Free radicals in lyophilised food materials

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Abstract
Food materials dried by the accelerated freeze drying (A.F.D.) process have been tested for free radicals and the concentration and properties of the free radicals compared with those in fresh heart muscle. In fresh muscle at 77° K, the free‐radical concentration was between 2.0 and 5.2 × 1015 per g. of tissue; A.F.D. minced beef 8.28 × 1015; A.F.D. herring 6.47 × 1014; A.F.D. maize 1.78 × 1014; A.F.D. rat cake 1.30 × 1014. No free radicals were detected in either the minced beef or maize before A.F.D. processing; nor could free radicals be detected in a quick‐frozen (−15° c) sample of minced beef stored some weeks. There is a higher concentration of free radicals when the lipid content of the food is high. The free‐radical concentration increased in A.F.D. food in the presence of air and oxygen and also when it was heated to 100° c. The addition of water to A.F.D. food reduced the free‐radical concentration to undetectable levels.