Department of Health and Nutrition, Takasaki University of Health and Welfare, 37-1 Nakaorui-machi, Takasaki-shi, Gunma, 370-0033, Japan.
Faculty of Nutritional Sciences, Tohto University, 4-2-7 Kamishiba-cho, Fukaya-shi, Saitama, 366-0052, Japan.
J Food Sci. 2021 Feb;86(2):563-570. doi: 10.1111/1750-3841.15567. Epub 2021 Jan 12.
Takuan-zuke is a traditional Japanese fermented pickle, prepared by dehydration of radish root (daikon) by salt-pressing or sun-drying followed by aging with salt. We previously reported that alanine, proline, and γ-aminobutyric acid (GABA) accumulate during daikon dehydration, whereas the level of glutamic acid, their precursor, decreases. We have also reported that dehydration and salt-aging markedly influence the dynamics of free amino acids. In this study, we quantitatively analyzed free amino acid levels, enzyme activity, and gene expression to characterize takuan-zuke amino acid metabolism. Enzyme activities related to alanine, proline, GABA, and glutamic acid metabolism were sustained during dehydration. Moreover, genes encoding alanine, proline, and GABA synthases (ALT1, P5CS1, and GAD4) were significantly upregulated during dehydration. These effects may represent cellular stress responses to the dehydration process. The biological response of daikon contributes to the healthy functional aspects that characterize takuan-zuke. These findings could guide the selection of suitable vegetable varieties to produce pickled vegetables with health-promoting properties. PRACTICAL APPLICATION: The fermented pickle takuan-zuke, prepared by dehydration of radish root (daikon), accumulates amino acids, such as alanine, proline, and GABA, during preparation that provide taste and health benefits. In this study, the aforementioned amino acids were found to accumulate because of the stress response of daikon during the dehydration process and not because of the action of microorganisms during fermentation. Takuan-zuke processing is a method for improving the nutrition of daikon.
高菜是一种传统的日本发酵咸菜，通过盐压或日晒将萝卜根（白萝卜）脱水后，再用盐进行陈化制成。我们之前报道过，在萝卜脱水过程中，丙氨酸、脯氨酸和γ-氨基丁酸（GABA）会积累，而谷氨酸（它们的前体）的水平则会降低。我们还报道过，脱水和盐陈化会显著影响游离氨基酸的动态变化。在这项研究中，我们定量分析了游离氨基酸水平、酶活性和基因表达，以表征高菜氨基酸代谢。与丙氨酸、脯氨酸、GABA 和谷氨酸代谢相关的酶活性在脱水过程中得以维持。此外，编码丙氨酸、脯氨酸和 GABA 合酶（ALT1、P5CS1 和 GAD4）的基因在脱水过程中显著上调。这些影响可能代表了细胞对脱水过程的应激反应。白萝卜的生物学反应有助于形成高菜的健康功能性特征。这些发现可以指导选择合适的蔬菜品种，以生产具有促进健康特性的腌制蔬菜。实际应用：发酵咸菜高菜是通过萝卜根（白萝卜）脱水制成的，在制备过程中积累了丙氨酸、脯氨酸和 GABA 等氨基酸，这些氨基酸赋予了高菜独特的风味和健康益处。在本研究中，这些氨基酸的积累是由于白萝卜在脱水过程中的应激反应，而不是由于发酵过程中微生物的作用。高菜加工是提高白萝卜营养价值的一种方法。
