Chapter 15. Biological Techniques

Abstract

DNA is a large molecule particularly sensitive to ionizing radiation, which suffers several kinds of damage: fragmentation resulting from both singlestrand and double-strand breaks, denaturation of the DNA helix, crosslinking (e.g., production of thymine dimers, or between DNA and a protein) and base damage. 1-3 It causes primarily single strand breaks (SSBs) in genomic DNA, in addition to double strand breaks (DSBs) at ratios of SSB/ DSB of 20/1 to 70/1, as well as some detectable membrane damage. 4 In foods, this DNA susceptibility is the cause of death of most if not all living contaminants, such as microorganisms, insects, or parasites, 4 and is also the cause of changes in the food's DNA itself, which can reflect on various morphological and physiological features. DNA damage occurs predominantly by the indirect action of gamma rays, which interact with other atoms or molecules, particularly water, to produce reactive free radicals. 5 Cell death (defined for proliferating cells as the loss of reproductive capability) is predominantly induced by double-strand breaks in DNA, separated by not more than a few base pairs, which cannot generally be repaired by the cell. 6 Since irradiation with just 1 Gy introduces about 1000 DNA single-strand breaks and about 50 double-strand breaks per cell, 7