Both vinegar and baking soda are effective natural deodorizers for a refrigerator. Your method of choice may depend on the type of odor you are trying to eliminate.
For mild odors, such as those caused by spilled milk or food, baking soda may be more effective as it can absorb and neutralize the odors. Simply place an open box of baking soda on one of the shelves in the refrigerator, and it will absorb the odors over time. You can also create a paste with baking soda and water and use it to scrub the interior of the fridge.