In life, we often encounter similar problems, such as taking a box of yogurt to go out in the morning and drinking it until noon, we will find that it is more sour than before. What's the matter? Can you still drink this kind of yogurt? There are many other things that are similar. You might as well have a look with Xiaobian!
Expression 1: roasted meat turns brown and steamed bread turns yellow.
Interpretation: Maillard reaction may produce carcinogens.
When foods containing carbohydrates and amino acids are cooked at a high temperature above 120 ℃, they will turn yellow and brown, and release attractive aroma. This reaction is called Maillard reaction. For example, braised meat, roast duck, baked bread, pancakes, fried & hellip; all kinds of deep brown color processing after cooking, almost all promote Maillard reaction. Acrylamide (a carcinogen) is a by-product of this reaction. It has nothing to do with aroma and has no color. But generally speaking, the darker the color of food after heating, the stronger the aroma, and the higher the content of acrylamide. Therefore, don't bake steamed bread and bread slices too yellow. Try to eat less baked, fried and puffed potato products, such as potato chips.
Expression 2: potatoes turn brown after being cut and fresh juice changes color.
Interpretation: the occurrence of enzymatic browning, loss of vitamin C.
Phenoloxidase is naturally found in fruits, vegetables and potatoes, and it is also rich in antioxidant polyphenols. If they meet together and oxygen is added, they will undergo enzymatic browning, that is, phenoloxidase catalyzes the oxidation of colorless polyphenols to produce colored quinones. These quinones can polymerize with each other to make the color darker and darker. Although no harmful substances were produced in this process, the antioxidant capacity of polyphenols decreased after browning, accompanied by the loss of vitamin C. To avoid this reaction, you should blanch the raw materials with boiling water before pressing the juice to inactivate the phenoloxidase, or add a piece of vitamin C when pressing the juice. If you can't cook potatoes, lotus root slices or yams immediately after cutting, you should put them into the water dripping with vinegar.
Expression 3: purple cabbage turns blue after blanching.
Interpretation: anthocyanins turn blue when they meet alkali, and their stability decreases.
Strawberry, purple cabbage, purple potato, purple rice and other foods are rich in anthocyanins, which is a powerful antioxidant and can protect human body from free radical damage. The characteristic of anthocyanins is that they are red in acid, blue in alkaline, purple, green in the middle, and weak alkaline in northern water. These discoloration are normal and can be safely eaten, but generally speaking, anthocyanins are relatively stable under acidic conditions. For example, with a little vinegar, purple cabbage will be more red.
Expression 4: green leafy vegetables turn yellow after frying.
Interpretation: chlorophyll can remove magnesium and lose magnesium.
The reason why green vegetables are green is mostly due to the magnesium ion in chlorophyll. When the light shines on chlorophyll, porphyrin (a compound in chlorophyll) containing magnesium ion will make the light of other colors come back and go, only let the green light reflect back. But during the heating process, chlorophyll is very unstable. Studies have shown that acetic acid (acetic acid) in vinegar will destroy the structure of chlorophyll, turn chlorophyll into 'magnesium free chlorophyll', and vegetables will quickly turn yellow brown. Therefore, stir fried green leafy vegetables to add less vinegar or not.
Expression 5: milk floccules after heating.
Interpretation: protein denaturation or microbial too much, has deteriorated.
There are two reasons for flocculent milk after heating. First, some proteases in milk change the structure of protein in milk, thus destroying the stability of milk, resulting in denaturation and coagulation during heating. Although this kind of milk has not passed the shelf life, it is not recommended to drink. Second, the proliferation of residual microorganisms in milk leads to the change of milk acidity, which further destroys the stability of milk, resulting in flocs. In a word, milk with floccules after heating is not recommended.
Expression 6: vinegar grows white hair.
Interpretation: the floating membrane of moldy flowers produced by Mucor may contain other pathogenic bacteria.
The 'white hair' in vinegar is probably the floating membrane of moldy flowers produced by Mucor, which is widely distributed in the environment. If the white hair of vinegar is caused by Mucor alone, it will not be a big problem to remove the floating film of moldy flowers and continue to eat. But there are other pathogenic bacteria in the air. If they also breed in vinegar, it may pose a health threat. Therefore, vinegar with white hair is best not to continue to eat.
Expression 7: yogurt turns sour.
Interpretation: lactic acid bacteria propagate rapidly, but their vitality declines.
The acidity of yogurt is limited. If yogurt is separated from the cold chain in the process of storage and logistics, such as being placed at room temperature or outdoor environment, lactic acid bacteria will multiply rapidly and lead to the increase of yogurt acidity, which is beyond the acceptable range. This kind of yogurt will taste very sour, and the activity of lactic acid bacteria will decline, and the degree of milk protein denaturation will increase, which is not conducive to human absorption and is not conducive to the development of yogurt Healthy intestines and stomach. The longer you keep it, the harder it is to guarantee the quality of yogurt. Therefore, don't buy a lot of yogurt at one time, try to buy and drink it now.
Expression 8: the surface of tofu is sticky.
Interpretation: bacteria breed and may contain toxins.
Like meat, tofu is rich in protein, so it is easy to breed bacteria in the case of poor ventilation and high temperature, which makes tofu sticky. If the strain is pure, there is no need to worry about its safety. However, there are many miscellaneous bacteria in the home environment, which can be mixed with harmful bacteria, some of which can produce toxins, and washing them with hot water can not guarantee complete washing. Therefore, sticky tofu is not recommended. In addition, dried beans, animal viscera and other high protein foods should also be thrown away if there are sticky and slippery substances on the surface. For our health, we must pay attention to food hygiene in our life.