(voluminosity about 2.2 ml per g dry casein). They are protected against
aggregation by a layer of protruding parts of thek-casein chains. Upon
addition of rennet, which contains the proteolytic enzyme chymosin, these
chains are slowly cut off, causing the micelles to aggregate, and a ‘‘rennet
gel’’ is formed. The physiological pH of milk is 6.7. Acidification can also
cause aggregation: at low pH the calcium phosphate goes into solution, and
FIGURE17.15 Effects of length scale (distancerfrom a ‘‘central’’ particle of
radiusa) on the fractal properties of a particle gel. (a) Log of the particle numberNp
in a sphere of radiusr/a(log scale). (b) Fractal dimensionalityDas a function of
log(r/a). Hypothetical and somewhat simplified example.