Characterization of the microstructure of dairy systems using automated image analysis

Abstract

International audienceA sound understanding of the microstructure of dairy products is of great importance in order to predict and control their properties and final quality. The aim of this study was to develop an automated image analysis procedure to characterize the microstructure of different dairy systems. A high pressure freezing coupled with freeze-substitution (HPF-FS) protocol was applied prior to transmission electron microscopy(TEM) in order to minimize any modification of the microstructure of the dairy systems investigated. The developed image analysis procedure was first validated on synthetic images of suspensions, and then on two types of concentrated milk suspensions. Microstructural data relating to casein micelles in milk suspensions were taken from the literature. The established procedure was then applied to the two corresponding rennet-induced milk gels, prepared from the same milk concentrates used for suspensions preparation. The automated image analysis procedure allowed the reliable estimation of several characteristic microstructural parameters including area fraction, porosity, boundary length per unit area, particle aggregate size, inter-particle aggregate distance and tortuosity. The relative ease of estimating these microstructural parameters from the automated image analysis method could make it useful for routine measurements of milk gels. Moreover, the method enabled a useful discrimination between two different types of milk gels. This novel approach can contribute to a better understanding of the effects of processing on the structure-property relationships in dairy products, and may be applied to other food systems

The influence of cheese composition and microstructure on the diffusion of macromolecules: A study using Fluorescence Recovery After Photobleaching (FRAP)

“…It was deduced from these results that the pore sizes of the model cheese were much larger than the diameter of the largest dextran molecule studied. This hypothesis was confirmed by image analysis of the microstructure of the model cheese obtained by transmission electron microscopy (Silva, Legland, Cauty, Kolotuev, & Floury, 2015). In this study, a protocol involving high pressure freezing coupled with a freeze-substitution was applied prior to transmission electron microscopy to minimize any modification of the microstructure of the cheese sample.…”

“…All of the results produced here were compared to the study of Silva et al (2013) carried out on a model cheese based on the rennet coagulation of ultrafiltered non-fat milk. This standardized cheese had a homogenous protein network whose microstructure was fully characterized by Silva et al (2015).…”

“…In the fresh curd, the diffusion behavior of dextrans (up to 500 kDa) was characteristic by that in an infinite diluted solution (De Gennes, 1979;Silva et al, 2013), implying that flexible macromolecules could diffuse throughout the protein network even without deforming. Silva et al (2015) used image analysis of TEM micrographs to measure the mean pore size of the protein network as 131 ± 7 nm in their model cheese. In the current study, the effective diffusion coefficients of dextrans were of the same order of magnitude for the soft cheese (at Day 1) as for the cited model cheese.…”

Effect of freezing on microstructure and reconstitution of freeze-dried high solid hydrocolloid-based systems

“…Firstly, binary SEM micrographs (see example of Fig. 2 1 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 FOOHYD4426_proof ■ 16 May 2018 ■ 8/12 of the top layers of the solids were analysed and porosity was defined as the ratio between pore area and total area of the image (Silva et al, 2015). This method takes into account both open and closed pores, and results are shown in Table 3.…”

Mechanisms of Clostridium tyrobutyricum removal through natural creaming of milk: A microscopy study

“…Transmission electron microscopy (TEM) has also been used as a tool to study the MFGM in different dairy products (Resmini et al, 1984;Schmidt and Buchheim, 1992;Zamora et al, 2012). Nevertheless, until now, no ultrastructural studies have been carried out to investigate interactions between fat globules and bacterial cells or spores in milk or cream, possibly because the high water content of these matrices represents a difficult task for electron microscopy (Silva et al, 2015).…”