Unfolding and Refolding of -Lactoglobulin Subjected to High Hydrostatic Pressure at Different pH Values and Temperatu
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- 作者：Josefina Belloque ; Rosa Chicó ; n ; Rosina Ló ; pez-Fandiñ ; o
- 刊名：Journal of Agricultural and Food Chemistry
- 出版年：2007
- 出版时间：June 27, 2007
- 年：2007
- 卷：55
- 期：13
- 页码：5282 - 5288
- 全文大小：168K
- 年卷期：v.55,no.13(June 27, 2007)
- ISSN：1520-5118
文摘
The unfolding of 
-lactoglobulin during high-pressure treatment and its refolding after decompressionwere studied by 1H NMR and 2H/1H exchange at pH 6.8 and 2.5 and at 37 and 25 
C. The extent ofunfolding increased with the pressure level. The structure of -lactoglobulin required higher pressuresto unfold at pH 2.5 than at pH 6.8. More flexibility was achieved at 37 C than at 25 C. Resultsindicated that the structural region formed by strands F, G, and H was more resistant to unfold underacidic and neutral conditions. The exposure of Trp19 at an earlier time, as compared to other proteinregions, supports the formation of a swollen structural state at pH 2.5. Refolding was achieved fasterwhen -lactoglobulin was subjected to 200 MPa than to 400 MPa, to 37 C than to 25 C, and toacidic than to neutral pH. After treatment at 400 MPa for 20 min at neutral pH, the protein nativestructure was not recovered. All samples at acidic pH showed that the protein quickly regained itsstructure. Hydrolysis of -lactoglobulin by pepsin and chymotrypsin could be related to pressure-induced changes in the structure of the protein. Compared to the behavior of the protein at atmosphericpressure, no increased proteolysis was found in samples with no increased flexibility (100 MPa,37 C, pH 2.5). Slightly flexible structures were associated with significantly increased proteolysis(100 MPa, 37 C, pH 6.8; 200 MPa, 37 C, pH 2.5). Highly flexible structures were associated withvery fast proteolysis (
200 MPa, 37 C, pH 6.8; 300 MPa, 37 C, pH 2.5). Proteolysis ofprepressurized samples improved only when the protein was significantly changed after the pressuretreatment (400 MPa, 25 C, 20 min, pH 6.8).
-lactoglobulin during high-pressure treatment and its refolding after decompressionwere studied by 1H NMR and 2H/1H exchange at pH 6.8 and 2.5 and at 37 and 25 C. The extent ofunfolding increased with the pressure level. The structure of -lactoglobulin required higher pressuresto unfold at pH 2.5 than at pH 6.8. More flexibility was achieved at 37 C than at 25 C. Resultsindicated that the structural region formed by strands F, G, and H was more resistant to unfold underacidic and neutral conditions. The exposure of Trp19 at an earlier time, as compared to other proteinregions, supports the formation of a swollen structural state at pH 2.5. Refolding was achieved fasterwhen -lactoglobulin was subjected to 200 MPa than to 400 MPa, to 37 C than to 25 C, and toacidic than to neutral pH. After treatment at 400 MPa for 20 min at neutral pH, the protein nativestructure was not recovered. All samples at acidic pH showed that the protein quickly regained itsstructure. Hydrolysis of -lactoglobulin by pepsin and chymotrypsin could be related to pressure-induced changes in the structure of the protein. Compared to the behavior of the protein at atmosphericpressure, no increased proteolysis was found in samples with no increased flexibility (100 MPa,37 C, pH 2.5). Slightly flexible structures were associated with significantly increased proteolysis(100 MPa, 37 C, pH 6.8; 200 MPa, 37 C, pH 2.5). Highly flexible structures were associated withvery fast proteolysis (200 MPa, 37 C, pH 6.8; 300 MPa, 37 C, pH 2.5). Proteolysis ofprepressurized samples improved only when the protein was significantly changed after the pressuretreatment (400 MPa, 25 C, 20 min, pH 6.8).