New Delhi, Dec. 3: Indian scientists have stretched the shelf-life of lychees from seven days to 24 days, using gamma radiation showers that they say could help reduce spoilage and expand the domestic market for this fruit.

The scientists at Pantnagar in Uttarakhand say that lychees coated with a dilute solution of salt and exposed to gamma radiation will after 24 days under refrigeration have nearly the same appearance, taste and flavour as fresh lychees.

India is the world’s second largest producer of lychees after China, with lychee-growing hubs around Muzaffarpur in Bihar and Ramnagar in Uttarakhand. But agricultural scientists believe post-harvest losses from spoilage can rise as high as 50 per cent of the annual harvest.

Lychees remain attractive to eat only about three days at room temperature and about seven days when refrigerated. Although scientists have spent years trying to extend the shelf-life of lychees, no method has been widely accepted or commercially adopted yet.

“A longer shelf-life would help many more people across India to eat this fruit,” said Chandra Pal Singh, professor of entomology at the Govind Ballabh Pant University of Agriculture and Technology in Pantnagar, the principal investigator of the research study.

Singh and his colleagues exposed lychees coated with sodium chloride solution to a controlled dose of gamma radiation at the Shriram Institute for Industrial Research in New Delhi, which maintains an irradiation facility.

The salt and radiation treatment appears to cause subtle changes in both vitamin-C and sugar content of the fruit, depending on the dose of the radiation. The scientists have published their work in the journal Radiation Physics and Chemistry.

India has for years been irradiating onions, potatoes, and mangoes to increase their shelf-life. Lychees require even more protection from spoilage than mangoes, said Neha Pandey, an entomologist and post-doctoral fellow at the GB Pant University.

“Lychees have to be harvested only when they’re ripe, unlike mangoes that can be plucked while green and then stored as they ripen over several days,” Pandey said. The scientists stored the irradiated lychees under refrigeration at 4°C.

The researchers say the combined salt and radiation treatment appears to reduce the population of microbes that contribute to the process of fruit spoilage. Singh said he plans to continue the research to further refine lychee processing to expand shelf-life even more.

“Eventually, it’ll have to be a combination of surface treatment, irradiation processing, packaging and suitable transport,” Singh said.

“These results should get people thinking about installing an irradiation facility at an appropriate site near Muzaffarpur,” said Rakesh Khandal, former director of the Shri Ram Institute, now vice-chancellor at the Gautam Budh Technical University in Lucknow.

“Such an investment would be worthwhile,” Khandal said. “It’ll help expand the supply of lychees to distant parts of India.”