Besides , the Hop Pellets which I use are bittering Hops and as far as I know , the antibacterial effect which
you mentioned is related to the aroma Hops which are usually added at the end of the Boil .
This is incorrect information (which in reading some of your posts you seem to be a victim of. for a lot of things.)
It is the isomerized alpha acids in the bittering addition from which the preservative action stems from. In fact if you look at many beers such as pilsners and light lagers,
they only have a bittering addition, there is no aroma or flavor stemming from the hops. So if what you believed was the case, then there would be no unsoured pilsners, vienna lagers, or just about any German Beer, since many of them only have a single bittering hop adidition.
As to the dfferent grade of extract, indeed there are too grades, the brewing grade is more pure in flavor than the baker's grade, BUT they are interchangable, just as you can bake with brewer's lme, you can make drinkable beer with the cooking grade extract. In fact the baker's grade LME you are getting is probably on par with the brewer's grade we got prior to legalization of homebrewing in 1978.
So that's not a source of your problem, the difference would be let's say if we made an all grain beer with grain we bought at the homebrew shop that may have been made and malted from last year's crop, and us growing our own barley, plucking it immediately , then malting it and making beer with it. Obviously the latter would be a tad better than the former, but they'd both work.
I think there's several issues at play here. I believe that you been given some bad fundamental information (like the hop info) and it's causing some problems. But I do wonder if initially the beer you dumped wasn't infected but just green,
but now that you have stopped using hops, you ARE making infected beer. Because all the sanitation in the world is NOT going to prevent un hopped beer from souring after a few days. A gruit is still a gruit whether or not you sanitized or not. The difference is going to be what type of infection grows in there.
I don't even no where to begin to get to the bottom of your issues, because there's so many variables at play here, from knowledge issues to ingredient issues to equipment issues to language issues.
I think before you brew again (whether it's with food grade extract or with beer extract") you need to post your recipe first and a step by step list of your brewing process, and let us see it, and then let us tweak it before you brew, and MAYBE we can get you step by steps past whatever it is you are doing to cause your beer to not survive.
There simply may be some 1 fundamental thing you are going incorrectly.
One thing though, when you use a vinyl tube to rack your wort, how are you starting the siphon? Also what is the % titratable Ioding in the providone you are using and what is your dillution ratio?