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Influence of ionic environment on acidified micellar casein gels.

D. Wilbanks




Influence of ionic environment on acidified micellar casein gels.
D. Wilbanks*1, J. Lucey1, S. Rahimi2. 1University of Wisconsin-Madison Madison, WI, 2Arla Foods Aarhus, Viby J, Denmark.

Recent advances in filtration have led to an increased interest in micellar casein products. These microfiltered milk products are mostly depleted of whey proteins and differ from caseinates as they are believed to retain much of the original micellar structure found in milk. While much is known about the impact of ionic strength on milk gels generally, research on whey-depleted micellar casein gels is limited. We found that the ionic environment of casein dispersions had a significant impact on acid gel properties. Micellar casein dispersions prepared in water at 4% protein exhibited low conductivity (0.9 mS cm−1), indicative of low ionic strength, compared with reconstituted skim milk (4.9 mS cm−1). When acidified with thermophilic starter cultures at 40�C, micellar casein dispersions made in NaCl or milk permeate gelled at lower pH and formed firmer gels (at pH 4.6) compared with samples prepared in water. 4% casein dispersions did not form a gel at pH 4.6 if prepared in NaCl at 150 mmol kg−1 and above. Dispersions were also prepared at 4 and 8% protein with increasing concentrations of NaCl and cold-acidified at 2�C to pH 4.6 using 0.5 M HCl. Cold-acidified dispersions were then warmed to 30�C at a rate of 0.5�C/min in a rheometer to measure gel development without gelation pH and time as confounding factors. Cold-acidified dispersions formed a gel around 25�C as long as ionic strength was below a certain threshold level, which was dependent on protein level. Storage modulus of cold-acidified casein gels increased, and loss tangent decreased, with increasing ionic strength and protein content. This research shows that weaker casein gels may be formed by lowering the ionic strength of the dispersion and the mechanisms for the weaker gel can be partially explained by the higher gelation pH but is also likely due to electrostatic and hydrophobic interactions resulting from the lower ionic strength. Very low ionic strength may encourage more hydrophobic interactions between caseins allowing for gelation at higher pH values. Control of the ionic environment of micellar casein dispersions greatly impacts its acid gelation behavior.

Keywords: casein, acid, gel.

Biography: Daniel graduated with a BS in Forensic Science and spent nearly 10 years in the infant formula industry. He worked in quality control and analytical method development at Mead Johnson Nutrition and was inspired by the innovative research of his colleagues to go back to school for his MS and PhD in Food Science. He is a 2nd year PhD student researching high protein fermented beverages.