Purple sweet potato contains a lot of anthocyanins. Purple sweet potato soup turns green because anthocyanins are an unstable water-soluble pigment, which changes color due to the degree of acid and alkali, and turns red when it meets acid. It will turn green when it meets strong alkalinity and blue when it meets weak alkalinity; Neutrality will remain the original purple. "
Li, a chemistry teacher in north university of china, said that this phenomenon was caused by water. The pH of tap water in different areas is different, which will affect the color of purple potato soup. Some people put some alkaline noodles in order to increase the viscosity of porridge. If it is purple potato, it is normal to cook green porridge. Don't worry, you can eat normally.
Extended data:
Nutritional value of purple sweet potato;
Purple sweet potato is rich in dietary fiber, starch, vitamins and trace elements (selenium, iron, calcium, potassium, etc. ), anthocyanin, glycoprotein, carotene, dehydroepiandrosterone and other functional factors, with antioxidant, anti-tumor, enhancing memory, preventing hypertension, repairing myocardium, relieving liver dysfunction and enhancing immunity.
1, rich in anthocyanin: anthocyanin is a water-soluble substance widely found in plants, belonging to flavonoids and polyphenols, which mainly exists in the cell sap of fruits, stems and leaves of plants. Anthocyanin from purple sweet potato has antioxidant, free radical scavenging, antimutagenic, anticancer, cardiovascular disease, hyperglycemia and liver function improving effects.
2. Other active ingredients and their functions: In addition to anthocyanins, purple sweet potato also contains many active ingredients such as β-carotene, dehydroepiandrosterone (DHEA), glycoprotein, dietary fiber and polyphenols. It is reported that the beta-carotene of purple sweet potato can reduce active oxygen and eliminate free radicals, and has physiological effects such as cancer prevention, anti-tumor and immunity improvement. β -carotene has the functions of sweating and beautifying.
Professor A. Sevez, a biochemist from Philadelphia Medical College, isolated DHEA from sweet potato, which is a precursor of sex hormone, and can regulate obesity, diabetes, anti-cancer and virus infection, improve memory, immune response and stress response, relieve tension, resist cortical diseases, delay aging and promote protein synthesis.
3. Glycoprotein in purple sweet potato can prevent fat accumulation in cardiovascular system, protect arterial elasticity, prevent connective tissue atrophy of liver and kidney, and promote lubrication of digestive tract, respiratory tract and joint cavity. Dietary fiber can prevent constipation, colon cancer, cardiovascular diseases and obesity, and eliminate exogenous harmful substances.
Polyphenols in purple sweet potato selectively combine with protein, the outer layer of HIV, to form immune function and hinder HIV infection, which is considered as an important substance to inhibit the onset of AIDS? .
References:
People's Network-Why is the soup cooked by purple potato green?
Baidu encyclopedia-purple potato