Why does food rot?
If you want to keep food fresh, you must first understand the reasons why food spoils.
Overall, there are four main reasons.
1. Caused by microorganisms.
During the production, processing, transportation, and storage of food, food may be contaminated by microorganisms commonly found in the environment. The growth and reproduction of microorganisms can decompose the nutrients in food, and eventually decompose the protein in food into peptides and organic acids, producing ammonia odor and sour taste. At this time, the food also loses its original toughness and elasticity, causing the color to become abnormal.
2. It is the function of enzymes.
Foods often contain lipase, protease, amylase, polyphenol oxidase and peroxidase. The action of these enzymes will accelerate the metabolism of food and promote the gradual deterioration of food. Rancidity of daily rice and fruits is caused by fermentation caused by the decomposition of carbohydrates by enzymes.
3. It is a chemical reaction of food.
Many fats and oils in food contain unsaturated bonds in their molecular formulas. These bonds are very unstable and can be easily oxidized, causing a series of chemical reactions. Oxidized fat has a strange smell, such as the fat turning from white to yellow. For fruits and vegetables, vitamin C and natural pigments (such as tomato pigments, etc.) will also be oxidized, reducing the quality of the fruits or even deteriorating.
4. Moisture.
Dry food can easily absorb moisture from the air and become damp, resulting in poor taste and even food mold and mildew. Deteriorated food not only changes its appearance, but also loses its original color, aroma and taste, and its nutritional value is reduced. It also contains corresponding toxins and is harmful to human health.
Therefore, food preservation can start from these points. Simply put, it is to destroy the living conditions of microorganisms, prevent food raw materials from being exposed to the air, reduce enzyme activity, and prevent food oxidation and moisture.
Common preservation methods and principles
Under normal circumstances, we will use the following 4 more commonly used methods.
1. Cryopreservation
Within a certain period of time, low-temperature preservation can inhibit the activity of microorganisms and enzymes in food and slow down food spoilage. Low-temperature storage can be divided into two methods: refrigeration and freezing, and refrigerators are generally used.
2. Vacuum storage
Also known as decompression packaging, all the air in the packaging container is extracted and sealed to maintain a high degree of decompression in the bag. The scarcity of air is equivalent to the effect of low oxygen, leaving most microorganisms without conditions for survival. At the same time, it also isolates bacteria from contact with the outside world and extends the shelf life of food.
3. Dehydration and drying
Dehydration and drying refers to reducing the moisture content of food, inhibiting the growth of spoilage microorganisms, and allowing food to be stored at room temperature for a long time through methods such as sun drying, shade drying, oven drying, and smoking. Dried sweet potatoes, dried beans, dried peppers, bacon, dried sausages, etc. are all applications for dehydration and drying.
4. Chemical preservation
Chemical preservation mainly includes sugar, salt, vinegar, etc. Generally, a salt concentration of 10% can inhibit most microorganisms, but cannot kill them. The sugar content of candied foods must reach 60%-65%. This type of food should also be stored in sealed, moisture-proof conditions, otherwise it will easily absorb water and reduce the preservative effect. Common salted fish, bacon, pickles, candied fruits, candied fruits, etc. Vinegar can increase the concentration of hydrogen ions and is mostly used in various vegetables, such as kimchi, sauerkraut, etc.
Commonly used saving tools
An organized refrigerator needs a little extra help. Let’s take a look at commonly used saving tools!
Under normal circumstances, the tools you will use are: plastic wrap
1. What is plastic wrap:
Plastic wrap is a thin layer of plastic film. Its principle of preservation is mainly to isolate food from surrounding links. There are three main functions of plastic wrap: first, to prevent food moisture loss; second, to prevent food moisture loss. The second is to reduce the mutual contamination between food odor and bacteria in the air; the third is to reduce the contact between food and external air, delay the oxidation of fruits and vegetables, and extend the storage time.
Polyethylene (PE): Does not contain plasticizers. It has excellent low temperature resistance (the lowest operating temperature can reach -100~-70℃), good chemical stability, and is resistant to most acids and bases (not resistant to oxidizing acids). But its stretchability and stickiness are not as good as PVC.
Polyvinyl chloride (PVC): has good stretchability, flexibility, and stickiness, but may contain plasticizers, antioxidants, etc. The plasticizers used in daily PVC are mainly dibutyl terephthalate, dioctyl phthalate, etc. These chemicals are toxic, and antioxidants such as lead stearate and polyvinyl chloride are also toxic. Therefore, when using PVC, please be careful to avoid contact between PVC and oily foods, and avoid heating in microwave ovens, which may cause the precipitation of toxic substances in PVC. But if it is only used for cooling, you can still use it with confidence.
Polyvinylidene chloride (PVDC): Does not contain plasticizers. It has excellent ability to block water vapor, oxygen, odor and fragrance, and is recognized as a plastic packaging material with good comprehensive performance in terms of barrier properties. The disadvantage is that the price is higher.
2. Precautions when using plastic wrap:
(1) Qualified plastic wrap products on the market themselves are safe and sterile, but we must pay attention to avoid external bacterial contamination when using them. Clean your hands and kitchen utensils (such as knives for cutting melons, chopping boards for placing food, etc.) in advance.
(2) Plastic wrap can only isolate food from the environment, but cannot inhibit the growth of bacteria. Therefore, after wrapping food in plastic wrap, remember to store it in the refrigerator or freeze it.
(3) To preserve fruits and vegetables, you can choose any kind of plastic wrap. But if heating or microwave heating is required, plastic wrap with obvious high temperature resistance and microwave heating markings is required.
3. Specific usage of plastic wrap
Such as banana, mango, lychee, etc.
For bananas with stems, wrap the banana head tightly with plastic wrap to slow down its rapid blackening and rotting.
Like lychees and longans, you can cut off the branches, put them in a plastic bag, tie the bag tightly, and put them in a cool place.
Principle: Most tropical fruits are not resistant to low temperatures and are not suitable for refrigeration. Otherwise, it is easy to suffer cold damage, the peel will be sunken, some dark brown spots will appear, and the nutrients will be destroyed, leading to deterioration.
Not only can you save money by learning to keep food fresh, but you can also be responsible for the vegetables you buy and avoid wasting food! Moreover, a neat refrigerator and a systematic storage method are also reflections of an exquisite lifestyle. It may be a small thing, but if done well, it will bring a lot of sense of accomplishment!
