At first I thought OP's sentence was badly-formed.
resistant against high temperatures means able to withstand high temperatures [without degrading].
...and without specialised knowledge of the "materials science" context,
resistant against stirring would ordinarily mean difficult to stir (by virtue of being viscous/thick).
Those two meanings involve very different roles for the term resistant against (like saying "I made haste and jam" to mean you made the jam quickly), which would be poor use of language.
BUT, per @Kris's answer and various comments, starch formulations may be degraded by stirring. Thus, in this particular context, resistant against stirring doesn't mean difficult to stir - it means not adversely affected by stirring.
Note that in more familiar "ability to withstand xxxx" contexts, we often encounter expressions like heat-resistant, frost-resistant, etc. However, given that Google Books records not a single instance of stirring-resistant, I don't think OP should feel too crestfallen at not having understood the usage.