TY - JOUR

T1 - Skimmed milk structural dynamics during high hydrostatic pressure processing from in situ SAXS

AU - Yang, Shuailing

AU - Tyler, Arwen I. I.

AU - Ahrné, Lilia

AU - Kirkensgaard, Jacob J. K.

N1 - Funding Information: We thank Diamond Light Source for the award of synchrotron beamtime (SM24374), Dr. Olga Shebanova and Prof. Nick Terrill for their support and assistance. We also thank Dr. Aleks Ponjavic from the University of Leeds for valuable help in performing the SAXS measurements. The Bragg Centre for Materials Research at the University of Leeds is also acknowledged. The present study was financially supported by the Dairy Rationalization Fund (DDRF), Arla Foods amba, the Innovation Fund Denmark through the FAPESP project Novel Aging – Technologies and solutions to manufacture novel dairy products for healthy aging (grant 2017/01189-0), and the Chinese Scholarship Council (grant 201706170082). Funding Information: We thank Diamond Light Source for the award of synchrotron beamtime (SM24374), Dr. Olga Shebanova and Prof. Nick Terrill for their support and assistance. We also thank Dr. Aleks Ponjavic from the University of Leeds for valuable help in performing the SAXS measurements. The Bragg Centre for Materials Research at the University of Leeds is also acknowledged. The present study was financially supported by the Dairy Rationalization Fund (DDRF), Arla Foods amba, the Innovation Fund Denmark through the FAPESP project Novel Aging ? Technologies and solutions to manufacture novel dairy products for healthy aging (grant 2017/01189-0), and the Chinese Scholarship Council (grant 201706170082). Publisher Copyright: © 2021 The Author(s)

PY - 2021

Y1 - 2021

N2 - Understanding the changes in milk at a nanostructural level during high-pressure (HP) treatment can provide new insights to improve the safety and functionality of dairy products. In this study, modifications of milk nanostructure during HP were studied in situ by small-angle X-ray scattering (SAXS). Skimmed milk was pressurized to 200 or 400 MPa at 25, 40 or 60 °C and held for 5 or 10 min, and the effect of single- and double-HP treatment was also investigated. In most cases, the SAXS patterns of skimmed milk are well fitted with a three-population model: a low-q micellar feature reflecting the overall micelle size (~0.002 Å−1), a small casein cluster contribution at intermediate-q (around 0.01 Å−1) and a high-q (0.08–0.1 Å−1) population of milk protein inhomogeneities. However, at 60 °C a scattering feature of colloidal calcium phosphate (CCP) which is normally only seen with neutron scattering, was observed at 0.035 Å−1. By varying the pressure, temperature, holding and depressurization times, as well as performing cycled pressure treatment, we followed the dynamic structural changes in the skimmed milk protein structure at different length scales, which depending on the processing conditions, were irreversible or reversible within the timescales investigated. Pressure and temperature of the HP process have major effects, not only on size of casein micelles, but also on “protein inhomogeneities” within their internal structure. Under HP, increasing processing time at 200 MPa induced re-association of the micelles, however, the changes in the internal structure were more pressure-dependent than time dependent.

AB - Understanding the changes in milk at a nanostructural level during high-pressure (HP) treatment can provide new insights to improve the safety and functionality of dairy products. In this study, modifications of milk nanostructure during HP were studied in situ by small-angle X-ray scattering (SAXS). Skimmed milk was pressurized to 200 or 400 MPa at 25, 40 or 60 °C and held for 5 or 10 min, and the effect of single- and double-HP treatment was also investigated. In most cases, the SAXS patterns of skimmed milk are well fitted with a three-population model: a low-q micellar feature reflecting the overall micelle size (~0.002 Å−1), a small casein cluster contribution at intermediate-q (around 0.01 Å−1) and a high-q (0.08–0.1 Å−1) population of milk protein inhomogeneities. However, at 60 °C a scattering feature of colloidal calcium phosphate (CCP) which is normally only seen with neutron scattering, was observed at 0.035 Å−1. By varying the pressure, temperature, holding and depressurization times, as well as performing cycled pressure treatment, we followed the dynamic structural changes in the skimmed milk protein structure at different length scales, which depending on the processing conditions, were irreversible or reversible within the timescales investigated. Pressure and temperature of the HP process have major effects, not only on size of casein micelles, but also on “protein inhomogeneities” within their internal structure. Under HP, increasing processing time at 200 MPa induced re-association of the micelles, however, the changes in the internal structure were more pressure-dependent than time dependent.

KW - Casein micelle

KW - Colloidal calcium phosphate (CCP)

KW - Multiple high-pressure processing

KW - Protein structure modification

KW - Small-angle X-ray scattering (SAXS)

U2 - 10.1016/j.foodres.2021.110527

DO - 10.1016/j.foodres.2021.110527

M3 - Journal article

C2 - 34399505

AN - SCOPUS:85108286828

VL - 147

JO - Food Research International

JF - Food Research International

SN - 0963-9969

M1 - 110527

ER -