Hey Terry,
Since you'll be preparing food, and ultimately eating the food that was on the wood I would not suggest using any type of coating (polyurethane, shellac etc...). This will chip off and little pieces will get in your food. Kinda like eating food prepared in a Teflon pan that's chipping away.
As far as I know, the best way to protect a natural wood surface that's designed for food preparation would be to give it an occasional coat of veggie/sunflower/olive oil. Let it soak in and reapply. No "Non natural" chemicals.
I'm curious to see what other suggestions there are.
Bob