Application of Gamma Radiation in order to Improve Postharvest Life and Preserve Quality of Onion Cultivars during Prolonged Storage

A factorial experiment was conducted to determine the effects of different doses of gamma irradiation on postharvest life and quality of bulbs of four Iranian onion cultivars (White-Ghom, White-Neyshabour, Red-Ridge-Lump, Red-Ray-Corrugated) during 120 days storage at 10-15 °C and 70% relative humidity. Interactive effects of cultivar and irradiation dose significantly affected sprouting, weight loss, firmness, soluble solids content (TSS), and contents of reducing sugars and pyruvic acid (PA) of the bulbs after 120 days of storage. Sprouting of the bulbs ranged between 10-100%. The untreated bulbs represented the highest sprouting and weight loss. Gamma irradiation (30-150 Gy) significantly restricted sprouting percentage and consequently decreased weight loss of the bulbs. Firmness of the irradiated bulbs (90-150 Gy) was higher than the control bulbs. Weight loss of the bulbs was positively correlated with sprouting and it was negatively correlated with bulb firmness. The irradiation treatments increased TSS (30-150 Gy) and reducing sugar content (60-150 Gy) of the bulbs. The untreated bulbs had the lowest PA content at the end of the experiment. Exposure to 90-150 Gy irradiation doses resulted in the highest PA content in the bulbs. In summary, application of 90 to 120 Gy of gamma radiation for improving postharvest shelf life and quality of onions can be considered as a general guideline.