Page 309 - Biosystems Engineering

286 Cha pte r Ni ne

Heavy steel
wheels
or mullers

Scrapers
Drive
shaft
Heavy steel
pan
Door lever

Discharge Slide door
opening

FIGURE 9.2 A pan crusher.

Cell Rupture by Pressure There are several varieties of laboratory
presses to disrupt cells; the Hughes press and the French press are
especially successful. The original Hughes press consisted of a split
block with a half cylinder hollowed in each face. The frozen cell paste
(with or without an abrasive) was placed in the hollow. The block
was clamped together, and a plunger driven by a fly press forced the
frozen paste from the cylinder into channels cut in the block. The fro-
zen disrupted cells were then scraped from the block. With the French
press, a hollow cylinder in a stainless steel block is filled with cell
paste and subjected to high pressure. The cylinder has a needle valve
at the base, and the cells burst as they are extruded through the valve
to atmospheric pressure.
Two continuous presses have been scaled up by Duerre and Ribi,
which are similar in principle to the French press. Duerre and Ribi
found that with Escherichia coli, most cells were ruptured at 1000 kg/
2
2
cm and cells were broken at 1700 kg/cm with little loss of enzyme
2
activity. However, at 2400 to 3800 kg/cm , the stability of some
enzymes was affected; arginine, decarboxylase, and formic hydrogen
lyase were destroyed. Formic oxidase was partially inactivated,
whereas lysine decarboxylase and glucose oxidase remained active.
Another mechanical press developed by Lars Edibo, Sweden, in
which frozen cells are forced to and fro through a small hole in a disc
between two cylinders at low temperature and pressure. Disruption of
the cells is probably caused by deformation of organisms embedded in