Hi Mohammed - have you considered using a masking material and using something to stain it like super-strong coffee? I'm thinking that food would be the best thing to stain the food-safe item with. Also a light wipe with mineral oil prior to engraving might let you just wipe some coffee on, gently wipe off and let it sit inside the engraving... maybe even let it dry. Could take a few applications but would definitely be food safe. I would also recommend food coloring as a stain - it stains wood well (both intentionally and accidentally) and you have color options...
- Mak