Behavior Analysis of <i>γ</i>-aminobutyrate and Glutamate Decarboxylase Activity in Salted Radish Roots (<i>Takuan-zuke</i>)

Abstract

We prepared salted radish roots and analyzed the changes in γ-aminobutyrate (GABA) and glutamate decarboxylase (GAD) activity during dehydration and long-term salting. The amounts of glutamate (Glu) and GABA in the fresh roots were 5.72±0.23 and 0.28±0.01 mg/g dry weight (DW), respectively. The amount of GABA by sundrying and salt-pressing process increased to 7.30±1.57 and 4.98±0.06 mg/g DW, respectively. In contrast, the Glu content decreased to 0.71±0.13 mg/g DW. The GABA content in salted radish was further increased by 1.2-3.0-fold by the addition of monosodium glutamate (MSG, 0.1-0.5 % weight of the radish) at the same time of salting. Fresh radish showed the highest GAD activity, which decreased during the dehydration and salting process. On the other hand, in the liquid leached from the radishes during the salting process (agari-mizu in Japanese) with MSG, a timedependent decrease of Glu and increase of GABA were observed. Thus, it was suggested that Glu was converted to GABA by microorganisms in the agari-mizu and transferred to the salted radish. The color of the salted radish without MSG was pale yellow, while that with MSG turned grayish in color after 2 months of salting.Thus, the addition of MSG during the salting process decreased the shelf-life of the product.

Consumption of Salted Pickles of Sun-dried Radish Roots (<i>Raphanus sativus cv. YR-Hyuga-Risou</i>) Attenuates Blood Pressure in Spontaneously Hypertensive Rats

“…Eggplants and tomatoes contain about 50 mg and 180 mg of GABA per 100 g fresh weight, respectively. Interestingly, GABA amounts increase during some processes such as soaking in water, anaerobic conditions, dehydration under the sun, and enzymatic treatments including fermentation (Kato et al, 2015;Mae et al, 2012;Oda et al, 2014;Ohtsubo et al, 2000;Saikusa et al, 1994;Streeter and Thompson, 1972). For example, the amount of GABA increased remarkably during the fermentation process using a bed of rice bran, reaching approximately 0.3% (Oda et al, 2014).…”

Metabolism of glutamic acid to alanine, proline, and γ‐aminobutyric acid during takuan‐zuke processing of radish root

“…Therefore, most commercial pickles are prepared by vegetables dehydrated with salt or brine before pickling to a seasoning liquid, which induces a temporary stress response in the vegetables leading to higher GABA accumulation. Moreover, as GABA content is self‐limited by the vegetable, more GABA is produced when LAB are fermented and immersed in a seasoning solution containing glutamic acid (Kato et al., 2015).…”

“…Our previous studies demonstrated that alanine, proline, and GABA from glutamic acid significantly increased during takuan‐zuke production (Kumakura, Kato, Kobayashi, Sekiguchi et al., 2017). Daikon dehydration activated GAD reduction and increased GABA concentration (Kato et al., 2015). The changes observed in the levels of different amino acids during dehydration were consistent with the results of our previous report (Kumakura, Kato, Kobayashi, Sekiguchi et al., 2017).…”

“…Our previous research revealed the effects of dehydration on the health‐promoting GABA levels in takuan‐zuke (Kumakura, Kato, Kobayashi, Sekiguchi et al., 2017). Salt‐pressing treatment only temporarily increased GABA levels due to initial osmotic shock, while sun‐drying treatment increased GABA levels over time (Kato et al., 2015; Kumakura, Kato, Kobayashi, Sekiguchi et al., 2017). Moreover, it has been shown that the consumption of takuan‐zuke containing GABA attenuated the blood pressure in spontaneously hypertensive rats (Tashiro et al., 2017).…”

Salted Radish Root Biology during Food Processing

“…As a result, they are convenient for activating GABA synthesis with simultaneous inhibition of GABA metabolism. Since our metabolomic analyses of takuan-zuke (Section 2) demonstrated an increase in GABA production, we further studied Glu-GABA during dehydration [33].…”