Structure and Scaling Behavior of Aging Rennet-Induced Casein Gels Examined by Confocal Microscopy and Permeametry

Abstract

A study is presented on the structure of rennet(-induced) casein or skim milk gels at three pH values (5.3, 6.0, and 6.65) and temperatures (20, 25, and 30°C). The structure was examined by confocal scanning laser microscopy and permeametry. Deconvolution was applied to the microscopic images. A fractal scaling analysis has been applied to the images and permeametry results. In this analysis, the fractal dimensionality (Df), lower cutoff length (R0), and apparent pore size (P) of the linear scaling regime were calculated from the microscopical data. The Df and apparent pore size were also calculated from the permeametry data. During aging of the gels, a coarsening of the structure was observed; the pore size increased and the clusters became more compact. This was reflected in the fractal parameters: R0 and P increased during gel aging. Their values are generally high (0.5-1.5 and 5.0-15 µm, respectively) compared to data obtained by computer simulations. The Df value is also high (∼2.2-2.6), which is an indication of slow aggregation or rearrangements during aggregation. The gel aging effects are probably mainly due to rearrangements such as particle fusion and strand fracture, which rates increase with increasing temperature, and even more pronouncedly, with decreasing pH.

Rennet gelation properties of milk: Influence of natural variation in milk fat globule size and casein micelle size

“…This in turn resulted in larger pores in the large CM gel structure. Pores of a typical rennet gel network tend to be in the range of 4e15 mm (Hussain, Bell, & Grandison, 2013;Mellema, Heesakkers, Van Opheusden, & Van Vliet, 2000). In this work, large void spaces up to approximately 15e16 mm are evident, representing the pores surrounded by the rennet gel network.…”

Interactive Effects of Milk Fat Globule and Casein Micelle Size on the Renneting Properties of Milk

“…The pore size of renneted casein gels is thought to be in the range of 4-15 μm as estimated from the confocal imaging analysis (Hussain et al 2013;Mellema et al 2000). Small CM gels are able to form a denser network compared to gels from larger CM, as shown by SEM imaging (Fig.…”

Characterization of the microstructure of dairy systems using automated image analysis

“…between the micelles, and the destabilized micelles thus begin to aggregate to form the gel (Mellema, Heesakkers, van Opheusden, & van Vliet, 2000). Table 3 sets out the values for the microstructural parameters obtained from the TEM images of MF-and UF-gels.…”