Comparative study of functional properties of eight walnut (Juglans regia L.) genotypes

Eight walnut (Juglans regia L.) genotypes were assessed for the glutathione (GSH) and total phenolic contents (TPC), as well as their antioxidant capacities. The GSH contents were between 1.1 and 7.2 mg 100 g-1. The TPC contents ranged from 33 to 50.3 mg GAE g-1, while the ferric ion reducing antioxidant power (FRAP) values ranged from 156 to 302 mg FeSO4 g-1. A strong correlation (r2=0.8258) was determined between the FRAP values and the TPC. Cupric ion reducing antioxidant capacity (CUPRAC) values ranged from 13 to 35 mg trolox g-1. The correlation between the CUPRAC values and the GSH contents was weak (r2=0.2069). The walnut extracts (0.2 mg mL-1 concentration) showed 16.2-40% DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activity. A strong correlation between DPPH-TPC was determined (r2=0.8538), and it was concluded that the TPC makes the most important contribution to the antioxidant capacity of the walnut. Additionally, the walnut may be appraised, in view of its nutritional value and health benefits, by considering the GSH content revealed in the current study.