Tempeh-type fermentation kinetics of tarwi (Lupinus mutabilis) and red quinoa (Chenopodium quinoa) with Rhizopus oligosporus: effects on texture, metabolite profile and nutritional potential.

Tempeh is a solid-state fermented food traditionally produced from soybeans using fungi of the genus Rhizopus, which modify the nutritional and functional properties of the substrate. The search for alternative raw materials has increased interest in underutilized Andean crops such as tarwi (Lupinus mutabilis cv. Cholo Fuerte) and quinoa (Chenopodium quinoa cv. Pasankalla), recognized for their high nutritional value and potential for sustainable food development. This study investigated the growth kinetics of Rhizopus oligosporus during nine days of tempeh-type fermentation of tarwi and quinoa, indirectly evaluated enzyme production through enzymatic activity, and characterized associated changes in texture and metabolomic profiles. Biomass growth was best described by the Gompertz model, whereas enzyme production followed the Luedeking-Piret model, indicating predominantly growth-associated behavior. Tarwi tempeh showed a better fit to both models and greater proteolytic activity, whereas quinoa tempeh exhibited poorer model fitting and predominantly amylolytic activity. Textural properties were influenced by fungal growth and enzymatic activity, with changes in hardness, cohesiveness, springiness, and fragility; optimal characteristics were observed between 48 and 72 h of fermentation. Metabolomic analysis identified 448 metabolites, revealing clear substrate-dependent clustering. Quinoa tempeh was characterized by metabolites related to carbohydrate metabolism, nucleotide turnover, and nucleoside derivatives, indicating active fermentative metabolism. In contrast, tarwi tempeh showed a metabolomic profile dominated by amino acid-related compounds, reflecting intensified proteolysis and amino acid metabolism. These findings highlight the key role of substrate composition in modulating fungal growth, enzyme activity, textural properties, and metabolomic profiles during tempeh fermentation.