Model Examination for the Effect of Treading Stress on Young Green Barley ( Hordeum vulgare )

Treading barley (“Mugifumi” in Japanese) is a barley culturing process that is unique and indispensable in Japan. Generally, roller machines or human feet are used to tread young barley several times (Figure 1). As a model examination, a stainless steel instrument was used for treading barley in this study (Figure 2(a)). Treading damages plants and decreases growth, such as the height and weight of aerial parts, which then recover gradually. In our study, the total amino acid contents increased with the treading stress. The treading stress induced a 1.7-fold increase in aspartic acid contents and an approximately 1.6-fold increase in glutamic acid, proline, cystine, and methionine contents. Isolation and purification suggested that the main components of the methanol-eluted fraction from the young green barley were six known phenolic compounds. Saponarin and lutonarin were the main components. The saponarin content was about 160 mg/g (methanol-soluble fraction) at 10 days after germination. We found that the higher antioxidant activity was due to the increased lutonarin/saponarin ratio from 10% to 24%. Therefore, our results suggest that treading stress is useful for young green barley.