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Fruit and vegetable spoilage problem: Irradiation solution
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Friday, 05 March, 2021, 14 : 00 PM [IST]
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Dr A.P Jayaraman
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We long for the freshest of fresh vegetables and fruits picked from the farm. When we walk into a market or a shop anywhere in the world, we have the irresistible urge to pick and choose according to their look and feel. We want firm tomatoes, yellow bananas, unwilted lettuce, apples without maggots, spot-free mangoes, and dark green spinach. Vendors constantly juggle through their stock to toss out damaged or overripe produce and keeping the good ones on top. Supermarkets package delicate items to prevent bruising and extend their shelf life. Greengrocers spray water on their stuff to keep leaves pert and flies away. We obviously do not have objective measurable standards or specifications of quality but we have a deep intuitive sense of conformance to our freshness requirements. Fighting spoilage is a perpetual game and more often than not an exercise in futility.
The perishability sword hangs mercilessly over every fruit and vegetable and they remain in a continuum of freshness to staleness to rottenness sensitive to time and place. This causes unacceptable levels of food loss and deplorable wastage at every step of the value chain, beginning with the farms all through the long logistic chain. As many fruits and vegetables are eaten raw, the risk for foodborne illnesses linked to pathogen contamination lingers as a public health hazard. Toxicity of chemicals used for preservation and extension of shelf life add yet another dimension in food safety.
Irradiation legacy
Technology mediates between our dream and reality by increasing the shelf life of foodstuff. Irradiation is the neoteric processing technology which involves ionizing radiation such as X-rays, gamma rays or high-energy electron beams. It has the venerably longest world history starting within early 1920s. Food irradiation currently boasts of a 100-year history of scientific research and testing, with more than 40 years preceding approval of the process for any foods. No other food technology has had such a long rich and rare legacy. Research has been comprehensive and has included toxicological and microbiological evaluation, as well as testing for wholesomeness. The need for food irradiation is three fold: Sanitary applications for the protection of consumers from food borne illness; phytosanitary applications, to replace fumigation and pesticides in the removal of agricultural pests; commercial applications to slow the ripening process for extension of shelf life and the reduction of food spoilage.
Freshness secured
Irradiation as an evidence based post-harvest treatment technology has created new supply chains. International trade in several varieties of irradiated fruit and vegetables is flourishing in over 60 countries. ‘Irradiated for freshness' is the attention arresting label Viet Nam has scripted in executing its export order US$ 20 million a year to the United States. A commercial irradiation facility at Bengaluru received the Australian government’s approval to process and export Indian mangoes to Australia. Irradiation has truly come of age and is gentle on the mango and to fatal to the pest inside.
An innovative chemical treatment technology has been developed using GRAS (Generally Recognised As Safe) chemicals and radiation processing to extend shelf life of fruits. It helps in retaining natural peel colour, reducing microbial load to below detectable level, extending shelf life by about 60 days and fulfilling quarantine requirement.
Mango and Tomato
Mango should be picked in mature green stage with a specific gravity index of more than 1.0. Fruits should be thoroughly dried before packaging and processing by radiation. Hot water treatment at 45° C for 2-5 min could be given prior to radiation processing to obtain the best results. Radiation processing of immature fruits should be avoided. A delay in ripening of 7-14 days could be obtained at ambient temperature after processing. The best results are obtained when fruits are stored at lower temperatures.
Tomato is a popular fruit-vegetable that makes a huge impact on human nutrition for its content of sugars, acids, vitamins, minerals, lycopene, and other constituents. It has a short shelf life. Experiments were conducted to determine the effect of postharvest treatment on the physicochemical properties of fresh tomato fruits. Freshly harvested tomato fruits were subjected to low levels of gamma radiation and stored at 10 °C and 28 °C. Storing Burkina variety at a low temperature preserves the tomato fruits better than storing them at ambient temperature.
Cucumber is another case study. It completely loses apparent attraction after two weeks while irradiated samples still showed consumer acceptability after three weeks. The irradiated cucumbers showed better retention of vitamin C and chlorophyll in peel and lost less water as compared to non-irradiated samples. Radiation processed cucumbers were juicier, softer and had longer shelf life with delayed onset of fungal growth by one week.
Indian initiatives
India took its first tottering step in radiation processing sometime in 1958 and has 62 years of uninterrupted scientific research, technology development and demonstration and commercially viable innovative deployment. The nuclear fuel rods discharged from a research reactor and stored underwater provided a great opportunity to study the effects of gamma radiation on mangoes, potatoes and onions. Delayed ripening and sprout inhibition were the desirable properties put under lens. In the saga of successful radiation processing of food, we have presently 15 plants operating and two more are on the anvil. Till 2007 India was not permitted to export mangoes to the US, Australia and other countries but ever since this radiation and chemical treatment technology came, mango exports have increased from 150 metric tonnes to 1150 metric tonnes since 2007 to 2017. Now litchis, pomegranates are also being exported. Dehradun is noted for litchi production, Yet there is no processing plant . In Bihar, litchi treatment plant was started which has been beneficial for exporters.
Global Scene
International trade of fresh fruit and vegetables represents only around 8 percent of total global production. Export is an important driving force for the expansion of the fruit and vegetables sector and it also stimulates domestic production and markets. The growth in exports has significantly outpaced the increase in production: global trade more than doubled between 2000 and 2018. Value addition for fresh fruit and vegetables includes radiation processing.
Like canning fruits and vegetables, or like pasteurizing milk, radiation processing can make food safer for the consumer. Storage of foods in freezer keeps common pests during monsoon season away when it is humid. Similarly irradiation prevents the microbial growth by treating them with gamma radiations. Portable irradiation devices could further increase the commercial appeal of the method, as these could be directly used at a fruit factory packing line. The misconception that irradiated food stuff may be radioactive has totally disappeared paving the path for the growth of radiation processing technology.
Future leap
The future growth of food irradiation depends in part in demonstrating to food producers and retailers that not only is the technology beneficial but also acceptable to the public. The market size and the market pool should be evident to the entrepreneurs. Cooperation between irradiation processors and the food trade is necessary to make the irradiation step as seamless as possible. Science communicators have the social responsibility of disseminating information on the advantages of radiation processing technology to the public.
(The author is chairman of National Centre for Science communicators)
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