Innovative systems and applications - Physical Gels from Biological and Synthetic Polymers - page 335

be distinguished from real salmon roe, until the arti cial roe is placed in hot water.

Under these conditions, real salmon roe forms an egg-white colour and texture. That
said, some consumers prefer arti

cial salmon roe because of its lower cholesterol
content. Crab sticks (imitation crab-meat sticks) are a form of kamaboko, a processed
seafood made of flesh (surimi), shaped and cured to

resemble crab leg meat, and a gelling agent such as egg white (albumen). Crab

finely pulverized white sh

avour-

ing and colouring is added. The fibrous texture is also appreciated in commercialized

' , which can be torn into thin strings just like dried squid, a favourite

Japanese snack.
Clearly another way to produce low-calorie products, many of which are sold by
volume rather than mass, is simply to aerate them. To stabilize the resultant air bubbles,
an appropriate gel can be added. The gas phase in a food matrix not only makes the
product softer but changes its appearance, colour and mouth-feel in a controllable
manner. As Campbell and Mougeot ( 1999 ) have pointed out, aeration has been used
for millennia in beer and bread products, and most commercial

string cheese '

ice creams
contain up to 50% air, together with a mixture of gelling/stabilizing agents including
guar, LBG, pectin, alginate and gelatin (Clarke, 2004 ). Commercial marshmallows are
another example of aerated gels: they usually contain gelatin and sometimes also
albumin.
Both the science and further applications of aerated gelatin gels have been discussed
by Zuniga and co-workers (Zuniga and Aguilera, 2008 , 2009 ; Zuniga et al., 2011 ). They
prepared a series of what they term gas-

' soft scoop '

lled gelatin gels (GGGs) and compared the
results with control samples. Originally they

with air, nitrogen and helium using
a syringe pump and gas cylinder assembly to bubble gas through a pre-gelled
solution, which they then allowed to cool. In the gel, gas bubble sizes lay mainly in the
range 40

' aerated '

m and volume fractions were c.70%. They then made a number of
measurements of both gas-

- 120 μ

lled and control gelatin gels, and subjected them to uniaxial
compression. As in Chapter 7 , the stress

were almost linear up to failure,
which occurred, in this case, at strains of around 60% for the control samples and around
40% for the aerated samples. In particular, the GGGs did not show the sigmoidal stress

- strain ' curves '

-

strain behaviour expected for cellular foams, an observation which may re ect the

small gas bubble sizes and the thick interface walls. In their most recent paper
(Zuniga et al., 2011 ), they generated the gas-

lled gels ultrasonically and studied the

interface stabilized with partially denatured -lactoglobulin samples. The latter samples

failed at lower strains than the control aerated samples, although the effect of the extent of
denaturation is limited.
There is interest in so-called

β

' nutraceutical microgels ' . A nutraceutical is de ned as a

food material containing a component with a speci c physiological bene t beyond

inherent general nutrition, thus preventing or alleviating speci c diseases (Zuniga and

Aguilera, 2008 ). Such a microgel includes those made from proteins and polysacchar-
ides. Proteins in particular have prospective tuneable release properties because of the
dependence of their charge on pH. In other work (Remondetto et al., 2004 ), in the
presence of proteolytic enzymes such as pepsin at pH 1.2 or pancreatin at pH 7.5,
particulate gels of β -lactoglobulin, typically made at pH > 6, have been shown to release