I am infusing olive oil with truffles. How can I do it safely? Heating the oil destroys the truffle smell and pickling it is a sure way to do the same. Are there any other methods? Perhaps some type of filter that will eliminate the particulates?
Edit This answer assumes that you want a shelf-stable oil. If you are going to use up the oil immediately (or within 3 days and refrigerate), methods like the pressure charging from moscafj's answer don't pose a safety problem.
Simply, you can't. I am not sure how industrial oils are made,
maybe they are irradiated or simply made under sanitized conditions and at the end microbiologically checked to ensure that a given batch isn't contaminated, but it isn't something you can do at home.
There are no methods accessible to home cooks to prevent botulinum in low-acid foods. Heat won't work, as botulinum bacteria don't just live like any other bacteria, they also form spores which will survive temperatures which would have incinerated other species with a single form. You can never reach these temperatures in a watery medium, e.g. in canning purees, in industry it is done in canners with much higher pressure than home pressure canners. In oil, you could theoretically reach the temperatures as you are not limited by the water's boiilng point, but as you pointed out, the flavor will change a lot. In the worst case, you will have to bring the oil to above smoking point to ensure safety.
Filters won't work, as any filters small enough to hold back bacteria are too tight to permit something as viscous as oil to flow through, and botulism toxin isn't "particulate matter", it is dissolved in the food.
Dave Arnold developed an effective way to infuse oil with aromatics that are heat sensitive. To employ it, you need an ISI or other brand whipper. Here is an example: https://www.starchefs.com/product_education/iSi/whipper/html/recipe-lemon-infused-extra-virgin-olive-oil-dave-arnold.shtml
I've had great success with the technique and see no reason why you couldn't use it with truffles. From a brief google search, it looks like you should refrigerate this oil and use it within a month to avoid any risk from botulism.