Fresh fruit & vegetable produce is bought under ripe & treated with sulphur dioxide and sulphites applied as a gas.
Other things like bags of cut salad leaves, fresh fruit salads etc... are washed in a strong chlorine solution. Whilst chlorine levels in tap water are tightly controlled and are typically restricted to no more than 0.5 mg/litre. It is common practice to use chlorine washes that contain up to 100 mg/litre of chlorine to rinse food that's sold as 'ready-to-eat', or to put it another way, 200 times as much chlorine as tap water.
Then as if that's not enough they are packed in 'modified atmosphere packaging'. Essentially the oxygen is removed from the bags & replaced with a mixture of primarily carbon dioxide & nitrogen to prevent any bacteria that survived the chlorine wash from multiplying. It is of paramount importance that foods packaged without oxygen are stored and used exactly according to instructions (usually within 24-72 hours of opening). The absence of bacteria means there will be no odours when the food starts to spoil, and you may not be aware when it becomes unsafe to eat. By the time it does start smelling even slightly off it would be a very bad idea to risk eating it.
