Advanced Microscopy:
Probing Food Structures
Probe microscopy is allowing us to see food structures we
could not always resolve using ‘conventional’ microscopes.
In some cases, we are able, for the first time, to study how
the building blocks of food (fats, carbohydrates and proteins)
interact to form the different structures that determine the
quality of foods. Because probe microscopy ‘feels’ the
surface rather than looks at it, we are able to ‘image’ samples
under more natural environments providing new information
on structure and behaviour.
Areas that we are currently
studying include:
Foams and emulsions
z What makes a stable foam or emulsion?
z Why is the ‘head’ on a beer so important and how can
we improve it?
z How is bubble structure in bread controlled?
z Can ‘better’ ice creams and whipped foods be made?
The images show how proteins and surfactants (fats)
compete at the interface created during the formation of
foams and emulsions. The protein forms a strong elastic
film but the surfactant is able to get into small holes left
between the proteins, compressing the protein network
which allows more surfactant to get to the surface. Eventually
the network breaks and lumps of protein leave the surface.
The battle for control of the interface causes instability and
weakens the foam or emulsion.
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.ac.uk
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.ac.uk
Starch
z What is the structure of starch and how are its properties
affected?
z What differences are there in starches from different
sources?
z How do enzymes break down starches?
Starch is made up of two carbohydrates, amylose and
amylopectin, the ratio of which alters with source. We are
able to observe the internal structure of granules to see
what structures are present. In granules the overriding
observation is that the internal structure is made up of
‘blocklets’:- partly crystalline packets of the branched
carbohydrate amylopectin suspended in a matrix of the
linear carbohydrate amylose. The detailed structure affects
the properties of different starches.
Certain enzymes involved in the breakdown of crystalline
starch are important in human digestion, the spoilage of
plant material and in commercial uses of starch as a
substrate. By visualising the way in which these enzymes
interact with starch we have been able to understand how
they work. This suggests ways of developing improved
enzymes.
Novel pectins
Pectin from apples or citrus fruit is familiar as a gelling agent
in jam making. The pectin obtained from sugar beet is
unusual: it can be used to emulsify oils. Imaging of the
extract shows that it contains pectin molecules (arrowed)
with proteins attached to the ends of the chains. The protein
component adsorbs at the oil-water interface at the surface
of the oil drops in the emulsion. The carbohydrate chains
coat the droplets stopping coalescence and separation of
the oil from the water. With the imminent withdrawal of EU
subsidies for sugar beet new applications are welcome.
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.ac.uk