decrease up to

Hi,
I wrote a sentence:
"Fungal fermentation resulted in pronounced decrease of the amount of sugars, on average up to 7%".
I meant that, as a result of fermentation, the amount of sugars lowered significantly and now it amounts 7% of its initial level. Is it correct?
I would be very grateful for your help.

The decrease amounts to 93% of the original amount. But I don't think you want to say that. You would have to talk about a decrease to 7% of the initial level and change your sentence accordingly (I am not supposed to do it for you).
Don't forget the indefinite article: "a pronounced decrease".

Thank you very much.