication prior to ingestion to break cell walls.Methods Wistar rats were fed a single test meal containing 15 N Spirulina that was either sonicated (n = 11) or not (control, n = 13). Rats were euthanized 6 h after the meal ingestion. Spirulina nitrogen digestibility was measured by assessment of 15 N recovery in digestive contents. Amino acid digestibility was measured by quantification of the caecal amino acid content and their 15 N enrichment.Results Real fecal nitrogen digestibility was 86.0 ± 0.7%, without any differences between groups. Mean 15 N amino acid caecal digestibility was 82.8 ± 1.3%, and values ranged between 77.9 ± 1.9% for serine and 89.4 ± 1.0% for methionine. No effect of sonication was observed. The most limiting AA was histidine, with a chemical score of 0.98 and a PD-CAAS of 0.84. Lysine was also limiting in a lesser extent.Conclusion The nitrogen and amino acid digestibility of Spirulina is relatively low, and showed no effect of prior sonication. Its amino acid composition is relatively well balanced but not enough to compensate for the poor digestibility.