Identification of Polyphenolic Compounds Responsible for Antioxidant, Anti-Candida Activities and Nutritional Properties in Different Pistachio (Pistacia vera L.) Hull Cultivars

The use of by-products from the agri-food industry is a promising approach for production of value-added, polyphenol-rich dietary supplements or natural pharmaceutical preparations. During pistachio nut processing, a great amount of husk is removed, leaving large biomass for potential re-use. The present study compares antiglycative, antioxidant, and antifungal activities as well as nutritional values of 12 genotypes belonging to four pistachio cultivars. Antioxidant activity was measured using DPPH and ABTS assays. Antiglycative activity was evaluated as inhibition of advanced glycation end product (AGE) formation in the bovine serum albumin/methylglyoxal model. HPLC analysis was performed to determine the major phenolic compounds. Cyanidin-3-O-galactoside (120.81–181.94 mg/100 g DW), gallic acid (27.89–45.25), catechin (7.2–11.01), and eriodictyol-7-O-glucoside (7.23–16.02) were the major components. Among genotypes, the highest total flavonol content (14.8 mg quercetin equivalents/g DW) and total phenolic content (262 mg tannic acid equivalent/g DW) were in KAL1 (Kaleghouchi) and FAN2 (Fandoghi), respectively. The highest antioxidant (EC(50) = 375 μg/mL) and anti-glycative activities were obtained for Fan1. Furthermore, potent inhibitory activity against Candida species was recorded with MIC values of 3.12–12.5 µg/mL. The oil content ranged from 5.4% in Fan2 to 7.6% in Akb1. The nutritional parameters of the tested cultivars were highly variable: crude protein (9.8–15.8%), ADF (acid detergent fiber 11.9–18.2%), NDF (neutral detergent fiber, 14.8–25.6%), and condensed tannins (1.74–2.86%). Finally, cyanidin-3-O-galactoside was considered an effective compound responsible for antioxidant and anti-glycative activities.