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I need a broad-spectrum antifungal (yeast and mold) agent for an aqueous non-food product (pH $\simeq$ 6) that contains 20% v/v alcohol (ethanol or isopropanol). A key requirement is that it not UV-yellow if it comes into contact with textiles (e.g., clothing) after drying.

I would prefer it to be a food-grade preservative—or, barring that, something not on the California Prop. 65 list. What preservative (or combination of preservatives) would work, and at what concentration should I use them?

Sodium benzoate and potassium sorbate can be effective anti-fungal agents when used in combination. However, these would not work here, since they don't have significant antimicrobial activity at pH $\simeq$ 6. In addition, potassium sorbate is known to yellow (at least in solution) when exposed to UV; and since sodium benzoate is aromatic, it might UV-yellow as well.

I've contacted both Sigma and Lonza (which has a specialist preservative division). Sigma said they can't make a recommendation at that level of detail, and Lonza said they would need to send me to their business office to set up a research contract for that.

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  • $\begingroup$ This is a question about formulation/toxicology. It may be better suited for biology or medical sciences SE. With regard to that, it has to be GRAS and is intended for topical use (will not be ingested)? $\endgroup$
    – Buck Thorn
    Commented Jan 14, 2021 at 8:13
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    $\begingroup$ It will not be ingested, correct. Biology SE and Medicine SE would know what compounds would be antifungal, but they won't know what won't yellow when exposed to UV, and particuarly how yellowing might be textile-dependent. And the latter two points are the trickier parts, which is why I asked it here. Indeed, I suspect if I posted this on either of those sites, they'd recommend it be moved to Chemistry SE. $\endgroup$
    – theorist
    Commented Jan 14, 2021 at 8:21
  • $\begingroup$ Is the preservative for preservation of the formula, or of the target textil ? Natural or man-made fibres ? $\endgroup$
    – Poutnik
    Commented Jan 14, 2021 at 9:46
  • $\begingroup$ @Poutnik For the preservation of the formula. Both natural (silk, linen, wool, cotton) and man-made textiles. $\endgroup$
    – theorist
    Commented Jan 14, 2021 at 9:54
  • $\begingroup$ You say it is a non-food product but it must be food for the fungi. What elements are the in the sample, and what metabolite is in it for the fungi to digest and get hold of some Gibbs energy? I didn't think yeast would grow at 20% ethanol or isopropanol. $\endgroup$
    – Karsten
    Commented Jan 18, 2021 at 21:54

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