Choy sum, also known as Chinese flowering cabbage, is a nutritious edible flower stalk in the Brassica (mustard) family of leafy vegetables. This cool-season green is also spelled “Cài xīn” ((菜心), which means “the heart of a cabbage".
Botanical name: Brassica rapa var. parachinensis.
Common Names – Yu Choy Sum, Cantonese pak choy, yellow flower choi sum, and sawi bunga (Malay).
Choy sum is a small, quick-growing, annual herbaceous plant reaching about 7 to 15 inches in height. It prefers frost-free, cool climates (15°C to 25°C), which promotes strong stalks and increases sweetness.
It is grown in mid-to-late spring and early autumn to avoid frost. It prefers well-drained, fertile soils with sufficient moisture.
Choy sum features alternate leaves with small, four-petaled, yellow flowers on the top of each shoot. The leaves are ovate and light to dark green or even purple on some purple-Cài xīn (Hon Tsai Tai). If continues to grow, the flowers develop into silique fruit with small, dark, round seeds inside.
Harvest begins 30–50 days after sowing when the flower buds are fully developed but not open. Harvest leaves, flower buds, and stems together for sale in the markets.
Choy sum leaves and stems are the storehouse of numerous phytonutrients that have health promotional and disease prevention properties.
It is low in calories (48 calories per 100 g raw leaves) and fats. Nonetheless, its dark-green leaves and stems carry plenty of health-benefiting antioxidants, vitamins, and minerals.
Choy sum greens are a good source of dietary fiber. Research studies suggest that inclusion of soluble and insoluble fibers in the diet helps control cholesterol levels through interfering its absorption in the colon. Dietary fiber also facilitates smooth bowel movements, and thereby, eases constipation as well offers protection against hemorrhoids and colon cancer.
Choy sum are a rich source of antioxidants like flavonoids, indoles, sulforaphane, carotenes, lutein, and zeaxanthin. Indoles, mainly Di-indolyl-methane (DIM) and sulforaphane, have proven benefits against prostate, breast, colon and ovarian cancers by virtue of their cancer-cell growth inhibition, and cytotoxic effects on cancer cells.
Fresh leaves are excellent sources of natural folates. 3.5 Oz (100 g) raw choi sum carries 425 μg or 106% daily recommeneded levels of folates. Folate-rich diet help allveiate anemia and play a role in the prevention of neural-tube defects in newborn babies.
The greens are also a moderate sources of other B-complex group of vitamins such as, thiamin, riboflavin, niacin, pantothenic acid, etc. Many of them paly a pivotal role as cofactos in the substrate metabolism inside the human body.
Fresh choi sum is an excellent sources of vitamin-C. 3.5 Oz (100 g) fresh leaves provide 46 mg or about 71% of recommended daily intake. Vitamin-C (ascorbic acid) is a powerful water-soluble antioxidant that offers protection against free radical injury and flu-like viral infections.
Choy sum leaves are also a very good sources of vitamin-A (provide 766 IU or 25.5% of RDA per 3.5 Oz (100 g). Vitamin-A is an essential nutrient required for maintaining healthy vision, hair and skin. Consumption of natural foods rich in and retinol equivalents (flavonoids) has been found to protect against lung and oral cavity cancers.
Fresh Choy sum are an excellent source of several essential minerals such as calcium 70 mg (7% RDA), iron 1.7 mg (21% RDA), magnesium, potassium, and zinc.
Regular consumption of choy sum in the diet is known to prevent osteoporosis, iron and folate deficiency anemia and believed to offer protection against cardiovascular diseases, and colon and prostate cancers.
|Principle||Nutrient Value||% of RDA|
|Total Fat||0.3 g||1.5%|
|Dietary Fiber||2.8 g||7%|
|Vitamin A||767 IU||25.5%|
|Vitamin C||46 mg||71%|
Choy sum is native to South China, and it is one of the most popular leafy-vegetables found at local markets across East-Asia and Southeast Asia. Today, it is also found at specialty grocers and Asian markets in Europe, Australia, and the United States.
Choy sum can be harvested at any stage- from tiny greens to flowering tops. While young, its leaves have a mild flavor and are prepared much like spinach. As the plant grows, the flavor grows stronger and pungent, similar to mustard greens.
Choy sum is cool-season crops. Fresh farm greens flood markets peaking fall through spring. However, the fresh choice is available year-round, thanks to greenhouse farming practices.
In the market, buy fresh, crispy, dark green choi sum leaves with smooth stalks and flowering tops. Avoid wilt, spotted, or discolored leaves.
At home, keep the leaves in the refrigerator soon after purchasing. Use fresh choy sum greens as soon as possible to enjoy the flavor and nutrition benefits.
Choi sum can be stored for up to 3-4 days in cold storage, set at 5-8°C and more than 90% relative humidity.
Choy sum is a common green leafy staple in the Cantonese diet. Fresh leaves, flower buds, and stems are used in a variety of cuisines all over East Asia as well as in the west, where a significant Chinese diaspora exists.
Before cooking, wash the leaves thoroughly in clean running water to remove sand/any insecticide residues. Trim away thick petioles and stems.
Here are some serving tips:
|Choy sum stir fry in garlic sauce. Courtesy: Jonathan|
Grown-up choy sum stems and leaves may be preserved as a pickled vegetable and are also fantastic added into soups and stews or braised with aromatics such as rice wine, soy sauce, ginger, garlic, and spring onions.
Fresh tender choi sum greens are eaten raw in salads.
Stir-fry whole or chopped choi sum in garlic oil and combine with oyster sauce.
Like all other leafy greens, reheating of choy sum leftovers may cause conversion of nitrates to nitrites and nitrosamines by certain bacteria that thrive on prepared nitrate-rich foods, such as choy sum, mustard greens, spinach. These poisonous compounds may prove harmful to health.
Phytates and dietary fiber present in the choy sum may interfere with the bioavailability of iron, calcium, and magnesium.
Choy sum, being a Brassica family vegetable, contains oxalic acid, a naturally occurring substance found in some vegetables which may crystallize as oxalate stones in the urinary tract in some people. People with known oxalate urinary tract stones are advised to avoid eating vegetables belong to the Brassica family. Adequate intake of water is, therefore, necessary to maintain normal urine output.
Choy sum may also contain goitrogens which may interfere with thyroid hormone production and can cause thyroxin hormone deficiency in individuals with thyroid dysfunction.
(Medical Disclaimer: The information and reference guides on this website are intended solely for the general information of the reader. It is not to be used to diagnose health problems or for treatment purposes. It is not a substitute for medical care provided by a licensed and qualified health professional. Please consult your health care provider for any advice on medications.)
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Refer Stanford School of Medicine Cancer information Page- Nutrition to Reduce Cancer Risk (Link opens in new window).
Production Guide for Choy Sum—An Emerging Asian Vegetable in Florida -University of Florida-IFAS Extension (Link opens in new window).
Specialty Produce (Link opens in new window).