*Article* **Evaluating the Potential of the Defatted By-Product of** *Aurantiochytrium* **sp. Industrial Cultivation as a Functional Food**

**João Reboleira 1, Rafael Félix 1, Carina Félix 1, Marcelo M. R. de Melo 2, Carlos M. Silva 2, Jorge A. Saraiva 3, Narcisa M. Bandarra 4,5, Bárbara Teixeira 4,5, Rogério Mendes 4,5, Maria C. Paulo 6, Joana Coutinho 6 and Marco F. L. Lemos 1,\***



Correspondence: marco.lemos@ipleiria.pt

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> **Abstract:** While *Aurantiochytrium* sp. is an increasingly popular source of polyunsaturated fatty acids (PUFAs), its extraction generates high amounts of waste, including the spent, defatted residue. The composition and bioactivities of this by-product could prove to be a major part of the sustainable valorisation of this organism within the framework of a circular economy. In this study, the defatted biomass of commercial *Aurantiochytrium* sp. was nutritionally characterised, and its amino acid profile was detailed. Additionally, the antioxidant and prebiotic potentials of an enzymatically digested sample of defatted *Aurantiochytrium* sp. were evaluated under a set of miniaturised in vitro assays. The nutritional profile of the spent *Aurantiochytrium* biomass revealed a protein and dietaryfibre rich product, with values reaching 26.7% and 31.0% for each, respectively. It also held high concentrations of glutamic and aspartic acid, as well as a favourable lysine/arginine ratio of 3.73. The digested samples demonstrated significant *Weissela cibaria* and *Bifidobacterium bifidum* growthenhancing potential. Residual ferric reducing antioxidant power (FRAP) activity was likely attributed to antioxidant amino acids or peptides. The study demonstrated that some of the nutritional and functional potential that reside in the defatted *Aurantiochytrium* sp. waste encourages additional studies and the development of food supplements employing this resource's by-products under a biorefinery framework.

> **Keywords:** spent biomass; prebiotic potential; enzymatic digestion; biorefinery; circular economy; by-products
