Tempeh and Fermentation—Innovative Substrates in a Classical Microbial Process

The growing consumer awareness of functional foods has increased interest in fermented plant-based products with enhanced nutritional and health-promoting properties. This comprehensive narrative literature review examines the potential of diverse raw materials for tempeh production beyond traditional soybeans, analysing their nutritional composition, bioactive compounds, and functional properties. A structured literature search was conducted on peer-reviewed publications up to July 2025, focusing on tempeh fermentation technology, chemical composition, and bioactive compounds from various substrates using recognised analytical methods according to Association of Official Analytical Collaboration (AOAC) standards. The analysis of over 25 different substrates revealed significant opportunities for enhancing tempeh’s nutritional profile through alternative raw materials including legumes, cereals, algae, seeds, and agricultural by-products. Several substrates demonstrated superior nutritional characteristics compared with traditional soybean tempeh, notably tarwi (Lupinus mutabilis) with exceptional protein content ((32–53% dry matter (DM)) and mung bean (Vigna radiata) exhibiting remarkably high polyphenol concentrations (137.53 mg gallic acid equivalents (GAE)/g DM). Fermentation with Rhizopus oligosporus consistently achieved substantial reductions in anti-nutritional factors (64–67% decrease in trypsin inhibitors, up to 65% reduction in phytates) while maintaining consistent antioxidant activities (39–70% 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition) across most variants. The diversity of bioactive compounds across different substrates demonstrates potential for developing targeted functional foods with specific health-promoting properties, supporting sustainable food system development through protein source diversification.