Background: Sialic
acids are a family of ninecarbon sugar compounds with carboxylic acyl
derivatives. It exists in bacteria, fish, mammals and other living organisms,
participates in and regulates many important life events, such as cell
recognition, membrane flow, endocytosis and so on. Sialic acid is usually
located in the outermost layer of the sugar part of the cell membrane and the
key positions of secreted glycoconjugates (glycolipids, glycoprotein and lipopolysaccharide).
Sialic acid (Sia) is an important material foundation for variety of the
structure and founction of glycoconjugates. Sia has been known as nearly 50
members, including N-acetylneuraminic acid (Neu5Ac), N-glycoulylneuraminic
acid (Neu5Gc) and deaminoneuraminic acid (KDN) as its core monomer. The rest of
the sialic acids are derived from these three monomers. The contents of Sia in
Chinese food products are unknown. Objective:
To determine the contents of Sia in raw and cooked red meat, seafood, poultry
and so on. Design: The following
food products were purchased from a Chinese supermarket:
pork, beef, lamb, salmon, cod, tuna, cow milk, cheese, butter, duck,
chicken and chicken eggs. Human milk was collected from Xiamen Maternity and
Child Health Care Hospital (Xiamen, China). All tissues were homogenized and
hydrolyzed with 0.05 M, 0.1 M and 0.2 M TFA
for 150 min at 80°C in dark, respectively. The concentrations of
Neu5Ac, Neu5Gc and KDN were determined by using HPLC with fluorescence
detector. Results: The contents
of total Sia (μg/g tissue or μg/mL liquid sample) in Chinese raw meat were
highest in lamb (269.60), followed by pork (254.88), duck (200.63), chicken (162.86)
and beef (88.03). The percentages of Neu5Gc were 36.08%, 26.48%, 0%, 0% and
28.40%, respectively. Cod contained higher levels of Sia (171.63) than salmon (104.43)
and tuna (77.98). Only Neu5Ac was 50 found in detected aquatic product. Egg
yolk contained the highest level of Sia (682.04), and a higher level of Sia (390.67)
was found in the egg white. Also our result showed that human milk contained extremely
high level of Sia (602.55). Neu5Ac was the predominant form of Sia in all the
deteced samples. KDN was found in cow milk only among the samples, the content was
1.14 μg/g. Conclusion: The
highest content of Sia in examined Chinese foods was found in 56 eggs, followed
by lamb, pork, duck, cod, chicken, salmon, beef and tuna. Knowledge of the
Sia content in conventional foods may help us to better understand possible
medical disorders involving the uptake of the “non-human” Neu5Gc from our diet.