The Liquid-State ³¹P-Nuclear Magnetic Resonance Study on Microfiltrated Milk

¹ Sapporo Research Laboratory, Snow Brand Milk Products Co., Ltd., 065-0043 Sapporo
² Department of Applied Physics, Graduate School of Engineering, Hokkaido University, 060-8628 Sapporo

To gain further insight into diversiform phosphorus in bovine milk, we separated skim milk into casein micelle and serum fractions by microfiltration and subjected them to liquid-state ³¹P-nuclear magnetic resonance (NMR) spectroscopy. As previously reported, the skim milk spectrum showed a broad and indistinct peak from phosphoserine residue (SerP) of casein. In the casein micelle spectrum, however, the SerP peak was more clearly observed with a phosphate peak that may be from micellar calcium phosphate (MCP). The serum spectrum was the same as skim milk spectrum, except for SerP peak. Furthermore, two types of casein micelle fractions, with 0.90 and 1.04 of [ß-casein + -casein]/[_s1-casein + _s2-casein] ratios were generated by different temperature microfiltrations, occurring because ß-casein is released from the micelle at a low temperature. The shape of SerP peaks changed dramatically in both the casein micelle spectra, when the temperature dropped from 35 to 5°C. Deconvolution analysis indicated that each SerP peak comprised the same set of four peaks. Half-width and composition discriminated between the two types of casein micelle fractions. As a consequence, there was significant interaction between casein micelle and milk serum, causing cloudiness of SerP in the liquid-state ³¹P-NMR spectrum of milk. Casein composition influenced the SerP-MCP interaction in micellar structure. Shape changing of the SerP peak was discussed in connection with ß-casein-release phenomenon.

Key Words: nuclear magnetic resonance • casein micelle • microfiltration

Submitted on November 27, 2000
Accepted on June 22, 2001