I don't know, I think you'll just need to give it some time. A sanitized strainer bag won't affect anything. So is the sour-ish component out of line with what you would get from pineapple ( because pineapple obviously has some tart acidity in its own right) ? I am guessing that the white residue is pectin, since you mention that you pasteurized.
I've made a lot of fruit beers, with fresh fruit and purees. Different schools of thought, but I've never pasteurized fruit and make good beer with fruit. I subscribe to Denny's attitude that beer that is fermented has a FAR less chance of infection at that point (hell, he's 'dry mushroomed'), as opposed to pre-fermentation. I've dry hopped a very large amount of hops, and a considerable amount of fruit post fermentation and never had an infection I could attribute to it. My idea is that the T58 could be contributing some tartness as well as the pineapple. I say give the beer time and cold conditioning and let us know what you end up with. I think you're good. Good Luck !