14A-20 |
Characterization of commercial whey protein isolates and whey protein concentrates using size-exclusion chromatography with multiangle laser light scattering (SEC-MALLS) |
T. WANG and J. A. Lucey. Dept. of Food Science, Univ. of Wisconsin, Madison, 1605 Linden Dr., 102 Babcock Hall, Madison, WI 53706-1519 Whey processing techniques may denature whey protein or even alter its protein composition, thereby significantly affecting functionality. Accurate analysis of the aggregation state of proteins could help us to not only better understanding or predict the properties of different whey protein products, but also to further optimize industrial manufacturing conditions. A range of commercial whey protein products was characterized by the use of size-exclusion chromatography (SEC) coupled with multi-angle laser light scattering (MALLS) as an on-line detector. The MALLS system detected some very large-sized material that eluted close to void volume in all samples; this material was hardly detected by concentration detectors; UV and differential refractive index (DRI), so the concentration was very low. Presumably, this peak was very small lipid globules or lipoproteins, which gave the “cloudy” appearance in upper layers after ultracentrifugation. The intensity of light scattering (LS) signal from this very large sized material was greatly reduced in subnatant from ultracentrifugation. Sample composition, molecular weight (Mw), and UV spectrum (200-400nm) were analyzed of major protein peaks, including: b-lactoglobulin (BLG), a-lactalbumin (ALA), bovine serum albumin (BSA), and immunoglobulins (Ig). The Mw of BLG, ALA, BSA, and Ig peaks in whey protein isolates (WPI) were 2.2-3.9x104, 1.4-1.6x104, 4.8-6.7x104and 1.2-1.7x105Da, respectively. The major protein constituents of various commercial WPI samples were similar, although they were produced by either membrane filtration or ion-exchange chromatography. Compared to whey protein concentrates (WPC), WPI has less large-sized residual lipid material, no minor protein peaks such as non-protein nitrogen (NPN). The major proteins in WPC were similar to WPI, but the minor constituents of WPC were variable and significantly different in commercial samples, depending on the type of whey used in their manufacture. SEC-MALLS is a powerful technique for detailed analysis of various proteins and aggregates in whey products.
Session 14A, Dairy Foods: General developments in dairy technology I
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