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Yang M.,Gansu Agricultural University | Yang M.,Functional Dairy Product Engineering Laboratory of Gansu Province | Shi Y.,Functional Dairy Product Engineering Laboratory of Gansu Province | Shi Y.,Gansu Agricultural University | And 2 more authors.
Dairy Science and Technology | Year: 2016

Microbial transglutaminase (mTGase) crosslinking is a useful method for significantly improving the physical functionality of proteins. This study focused on the effect of mTGase modification on the functional properties of yak and cow caseins, including solubility, emulsifying property, water and oil absorption capacity, foaming property, and stability in the presence of Na+, Ca2+, and Mg2+. The results showed that the crosslinking degree of yak and cow caseins differed at the same mTGase concentration, but the change in functional properties of cow and yak caseins was similar. After mTGase crosslinking, the solubility of caseins decreased, while the emulsifying properties increased because of casein polymerization. MTGase crosslinking was very effective in improving water and oil absorption properties, stability in the presence of Na+, Ca2+, and Mg2+, and foaming activity, but did not affect the foam stability of cow acid caseins (caseins content of 94.22 %, w/w) and yak acid caseins (caseins content of 94.28%, w/w). The results could be used as a reference for selecting the proper modification method to improve the predetermined functional properties of caseins according to industrial processing requirements. © 2015, INRA and Springer-Verlag France. Source


Yang M.,Gansu Agricultural University | Yang M.,Functional Dairy Product Engineering Laboratory of Gansu Province | Cui N.,Gansu Agricultural University | Cui N.,Functional Dairy Product Engineering Laboratory of Gansu Province | And 5 more authors.
Food Chemistry | Year: 2015

Succinylation modifies the physicochemical characteristics and improves the functional properties of proteins. This study assessed the effects of succinylation on the conformation of yak casein micelles with seven degree of modification. The results revealed that succinylation contributed to the dissociation of casein micelles. With the increase of succinylated degree, soluble nitrogen and minerals content increased, while casein micelle size and polydispersity index of micelles decreased. Succinylation affected the spatial conformation of yak casein micelles: turn decreased, ß-sheet and α-helix increased, and irregular structure were non-significantly affected. The intrinsic and ANS fluorescence intensity decreased and the maximum emission wavelength shifted red with increasing succinylation. Based on the results, the structure of yak casein micelles was characteristic of the sub-micelle model. © 2015 Elsevier Ltd. Source


Yang M.,Gansu Agricultural University | Yang M.,Functional Dairy Product Engineering Laboratory of Gansu Province | Zhang W.,Gansu Agricultural University | Zhang W.,Functional Dairy Product Engineering Laboratory of Gansu Province | And 6 more authors.
Dairy Science and Technology | Year: 2014

Heat treatment is one of the essential operations widely used in most dairy processes, and heat stability is one of the essential properties of milk. Casein micelles are the major component in milk responsible for the heat stability of milk during processing. This study assessed the effects of heat treatment temperature and duration on the average size, turbidity, polydispersity index and heat stability of casein micelles in yak skim milk and distilled water. The results showed that whey protein had an important role in influencing the heat stability of casein micelles. The average size, polydispersity index and turbidity of micelles in skim milk were higher than those of micelles in distilled water in all cases while the heat stability of casein micelles in skim milk was lower than those in distilled water. As a result of the heat treatment, the size of micelles in skim milk increased due to complex of casein/whey protein formed via covalent bonds, whereas it decreased in distilled water attributed to the change of hydrophobicity in micelles. The size distribution of particles broadened with increasing heating temperature, resulting in the increase in turbidity and polydispersity index of casein micelles both in skim milk and distilled water. The micelles in skim milk combined with whey protein during heating. These findings will help processors design appropriate heating conditions for yak milk and yak casein products and help identify new opportunities for product development. © 2014 INRA and Springer-Verlag France. Source

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