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15. Non-local effects in the shear banding of a thixotropic yield stress fluid

Author

Serial, Raquel, Bonn, Daniel, Huppertz, Thom, Dijksman, Joshua A., van der Gucht, Jasper, van Duynhoven, John P. M., and Terenzi, Camilla

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

We observe a novel type of shear banding in the rheology of thixotropic yield-stress fluids that is due to the coupling of both non-locality and thixotropy. The latter is known to lead to shear banding even in homogeneous stress fields, but the bands observed in the presence of non-local effects appear different as the shear rate varies continuously over the shear band. Here, we introduce a simple non-local model for the shear banding (NL-SB), and we implement it for the analysis of micron-scale rheo-MRI velocimetry measurements of a milk microgel suspension in a cone-and-plate geometry. The proposed NL-SB model accurately quantifies the cooperativity length and yields values in the order of the aggregate size in the microgel.

Published
2021
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37. LacdiNAc to LacNAc: remodelling of bovine α-lactalbumin N-glycosylation during the transition from colostrum to mature milk.

Author

Gazi, Inge, Reiding, Karli R, Groeneveld, André, Bastiaans, Jan, Huppertz, Thom, and Heck, Albert J R

Subjects
GLYCAN structure, MILK proteins, CATTLE parturition, COLOSTRUM, GLYCANS
Abstract

α -Lactalbumin, an abundant protein present in the milk of most mammals, is associated with biological, nutritional and technological functionality. Its sequence presents N -glycosylation motifs, the occupancy of which is species-specific, ranging from no to full occupancy. Here, we investigated the N -glycosylation of bovine α-lactalbumin in colostrum and milk sampled from four individual cows, each at 9 time points starting from the day of calving up to 28.0 d post-partum. Using a glycopeptide-centric mass spectrometry-based glycoproteomics approach, we identified N -glycosylation at both Asn residues found in the canonical Asn-Xxx-Ser/Thr motif, i.e. Asn45 and Asn74 of the secreted protein. We found similar glycan profiles in all four cows, with partial site occupancies, averaging at 35% and 4% for Asn45 and Asn74, respectively. No substantial changes in occupancy occurred over lactation at either site. Fucosylation, sialylation, primarily with N -acetylneuraminic acid (Neu5Ac), and a high ratio of N,N′- diacetyllactosamine (LacdiNAc)/ N- acetyllactosamine (LacNAc) motifs were characteristic features of the identified N- glycans. While no substantial changes occurred in site occupancy at either site during lactation, the glycoproteoform (i.e. glycosylated form of the protein) profile revealed dynamic changes; the maturation of the α-lactalbumin glycoproteoform repertoire from colostrum to mature milk was marked by substantial increases in neutral glycans and the number of LacNAc motifs per glycan, at the expense of LacdiNAc motifs. While the implications of α-lactalbumin N -glycosylation on functionality are still unclear, we speculate that N -glycosylation at Asn74 results in a structurally and functionally different protein, due to competition with the formation of its two intra-molecular disulphide bridges. [ABSTRACT FROM AUTHOR]

Published
2024
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