Food Storage

Before our food is available to us in food markets after industrial processing, it is subjected to long periods of storage. The storage period has a strong impact on the nutritional and vital substance content of the food. The most important environmental factors in food storage are oxygen, light, temperature and storage duration. They particularly influence the nutrient and vital substance value (macro- and micronutrients) of the respective foods. Vitamin C should be emphasized here, as it is water-soluble, very sensitive to heat and oxygen. Any way of storage under the influence of these factors leads to losses of vitamin C, the degree of which depends on the intensity of external influences – high/low temperature, much/less exposure to light – as well as on the period of storage. In the presence of oxygen, oxidation processes often occur, which are of particular importance for vital substance loss and food spoilage. Carbohydrates and proteins are relatively stable to oxygen. Essential unsaturated fatty acids, on the other hand, transform into toxic compounds – for example, the so-called trans fatty acids – take on an unpleasant odor – “rancidity” – and lose nutritional value. In addition, oxygen and light accelerate enzymatic reactions and thus vitamin degradation – especially of vitamins A, C, D, K, E and B2, B6 – as well as food spoilage. This is additionally favored by pollutant inputs and injuries to foodstuffs. Oxygen thus limits the nutrient and vital substance content and the edibility of the food in terms of time. This is followed by interactions due to external influences with the food ingredients, with traces of heavy metals damaging the oxidation-sensitive vitamins A and C in particular. If the body lacks vitamin A, the regeneration of the red visual pigment rhodopsin is disturbed and night blindness and hypersensitivity to bright light are the result. When light hits our eyes, rhodopsin breaks down and must be regenerated. This is only possible with the help of vitamin A. In addition, the mucous membranes are damaged – they become dry – and the susceptibility to infections and the risk of cancer are increased [4.1]. Vitamin B1 can be destroyed by exposure to nitrite and, together with vitamin B12, is sensitive to sulfite. Sulfites are preservatives with antibacterial properties, which have antioxidant and enzyme-inhibiting effects in food to delay spoilage. For example, they are used in fresh lettuce, wine, dried fruits and in potato products. When potatoes are exposed to light and oxygen, they germinate and take on a greenish color, forming the harmful solanine. Cooking cannot destroy it, and in high concentrations it causes headaches, fever, and convulsions in humans. The ambient temperature also plays a decisive role, because the higher it is in relation to storage, the more loss of vital substances (micronutrients) occurs and the faster the food spoils due to strong enzymatic and bacterial activity. If ripe apples, which contain 10 mg of vitamin C per 100 g after fresh harvest, are stored at room temperature, the vitamin C is already degraded after a few weeks. Storing the same apples at 0°C shows no vitamin C loss in the same period. In the case of plant and animal products, the loss of vital substances during storage also depends on the previous processing. If, for example, vegetables are blanched before freezing, considerably more vitamins are retained during storage – for example, around 65% of vitamin C after 24 months – due to the effect of heat and the rapid cooling and freezing during the blanching process than in the case of unblanched frozen products – complete vitamin C degradation after just 6 months. However, this only applies to the heat-stable vitamins D, E, and K. The content of the heat-labile vitamins A, C, B1, B6, and B12, as well as that of the mineral potassium, is already greatly reduced during blanching.Unprepared vegetables that are kept refrigerated for fourteen days, such as in warehouses or refrigerators, show vitamin C losses of about 77%. The nutrients and vital substances are degraded from day to day, as the higher temperatures than for frozen foods accelerate the enzymatic and bacterial processes and facilitate the entry of free radicals – environmental toxins, harmful chemicals, industrial and cigarette smoke – which then support vitamin degradation.At room temperature, spinach can have only 30% of its original folic acid content after 3 days of storage. Similar losses can also be expected for vitamin C:

Vitamin C loss in spinach as a function of temperature and storage time:

In addition to temperature and time period, a cool, dry storage area, which should be clean and free of pests, is also an important measure for storage, which allows people to determine and control the micronutrient content of food. Low temperature, high relative humidity and short storage time contributes to food preservation with all its ingredients and maintains original good quality. In addition, spraying, leaching as well as dripping losses lead to low nutrient and vital substance content in food and deterioration of its enjoyment value. Either food that has already been prepared and cleaned is not adequately dried and covered for storage, or the product has been improperly packaged, has cracks and damage that causes liquid leaching and promotes quality loss due to oxygen and light exposure. If the cold chain is interrupted in the case of frozen products and the thawing process begins, valuable vital substances are lost due to the loss of water. Natural colorings and flavorings leach out and undesirable odors and flavors can form. To avoid accelerating the ripening of fruit, it should not be placed together with vegetables or potatoes. The fruit could also acquire a foreign taste.