Metabolic Profiling of Pistachio Hulls: Comparative Analysis of Volatiles, Phenolics, and Organic Acids in Wild and Cultivated <i>Pistacia</i> Species

Pistachio ( Pistacia vera L.) hulls are a voluminous agricultural by-product often discarded despite their potential bioactive value. This study establishes a comprehensive metabolic framework comparing the soft hulls of three commercial cultivars (‘Siirt’, ‘Kırmızı’, ‘Uzun’) and three wild species ( P. eurycarpa, P. atlantica, P. terebinthus ) using HS-SPME-GC-MS and HPLC techniques. The results reveal a significant “domestication effect” on the metabolic profile. Cultivated varieties exhibited significantly higher sugar and organic acid accumulation (up to 2477 mg/100 g in ‘Kırmızı’), reflecting selection for energy storage and fruit quality. In contrast, wild species retained high concentrations of defense-related phenolics, specifically kaempferol (up to 201.2 mg/kg) and ellagic acid, which were largely reduced in cultivated genotypes. Notably, the ‘Siirt’ cultivar demonstrated a unique chemotype characterized by exceptionally high myricetin (247.8 mg/kg) and limonene (64.2%) contents, suggesting superior potential for nutraceutical applications. The reddish hull of ‘Kırmızı’ was chemically validated by high anthocyanin levels (pelargonidin-3-glucoside). Furthermore, a novel chemotaxonomic marker was identified for P. eurycarpa, which exclusively accumulated ferulic acid (185.7 mg/kg) and xylose, compounds negligible in other taxa. These findings highlight the impact of domestication on secondary metabolism and support the valorization of specific pistachio hulls as sustainable sources of natural antioxidants.