What is the ruling on using the substance "sodium metabisulfite" (E223) in kunafa dough, given that it improves thread consistency and speeds up cooking? Is it permissible to add it to flour dough, and what are the safe alternatives that provide the same quality and quantities?

There is no harm in using foods that contain ingredients symbolized by (E), and there is no prescribed need to search for them meticulously. As for discussing this specific substance, its harms, benefits, method of use, and alternatives, that is not within our area of expertise.