White plastic turns yellow after some time due to a chemical reaction that occurs when it is exposed to light, oils, etc. Below are different ways to get rid of yellow stains.
Baking soda may help to lighten the yellowed plastic. Take 1 cup of baking soda into a bowl and add enough water to make a thick paste. Apply it to the stained areas of your containers and scrub gently with a sponge. Now, leave this for 10 minutes. Rinse off and allow to dry completely before reusing. It may take several tries to lighten the plastic completely.
Lemon juice is very effective for removing stains. Slice a lemon in half and squeeze the juice into a bowl. Dip a sponge into the lemon juice to soak it. Rub this on the stained area of your containers, then set it outside in the sunshine for at least 1 to 2 days and then rinse off. The sun and lemon juice work together to remove the stains.
Bleach helps to remove stains and discolorations. Take 1 tablespoon of bleach into a bowl and add 1 cup of water. Fill your plastic container with this solution and let it soak for about half an hour. After soaking in the solution, give the container a good scrubbing with warm water and let it dry.
Mix equal parts of water and vinegar to create natural cleaning agent. Let the container soak in this solution for a few minutes. After soaking, wash the container as normal and let dry. If you are worried about the vinegar smell, then don‘t worry. It disappears after it dries.