Effects of Amaranth Seed- and Bambara Groundnut-Based Media on the Aroma-Active Volatile and Amino Acid Profiles of Oyster Mushroom (Pleurotus ostreatus) Mycelia

The growing demand for sustainable alternative proteins has intensified interest in fungal mycelia as a nutrient-dense biomass for food applications. This study compared Pleurotus ostreatus fruiting bodies with mycelia grown in liquid state on amaranth seed- and Bambara groundnut-based media, evaluating aroma-active volatiles and amino acid composition. Across 52 identified volatiles, C8 oxylipin-derived compounds dominated all matrices, with exceptionally high odour activity values (OAVs) for 1-octen-3-one (~4.1 × 103), 3-octanone (~1.5 × 103), 1-octen-3-ol (~8.3 × 102) and 3-octanol (~5.3 × 102). Amaranth-grown mycelia showed intensified mushroom/green/fatty notes due to elevated C8 ketones and unsaturated aldehydes, whereas Bambara-grown mycelia exhibited reduced C8 prominence and stronger malty, nutty and fermented nuances driven by Ehrlich-pathway aldehydes (e.g., 3-methylbutanal ~2.0 × 103), with floral contributions from linalool (~3.8 × 102). Mycelial protein contents ranged from 35.8 to 36.1 g/100 g (amaranth) and up to 38.2 g/100 g (Bambara), compared with 39.5 g/100 g in the fruiting body. Amino acid scores (AAS) identified cystine + methionine as limiting; mycelia exhibited higher AAS, with more indispensable amino acids exceeding reference requirements. Elevated glutamic and aspartic acids underscore the umami potential of the mycelial biomass. Overall, these plant-based substrates can strategically modulate both flavour chemistry and amino acid balance in P. ostreatus mycelia, supporting their use as nutritionally relevant, flavour-active ingredients in alternative protein and hybrid food systems.