Roasted Barley Extract Affects Blood Flow in the Rat Tail and Increases Cutaneous Blood Flow and Skin Temperature in Humans

Roasted barley extract (RBE, “Mugicha”) is a traditional Japanese beverage reported to improve blood viscosity and affect food functionality. RBE is suggested to contain 2,5-diketopiperazines, which are the functional component with neuroprotective and immunostimulatory effects that are produced in food through roasting. In this study, we investigated the effects of RBE on blood circulation, both clinically and in rats. At first, we confirmed five 2,5-diketopiperazine derivatives in RBE by LC-MS analysis. Secondarily, we revealed that RBE affects blood flow in the rat tail and compared the efficacy on rat tail blood flow among five 2,5-diketopiperazines in RBE. Especially, cyclo­(d-Phe-l-Pro) was the most effective in increasing blood flow in the rat tail. We also researched the mechanism of cyclo­(d-Phe-l-Pro) with rat aorta study. As a result, we confirmed that cyclo­(d-Phe-l-Pro) has an effect on vasodilatation through the release of nitric oxide in the vascular endothelium. Finally, we also confirmed that RBE affects cutaneous blood flow and increases skin temperature in humans

Roasted Barley Extract (Mugi-cha) Containing Cyclo(d‑Phe‑l‑Pro) Prevents Lowering of the Cutaneous Blood Flow and Skin Temperature under Air Conditioning: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study

Roasted barley extract (RBE), also known as mugi-cha, is a well-known healthy non-caffeinated beverage, and its health functionality has been widely reported. Our previous clinical study showed that RBE affects the cutaneous blood flow and skin temperature after cold-water immersion and that cyclo­(d-Phe-l-Pro) is responsible for its effect. In this study, we investigated whether cyclo­(d-Phe-l-Pro)-containing RBE prevents the decrease in the cutaneous blood flow and skin temperature. Subjects remained in the air-conditioned room while ingesting RBE or a placebo. We measured the cutaneous blood flow and skin temperature. We evaluated the effect of RBE administration by two-way repeated measures analysis of variance. A total of 15 subjects were enrolled. The change in cutaneous blood flow in the RBE and placebo groups was −0.79 ± 0.38 and −2.03 ± 0.35 mL min^–1 100 g^–1, respectively (<i>p</i> value of 0.041). The change in the skin temperature in the RBE and placebo groups was −1.85 ± 0.35 and −3.02 ± 0.30 °C, respectively (<i>p</i> value of <0.001). We also did subclass analysis with cold-feeling subjects. For the seven subjects who had cold sensation, the change in the cutaneous blood flow in the RBE and placebo groups was −0.48 ± 0.58 and −2.56 ± 0.48 mL min^–1 100 g^–1, respectively (<i>p</i> value of 0.008). The change in the skin temperature in the RBE and placebo groups was −1.46 ± 0.74 and −2.89 ± 0.39 °C, respectively (<i>p</i> value of 0.009). Thus, RBE containing cyclo­(d-Phe-l-Pro) prevents the decrease in the cutaneous blood flow and skin temperature under air conditioning