Effects of gamma irradiation on bio-chemical and physico-chemical parameters of fresh-cut red beet (Beta vulgaris L. var. conditiva) root

Red beet (Beta vulgaris L. var. conditiva) root is a popular item present in ready to eat salads and minimally processed foods. In this research, the effect of low doses of gamma radiation (1 and 2kGy) on peroxidase (POX), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities, as well as on the levels of compounds related to the response to the oxidative stress of plant metabolism, the changes in colour and the mechanical behaviour of fresh-cut red beet root were analyzed, with the purpose of understanding the influence of the processing on tissue characteristics. Cell wall modifications were also studied through sequential extractions of polysaccharides from the alcohol-insoluble residues (AIR) obtained from each tissue. Irradiation seemed to contribute to higher cell-cell adhesion through increasing of calcium-cross linking at the middle lamellae regions, in addition to an increment of cross-links of polymers into the cell wall. Chemical modifications produced in the cell walls as a response to higher levels of H₂O₂ and subsequent POX mediated effects, were visualized structurally as a more elastic behaviour of irradiated tissues and rigidification of cell walls of treated roots, though puncture test did not reveal significant differences. Microscopy showed a continuum of thick cell walls in beet root tissue, which suffered slight modifications after irradiation, coherent with the bio-chemical results obtained. It can be concluded that irradiation doses of 1 or 2kGy produced bio-chemical changes in cellular contents as well as in the cell wall constitutive networks which not necessarily could be sensed by consumers as it was objectively evaluated through a puncture test. At the same time, the mentioned changes involved an increase in the antioxidant capacity of red beet root tissue, showing that studied doses could be interesting to be used in the frame of a combined technique for red beet processing.