ANSWER
Carrageenan is a family of linear sulfated polysaccharides that are extracted from red seaweeds (Kariduraganavar et al., 2014). There are three main types of carrageenan: kappa (κ), iota (ι) and lambda (λ). Each of them provides different gelling or thickening effect. Κ-carrageenan can produce a strong and brittle gel. Ι-carrageenan possesses cohesive and thixotropic (shear-thinning) gelling behaviour. λ-carrageenan is non-gelling but it gives a thickening and creamy viscosity with a full body mouthfeel and it is the only carrageenan that is soluble in cold water as well as in milk. This characteristic of λ-carrageenan makes it turn out to be the only choice for stabilizing cold instant dairy powders (Laustsen, 2011).
Casein micelles exist in milk as a very stable colloidal dispersion. As a protein, casein may have a positive or a negative charge, depending on the pH of milk system (Sarode et al., 2016) while carrageenan is anionic (dos Santos & Grenha, 2015).
K-carrageenan has strong synergy with milk proteins in particular casein, which results in the formation of a milk gel (Hotchkiss et al., 2016). The isoelectric point (IEP) for casein is pH 4.6, a point where casein is least soluble. Milk have a pH of about 6.6, which a casein micelles have a net negative charge and are quite stable (Sarode et al., 2016).
When the pH is lower than 4.6, the negatively charged carrageenan molecules interact with the positively charged casein proteins in the milk to form a weak gel network that allows the cocoa particles to be suspended in chocolate milk drinks (Hotchkiss et al., 2016). Carrageenan may interact with other casein fractions (αs1 and β) in milk, but the binding is much weaker than that with κ-casein, and does not result in gel formation (Harris, 2012).
The formation of complexes between whey protein isolate and carrageenan is largely driven by electrostatic attractive forces between biopolymers of opposing net charge (Stone & Nickerson, 2012). At neutral pH, whey protein addition did not alter the viscosity and gel strength of κ–carrageenan and there was no phase separation in mixture of whey protein and κ–carrageenan. However, a weak gel matrix is then formed, entrapping insoluble particles, like cocoa or calcium particles (Tercinier, 2019).
A steep increase in viscosity was observed at κ–carrageenan concentration more than 0.3% and was related to segregating conditions at pH 7. Whey protein and carrageenan complex showed enhanced emulsion stability, regardless of the carrageenan types (κ, ι and λ), comparing to individual whey protein solutions (Stone and Nickerson, 2012). Lizarraga et al. (2006) found that the mixture of λ-carrageenan and whey protein showed shear-thinning behaviour and higher apparent viscosity than individual solution.
References
dos Santos, M., & Grenha, A. (2015). Polysaccharide Nanoparticles for Protein and Peptide Delivery. Advances In Protein Chemistry And Structural Biology, 223-261. https://doi.org/10.1016/bs.apcsb.2014.11.003
Harris, P. (2012). Food gels (pp. 97-98). London: Springer Science & Business Media.
Hotchkiss, S., Brooks, M., Campbell, R., Philp, K. & Trius, A. (2016). The Use of Carrageenan in Food. In Pereira, L. (Ed.), Carrageenans: Sources and Extraction Methods, Molecular Structure, Bioactive Properties and Health Effects (pp. 229-243). Ireland: Nova Science Publishers.
Kariduraganavar, M., Kittur, A., & Kamble, R. (2014). Polymer Synthesis and Processing. Natural And Synthetic Biomedical Polymers, 1-31. https://doi.org/10.1016/b978-0-12-396983-5.00001-6
Laustsen, K. (2011). Dairy Products and Carrageenan: a Perfect Pairing. Food Marketing & Technology, 7-11.
Lizarraga, M., Piantevicin, D., Gonzalez, R., Rubiolo, A., & Santiago, L. (2006). Rheological behaviour of whey protein concentrate and λ-carrageenan aqueous mixtures. Food Hydrocolloids, 20(5), 740-748. https://doi.org/10.1016/j.foodhyd.2005.07.007
Sarode, A., Sawale, P., Khedkar, C., Kalyankar, S., & Pawshe, R. (2016). Casein and Caseinate: Methods of Manufacture. Encyclopedia Of Food And Health, 676-682. https://doi.org/10.1016/b978-0-12-384947-2.00122-7
Stone, A., & Nickerson, M. (2012). Formation and functionality of whey protein isolate–(kappa-, iota-, and lambda-type) carrageenan electrostatic complexes. Food Hydrocolloids, 27(2), 271-277. https://doi.org/10.1016/j.foodhyd.2011.08.006
Tercinier, L. (2019). Study of the interactions between milk proteins and hydroxyapatite particles (Doctoral dissertation). Massey University, Palmerston North, New Zealand.
