Effect of egg yolk lipids on structure and properties of wheat starch in steamed bread

Abstract Hen egg is commonly used in bakery products, such as cakes, bread, and cookies, which are all abound with starch. Egg yolk lipids (EYL) with different polarity can affect the structure and properties of starch, as well as steamed bread-making performance. EYL were mainly divided into neutral lipids, cholesterol and phospholipids with increasing polarity by thin layer chromatography. Results from Rapid Visco Analyzer showed that both cholesterol and phosphatidylcholine (PC) promoted gelatinization of wheat starch, but neutral lipids did not. Texture analysis indicated that hardness of wheat starch gels significantly decreased only with PC, caused by an increasing in the spacing between double helical cross-links as characterized by differential scanning calorimetry. Furthermore, a single helix structure of amylose-PC complex was confirmed by molecular simulation and X-ray diffraction. Finally, yolk can be used to soften the firmness of starch-based food such steamed bread.