Does the "Popular Science Times" "dyed kelp" really exist?

The picture shows a kelp drying ground in Chengshan Town, Rongcheng City, Shandong Province, where workers dry kelp.

(Courtesy of Visual China)

□ Liu Xiaoman Cheng Jingmin

Kelp, also known as kelp and river cabbage, are perennial large edible algae. Kelp is inexpensive and nutritious and is an important seafood resource.

Kelp is rich in kelp polysaccharides, fucoidan, fucoidan, brown algae starch, and contains acidic polysaccharides, and also contains taurine, bifidocrine and other active ingredients. Kelp also contains protein, fat, carotene, vitamin B, calcium, iron, phosphorus and other trace elements. Kelp is an ideal food with low calories; for people who are deficient in iodine, kelp can treat goiter; kelp has anti-radiation and slimming, skin beautification, hair treatment. Studies have found that kelp has a good regulatory effect on blood lipids and blood sugar, and has anti-immunity, anti-anemia, anti-tumor, antioxidant, including some lead removal, detoxification and other functions. But recently many netizens said that the kelp they bought was dyed, what is going on?

"Dyed kelp" really exists

We usually talk about dyeing, it is more common to soak copper sulfate in kelp, and individual unscrupulous traders will choose to use copper sulfate to dye kelp to make kelp look more bright, because it can make kelp green and not fade. From a safety point of view, if a large amount of short-term intake will cause acute copper poisoning, patients will have some vomiting and diarrhea and other symptoms, more seriously, there are a very small number of people will have kidney failure; if a long-term large amount of kelp treated with copper sulfate will affect the growth and development of children, adults, will cause heavy metal accumulation poisoning, the most worrying situation is that it may cause some necrotizing hepatitis, including hemolytic anemia.

How to identify "dyed kelp"

In this regard, ordinary people are difficult to distinguish, we can share several simple methods: first, touch the surface of kelp, if the texture is relatively hard, the surface is not very sticky, and smells lighter than the taste of normal kelp, then this kelp does not have to buy; second, soak the kelp in water, observe whether it will fade; third, soak the kelp in water, find a thin wire to soak for a minute or two at the same time, if the kelp is soaked with copper sulfate, then the water soaked in kelp will slowly darken the surface of the wire, Fourth, fresh kelp has a strong fishy taste, and the kelp seafood taste soaked with pigment is not obvious; fifth, identify it with vinegar, boil the kelp with vinegar, if the green of kelp is from its own chlorophyll, then the chlorophyll will fade after encountering acid, becoming light olive green, if the kelp does not change color, it means that the green on the kelp is not its own color, but is dyed; sixth, the kelp skin that has been soaked with pigments and so on is very brittle, easy to break by hand, and the real fresh kelp skin is smooth and not easy to be broken.

A few tips for picking kelp

First, look at the color. Brown-green or earthy yellow kelp is a relatively normal color; dark green kelp is fresh kelp after boiling the color turns green, and then after cooling, salting, dehydration and other processes processing, generally used as a cold dish; and emerald green kelp may be soaked by adding pigments, consumers should pay special attention when choosing, do not buy brightly colored kelp.

Second, the touch should be sticky, the brown-green kelp selection is sticky, and the dark green kelp is processed, and the surface is not sticky. However, the chemically treated kelp does not feel sticky to the touch.

Third, choose one with white frost on it. The layer of white powder on the kelp is called mannitol, and after the kelp water is dried and dried, the mannitol will precipitate and attach to the surface of the kelp, thus forming white frost. Mannitol has the effect of lowering blood pressure, diuresis and reducing swelling. If the dried kelp is partially red or partially yellow, do not choose, such kelp may be contaminated, and the quality and nutritional value will be greatly reduced.

(The first author is a master's degree student in social medicine and health management of Shanxi Medical University, and the second author is a director of the Chinese Society of Food Science and Technology and a professor of Shanxi Medical University)