PROBLEM TO BE SOLVED: To provide solutions of extract of plants, such as passion fruits, Rhodomyrtus tomentosa, and Callistemon speciosus； to provide stabilization methods of piceatannol which is included in the solution of the plant extract, has melanin generation inhibition, ultraviolet ray damage restorative effect, and MMP inhibiting action and the like, and is represented by the following left formula； and to provide methods of reducing scirpusin B (a dimer of piceatannol) included in the solutions of the plant extracts.SOLUTION: Disclosed is a method comprising blocking a solution of a plant extract from a gas containing oxygen. Preferably, the stabilization method further comprises blocking the solution from light.SELECTED DRAWING: Figure 2【課題】パッションフルーツやテンニンカやブラシノキ等の植物抽出物の溶液、及び植物抽出物の溶液に含まれ、メラニン生成の抑制、紫外線ダメージ回復効果及びＭＭＰの阻外作用等を有し、下記の左側の式で表される、ピセアタンノールの安定化方法、及び前記植物抽出物の溶液に含まれるスキルプシンＢ（ピセアタンノールの二量体）を減少させる方法の提供。【解決手段】植物抽出物の溶液を、酸素を含有する気体から遮断する工程を含む方法。前記安定化方法は、溶液を光から遮断する工程をさらに含むことが好ましい。【選択図】図２
