Acid-responsive properties of fibrils from heat-induced whey protein concentrate.
The heat-induced fibrils of whey protein concentrate (WPC) have demonstrated an acid-responsive property; that is, the fibrils went through formation-depolymerization-reformation as pH was adjusted to 1.8, 6.5, and back to 1.8. We investigated the microstructure, driving force, and thermal stability of 3.0% (wt) WPC nanofibrils adjusted between pH 6.5 and 1.8 twice. The results showed that the nanofibrils had acid-responsive properties and good thermal stability after reheating for 10h at 90°C and adjusting pH from 1.8 to 6.5 to 1.8. The content of WPC fibril aggregates was not much different with the prolongation of heating times during pH variation. Although the nanofibrils' structure could be destroyed only by changing the pH, the essence of this destruction might only form fiber fragments, polymers that would restore a fibrous structure upon returning to pH 1.8. A described model for the acid-responsive assembly of fibrils of WPC was proposed. The fibrils went through formation-depolymerization-reformation by weaker noncovalent interactions (surface hydrophobicity) as pH changed from 1.8 to 6.5 back to 1.8. However, the fibrils lost the acid-responsive properties because much more S-S (disulfide) formation occurred when the solution was adjusted to pH 6.5 and reheated. Meanwhile, fibrils still possessed acid-responsive properties when reheated at pH 1.8, and the content of fibrils slightly increased with a further reduction of α-helix structure.
Key Laboratory of Dairy Science, Ministry of Education, Northeast Agricultural University, 150030 Harbin, People's Republic of China. Electronic address: xhh3161@126.com.
Hong-Hua
HH
Xu
Key Laboratory of Dairy Science, Ministry of Education, Northeast Agricultural University, 150030 Harbin, People's Republic of China.
Jing
J
Wang
Key Laboratory of Dairy Science, Ministry of Education, Northeast Agricultural University, 150030 Harbin, People's Republic of China.
Shi-Rong
SR
Dong
Key Laboratory of Dairy Science, Ministry of Education, Northeast Agricultural University, 150030 Harbin, People's Republic of China.
Wen
W
Cheng
Key Laboratory of Dairy Science, Ministry of Education, Northeast Agricultural University, 150030 Harbin, People's Republic of China.
Bao-Hua
BH
Kong
Key Laboratory of Dairy Science, Ministry of Education, Northeast Agricultural University, 150030 Harbin, People's Republic of China.
Jun-Yan
JY
Tan
D000143:Acids / Q000737:chemistry*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008894:Milk Proteins / Q000737:chemistry; D008956:Models, Chemical; D012996:Solutions; D000067816:Whey Proteins / Q000737:chemistry*
D000143:Acids; D008894:Milk Proteins; D012996:Solutions; D000067816:Whey Proteins
acid responsive; fibrils; microstructure; whey protein concentrate