askST: Are there differences in eggs from kampong chickens, free range chickens and black chickens?

Reader Linda See wrote in to ask about the differences between kampong/free-range chicken eggs, those laid by black chickens and generic brown eggs: "How do we differentiate between these eggs and if kampong/free-range eggs and black chicken eggs have more nutritional value as compared to generic eggs?"

Food reporter Kenneth Goh found out.

According to Ms Petrina Lim, head of the Centre for Applied Nutrition Services at Temasek Polytechnic's School of Applied Science, it is difficult to use the attributes of eggs such as the shell colour and colour of egg yolk to determine the breed of chickens that they come from.

All eggs start off white and as they pass through the hen's oviduct. Protoporphyrin pigment is deposited on the surface of eggs as the shell is being formed. The colour of the egg depends on the breed of hens, and each breed of hen has a few varieties.

The colour of kampong chicken egg shells are light brown while those of black chicken, which is from the Silkies breed, is cream or brown-coloured.

A shopper at the NTUC Fairprice outlet at Toa Payoh HDB Hub.  ST PHOTO: KUA CHEE SIONG

As for the colour of the yolk, it is reflective of the type of feed that the hens are given. If the hens feed on wheat, they will produce pale yellow yolks, while those which feed on green plants or corn-based diets will produce yolks darker in colour.

Ms Lim points out, however, that the sizes of chicken eggs can be determined from the breed of the hen.

Kampong and black chickens produce smaller eggs ranging from 39g to 42g per egg. This is because they are not good egg producers as they tend to be broody (hens that want their eggs to hatch). A generic egg weighs from 50 to 54g.

Nutrition-wise, contrary to what many believe, the nutrition value in kampong and black chicken eggs are not necessarily higher than that in generic eggs.

All eggs have the same protein and fat content regardless of their colour and grade.

Eggs also contain proteins and 14 essential vitamins and minerals, like Vitamins A, D, and E, as well as anti-oxidants.

However, some egg producers in the market have come up with "designer eggs" by altering the feed of hens with specific nutrients such as Omega-3 and Vitamins D & E. These nutrients are passed from the hen's diet into the eggs.

Ms Lim notes that these eggs are more expensive due to higher production costs.