Optimized Co-Fermentation of Seed Melon and <i>Z. bungeanum</i> Seed Meal with <i>Saccharomyces cerevisiae</i> L23: Valorization into Functional Feed with Enhanced Antioxidant Activity

This study aimed to enhance the value of agricultural by-products by developing seed melon compound fermented feed (SMFF) using <i>Saccharomyces cerevisiae</i> L23. A two-stage optimization strategy was implemented. First, seed melon juice seed culture medium (SMCM) composition and fermentation conditions were optimized to maximize <i>S. cerevisiae</i> L23 biomass through single-factor and response surface methodology (RSM) approaches. The SMCM medium was optimized to contain 0.06% MgSO₄·7H₂O, 0.2% KH₂PO₄, 0.65% (NH₄)₂SO₄, 0.1% pectinase, and 1.0% urea, and fermentation conditions with inoculation amount, fermentation time, fermentation temperature, and glucose addition were 6%, 28 h, 30 °C, and 0.5%, respectively. Furthermore, SMFF fermentation parameters were optimized via RSM, achieving <i>S. cerevisiae</i> L23 (10.35 lg CFU/g) and sensory evaluation score (83.1) at substrate ratio of 7:3 (seed melon juice: <i>Zanthoxylum bungeanum</i> seed meal), inoculation amount of 8%, and fermentation time of 36 h. Fermentation process significantly improved the nutritional profile of SMFF, increasing crude protein (13%) and vitamin C (VC) content (21%) while reducing neutral detergent fiber/acid detergent fiber (NDF/ADF) levels. SMFF also improved in vitro antioxidant capacity, with higher DPPH, ABTS, hydroxyl radical, and superoxide anion scavenging activities compared to SMFF control. This process efficiently valorized agricultural by-products into nutritionally enriched functional feed.