What color changes do foods have in commercial refrigerators and freezers?
Everyone in real life will find that the food in the freezer sometimes changes color. What is the reason? Why does color change occur in the freezer in the freezer?
Presumably, many people don't know what is going on. Today, Cookeryaki is here to give you a brief explanation. Freezing food in the freezer during the freezing process, except for the discoloration caused by refrigerant leakage (for example, when the ammonia leaks, the orange color in the carrot will turn blue, the white color of the onion, cabbage, and lotus seeds will turn yellow), and the others will be at room temperature. The discoloration that occurs underneath occurs during the long-term frozen storage of commercial refrigerators, but the speed is very slow.
(1) Discoloration of fat:
As mentioned above, poly-fat fish such as octopus, sardines, etc., will be oxidized and rancid due to fat oxidation during the freezing process of the freezer. In severe cases, it will become sticky, produce odor and lose the commercial value of the food.
(2) Discoloration of vegetables:
The surface of plant cells has a cell wall with cellulose as its main component, which has no elasticity. When the plant cells are frozen in the freezer, the cell wall will swell, and under the action of oxidase, the fruit and vegetable foods are prone to browning. Therefore, before the quick-frozen vegetables, the raw materials are usually blanched, and the peroxidase is passivated so that the frozen vegetables do not change color in the frozen storage.
If the temperature and time of blanching are not enough, the peroxidase inactivation is incomplete, and the green vegetables will turn yellow brown during the freezing process; if the blanching time is too long, the green vegetables will also yellow brown, which is because vegetables The leaves contain chlorophyll and are green. When chlorophyll becomes pheophytin, the leaves lose their green color and are yellowish brown. Acidic conditions promote this change. Vegetables are blanched in hot water for too long, and the organic acid in vegetables is dissolved in water to become acidic water, which promotes the above-mentioned color change reaction. Therefore, correctly grasping the temperature and time of vegetable blanching is an important part of ensuring the constant color of frozen vegetables in the freezer.
Let's briefly talk about why there are color changes in food in commercial refrigerators and freezers. Then let the freezer price tell you by example, so that everyone can understand the process of food color change in the freezer in more detail. In the case of fish, for example, the browning of red fish is most representative of the browning of tuna meat. Tuna is a fish with high economic value, and Japanese people have the habit of eating tuna sashimi.
The tuna meat is frozen in the freezer at -20 °C for more than 2 months, and its flesh color changes from red to dark red, reddish brown, maroon, and brown, and the commercial value of the sashimi decreases. This phenomenon occurs because myoglobin in the muscle is oxidized to produce oxidized myoglobin. Tuna is a red meat fish with a large amount of myoglobin in the muscles. When the fish dies, the muscle protein is separated from the oxygen into a reduced state due to the end of oxygen supply in the muscle, which is dark red. If the fish is cut and placed in the air, the reduced myoglobin obtains oxygen from the cut surface and combines with oxygen to form oxygenated myoglobin, which is bright red.
Oxygenated myoglobin and reduced myoglobin containing divalent iron ions are automatically oxidized if they continue to be left for a long time, and oxidized myoglobin containing ferric ions is formed to be brown. The discoloration of frozen tuna meat in the freezer has a great relationship with the freezing temperature. When the freezing temperature is -18 °C, the browning of tuna meat is more significant. After storage for 2 months, the oxidized myoglobin production rate Has reached 50%. As the freezing temperature decreases, the rate of myoglobin oxidation slows down and browning delays. When the freezing temperature of the freezer is in the range of -35 to -78 °C, the generation rate of oxidized myoglobin does not change much, and the color retention time is long. Therefore, in order to prevent the discoloration of frozen tuna meat, the freezing temperature should be at least -35 ° C. If the ultra-low temperature freezer of -60 ° C is used, the color retention effect is better.
