title: Incorporated glucosamine adversely affects the emulsifying properties of whey protein isolate polymerized by transglutaminase.
abstract: Glucosamine (GlcN) and microbial transglutaminase (Tgase) are used separately or together to improve the emulsifying properties of whey protein isolate (WPI). However, little is known about how the emulsifying properties change when GlcN residues are incorporated into WPI cross-linked by Tgase. We used Tgase as a biocatalyst to cross-link WPI in the presence of GlcN in a liquid system for 12 h at a moderate temperature (25°C). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analyses indicated that protein polymerization and GlcN conjugation occurred simultaneously, phenomena also supported by the loss of free amines (9.4-20.5%). Addition of 5 U Tgase/g protein improved the emulsifying properties of moderately cross-linked WPI polymers. The Tgase-treated WPI polymers had a larger particle size (∼2.6-fold) than native WPI, which may have reduced coalescence and flocculation in an oil-in-water emulsion system. However, the incorporation of GlcN residues into WPI, predominantly via enzymatic glycation, partly inhibited the cross-links between the WPI molecules catalyzed by Tgase, reducing the size of the WPI polymers 0.81- to 0.86-fold). Consequently, WPI+GlcN conjugates provided less stability to the emulsion. Moreover, high NaCl concentration (0.2 M) decreased the emulsifying properties of the WPI+GlcN conjugates by neutralizing negative electric charges in the glycoconjugates. However, the improved emulsifying properties of WPI cross-linked by Tgase may be useful in food processing at higher NaCl concentrations due to the formation of the thicker steric barrier at the oil-water interface.
authors.affiliation: College of Food Science and Engineering, Northwest A&F University, No. 22 Xinong Road, Yangling, Shaanxi 712100, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Chen
authors.affiliation: College of Food Science and Engineering, Northwest A&F University, No. 22 Xinong Road, Yangling, Shaanxi 712100, China.
authors.forename: Niamat
authors.initials: N
authors.lastname: Ullah
authors.affiliation: College of Food Science and Engineering, Northwest A&F University, No. 22 Xinong Road, Yangling, Shaanxi 712100, China.
authors.forename: Chenyi
authors.initials: C
authors.lastname: Li
authors.affiliation: College of Agricultural and Environmental Sciences, University of California, Davis, 1 Shields Avenue, Davis 95616.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Hackman
authors.affiliation: College of Food Science and Engineering, Northwest A&F University, No. 22 Xinong Road, Yangling, Shaanxi 712100, China.
authors.forename: Zhixi
authors.initials: Z
authors.lastname: Li
authors.affiliation: Laboratory of Meat Processing and Quality Control of Ministry of Education, College of Food Science and Technology, Synergetic Innovation Center of Food Safety and Nutrition, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Xinglian
authors.initials: X
authors.lastname: Xu
authors.affiliation: Laboratory of Meat Processing and Quality Control of Ministry of Education, College of Food Science and Technology, Synergetic Innovation Center of Food Safety and Nutrition, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Guanghong
authors.initials: G
authors.lastname: Zhou
authors.affiliation: College of Food Science and Engineering, Northwest A&F University, No. 22 Xinong Road, Yangling, Shaanxi 712100, China. Electronic address: fengxianchao1@hotmail.com.
authors.forename: Xianchao
authors.initials: X
authors.lastname: Feng
mesh_terms: D000818:Animals; D004655:Emulsions / Q000737:chemistry; D005944:Glucosamine; D008894:Milk Proteins / Q000378:metabolism*; D011503:Transglutaminases / Q000378:metabolism; D000067816:Whey Proteins
chemical_list: D004655:Emulsions; D008894:Milk Proteins; D000067816:Whey Proteins; D011503:Transglutaminases; D005944:Glucosamine
keywords: cross-linked whey protein isolate; glucosamine; microbial transglutaminase; whey protein isolate and glucosamine conjugates