What’s the difference between red and black grapes, or white and purple cabbage? And why should you take note of such colour differences?

We sort through these multi-coloured foods and ask three Singapore experts – chef Rosalind Lim, nutritionist Vinitha Ang and senior lecturer of nutrition Kalpana Bhaskaran – on the significance of these colour variations.


  • Red, purple and black grapes contain resveratrol and quercetin – antioxidants not present in green grapes. The darker the skin, the more antioxidants they contain.
  • Darker grapes also have more catechin – another antioxidant – that prevents viral infection and lowers the risk of heart disease.
  • Green grapes are less sweet and contain fewer calories compared to the same amount of red grapes.

Tip: To get rid of their waxy coating, rub flour over the grapes before washing them.


  • Red-fleshed watermelons: These are generally less sweet than the yellow variety. The red colouring comes from lycopene, an antioxidant that reduces the risk of cancer.
  • Yellow-fleshed watermelons: They contain more vitamin C to boost your immune system and help you battle the flu.
  • Watermelon seeds are full of nutrients – protein, calcium, magnesium, potassium, iron, phosphorous and zinc. Chew and swallow, if you don’t mind them; unfortunately, there’s no way to make them more palatable.

Tip: For juicier watermelons, choose the heavier ones. Those with white patches on the skin also tend to be sweeter.


  • Purple cabbage: Contains anthocyanin, a potential cancer-fighting antioxidant that gives the cabbage its colour. It also has more than six times the vitamin C of white cabbage. Eat it braised in a stew where it’s slightly bitter, or raw in a salad.
  • White cabbage: Even though it has less nutrients than purple cabbage, it’s a great source of calcium, folic acid and fibre. Studies have indicated that cabbage may help reduce breast cancer risk. Best in soups and stir-fries.

Tip: For more flavourful white cabbage, choose those with darker green leaves.

A study at the University of Bern, Switzerland, suggests that eating onions could lower the risk of osteoporosis. They’re great in all dishes, from stews and soups to sauteed dishes.

  • Red onions: These make you tear more than white onions because of the higher content of pyruvic acid, which causes more tearinducing enzymes called alliinase to be released when the onions are cut. The natural chemical also makes them more pungent. The red colour of the onions indicates that they contain more flavonoids. They can be stir-fried, boiled in a broth or eaten raw in salads or burgers.
  • Yellow onions: The different onions are fairly similar in nutrient content – they are rich in vitamin C, dietary fibre, folic acid and quercetin, an antioxidant with antiinflammatory properties that could reduce arthritic pain.

Tip: Cook onions over low or medium heat; high heat makes them bitter.


  • Red bell peppers: They are rich in lycopene, the antioxidant that makes them red. Lycopene is believed to lower blood pressure, reduce cholesterol and minimise the risk of cancer. Red bell peppers also have more carotenoids, which build your immune system.
  • Green bell peppers: While they have less lycopene and carotenoids, they are still a good source of fibre, vitamin K and manganese. Vitamin K helps the body absorb calcium while manganese regulates blood sugar levels.

Tip: Best served stir-fried as they are less tasty than red bell peppers and are not as palatable when eaten raw.


  • Orange sweet potatoes: The orange hue comes from betacarotene and other carotenoids – compounds that are good for your immune system. They also contain more dietary fibre and are softer and sweeter.
  • Purple sweet potatoes: They contain the highest amounts of cyanidins and peonidins – antioxidants that reduce the risk of cancer and cardiovascular disease. They are firm, dry and crumbly, with a yam-like texture.

Tip: To bake sweet potatoes, wash them but leave them unpeeled. Then prick them all over with a fork and cook in the oven at 200 deg C for 45 min to an hour.


  • Golden kiwi fruit: They have slightly more vitamin C (about 13mg per 100g) than green kiwi fruit. They are also sweeter and do not leave a metallic aftertaste like the green ones sometimes do.
  • Green kiwi fruit: They are less sweet, but they contain more chlorophyll, which gives them their green colour. Chlorophyll helps tissue repair, and stimulates the growth of red blood cells. It’s also a natural breath freshener.

Tip: Studies from the University of Oslo show that two to three kiwi fruit a day can protect you from stroke and deep vein thrombosis.

Vinitha Ang is a nutritionist and instructor at Nutrihub – the Organic Fusion Cafe. The cafe is located at 46 Temple Street. Visit www.nutrihub.blogspot.com for more information on the cafe.

Rosalind Lim is the co-founder and chef of Onaka Healing Kitchen and Cooking Studio. The Onaka group provides classes aimed to educate individuals and families on maintaining healthy dietary and lifestyle habits. To find out more, go to www.onakagroup.com.

Kalpana Bhaskaran is a senior lecturer of nutrition at Temasek Polytechnic.

This article was originally published in SimplyHer May 2011.