Roasting Effects on Aroma Volatiles and Antioxidant Activity in Pistachio Kernels (cv. Siirt)

Roasting is a key processing step that strongly influences the sensory and chemical quality of pistachio kernels. This study investigated the effects of roasting (160 °C for 25 min) on Turkish pistachio (Pistacia vera L., cultivar "Siirt") kernels by comparing raw and roasted samples. Color parameters (L*, a*, b*, hue angle), total phenolic content (TPC), and antioxidant activity (DPPH assay) were evaluated. Sugars and organic acids were quantified by HPLC, while volatile compounds were characterized using HS-SPME/GC–MS. Roasting caused a significant decrease in L* and hue angle values, indicating kernel darkening and loss of green coloration, while a* values increased, reflecting development of reddish-brown tones. Total phenolic content decreased significantly from 343.38 to 284.72 mg GAE/100 g, whereas DPPH radical scavenging activity increased markedly from 21.56% to 57.19%. Roasting significantly increased sucrose, glucose, and fructose concentrations and enhanced levels of citric, malic, and succinic acids, while ascorbic acid decreased. Volatile analysis revealed an increase in identified compounds from 23 to 30, with monoterpene hydrocarbons remaining dominant and limonene as the major compound. Aldehydes and Maillard-derived heterocyclic compounds such as pyrazines and pyrroles were detected mainly in roasted kernels. Overall, roasting enhanced aroma complexity and antioxidant activity while reducing some heat-sensitive compounds, providing valuable information for optimizing roasting conditions in "Siirt" pistachios.