Impact of Gamma Irradiation as Preservation Technique on Phenolic Contents and Antioxidant Capacity of Two Mature Date’s Cultivars to Extend the Shelf Life

Abstract

Date fruit is a functional food endowed with several pharmacological properties resulting from its diversified composition of nutrients and secondary metabolites. It is often stored for long periods after its harvest; however its initial nutritional and organoleptic properties are not always preserved. This study aimed to test the effect of three doses of γ radiations (0.6, 1.3, 2 kGy) on some nutritional and organoleptic properties of stored Deglet Nour and Ghars dates during ten months. pH, titratable acidity, and contents of total polyphenols, flavonoids and ascorbate as well as scavenging activity of date extracts have been periodically tested adopting appropriate methods. Radiation slowed, regardless of dose, a decrease in pH of Deglet Nour samples stored at low T, also the decrease in pH of Ghars samples (0.6, 1.3 kGy) stored at room T and (1.3, 2 kGy) at low T. Oscillations of decreases and increases of titratable acidity rates were obtained comparing to controls, but the treatment effectively increased, independently of the dose, the titratable acidity levels of Ghars samples during storage at low temperature. Doses 2 kGy at low T and 0.6 kGy at ambient T slowed down the decrease in polyphenols content of Deglet Nour samples (39.96%, 34.88%) versus controls (80.39%, 87.58%) respectively. However, TPC of Ghars samples underwent a progressive increase at ten months of storage ranging from 145.22 mg obtained before exposure to radiation to a level of 389.55 mg (2 kGy) at room T and a maximum of 256.22 mg (0.6 kGy) at low T. Deglet Nour samples irradiated at 0.6 and 2 kGy retained more flavonoids contents for both storage temperatures. Ghars samples, 2 kGy at room T and 0.6 kGy at low T, considerably increased flavonoids contents after ten months of storage. More pronounced increase was obtained for Deglet Nour samples (2 kGy) till 2.5 months of storage at room T, whereas, all samples gave significant increase until 5 months at low T. Up to 5 months at room T and 7.5 months at low T, irradiated Ghars samples increased significantly in ascorbate contents regardless of dose. However, only, 0.6 kGy of Deglet Nour stored at ambient T preserved its initial antiradical activity besides the slowing down of decrease of all irradiated samples. In addition, a considerable increase was observed for Ghars irradiated samples regardless of dose and involvement of phenolics in this activity was confirmed.