Cryo-TEM of isolated milk fat globule membrane structures in cream

Abstract

This study has focused on structures formed through the release of lipid membrane material from milk fat globules. The aim of the study was to describe vesicles in the cream plasma and processing-induced vesicular structures in cream and buttermilk. The dairy samples were divided into three fractions through centrifugation, using D₂O for density control. These fractions were examined using cryogenic transmission electron microscopy (cryo-TEM). The cream layer contains submicron-sized emulsion droplets, which are spherical and partly covered with loosely associated protein aggregates. The structures of the coalescence-induced vesicles are mostly unilamellar but bilamellar and multilamellar vesicles are also present. Some spherical structures are observed but facetted particles dominate. In the buttermilk sample, spherical and slightly deformed vesicles are visible but no facetted structures are observed. The butter oil serum sample shows interesting membrane vesicle-fat globule aggregate. These types of structures were also visible in the skim milk sample. The results show that that vesicular material may be found in a range of dairy products. To our knowledge this is the first time that the existence of these types of structure has been unambiguously demonstrated in these systems.