Optimization of Phenolic Compound Extraction from Freeze-Dried Brassica oleracea Cultivars Using Response Surface Methodology

Optimizing the recovery of bioactive compounds is critical for the accurate assessment of the quality of freeze-dried vegetables. In this context, Response Surface Methodology (RSM) was performed to optimize the ultrasound-assisted extraction (UAE) of phenolic compounds from freeze-dried broccoli (cv ‘Thassos’) and cauliflower (cv ‘Cercy’) florets. The influence of three process parameters, namely solvent-to-material ratio (20 to 60 mL/g), extraction time (10 to 40 min) and solvent mixture (methanol: water) composition (60 to 100% methanol) was evaluated. Multi-response optimization identified the optimal process conditions for both cultivars (composite desirability = 0.996) as a 60 mL/g ratio, 10 min extraction time and 76% methanol content. The application of the optimized extraction conditions to broccoli ‘Naxos’ and cauliflower ‘Guideline’ cultivars, confirmed the model applicability and revealed significant genotypic heterogeneity (p < 0.05). Pearson’s Correlation Analysis revealed a very high positive (r > 0.9) correlation between TPC and ABTS for both broccoli and cauliflower, high (r = 0.78) correlation between TPC and FRAP for broccoli and moderate (r = 0.63) for cauliflower. These findings confirm that process parameter optimization is crucial for the maximum recovery of phenolic compounds from freeze-dried broccoli and cauliflower, and UAE conditions should be carefully selected to ensure accurate cultivar evaluation.