Question

how do food industries prevent rancidity

Answer 1

Food industries store the products under refrigeration or make the food stored in an airtight container. Rancidity occurs because of the presence of Oxygen in the air. So, if the food is some type of packed food, they remove air and fill the package with hydrogen which does not spoil the food.

Answer 2

This is done either by vacuum packing or packing under inert(usually nitrogen) atmosphere. The food does not come in contact with atmospheric oxygen and get rancid unless pakage is opened.

Wet food stuffs are aseptically packed by use of steam to ensure elimination of bacteria or moulds if any. Like tetrapack. As long as the pack is sealed it remains good.

However all materials has dome porosity and over prolonged storage (6 months to one year), there is a possibility of food getting degraded.