Life Sciences Commons^™

Practical Aspects Of Electron Microscopy In Dairy Research, Miloslav Kalab

Food Structure

Milk products are based mostly on casein micelles, fat globules, and whey proteins. The former two constituents are corpuscular and whey proteins become corpuscular when coagulated. Structural changes in these basic constituents during processing have been studied by electron microscopy. This review discusses the structures of yoghurt, curd, cheeses (hard cheeses, mould-ripened cheeses, cream cheeses, and process cheese), cream, milk powders, and nontraditional dairy products. Defects and deviations from traditional structures of these products are explained where the causes are known. Examples of such causes are foaming of milk, presence of unusual ingredients (bacterial polysaccharides, whey protein concentrates), and alterations …

Structure, Meltability, And Firmness Of Process Cheese Containing White Cheese, Miloslav Kalab, H. Wayne Modler, Marijana Caric, Spasenija Milanovic

Food Structure

White cheese made by coagulating heated milk (90"C) with a 2.5% citric acid solution to pH 5.5 consists of casein particles having a characteristic core-and-shell ultrastructure. The presence of this White cheese in process cheese can be detected by transmission electron microscopy on the basis of the core-and-shell ultrastructure which is stable during cheese processing. White cheese additions may be detected at levels equal to or higher than 8%.

White cheese, which does not melt alone when heated, increases meltability of the process cheese in which it is present as an ingredient. Meltability in creases at all White cheese concentrations …

Effect Of Heating To 200 C On Casein Micelles In Milk: A Metal Shadowing And Negative Staining Electron Microscope Study, V. R. Harwalkar, Paula Allan-Wojtas, Miloslav Kalab

Food Structure

Milk was heated to 200 C for 3 min in sealed inverted-Y-shaped glass vials and reacted with a glutaraldehyde solution at that temperature. Electron microscopy of the metal-shadowed and negatively stained samples revealed that casein micelles in the milk did not disintegrate extensively at the high-temperature used but, rather, became enlarged. Some of them were found to be either clustered or distorted.

Rheology And Microstructure Of Strained Yoghurt (Labneh) Made From Cow's Milk By Three Different Methods, A. Y. Tamime, M. Kalab, G. Davies

Food Structure

Labneh is the name for strained yoghurt, i.e., yoghurt made with an elevated solids content, which has originated in the Middle East. For this study , three types of Labneh were made from cow' s milk: (a) "Traditional Labneh" was produced by straining yoghurt in a cloth bag, (b) "UF Labneh" was made by ultrafiltration of warm yoghurt , and , (c) "UF Retentate Labneh" was obtained by culturing homogenised ultrafiltration (UF) milk retentate. A 11 products were passed through a lactic curd homogen is er to smoothen the Labneh curd . Total solids contents of t he products were …

The Size Distribution Of Casein Micelles In Camel Milk, Z. Farah, M. W. Ruegg

Food Structure

The size distribution of casein micelles in camel milk has been determined by electron microscopy. Individual and pooled samples were cryo-fixed by rapid freezing and freeze-fractured. Electron micrographs of the freeze-fracture replica revealed a relatively broad size distribution, with an average micelle dimeter around 280 nm in the volume distribution curve. The distribution was significantly broader than that of the particles of cow's or human milk and showed a greater number of large particles. The submicelles were also somewhat larger than those observed in cow's and human milk (approx. 15, 10 and 7 nm, respectively). The average values for the …

The Effects Of Polysorbate 80 On The Fat Emulsion In Ice Cream Mix: Evidence From Transmission Electron Microscopy Studies, H. D. Goff, M. Liboff, W. K. Jordan, J. E. Kinsella

Food Structure

Emulsifiers are used in ice cream to produce a dry, smooth textured product with desireable melting properties. They function by promoting a partial destabilization of the fat emulsion. Polyoxythylene sorbitan monooleate is used very commonly in the ice cream industry for this purpose. The objective of this research was to examine by transmission electron microscopy the differences in the fat globules in typical ice cream mix emulsions prepared with and without 0.08% polyoxyethylene sorbitan monooleate.

Ice cream mix was combined 3:1 with a 2% solultion of ultralow gelling temperature agarose at 20 degrees C, fixed with 4% glutaraldehyde, postfixed with …

Microstructure Of Set-Style Yoghurt Manufactured From Cow's Milk Fortified By Various Methods, A. Y. Tamime, M. Kalab, G. Davies

Food Structure

Five different batches of skim milk were prepared and fortified by the addition of skim milk powder (SMP) or sodium caseinate (Na-cn) or by concentration using a vacuum evaporator (EV), ultrafiltration (UF), or reverse osmosis (RO) to contain similar levels of protein (5.0-5.5%). Yoghurts were made by inoculating the milks with one of 3 commercial yoghurt starter cultures and by incubating the mixes at 42°C for 2.5 h. The following factors were found in this study to affect firmness of the yoghurts: (a) Lactic acid production (acidity) - Yoghurts containing 1.02% of lactic acid or more (pH 4.54 or less) …

Development Of Microstructure In Set-Style Nonfat Yogurt - A Review, Miloslav Kalab, Paula Allan-Wojtas, Beverley E. Phipps-Todd

Food Structure

The development of microstructure in natural set-style nonfat yoghurt was stud i ed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition to thin-sectioning and conventional SEM described in the literature, this review illustrates gelation of milk with micrographs obtai ned by rotary shadowing of casein micelles and their clusters. The existence of void spaces occupied by lactic acid bacteria in yoghurt was con finned by cold-stage SEM of uncoa ted specimens. The microstructure of yoghurt is affected by the preheat treatment of milk, bacterial starter cultures, total solids content , and the presence of thickening agents. …

Structure And Properties Of The Particulate Constituents Of Human Milk. A Review., M. Ruegg, B. Blanc

Food Structure

Milk contains different types of colloidal or coarsely dispersed particles, such as casein micelles, membrane fragments, fat globules and cells. The fat globules are composed of subpopulations of differently sized particles. In contrast to COW 1S milk, the overall average diameter (dys), increases with advancing lactation from about 1.8 ~min colostrum to 4.0 ~min mature milk. Membrane materials originating from the milk fat globule membrane, plasma membrane, secretory vesicles and other sources can be found in milk serum. These particles have also been called lipoprotein particles. Their size ranges from about 10 - 400 nm. New results concerning the structure …

Electron Microscopy Of Milk And Milk Products: Problems And Possibilities, D. G. Schmidt

Food Structure

Milk and dairy products have frequently been studied by transmission- and scanning electron microscopy. The specimen preparation procedure may considerably influence the final result, and formation of artefacts is frequently observed. In this respect, formation of ice crystals during cryofixation is a well-known phenomenon. But dehydration, to an extent such as is required for embedding procedures, also appears to be harmful to dairy products. Micrographs of thin sections of plastic- embedded samples of casein submicelles show threadlike material, whereas in freeze-etched specimens only spherical particles are found. Similar observations are made when samples of cheese and of concentrated milk are …