Physical Chemistry of Foods

should now be transformed into

Np

np

¼

R

aeff

D

ð 13 : 19 Þ

Moreover, the value ofDis generally increased, by an amount up to 0.2, but
not above the 2.3–2.4 mentioned above. For smalljthis increase becomes
manifest. Figure 13.8c illustrates the difference between results according to
the two equations.
Short-term rearrangement is a very common phenomenon in
perikinetic aggregation, often withnpvalues of order 10. Rearrangements
on a larger scale can also occur, though generally after a space-filling
network has formed. The fractal geometry will then gradually disappear. As
mentioned, large-scale rearrangement during aggregation generally leads to
a precipitate.

Note It is interesting to compare the discussion in this section with

that of Section 6.2.1 on the conformation of random-coil linear

polymers. Also in that case a larger molecule, i.e., one consisting of

a higher effective number of chain elementsn^0 , is more tenuous.

Equation (6.4) reads rm¼b(n^0 )n, where rm may be considered

proportional to the parameter Rin Eq. (13.12); bthen would

correspond toain (13.12), andn^0 toNp. For a polymer molecule

conformation that follows a ‘‘self-avoiding random walk,’’ the

exponentnis equal to 0.6. Rewriting of Eq. (6.4) then leads to

n^0 ¼(rm/b)1.67, which is very similar to Eq. (13.12) with a ‘‘fractal

dimensionality’’ of 1.67. Depending on conditions, the exponent

can vary between about 1.6 and 2.1.

Question

A food company wants to produce a gelled oil-in-water emulsion. In a laboratory
trial an emulsion of 5%(v/v) triglyceride oil in a 1%(w/w) solution of Na-caseinate is
made. It is homogenized to obtain an average droplet sized 32 ¼ 1 mm. To cause
aggregation, glucono delta-lactone (GDL) is added. This substance slowly
hydrolyzes in water to yield gluconic acid, which lowers the pH. Sufficient GDL is
added to obtain pH 4.6, the isoelectric pH of casein. It has been established in several
studies that caseinate-covered emulsion droplets do aggregate at low pH. Would they
form a gel?