Question

what is the use of keeping food in air tight containers

Answer 1

Thanks for asking the question.
Keeping food in air tight containers helps against rancidity. .When oxygen molecules come in contact with other substances from metals to tissues, they oxidize. So when fats and oil oxidizes they become rancid which changes their smell and taste.
Since the food is completely sealed, we can store it for a log time without spoiling.
Food remains fresh in containers without losing its moisture to air.
Hope I helped.

Answer 2

you can also try some more

we keep them in tight containers because food contains fats and oil.As oils and fats gets oxidized they become rancid .The smell and taste changes. This is called rancidity .This, to avoid rancidity we use tight containers .