Fridge odours are something that every commercial kitchen owner suffers at some point. This is quite understandable when you think about it, due to all the foodstuffs and drinks that are stored in refrigerators, particularly when spillages occur.
The first place to check in a fridge (not frost-free) is the drain channel at the back, this can also be referred to as a "wet-wall" fridge. The moisture formed by condensation gathers on the back wall or, in older models, on the evaporator plate (also on the back wall of the appliance). This moisture forms small droplets of ice as the fridge cools and turns back into liquid as the fridge enters a defrost cycle; obviously that water has to go somewhere.
You can also check the tray that collects water on the top of the compressor at the back (motor, usually black) as foodstuffs can work their way down there and create an awful smell. Calcium build up can also occur again leading to bad odours.
In virtually every appliance of this type there is a drain hole below that wall, or plate, that the water runs into this goes to a tube that deposits the water in a tray on top of the compressor. The heat from the compressor evaporates the liquid into the air harmlessly. Often that drain hole can get blocked and this can lead to water in the fridge another fault caused by poor cleaning, check that first if you do have a problem as it may well not be a fault covered by warranty. If that drain is blocked, or partially blocked with spilled foodstuff then it can create a terrible smell in the fridge as the foodstuffs decompose as well as presenting a potential health risk.
Next, check the door seals. If you gently pull the seal away from the door you will see a cavity where spilled (particularly liquids) foodstuffs can be trapped, again leading to a bad smell as they decompose and, again, raise a potential health risk.
Fridges themselves do not use parts or gases which produce smells, In more or less every case it is food or drink which has either been spilt, containers left open/broken or produce that has been over looked which has past its use by date. It is for this reason each and every shelf, compartment and standing area should be cleaned on a regular basis.
Lemon based agents, or lemon juice itself acts as an excellent cleaning product, being acidic it does cut through most grease etc. whilst leaving a pleasant odour. If you have had an odour problem leaving a lemon, cut in half in the fridge will help remove any lingering smells. Baking soda is also a good way to keep smells at bay. Either wash you fridge out with baking soda and water or place an open box of baking soda somewhere near the bottom of the fridge which will ensure an odour free fridge for some time.
There also many commercial products on the market that work equally as well. Fridge de-odourisers and fridge mats are available from online retailers at relatively modest prices.