Calidad

Miloslav Kaláb

The Beauty of
Milk at High
Magnification

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Issue 18 JuNe 2010

T

he task of designing milk protein-based
frankfurters compelled me to use electron
microscopy to understand the formation
of microstructure in the product. Later, I
extended microscopic studies to dairy products. Their
microstructures reflect the variety of interactions which
the milkconstituents (caseins and whey proteins, milkfat
and lactose) undergo during manufacturing, often
with the participation of microorganisms (bacteria or
fungi). electron microscopy reveals the details of such
interactions to manufacturers and may also be used to
protect the consumer.

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What a treat - a refreshing

products can take a short time, such

strawberry yogurt, fizzing

as withyogurt, or it can take much

kefir, forty ice cream flavours,
These products are all made

Milk is a unique food – it comes

from milk and they all have

in liquid form and contains all

transformation of milk into milk
Fig. 1. Food Structure – journal cover.The
micrograph on issue 4, vol. 12, 1993 shows a
high-resolution SEM image of cryofractured one-day
old Mozzarella cheese fromwhich fat and the liquid
phase had been removed (McManus et al., 1993).

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Issue 18 JuNe 2010

the

nutritionally

important

components, such as proteins
(corpuscular

casein

and

dissolved whey proteins), fat
(fat globules) and carbohydrates
(milk sugar, i.e., lactose), which are required for a

contrast to lactose-intolerant people who lack this

raised cattle,goats, buffaloes, sheep, camels, yaks, or

enzyme. Microorganisms (bacteria, yeasts and other

horses, and used their milk as food, have retained

longer, such as with cheese.

cheese and wine, cheesy pizza.

excellent nutritional value. The

Fig. 2. Casein micelles in cow milk by metal shadowing with platinum and carbon. False colour TEM. Bar: 0.5 µm.

newborn mammal. Human cultureswhose ancestors

fungi) participate in the production of the majority

the enzyme lactase in their gastrointestinal tract in

of milk products and many lactic acid bacteria called

adulthood and are thus able to digest lactose, in

"probiotic bacteria" are beneficial to human health.

Milk is a unique food – it
comes in liquid form and
contains all the nutritionally
importantcomponents.

Examining milk with an optical microscope brings
great disappointment since there is nothing to see
except fat globules. Milk protein particles (casein
micelles) are only a fraction of a micrometre in
diameter. Electron microscopy is needed to see

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Fig. 3. Casein micelles in a heat-induced skimmed milk gel. Reconstituted (40% total solids) skimmed milk powder in water washeated for 10
min in a boiling water bath and then cooled at 6°C for 2 hours.The resulting gel was trimmed, fixed in a buffered 2.5% glutaraldehyde solution,
dehydrated in ethanol, freeze-fractured and gold-coated for SEM. Bar: 0.5 µm.

Fig. 4. Yogurt protein matrix is composed of casein particles and attached k-casein-ß-lactoglobulin complexes in the form of branching chains
which hold theliquid phase initially present in the milk.Two streptococci are also shown. Bar: 2 µm.

them as they are converted into various dairy

fat irrespective of their composition. This finding is

milk (Knoop, 1972). Both academic and industrial

television station was blunt: "We would not show

foods.Their structures depend on pH, temperature,

the principle of modern fat replacers made fromresearch establishments started to acquire electron

that there are bacteria in yogurt – if consumers

and the effects of microorganisms. Structural

microparticulated milk proteins (Singer & Dunn,

microscopes and annual international meetings

stopped buying yogurt because you show bugs

studies, particularly at the microscopical scale, are

1990). Professional tasters did not...