Nutritional content and health benefits of sun-dried and salt-aged radish (takuan-zuke)

- Takuan-zuke, or pickled daikon, is a popular and traditional pickle in Japan.
- Different nutritional substances were reported during takuan-zuke processing.
- Sun-drying increases the content of secondary metabolites in takuan-zuke compared with salt pressing.
- The long salt-aging treatment increased free fatty acids.
- Adding rice bran to long salt-aging treatment increased niacin levels.

We investigated the nutritional characteristics of salted radish roots (takuan-zuke) prepared using different methods: takuan-zuke based on sun-drying (hoshi) or salt-pressing (shio-oshi) dehydration, different salt-aging temperatures, and salting with rice bran. We examined differences in nutritional substances in salted radish using chromatographic analysis, bioassay methods, and multivariate analysis. We previously reported that the amount of γ-aminobutyrate in takuan-zuke was increased by both dehydration treatments. In the present study, we observed that sucrose and proline were increased by sun-drying treatment, while little change occurred with salt-pressing treatment. Branched-chain amino acids were increased by both treatments. Interestingly, free fatty acids increased with salt-aging duration, irrespective of the dehydration method. Addition of rice bran to long salt-aging treatment increased the levels of niacin, glutamate, and acetate. Metabolite concentrations were higher in hoshi takuan-zuke than shio-oshi takuan-zuke. Our comprehensive analysis reveals effects of specific manufacturing conditions on beneficial components of takuan-zuke.