Effect of pH on Structural Properties of Heat-Induced Whey Protein Gels

Subject Areas : food microbiology

F.  Farrokhi ¹ (PhD Graduated of the Department of Food Science and Technology, Science and Research Branch, Islamic Azad University, Tehran, Iran.)
M.R.  Ehsani ² (Professor of the Department of Food Science and Technology, Science and Research Branch, Islamic Azad University, Tehran, Iran.)
F.  Badii ³ (Associate Professor, Agricultural Engineering Research Institute (AERI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran.)
M.  Hashemi ⁴ (Associate Professor, Agricultural Biotechnology Research Institute of Iran (ABRII), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran.)

Received: 2019-12-16 Accepted : 2019-12-16 Published : 2020-01-01

Keywords: Atomic force microscopy (AFM), Heat-Induced Whey Protein Isol, pH Modifications, Structural properties, Textural Analysis,

Abstract :

Formation and structure of whey protein heat-induced gels (100 mg mL-1) through heat treatment at 80 °C and pH modifications at three pH values of acidic (2), isoelectric (5.6) and neutral (7) were studied. The obtained results indicated that the nature of the primary gel networks was different at each pH value. The heat-induced gels produced at pH of 2 and 7, had acceptable overall shape and consistency which confirmed the significant effect of pH on the regular gel structures. Conversely, the amorphous gel structure was observed at isoelectric pH. According to Atomic Force Microscopy images, the structural unfolding of the protein during denaturation and formation of the fibrillar structures was observed in gel at pH of 2 and stranded aggregates at pH of 7. In terms of textural analysis, in samples at pH of 2 and 7, the required force to fracture gel structure was approximately equal and less than that of the sample at pH of 5.6 which goes back to the amorphous large protein aggregates in gel network at isoelectric pH. The ordered, regular and stable gel structures and high ionic balance were reflected in color parameters and lower amounts of moisture content in the gel matrix of samples at pH of 2 and 7 (P<0.05). The well-organized structure and stable gels network along with their desirable functional characteristics, might reinforce their application as food ingredients in terms of improving the qualitative and textural qualities of food products. This property can facilitate the use of these protein gels in novel food systems.

References:

AOAC. (2000). Official methods of analysis of AOAC international, 17th edn. Moisture Content. AOAC International, Md., USA.

Barbut, S. & Drake, D. (1997). Effect of reheating on sodium-induced cold gelation of whey proteins. Food Research International, 30(2), 153-157.

Bolder, S. G., Hendrickx, H., Sagis, L. M. C. & Van der Linden, E. (2006). Fibril Assemblies in Aqueous Whey Protein Mixtures. Journal of Agriculture & Food Chemistry, 54, 4229-4234.

Boye, J., Kalab, M. & Ma, C. Y. (2000). Microstructural Properties of Heat-set Whey Protein Gels: Effect of pH. LWT- Food Science & Technology, 16, 165-172.

Cavallieria, A. L. F., Costa-Nettob, A. P., Menossib, M. & Da Cunhaa, R. L. (2007). Whey protein interactions in acidic cold-set gels at different pH values. Lait, 87, 535-554.

Clark, A. H., Kavanagh, G. M. & Ross-Murphy, S. B. (2001). Globular protein gelation - theory & experiment. Food Hydrocolloids, 15, 383 - 400.

Comfort, S. & Howell, N. (2002). Gelation properties of soya & whey protein isolate mixture. Food Hydrocolloids, 16, 661-672.

Durand, D., Gimel, J. C. & Nicolai, T. (2002). Aggregation, gelation & phase separation of heat denatured globular proteins. Physica A: Statistical Mechanics & its Applications, 304, 253-265.

Havea, P., Watkinson, Ph. & Kuhn-Sherlock, B. (2009). Heat-Induced Whey Protein Gels: Protein-Protein Interactions & Functional Properties. Journal of Agriculture & Food Chemistry, 57, 1506–1512.

Hoffmann, M. A. M. & van Mil, P. J. J. M. (1999). Heat-Induced Aggregation of β-lactoglobulin as a Function of pH. Journal of Agriculture & Food Chemistry, 47, 1898-1905.

Ikeda, Sh. (2003). Heat-induced gelation of whey proteins observed by rheology, atomic force microscopy & Raman scattering spectroscopy. Food Hydrocolloids, 17, 399-406.

Ikeda, S. & Morris, V. J. (2002). Fine-Stranded & Particulate Aggregates of Heat-Denatured Whey Proteins Visualized by Atomic Force Microscopy. Biomacromolecules, 3, 382-389.

Jagtap, R. & Ambre, A. (2006). Overview literature on atomic force microscopy (AFM): Basics & its important applications for polymer characterization. Indian Journal of Engineering & Materials Sciences, 13, 368-384.

Jiménez, X., Cuenca, A., Jurado, A., Corona, A. & Muro Urista, C. (2012). Traditional Methods for Whey Protein Isolation & Concentration: Effects on Nutritional Properties & Biological Activity. Journal of Mex. Chemistry, 56(4), 369-377.

Jones, O., Andrew, E. D. & McClements, D. (2010). Thermal analysis of β-lactoglobulin complexes with pectin or carrageenan for production of stable biopolymer particles. Food Hydrocolloids, 24, 239-248.

Jovanović, S., Barać, M. & Maćej, O. (2005). Whey Proteins-Properties & Possibility of Application. Mljekarstvo, 55 (3), 215-233.

Kavanagh, G. M., Clark, A. H. & Ross-Murphy, S. B. (2000). Heat-induced gelation of globular proteins: part 3. Molecular studies on low pH β-lactoglobulin gels. International Journal of Biological Macromolecule, 28(1), 41-50.

Kinekawa, Y. & Kitabatake, N. (1995). Turbidity & Rheological Properties of Gels & Sols Prepared by Heating Process Whey Protein. Bioscience, Biotechnology & Biochemistry, 59, 834-840.

Lakemond, C. M. M., de Jongh, H. J., Paques, M., van Vliet, T., Gruppen, H. & Voragena, A. G. J. (2003). Gelation of soy glycinin; influence of pH & ionic strength on network structure in relation to protein conformation. Food Hydrocolloids, 17, 365-377.

Langton, M. & Hermansson, A.M. (1992). Fine-stranded & particulate gels of β-lactoglobulin & whey protein at varying pH. Food Hydrocolloids, 5(6), 523-539.

Lorenzen, P. C. & Schradera, K. (2006). Comparative study of the gelation properties of whey protein concentrate & whey protein isolate. Lait, 86, 259–271.

Loveday, S., Rao, M., Creemer, L. & Singh, H. (2009). Factors affecting rheological characteristics of fibril gels: the case of β-lactoglobulin & α-lactalbumin. Journal of Food Science, 74, 47-55.

Monahan, F. J., German, J. B. & Kinsellat, J. E. (1995). Effect of pH & Temperature on Protein Unfolding & Thiol/Disulfide Interchange Reactions during Heat-Induced Gelation of Whey Proteins. Journal of Agriculture & Food Chemistry, 43, 46-52.

Morr, C. V. & Ha, E. Y. W. (1993) Whey protein concentrates & isolates: Processing & functional properties. Critical Reviews in Food Science & Nutrition, 33(6), 431-476.

Ohgren, C., Langton, M. & Hermansson, A. M. (2004). Structure-fracture measurements of particulate gels. Journal of Materials Science, 39, 6473–6482.

Ryan, K., Zhong, Q. & Foegeding, E. A. (2013). Use of Whey Protein Soluble Aggregates for Thermal Stability-A Hypothesis Paper. Journal of Food Science, 78 (8), 1105-1115.

Schmitt, C., Bovay, C., Rouvet, M., Shojaei-Rami, S. & Kolodziejczyk, E. (2007). Whey Protein Soluble Aggregates from Heating with NaCl: Physicochemical, Interfacial & Foaming Properties. Langmuir, 23, 4155-4166.

Stading, M. & Hermansson, A. M. (1991). Large deformation properties of β-lactoglobulin gel structures. Food Hydrocolloids, 5(4), 339-352.

Tang, Q., McCarthy, O. J. & Munro', P. A. (1994). Oscillatory Rheological Comparison of the Gelling Characteristics of Egg White, Whey Protein Concentrates, Whey Protein Isolate & β-Lactoglobulin. Journal of Agriculture & Food Chemistry, 42 (10), 2126-2130.

Tobitani, A. & Ross-Murphy, S. B. (1997). Heat-Induced Gelation of Globular Proteins, 1.