Optimized ultrasound-assisted tryptophan extraction from Kappaphycus spp.: Enhancing bioactive compound profiling and cultivation strategies

• Ultrasound-assisted extraction optimized for sustainable Kappaphycus spp. cultivation. • Enhanced tryptophan recovery supports seaweed-based bioactive compound profiling. • Method validation ensures reliable analysis of food and agricultural matrices. • Demonstrates environmental and cultivation impacts on bioactive compound yields. • Provides strategies for improving the agricultural value of seaweed products. Kappaphycus spp., a widely cultivated seaweed, is valued for its diverse bioactive compounds, including tryptophan. This study aimed to optimize and validate an ultrasound-assisted extraction (UAE) method to quantify tryptophan using a Box-Behnken design integrated with response surface methodology. The factors evaluated included solvent composition (50–90% methanol in water), pH (2–8), ultrasound amplitude (25–75%), and pulse duty cycle (0.2–1.0 s⁻¹). The optimized extraction variables—73% methanol in water, pH 8, 58% ultrasound amplitude, and a 0.8 s⁻¹ pulse duty cycle at 60°C for 10 minutes—achieved high recovery (>90%) and precision (CV <5%). This method was applied to 36 samples of Kappaphycus alvarezii and Kappaphycus striatum , revealing significant variations in tryptophan content based on species, environmental factors, and farming methods. Notably, K. striatum from Sekotong (Lombok) cultivated via the longline method exhibited the highest tryptophan yield. The findings underscore the potential of optimized UAE for supporting seaweed biotechnology and enhancing bioactive compound production through improved cultivation strategies.