Additives to bacterial cultures to improve soluble expression of proteins

We are considering trying to add additives to bacterial cultures to see if they improve solubility of some proteins we express: L-arginine, glycyl-glycine, sorbitol and betaine. I would be glad to receive recommendations and experiences, also if they haven't worked.
Side-question: should we get cell culture-certified compounds, or would "normal", much more economical ones suffice? (i.e. are they likely to contain side-products that would affect bacterial growth?).