The effects of gamma irradiation on the total phenolic content, scavenging capacity, mineral and vitamin content of Laurus nobilis L․

Bay leaf is a well-known culinary spice made from the aromatic leaves of the evergreen bay laurel tree, native to the Mediterranean. This study examined how different gamma radiation doses ranging from 2 to 16 kGy affect the total phenolic content, antioxidant capacity, mineral, and vitamin contents of bay leaf powder samples analyzed immediately after irradiation and after three and six months of storage. The total phenolic content was measured using the Folin-Ciocalteu method, antioxidant activity was assessed with the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) assay, and mineral and vitamin levels were determined with standard analytical techniques. The results showed a progressive decline in total phenolic content with increasing dose, decreasing from 1.52 mg GAE/g in the control to 1.15 mg GAE/g at 14 kGy at 0 months, and further dropping to 0.0035 mg GAE/g after 3 months and 0.002 mg GAE/g after 6 months at the highest doses. Antioxidant activity followed a similar pattern, decreasing from 64.23% in the control to 38.71% at 16 kGy immediately after irradiation and further to 18.7% after six months of storage. Mineral contents such as calcium, magnesium, manganese, and phosphorus remained largely unchanged across doses and storage times. In contrast, fat-soluble vitamins were highly radiosensitive: vitamin A decreased from 0.08 mg/100 g at 0 kGy to 0.02 mg/100 g at 16 kGy, while vitamin E declined from 0.08 mg/100 g to 0.002 mg/100 g. Vitamin B6 showed only a minor reduction (1.78 to 1.59 mg/100 g), whereas vitamin C remained relatively stable, ranging from 142 mg/100 g at 0 kGy to 137 mg/100 g at 16 kGy after six months. Overall, the results demonstrated that while gamma irradiation is effective for decontamination, doses above 4 kGy significantly reduce phenolic antioxidants and fat-soluble vitamins. Therefore, doses ≤ 4 kGy are recommended to balance microbial safety with nutritional and functional quality preservation in bay leaf powder samples.