Understand the "deteriorated expressions" of eight kinds of food

"Speaking" seems to be the patent of higher animals. Whether they are happy or not, whether they are physically comfortable or not, they will tell each other through language. In fact, in a sense, food can also "speak". It will "convey" certain specific information to you through some external changes. Let’s take a look at how to “listen” to the expressions of food.

Expression 1: Yogurt becomes sour

Interpretation: Lactic acid bacteria multiply rapidly, but their vitality decreases

The acidity of yogurt is limited. If the yogurt is separated from the cold chain during storage and logistics, such as being left at room temperature or outdoors, the lactic acid bacteria will multiply rapidly and cause the acidity of the yogurt to increase and exceed the acceptable range. Such yogurt will taste very sour, and the activity of lactic acid bacteria will decrease, and the degree of milk protein denaturation will increase, which is not conducive to human absorption and is not conducive to gastrointestinal health. The longer the yogurt is stored, the harder it is to ensure its quality. Therefore, do not buy a lot of yogurt at one time, and try to drink it immediately after purchase.

Expression 2: Potatoes turn brown after being cut, and freshly squeezed juice changes color

Interpretation: Enzymatic browning occurs, vitamin C is lost

"Phenol oxidase" exists naturally in fruits, vegetables and potato foods, and they are also rich in "polyphenols" with antioxidant effects. If they come into contact with each other and are combined with oxygen, "enzymatic browning" will occur, that is, phenol oxidase catalyzes the oxidation reaction of colorless polyphenols to produce colored "quinones". These quinones can polymerize with each other, making the color darker and darker. Although no harmful substances are produced in this process, the antioxidant capacity of polyphenols decreases after browning, and vitamin C is also lost. To avoid this reaction, you should scald the raw materials with boiling water before juicing to inactivate the phenol oxidase, or add a tablet of vitamin C when juicing. If potatoes, lotus root slices or yam cannot be cooked immediately after cutting, they should be put in water with a drop of vinegar.

Expression 3: Roasting meat produces a brownish red color, and roasting steamed buns turns yellow

Interpretation: Maillard reaction may produce carcinogens

After being cooked at high temperatures above 120°C, foods containing carbohydrates and amino acids will turn yellow and brown and release an attractive aroma. This reaction is called the Maillard reaction. For example, braised pork, roast duck, toast, pancakes, fried food... almost all processing that turns food darker or browner after cooking promotes the Maillard reaction. Acrylamide (a carcinogen) is a by-product of this reaction. It itself has nothing to do with aroma and has no color, but generally speaking, the darker the color and the stronger the aroma of the food after heating, the higher the acrylamide content will be. Therefore, do not bake steamed bread slices or bread slices until they are too yellow, and try to eat less baked, fried, or puffed potato products, such as potato chips.

Expression 4: Purple cabbage turns blue after blanching

Interpretation: Anthocyanins turn blue when exposed to alkali, and their stability decreases

Foods such as strawberries, purple cabbage, purple sweet potatoes, and purple rice are rich in anthocyanins, which are powerful antioxidants that can protect the human body from damage by free radicals. The characteristic of anthocyanin is that it appears red in acidic conditions and usually turns blue in alkaline conditions. There may also be transitional colors such as purple and green in between. The water in the north is generally weakly alkaline. These color changes are normal and you can eat it without worry, but generally speaking, anthocyanins are relatively stable under acidic conditions. For example, if you add a little vinegar, the color of purple cabbage will become more red.

Expression 5: Green leafy vegetables turn yellow after being fried

Interpretation: Chlorophyll demagnesium, loss of magnesium

The reason why green vegetables appear green is mostly due to the magnesium ions in chlorophyll. When light shines on chlorophyll, porphyrin (a compound in chlorophyll) containing magnesium ions will prevent other colors of light from coming in and out, and only reflect green light back. But during heating, chlorophyll is very unstable. Studies have shown that the acetic acid (acetic acid) in vinegar will destroy the structure of chlorophyll, turning chlorophyll into "de-pheophyll", and the vegetables will quickly turn yellow-brown. Therefore, add less vinegar or no vinegar when stir-frying green leafy vegetables.

Expression 6: Floccules appear after heating milk

Interpretation: The protein is denatured or there are too many microorganisms, and it has gone bad.

There are two reasons why flocs appear after heating milk. First, certain proteases present in milk change the structure of the protein in the milk, thereby destroying the stability of the milk and causing denaturation and coagulation during the heating process. Although this kind of milk has not exceeded its shelf life, it is not recommended to drink it. Second, the proliferation of residual microorganisms in the milk causes the acidity of the milk to change, further destroying the stability of the milk, resulting in the appearance of flocs. In short, it is not recommended to drink milk that has flocs after heating.

Expression 7: The surface of tofu is sticky

Interpretation: Bacteria grow, may contain toxins

Tofu, like meat, is a protein-rich ingredient, so it is easy for bacteria to grow in poorly ventilated and high-temperature conditions, causing the tofu to become sticky. If the strain is pure, there is no need to worry about its safety. However, there are many different bacteria in the home environment, including harmful bacteria, some of which will produce toxins, and washing with hot water cannot guarantee that they will be completely washed away. Therefore, it is not recommended to eat sticky tofu. In addition, high-protein foods such as dried tofu and animal offal should also be thrown away if there are sticky or slippery substances on the surface.

Expression 8: Vinegar grows white hair

Interpretation: The moldy film produced by Mucor may contain other pathogens

The "white hair" growing in vinegar is most likely the mold film produced by Mucor, which is widely present in the environment. If the white hair on the vinegar is simply caused by Mucor, there will be no big problem if you remove the mold film and continue to eat it. However, there are other pathogenic bacteria in the air. If they also multiply in vinegar, they may pose a health threat. Therefore, it is best not to consume vinegar that has white hair on it.