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J. Dairy Sci. 2007. 90:2705-2709. doi:10.3168/jds.2006-629
© 2007 American Dairy Science Association ®
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Solubilized Micellar Calcium Induced Low Methoxyl-Pectin Aggregation During Milk Acidification

F. M. Harte1, C. Montes, M. Adams and M. F. San Martin-Gonzalez

Department of Food Science and Technology, The University of Tennessee, 2509 River Dr., Knoxville 37996

1 Corresponding author: fede{at}utk.edu

Low methoxyl (LM) pectin was combined with 3-kDa molecular weight cut-off permeates from milk subjected to pH 6.7 to 5 and 7°C or 40°C with the objective of studying the effect of solubilized micellar calcium on viscoelastic properties of LM-pectin-milk mixes. Lowering the pH of skim milk with hydrochloric acid during ultrafiltration gradually promoted permeates to exhibit gel-like behavior when combined with LM-pectin. The onset of the gel-like behavior (G' > 1) occurred at a higher pH when permeates were obtained from milk filtered at 7°C compared with 40°C. As pH value during ultrafiltration approached 5 and regardless of temperature, G' for permeate-pectin mixes approached the same values (~70 Pa) as G' for skim milk-pectin mixes. In all cases G' was highly correlated with free calcium concentration (r > 0.95). The gradual acidification of skim milk-LM-pectin using glucono-{delta}-lactone, promoted a sharp increase in storage modulus as pH approached 5.2 and a maximum G' increment ({Delta}G') at pH ~4.9. From pH 4.9 to 4, G' continued to increase but at smaller increments. It was concluded that LM-pectin–casein micelle interaction in milk is a 2-step process: 1) solubilized micellar calcium dependent pectin-pectin interaction as pH approaches 5.0 to 4.9, and 2) pectin–casein micelle interaction in the 5.0-4.9 to 4.0 pH range.

Key Words: casein micelle • pectin • calcium • milk






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