explode () and mySQL query

I am trying to add a search feature to my shopping cart.

I am wanting to use PHP to develop the query for mySQL.  I have the
following code figured out:

foreach(explode(" ", $keyword) as $key) $query .= " $key, ";

This produces:

WHERE shopping_cart_product.product_description IN ( Jesus, is, Lord, )

The weakness is the trailing , after the last word the user types in.

How can I eliminate this?

Ron