Effects of combined nonthermal treatment on microbial growth and the quality of minimally processed yam (Dioscorea japonica Thunb) during storage

The effects of combination treatment with aqueous chlorine dioxide (ClO2) and ultraviolet-C (UV-C) on the quality of yams were examined. Yam samples were treated with distilled water, 50 ppm aqueous ClO2, 5 kJ m-2 UV-C or a combination of 50 ppm aqueous ClO2 and 5 kJ m-2 UV-C. The microbiological analysis of the yams after aqueous ClO2 treatment, UV-C irradiation or combination treatment indicated significant reductions in the populations of pre-existing microorganisms. In particular, the combination treatment reduced the populations of total aerobic bacteria, yeast and mould, and coliform bacteria in the yams by 3.2, 3.4 and 3.8 log CFU g-1, respectively. The combination treatment also maintained the colour of the yams during storage. Sensory evaluation results indicated that the qualities of the yams treated with the combination of aqueous ClO2 and UV-C were better than those of the other treatments. These results clearly indicate that combination treatment with aqueous ClO2 and UV-C could be useful in improving the microbial safety and extending the shelf life of the yams.