Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2021 Mar 9;9(5):2436-2445.
doi: 10.1002/fsn3.2157. eCollection 2021 May.

The effects of pH and NaCl concentration on the structure of β-casein from buffalo milk

Kong Yang Wu  1 , Tong Xiang Yang  2 , Quan Yang Li  3
Affiliations

The effects of pH and NaCl concentration on the structure of β-casein from buffalo milk

Kong Yang Wu et al. Food Sci Nutr. .

Abstract

In the present study, we aimed to investigate the effects of pH and sodium chloride (NaCl) concentration on the structure of β-casein (β-CN) purified from buffalo milk using circular dichroism (CD), intrinsic tryptophan, and anilino-8-naphthalene sulfonate (ANS) fluorescence spectroscopy. We found that NaCl concentration played a critical role in the stability of the secondary structure of β-CN. The CD negative peak had a redshift as the NaCl concentration was increased and accompanied by a decrease of β-sheet content and an increase of α-helix content. ANS fluorescence spectroscopy also indicated that higher NaCl concentration and lower pH significantly affected the tertiary structure of β-CN. Dynamic light scattering (DLS) results showed that the particle size of buffalo β-CN had a blueshift, and then a redshift within the pH range of 5.0-7.5, and it showed a redshift when the NaCl concentration was increased.

Keywords: buffalo milk; circular dichroism; fluorescence spectrometry; β‐casein.

PubMed Disclaimer

Conflict of interest statement

All authors declare that there is no conflict of interest.

Figures

FIGURE 1
FIGURE 1
Sodium dodecyl sulfate—PAGE electrophoresis of buffalo β‐CN samples. Electrophoresis was carried out with a vertical electrophoresis system and on 12% acrylamide separating gel and 4% stacking gel with the help of standard mixtures of marker proteins. Lane 1: standard of β‐CN; Lane 2: standard of αs‐CN; Lane 3–6, 8, 9: purification of casein by column chromatography; Lane 7: molecular weight markers 10–200 kDa
FIGURE 2
FIGURE 2
Far UV circular dichroism (CD) spectra of native buffalo β‐CN as a function of pH (5.0, 5.5, 6.0, 6.5, 7.0, and 7.5), the internal illustration is the content of α‐helix, β‐Sheet, β‐Turn changing at various pH value in 10 mM sodium phosphate buffer
FIGURE 3
FIGURE 3
Far UV circular dichroism (CD) spectra of native buffalo β‐CN as a function of NaCl concentration (0.01, 0.05, 0.08, 0.1, 0.2, and 0.3 M), the internal illustration is the content of α‐helix, β‐Sheet, β‐Turn changing at various NaCl concentration
FIGURE 4
FIGURE 4
Tryptophan in trinsic fluorescence spectra of buffalo β‐CN (a), λmax (b), surface hydrophobicity index (c) as a function of pH value (5.0, 5.5, 6.0, 6.5, 7.0, and 7.5) in 10 mM sodium phosphate buffer
FIGURE 5
FIGURE 5
Tryptophan in trinsic fluorescence spectra of buffalo β‐CN (a), λmax (b), surface hydrophobicity index (c) as a function of NaCl concentration (0.01, 0.05, 0.08, 0.1, 0.2, and 0.3 M) at pH 7.0
FIGURE 6
FIGURE 6
The relative fluorescence intensity of buffalo β‐CN (a), λmax (b), surface hydrophobicity index (c) treated by pH (pH 7.5, 7.0, 6.5, 6.0, 5.5, and 5.0) in 10 mM sodium phosphate buffer using 1‐anilinonaphthalene‐8sulfonic acid probe (ANS)
FIGURE 7
FIGURE 7
The relative fluorescence intensity of buffalo β‐CN (a), λmax (b), surface hydrophobicity index (c) treated by various NaCl concentration (0.01, 0.05, 0.08, 0.1, 0.2, and 0.3 M) at pH 7.0, in 10 mM sodium phosphate buffer using 1‐anilinonaphthalene‐8sulfonic acid probe (ANS)
FIGURE 8
FIGURE 8
Distribution of hydrodynamic diameters of buffalo β‐CN particles treated by different pH (a) and NaCl concentration (b)
See this image and copyright information in PMC

Similar articles

See all similar articles

References

    1. Akintayo, E. T. , Oshodi, A. A. , & Esuoso, K. O. (1999). Effects of NaCl, ionic strength and pH on the foaming and gelation of pigeon pea (Cajanus cajan) protein concentrates. Food Chemistry, 66, 51–56. 10.1016/S0308-8146(98)00155-1 - DOI
    1. Boulet, M. , Britten, M. , & Lamarche, F. (2001). Dispersion of food proteins in water‐alcohol mixed dispersants. Food Chemistry, 74, 69–74. 10.1016/S0308-8146(01)00099-1 - DOI
    1. Buitenhuis, B. , Poulsen, N. A. , Gebreyesus, G. , & Larsen, L. B. (2016). Estimation of genetic parameters and detection of chromosomal regions affecting the major milk proteins and their post translational modifications in Danish Holstein and Danish Jersey cattle. BMC Genetics, 17, 114. 10.1186/s12863-016-0421-2 - DOI - PMC - PubMed
    1. Chakraborty, A. , & Basak, S. (2007). pH‐induced structural transitions of caseins. Journal of Photochemistry and Photobiology B‐Biology, 87, 191–199. 10.1016/j.jphotobiol.2007.04.004 - DOI - PubMed
    1. Chang, C. T. , Wu, C. S. C. , & Yang, J. T. (1978). Circular dichroic analysis of protein conformation: Inclusion of the β‐turns. Analytical Biochemistry, 91, 13–31. 10.1016/0003-2697(78)90812-6 - DOI - PubMed

LinkOut - more resources