Nuts are 40-80% composed of unsaturated fatty acids. These unsaturated fatty acids are beneficial to the human body. When unsaturated fatty acids are oxidized due to the radiation effect of the sun or contact with oxygen in the air, Hydroperoxides are generated, which are then decomposed into aldehydes, and ketones. These substances cause the rancid aroma. When the oil is oxidized some fatty acids will be released, which will increase the acidity of the oil and destroy the nutrients in the food. Therefore, when the nut start to have the rancid odor it means that the quality of the nut is declining.
Data from: https://health.udn.com/health/story/6037/3442104

Meat will deteriorate after long-term storage because oxygen free radicals react with meat protein, fat and other components, changing the original properties of these molecules. Most people think that as long as the meat is frozen, it can delay preservation, this is not the case; because low temperature can delay the growth of microorganisms, but if the preservation tool does not block oxygen, the lipolytic enzyme that causes fat oxidation rancidity is still active at -30. Long-term freezing still has the problem of deterioration of fat and oil, especially in frozen meat that has been frozen for a long time.
Data from:https://www.agriharvest.tw/archives/15114

There are many large and small mold and bacteria particles in the air. If they fall on the food and are in an oxygen-rich condition, matched with Taiwan’s humid climate, the food will easily spoil or become moldy.