The relationship between ultra-small-angle X-ray scattering and viscosity measurements of casein micelles in skim milk concentrates

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Skim milk concentrates have important applications in the dairy industry, often as intermediate ingredients. Concentration of skim milk by reverse osmosis membrane filtration induces water removal, which reduces the free volume between the colloidal components, in particular the casein micelles. Thermal treatment before or after concentration impacts the morphology of casein micelles. These changes affect the flow behavior and viscosity, but the consequences for supermicellar structure have not been elucidated. In the present study, skim milk concentrates with different total solid contents from 8.7% (control) up to 22.8% (w/w), prepared by reverse osmosis membrane filtration of non-heated and pasteurized skim milk, were heat treated at 75 °C for 18 s, and compared with non-heated concentrates. The structure of the concentrates was studied using Ultra Small Angle X-ray Scattering (USAXS), and the viscosity of concentrates was measured. The USAXS intensity I(q) was fitted at small and intermediate q-regions (0.0005 < q < 0.003 Å−1 and 0.0035 < q < 0.03 Å−1, respectively) with a power law. The value of the power law exponent was used to assess the heat- and concentration-induced aggregation of the milk solids and correlate it with the apparent viscosity. The results showed that increased viscosity of skim milk concentrates, due to water removal and heat-load, can be explained by increased aggregation of the casein micelles into elongated aggregates and increased smoothening of the casein micelle surface.

OriginalsprogEngelsk
Artikelnummer110451
TidsskriftFood Research International
Vol/bind147
Antal sider10
ISSN0963-9969
DOI
StatusUdgivet - 2021

Bibliografisk note

Funding Information:
The authors wish to thank Dr Jan Ilavsky and his team at beam line 9ID-C at APS Argonne National Laboratory, IL, for their support with data collection. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Funding Information:
The authors wish to thank Dr Jan Ilavsky and his team at beam line 9ID-C at APS Argonne National Laboratory, IL, for their support with data collection. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work is partly funded by the Dairy Rationalization Fund (DDRF) as part of the Platform for Novel Gentle Processing. Additionally, this work is partly funded by the Innovation Fund Denmark (IFD) as part of project Linking Industry to Neutrons and X-rays (LINX) under File No. 5152-00005B. We thank the Danish Agency for Science, Technology, and Innovation for funding the instrument center DanScatt. Finally, this work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union's Horizon 2020 research and innovation programme under the SINE2020 project, grant agreement No 654000.

Funding Information:
This work is partly funded by the Dairy Rationalization Fund (DDRF) as part of the Platform for Novel Gentle Processing. Additionally, this work is partly funded by the Innovation Fund Denmark (IFD) as part of project Linking Industry to Neutrons and X-rays (LINX) under File No. 5152-00005B. We thank the Danish Agency for Science, Technology, and Innovation for funding the instrument center DanScatt.

Funding Information:
Finally, this work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union’s Horizon 2020 research and innovation programme under the SINE2020 project, grant agreement No 654000.

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© 2021 Elsevier Ltd

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