Grapefruit juice to extract herbs for tincture
Use the old school method and extract with aqueous ethanol. It is more efficient and more healthy:


The solubility of most compounds to be extracted from herbs is likely to be much higher in ethanol than in water (or juice). You get more out of the plants. 
The juice was initially pasteurized, but once opened, it will not necessarily stay free from microbes and/or might get mouldy. The risk of infections is definitively lower when staying with aqueous ethanol for extraction.