Porphyra

CCTV News (Reporter Zhang Ke-yin): Recently, a video about "the indestructible porphyra is made of plastic film" has gone viral online. Can we still happily make friends with porphyra egg drop soup in the future? The reporter learned from several affected local porphyra processing companies that they have reported the case to the public security organs. To clear up your doubts, we will now sort out the past and present of porphyra.

What are porphyra and plastic film

Porphyra is a general term for symbiotic algae in the sea, a kind of organism. The algae are membranous, purple or brown-green, and the shape varies with the species. It grows on rocks in the intertidal zone of shallow seas. There are many species, mainly porphyra yezoensis, porphyra haitanensis, porphyra gansuensis, etc. Artificial cultivation has been carried out in coastal areas of China. Artificial cultivation species include porphyra yezoensis and porphyra haitanensis, and the dried products sold on the market are mainly these two varieties.

Plastic film is generally made of thermoplastic plastics such as polyvinyl chloride, polyethylene, and polypropylene, and is a chemical product.

Identification by naked eyes

Four methods are simple and easy to operate

According to the previous rumors about "fake laver" by relevant units and media, there are four simple and easy methods: water blistering, burning, hand tearing, and boiling. The first is the water blistering method: real laver absorbs water and is smooth after being soaked in water, while plastic film does not absorb water and is not smooth. The second is the burning method: the burning of real laver will produce a smell similar to burning hair, and after the flame is extinguished, a substance like ash is left; the burning flame of plastic film is very large, dripping with grease and having a pungent smell, and the remaining burning substances are shrunken together. The third is the hand tearing method: tear the soaked sample by hand, the real laver is easy to tear and has little elasticity, while the plastic film is not easy to tear and has strong elasticity. The fourth is the boiling method: boil the unsoaked laver in water, which floats on the water surface before boiling, and increases slightly in volume after boiling, not completely floating on the water surface. The volume of plastic film remains unchanged before and after boiling, and floats on the water surface.

Laboratory testing

Lavender and plastic film are very different

In order to further verify that "plastic film is not reliable for laver", let's see how the laboratory tests? Dr. Wu Yantao of Beijing Food Safety Monitoring Center introduced to reporters that considering the quality characteristics of laver and plastic bags and the differences between the two, Beijing Food Safety Monitoring and Risk Assessment Center has formulated a laver identification plan, using amino acid analyzer, infrared spectrometer, scanning electron microscope and other advanced technical means to identify the authenticity of 45 laver samples and detect certain characteristic components. The results analysis shows:

Scanning electron microscope results of laver sample cross section

Scanning electron microscope results of plastic bag sample cross section

From the appearance, the microscopic morphology of laver and plastic bag cross sections is significantly different. The cross-section structure of laver is complex, with two layers of film on each side, and neatly arranged laver cells in the middle, while the cross-section structure of the plastic bag is dense, with only tear marks left when shearing, and no complex multi-level structure;

Infrared spectrum of laver sample

Infrared spectrum of plastic bag sample

From the spectrum, the infrared spectra of laver samples of different brands are highly similar, with protein characteristic absorption peaks near 1643cm-1 and 1539cm-1, while plastic bags have no characteristic absorption in the above bands.

From the perspective of ingredients, high levels of protein and amino acids were detected in laver, and the content distribution was relatively concentrated, and high levels of organic arsenic, phosphorus and calcium were enriched, with average contents of 35.8mg/kg, 5989mg/kg and 4124mg/kg; no protein and amino acids were detected in plastic bags, and the corresponding organic arsenic, phosphorus and calcium contents were <1mg/kg, <0.05mg/kg and 1038mg/kg respectively. Organic arsenic and phosphorus can effectively identify the use of plastic bags in laver adulteration.

Dr. Wu said that according to the test results, none of the 45 laver samples sent for inspection found the problem of using plastic bags to make fakes as mentioned in the online video, and the problem of deliberately using waste plastic to make laver should not exist.

No plastic film counterfeiting was found in the sampling inspection in the past three years

In the final analysis, what everyone is most concerned about is the situation of laver on the market. Zhang Weimin, deputy director of the Risk Monitoring Department of the Beijing Food and Drug Administration, said that according to statistics from the supervision and sampling database, Beijing has sampled 278 laver samples in the past three years, testing preservatives such as benzoic acid and sorbic acid, colorants such as lemon yellow and sunset yellow, heavy metals such as lead, inorganic arsenic, methylmercury, polychlorinated biphenyls, nitrites, sulfur dioxide, pathogenic bacteria, molds and nearly 30 other items. Three samples failed, with a pass rate of 98.9%. The unqualified factors were that two samples exceeded the lead standard and one sample exceeded the sulfur dioxide standard. No fake plastic film samples have been found so far. It seems that everyone can enjoy the nutritious laver without worry!

How to choose high-quality laver

Dr. Wu Yantao suggested that you should pinch and smell the laver before buying it. High-quality laver is usually dark brown or purple brown, has a natural luster, feels fluffy and elastic, and has no odor.

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