Heat treatments may harm healthy compounds in soymilk

By Francis Yang

- Last updated on GMT

Related tags Soybean China

Heat treatments used to kill harmful bacteria in soymilk may be
damaging the healthy compounds found in the beverage, according to
a Chinese scientist.

Huang Huihua, a researcher at the South China University of Technology in Guangzhou, told AP-Foodtechnology.com that he has found both pasteurization and UHT decreases the amount of isoflavones in soymilk. Isoflavones are found in high concentrations in soybeans, and appear to act like the female hormone oestrogen. They have been widely researched for their potential to prevent diseases related to lower levels of this hormone, such as osteoporosis, breast cancer and prostate cancer. But a study carried out by Huang and colleagues at the Hong Kong Polytechnic University last year shows that consumers are unlikely to get any isoflavone-related benefits from drinking soymilk. The study, published in the 6 March online edition of the Journal of the Science of Food and Agriculture​ (86; 1110-1114), investigated the effect of heat on degradation of three isoflavones - genistein, daidzein and glycitein - in soymilk processed over a range of temperatures and time. It found that "heating substantially decreased the daidzein and glycitein contents in soymilk"​. Given that commercial soymilk is heated both before and after packaging to extend its shelflife, the beverage may contain few isoflavones when eventually consumed. Heat also caused degradation of one of the best-known isoflavones, genistein, although this one proved more stable than the others. For example, in-bottle sterilization of soymilk, which requires heating at 121 degrees Celsius for five minutes, "will destroy about 87 per cent of daidzein, 72 per cent of glycitein and 17 per cent of genistein"​, said the researchers. However, pasteurization - heating at 95 degrees for one hour - will degrade 77 per cent of daidzein, 66 per cent of glycitein but increase genistein by 33 per cent. The findings could be significant for China's infant soymilk industry, which is relying on soymilk's benefits to boost sales. Although soymilk has long been consumed in China and is recognized as a healthy beverage, it is now facing competition from the growing dairy industry, which offers liquid milk at much lower prices. Soymilk producers tend to focus on preserving the protein and vitamin content of soymilk rather than the isoflavones. The Jiangsu-based VV Group, the biggest producer of soymilk powder in China and a recent entrant to the soymilk market, never checks the isoflavone quantity in its finished product, according to a production worker. Huang Yushu, product control manager at leading soymilk firm Yeo Hiap Seng, said his firm tests the protein content of its soymilk every day but tests isoflavones once a month. However Tu Shunming, a soymilk industry expert in China's National Research Institute of Food and Fermentation Industries, sounded a note of caution about the research. "China has long practiced heating soymilk to temperatures ranging from 95 to 110 degrees celsius to asepticize it and Chinese women are still healthier than western women, a phenomenon that led the West to conduct research into soy,"​ he said. According to Tu, China produced around 300,000 tons of soymilk last year.

Related topics Soy-based ingredients

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