Crystal networks, partial coalescence, and rheological properties of milk fat fraction model systems

Yunna Wang; Richard W Hartel; Yan Li; Liebing Zhang

doi:10.3168/jds.2022-23200

Crystal networks, partial coalescence, and rheological properties of milk fat fraction model systems

J Dairy Sci. 2023 Nov;106(11):7486-7500. doi: 10.3168/jds.2022-23200. Epub 2023 Aug 23.

Authors

Yunna Wang¹, Richard W Hartel², Yan Li³, Liebing Zhang⁴

Affiliations

¹ Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences, Beijing 100193, China; Department of Food Science, University of Wisconsin-Madison, Madison, WI 53706; College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
² Department of Food Science, University of Wisconsin-Madison, Madison, WI 53706. Electronic address: rwhartel@wisc.edu.
³ Beijing Engineering and Technology Research Centre of Food Additives, School of Food and Health, Beijing Technology and Business University, Beijing 100048, China.
⁴ College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China. Electronic address: liebzhang@gmail.com.

PMID: 37641264
DOI: 10.3168/jds.2022-23200

Abstract

This study aimed to investigate the crystal network of bulk milk fat fractions and the partial coalescence, and the rheological properties of their oil-in-water (O/W) emulsions. Different milk fat fraction model systems were compared for their physicochemical properties, crystallization kinetics, and fat crystal networks across a range of temperatures. The extent of partial coalescence and rheological properties of the O/W emulsion prepared by different milk fat fractions were further analyzed. The results demonstrated that the ratio between saturated fatty acids (SFA) and unsaturated fatty acids and triacylglycerides (TAG) influenced the melting thermal behaviors, solid fat contents (SFC), and crystal networks of various milk fat fractions, which in turn influenced the partial coalescence and rheological characteristics of their O/W emulsions. Moreover, an excellent fit of the trend line confirmed that hardness increased exponentially with SFC. Trisaturated TAG in fractions with high melting points (HMF) such as milk fat fraction MF45, whose clarification temperature was 45°C, enriched long-chain SFA (saturated:unsaturated fatty acid = 2.2:1). We found that MF45 achieved higher SFC and hardness in the range of 0 to 40°C and, ultimately, formed a well-defined microstructural network with thick, rod-like crystals. Further, TAG in fractions with low melting points (LMF) such as MF10, whose clarification temperature was 10°C, were enriched with short-chain and unsaturated fatty acids (saturated:unsaturated fatty acid = 1.5:1), and a disordered crystal network in MF10, composed of randomly arranged, translucent platelets, was detected. Although fat globules of HMF and LMF were stabilized against coalescence, this could be attributed to a variety of mechanisms involving SFC, liquid fat, protective film around the fat globule, and minor lipids. According to the rheological profiles, all O/W emulsions exhibited weak viscoelastic "gel-like" structures [storage modulus (G') > loss modulus (G")] over most of the measured range. The G' values and apparent viscosity of HMF were greater than those of other fractions, indicating that the large and rigid crystals strengthen the networks more effectively.

Keywords: crystal network; milk fat; partial coalescence; rheological properties.

© 2023, The Authors. Published by Elsevier Inc. and Fass Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).