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H-P Cross-polarization magic angle spinning (CP-MAS) measurements of 40-d-old Mozzarella cheese and 20 mM EDTA-treated casein micelles revealed that each sample had immobile phosphorus with the same spectral pattern, which did not match that of native casein micelles. To identify the immobile phosphorus bodies, H-P CP-MAS spectra and cross-polarization kinetics measurements were undertaken on native casein micelles, EDTA-chelated casein micelles, and reference samples of β-casein and hydroxyapatite. The results showed that the immobile phosphorus bodies in the mature Mozzarella cheese had the following characteristics: they are immobile phosphoserine residues (not colloidal calcium phosphate); they are not the product of phosphoserine to colloidal calcium phosphate bridging; the phosphate is complexed to calcium; their rigidity is localized to a phosphorus site; their rigidity and bond coupling is unaffected by protein hydration; and the immobile bodies share a narrow range of bond orientations. Combining these observations, the best explanation of the immobile phosphorus bodies is that bonding structures of phosphorus-containing groups and calcium exist within the casein micelle that are not yet clearly classified in the literature. The best candidate is a calcium-bridged phosphoserine-to-phosphoserine linkage, either intra- or inter-protein.

Heat-induced gelation (80 degrees C for 30 min or 85 degrees C for 60 min) of whey protein concentrate (WPC) solutions was studied using small deformation dynamic rheology, small and large deformation compression, and polyacrylamide gel electrophoresis (PAGE). The WPC solutions (15% w/w, pH 6.9) were prepared by dispersing WPC powder in water (control), 1% (w/w) sodium dodecyl sulfate (SDS) solution, and N-ethylmaleimide (NEM) solution at a protein/NEM molar ratio of 1:1 or in 10 mM dithiothreitol (DTT) solution. PAGE analyses showed that the heat treatment of control solutions contained both disulfide and non-covalent linkages between denatured protein molecules. Only disulfide linkages were formed in heated SDS-WPC solutions, whereas only non-covalent linkages were formed in DTT-WPC and NEM-WPC solutions during heating. In heated NEM-WPC solutions, the pre-existing disulfide linkages remained unaltered. Small deformation rheology measurements showed that the storage modulus (G') values, compared with those of the control WPC gels (approximately 14000 Pa), were 3 times less for the SDS-WPC gels (approximately 4000 Pa), double for the NEM-WPC gels (approximately 24000 Pa), and even higher for the DTT-WPC gels (approximately 30000 Pa). Compression tests suggested that the rubberiness (fracture strain) of the WPC gels increased as the degree of disulfide linkages within the gels increased, whereas the stiffness (modulus) of the gels increased as the degree of non-covalent associations among the denatured protein molecules increased.

Summary -Trends in the fracture strain, modulus of deformability and chemical properties as a function of storage time were determined for Cheddar cheese made in the New Zealand Dairy Research Institute' s pilot plant. The apparent fracture strain of Cheddar cheese increased during the first 14---28days and thereafter decreased, asl-Casein levels decreased monotonically and non-protein nitrogen levels increased with storage. Fusion of curd particles probably contributed to the initial increase in fracture strain, and the decrease in strain can be rationalized in terms of increasing proteolysis, The modulus of deformability increased by at least a factor of two over the initial several weeks of storage and then increased slightly or remained constant. However, the moi sture content of Cheddar cheese changed very little (the maximum range being 34.6-33.0% with no monotonie change over time). The increase in the modulus over the first 14 days was not associated with a decrease in moisture content. Differentiai scanning calorimetry indicated there was sorne crystallization of milkfat from 91 to 210 days of storage, and this (together with small moisture los ses) may partly explain the small increase in the modulus of deformability over this period of time.

Germanium-73 n.m.r. observations have been extended to a wider range of hydrides, alkyls, and polygermanes, together with further observations on mixed halides. Chemical shifts, coupling constants, linewidths, relaxation times, and derived parameters are reported. The current limits of observa bi lity are indicated As 73Ge is the most difficult Group 4 isotope for n.m.r. work (gyromagnetic ratio, y = -0.9332 x rad T-' s-l, spin I = Q, nuclear electric quadrupole moment, Q = -0.18 x m, natural abundance 7.76%), it is not surprising that there have been only limited reports of its observation. In an earlier paper the enhancement of sensitivity in hydrides and alkyls by proton polarization transfer was explored, and fuller results are now presented.The earliest ',Ge n.m.r. data stem from a survey by Schwenk and co-workers ' which included T2 determinations by the Carr-Purcell sequence. Soon after, Kidd and Spinney observed binary and ternary mixtures of germanium tetrahalides, assigning 73Ge shifts to all possible Cl/Br/I species. More recent work has extended 73Ge observations to germatrane~,,.~ carbofunctional tetra-alkyls,6 shifts and relaxation times of tetrasubstituted germanes 7,8 including methylgermacyclohexanes,9 and to silicon-germanium hydrides." There are few reports on arylgermanes, apart from GePh,, and Ge directly bonded to a transition metal has not been observed. Comparisons of chemical shifts between pairs of C/Si, Si/Sn, and Sn/Pb analogues" have been extendedI2 to include the Si/Ge and Ge/Sn pairs, but with fewer than 30 examples available. Very recently, a fuller study of tetra-alkoxygermanes l 3 produced a different linear relationship between 6(Ge) and 6(Si) for this class of compound, reinforcing earlier 6 , 7 , 1 ' relations based on limited data. We now report further 73Ge observations including chemical shifts, linewidths, coupling constants, relaxation times, and derived parameters. Table 1 lists all the compounds examined by 73Ge resonance in this work. A full listing of all published data, for approximately one hundred compounds, will be published elsewhere.', The only other available data are a handful of coupling constants measured via the bonded element, including 'J(GeH) = -97.6'' or -87.8 Hz l 6 for GeH,, 'J(GeC) = -18.717 and 2J(GeH) = 2.94 Hz'*,19 for GeMe,, 'J(GeF) = 178.5 Hz for GeF," and 98 Hz for CNH4I 2 CGeF,I. ' ' ResultsThe germanium-73 chemical shifts, linewidths, and coupling constants, given in Table 1, were measured on samples ranging in concentration from neat liquids (7-9 mol drn-,), requiring only two or three scans, to about 0.1 mol drn-,, requiring several thousand scans to recognize the signal (signal-to-noise ratio > 2.5). Experimental errors in chemical shifts for clear signals ranged from f 0.1 p.p.m. for sharp signals to & 1 p.p.m. for broad signals, and similarly for the other parameters. The higher polygermanes and methyldigermanes were difficult to free from related species and the results for Ge,H,, Ge4Hl0, and the two dimethyldigermanes are of lower qual...