Mineral oil is great for butcher block tops. You can get it at drugstores. Rub it on, let it sit, and then wipe off the excess. Repeat this treatment periodically.
Even better is to mix mineral oil and parafin about 50/50 and carefully melt it. It will mix together easily when warm. While it is warm (not hot) wipe it on with a paper towel and rub it into the wood. Let it dry overnight, scrape off the excess wax with a spatula or scraper, and wipe the top with a cloth until it has a nice sheen.
The wax bridges the small cracks in the wood block and prevents bacteria and stains from getting down into the wood.