Bioactive Compounds from Cucurbita spp. and Their Processing By-Products: A Critical Review

Pumpkin (Cucurbita spp.) processing generates peels, seeds, seed coats, pomace, and press cakes containing carotenoids, phenolics, proteins, unsaturated lipids, tocopherols, phytosterols, polysaccharides, and dietary fiber. This critical narrative review integrates composition and analytical characterization across anatomical fractions with extraction technologies, processing effects, biological evidence, and application readiness. Conventional extraction, pressing, supercritical carbon dioxide, deep eutectic solvents, enzyme-assisted extraction, ultrasound, microwaves, pulsed electric fields, and high-pressure homogenization differ in selectivity, recovery, and scalability. The reviewed evidence does not establish the environmental superiority of green extraction technologies without full process-level assessment. Processing can improve extractability or simulated bioaccessibility but also cause degradation or losses; concentration following water removal does not establish true retention. Experimental studies support potential antioxidant, anti-inflammatory, glycemia-related, antimicrobial, and antiproliferative activities, but most evidence remains chemical, cellular, or animal-based. Human evidence is preparation-specific and most developed for lower urinary tract symptoms; controlled evidence for glycemic and other systemic outcomes remains limited or inconsistent. Near-term opportunities include food ingredients, oils, protein fractions, pigment delivery, and selected packaging materials. Translation requires authenticated materials, validated analytical fingerprints, standardized preparations, safety and stability testing, adequately powered clinical trials for health-related claims, and mass, energy, economic, and life-cycle assessments.