Preservatives: Grapefruit seed extract (GSE) is NOT a preservative

Grapefruit seed extract (GSE) is derived from the seed and pulp of grapefruits, and it may contain many lovely things - anti-oxidants, flavonoids, Vitamin C, citric acid, phytosterols, and tocopherols - but it is NOT a preservative. It may behave as an anti-oxidant in our products, but it will not keep the beasties out of your lotions and other creations.

Study after study has shown that the preserving power of GSE comes from the preservatives added to the product. Various studies have shown GSE contains benzethonium chloride, benzalkonium chloride, triclosan, and various parabens, and these are what offer the bacteria, fungus, yeast, and mould fighting powers attributed to GSE.

Here are a few studies that might interest you. I could post more, but I think these really do make the point pretty well.
Identification of benzethonium chloride in grapefruit seed extracts.
More information on benzethonium chloride in GSE. 
Aspects of the antimicrobial efficacy of GSE and its relation to preservative substances contained.