GAMMA IRRADIATION OF FRESH FRUIT 



William J. Brajnlage 

 Department of Plant and Soil Sciences 



When man learned to release the tremendous forces of atomic energy, 

 his first use of that power was to build a bomb - the Atomic Bomb. But 

 before the first bomb was exploded, he was already dreaming of harness- 

 ing these same atomic forces for peaceful uses. 



Among the forces produced from radioactive materials are gamma rays. 

 These are highly penetrating rays with the capacity to kill living cells 

 of both plants and animals. Scientists soon learned to apply controlled 

 doses of these gamma rays to kill unwanted or dangerous cells, and this 

 is the basis for using radioactive materials to treat cancer patients. 

 Similarly, attempts have been made to kill, through irradiation, the fungi 

 and bacteria that cause decay of food. It is with this aspect of irrad- 

 iation that we, as agriculturists, are personally concerned. 



Much work has been done on food irradiation, and we frequently find 

 articles in the newspapers and magazines giving glowing accounts of the 

 use of these "magic rays" to preserve food indefinitely - without refrig- 

 eration. Indeed, there have been some notable successes: irradiated 

 bacon, requiring no refrigeration, may soon be on the market; irradiated 

 potatoes, that won't sprout, are now being sold in Canada; and research 

 continues to look promising for retarding spoilage of fresh strawberries 

 through irradiation. However, most of the press reports have been unduly 

 optimistic, for food irradiation is beset with severe problems. 



To sterilize a food product, that is, to kill all the bacteria and 

 fungi on and in it, requires a massive dose of radiation. Such doses 

 very often not only kill the microbes, but also cause severe changes in 

 the foods, for example, changes in the color, taste, odor, or texture 

 of the food. Dreams of replacing canning and refrigeration with irrad- 

 iation have been largely abandoned because of the failure to prevent 

 these changes. A notable exception to this problem, however, is bacon, 

 which tolerates a sterilizing dose of radiation without undergoing change. 



When we consider irradiation of fresh fruits, we run into another 

 immense problem. UnJ.ike processed foods, fresh fruits are living organ- 

 isms, and so, they as well as bacteria and fungi can be killed by gamma 

 rays. All living cells are not equally susceptible to these rays-, so 

 our only hope is that we can seriously injure or kill disease-causing 

 organisms without seriously injuring the fruits. Fortunately, some of 

 the most serious disease-causing fungi are among the most radiation- 

 sensitive organisms. These are the Penicillium species, which cause 

 blue mold of apples and blue and green molds of citrus; Botrytis cinerea. , 

 which causes much of the decay of strawberries; and Monilinia fructicola , 

 which causes Brown Rot of peaches and plums. These fungi can be injured, 

 though not completely killed, by relatively light doses of radiation. 



