Jeff is right, never never never use any vegetable oils on it. You can get mineral oil at your local pharmacy if the paint store doesn't have it. It is non-toxic and won't go rancid. Get the "light" variety because it soaks in better.
I made a cutting board for my mother in grade school. At the instruction of the teacher , I treated it with vegetable oil. That was almost 30 years ago. She's still using it and it hasn't yet gone rancid.I'm not saying it can't happen but it hasn't happend to this one yet.
Seeing as how this butcher block is to be used in a restaurant, it will see a lot of use daily.
I would be inclined to just leave it alone with no finish at all. You could argue that the wood will soak up the juices of the food being prepared on it and thus pose a helth risk but how long would any finish protect it from doing that under those conditions.
A point of intrest.
I recently saw a TV program , were several differant materials were tested for use as cutting boards. They were tested for bacteria left behind after heavy use.
Wood scored the highest of all the materials tested.
I found out from experance.I made a cutting block to fit in a sink,finished it with veg.oil and it turned rancid so I got it back,sanded it all down
and redid it with mineral oil and it is still in use and that was 10 or 12 yr. ago
I have a maple butcher block that is at least 40 years old. It measures 24" x 30" x 18" deep. The surface is end grain as the 2 x 2 blocks are all dovetailed ( sliding ) together. I have treated it as did my folks with vegatable / peanut/ olive oil and have had no problems with bacteria. Like JP says, you always wipe it clean with mild detergent when done cutting food.
Thanks everybody,I think I'll give it a couple of wipes with mineral oil.Should any time lapse between the last treatment and usage,and should my sister also do follow-ups,or just wipe it clean?
The Taunton book on kitchen projects, recommends routine clean-up with soap and water, and periodic wipe down with a mild bleach solution (10 parts water to 1 part bleach). They also recommend periodic re-oiling after the bleach treatment.