Formation of free radicals in food constituetns by y-irradiation

Radicals formed on y-irradiation of monosaccharides may be detected by spin trapping but their identification in this way is difficult. To aid identification, methods have been developed which allow generation of specific radicals from monosaccharides and also specific spin adducts derived from sugar nitrones. INTRODUCTION Preservation of food by y-irradiation is an important and controversial issue worldwide. Concern has been expressed about the effect which ionising radiation has on the wholesomeness of food and especially whether toxic radiolytes are formed. Previously, we have reported on the structures and concentrations of radicals formed on y-irradiation of spices (ref. 1 ) and vitamins (ref. 2 ) . The present communication describes related work on monosaccharides. Identification of radicals formed from monosaccharides by y-irradiation by direct e.s.r. measurements is not feasible. Accordingly, spin trapping techniques have been used but even these have not been satisfactory mainly because of the range and number of radicals present in the solid some of which arise by rearrangement of initially formed radicals. Complex e.s.r. spectra of spin adducts are invariably produced whose full interpretation has not been achieved. Three approaches to the resolution of this problem have been tried by the groups of Riesz (ref. 3 ) , Raffi (ref. 4 ) and ourselves (ref. 5 ) ; (a) a range of structurally similar monosaccharides has been irradiated and then added to solutions of spin traps; ( b ) spin trapping of isotopically labelled glucose-derived radicals has has been used in an attempt to separate and identify the components of the mixture of spin adducts. These approaches have failed to provide a satisfactory solution although the following tentative generalisations can be made which relate observed coupling constants of spin adducts to structure. 4.8-5.6G have general structure l j those with two doublet splittings a = 1 .5 -2 .25 and aH% 0.5G have general structure 2 and those with only one doublet splitting aH = 1 .5 -2 .256 have general structure 2. been examined; (c) hplc/esr Spin adducts which show a proton splitting in the range H There are a number of unexplained exceptions to these generalisations and the assignments at this stage are no better than provisional. Importantly, there have been no unambiguous structural assignments of the spin adducts of simple monosaccharides mainly because there is no method available for the specific generation of sugar-derived radicals. It was the aim of this work to develop methods for the generation of radicals of known structure derived from monosaccharides, to trap such radicals and then to assign the esr proton coupling constants, unambiguously,of their spin adducts. RESULTS AND DISCUSSION Homolytic dehalogenation of halosugars was given first consideration since Sustmann and his coworkers (ref. 6 ) had previously generated a number of protected sugar radicals in organic solvents by dehalogenation of the corresponding halosugars with tributyltin radicals. method is not applicable in aqueous-solution since no water soluble tin hydride is available. The carbon dioxide radical-ion (CO a ) also dehalogenates certain alkyl halides by electron transfer followed by halide ion loss and this was the reactant of choice in this work. It is formed by hydrogen atom removal from formate and this had to be done in a way which did not destroy the spin trap. Of the three methods examined (i-iii) that summarised in (i) was the most useful because it did not require UV photolysis which converts the trap to di-t307 This