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Intermicellar relationships in rennet-treated separated milk: I. Preparation of representative electron micrographs

Published online by Cambridge University Press:  01 June 2009

Margaret L. Green ,
David G. Hobbs  and
Steven V. Morant
Margaret L. Green
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading, RG2 9AT
David G. Hobbs
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading, RG2 9AT
Steven V. Morant
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading, RG2 9AT
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Summary

Separated milk was treated with rennet at 30 °C for known proportions of the visually-determined clotting time. Samples were fixed with glutaraldehyde, which inhibited aggregation of casein micelles, mixed with agar, and stained sections examined. Bias in the preparation of the electron micrographs was minimized by replication, particularly in the early stages of sample preparation, and, for thin (60–90 nm) sections, by systematic selection of the areas examined.

Whole casein micelles, viewed in stereo micrographs of thick (about 1 μm) sections, had open, diffuse structures and their appearance did not change on treatment with rennet. Micrographs of thick sections taken at 90° to each other showed that casein micelles form a network-type of gel, with the same structure in all dimensions. Counts of micelles larger than about 20 nm diam. in fields of thin sections showed that each of 3 sets of fields was similar and representative for each sample. The number of micelles/μm2 appeared to increase between 60 and 130 % of the clotting time, but this change was not statistically significant.

Type
Original Articles
Information
Journal of Dairy Research , Volume 45 , Issue 3 , October 1978 , pp. 405 - 411
Copyright
Copyright © Proprietors of Journal of Dairy Research 1978

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