| Extrusion is a uniquely energy
efficient process. Its application in food industries is relatively recent
and the practice is one of trial and error. Fundamental studies are underway
to elucidate the chemical and physical changes of biomaterials under extrusion
conditions as affected by thermal and mechanical energy inputs. In the
typically fast process of extrusion, appropriate kinetic equations are
formulated to model the process. An energy equivalent concept has been
developed to treat the interacting effect of thermal and mechanical (shear)
energy inputs. The conversion induced by mechanical energy has, in contrary
to that by thermal energy, a negative temperature coefficient. Tribologically
induced changes are unique to extrusion process. Fundamental studies of
the tribochemistry of starch, protein, lipids and their inter-actions are
important to the design, operation and control of food extrusion processes.
The growth and maintenance of animal cells in vitro as a suspension
culture requires special bioreactors. Mouse-mouse hybridoma cells can constitutively
produce monoclonal antibodies under appropriate conditions. High cell densities
(>5x106 cells/ml) will lead to much higher productivity of antibody. A
perfusion system is best suited for continuous operation of a high cell
density reactor. One system utilizing a hollow fiber cartridge with a microporous
membrane in a tangential flow mode of operation permits retention of cells
in the reactor so high cell densities can be achieved. Long term persistent
shear force generated by the cell retention devices (recycle pump and hollow
fibers) greatly contribute to cell damage and cell death. These effects
should be quantified and considered for operation of the perfusion system.
A bleed stream can be introduced to control cell growth rate and to maintain
proper operation. The ultimate goal of this research is to produce large
quantities of a cell-free product which can be easily integrated with an
on-line downstream purification system. The purification scheme consists
of precipitation and ultrafiltration stages along with affinity or ion
exchange chromatography stages. Relatively pure antibodies can then be
produced on a regular basis.
|
Recent Publications
D. Qu and S.S. Wang, Modeling Extrusion Conversion of Starch in a
Single-Screw Extrusion
Process, J. Chin. Inst. Chem. Engrs., 33 (1), 33-51, 2002.
Y. Kim, M.N. Faqih and S.S. Wang, Factors Affecting Gel Formation
of Insulin, Carbohydrate
Polymers, 46 (2), 135-145, 2001.
Xiao-Ming Yang and S. S. Wang, Phase-specific Optimization of Multiple
Endotoxin-Protein
Production with Genetically Engineered Bacillus Thuringiensis,
Biotechnol. Appl. Biochem (2000),
31, 71-76, 2000.
S. S. Wang, Kinetics of Food Process Engineering, in Encyclopedia
of Food Science and
Technology, ed. F. J. Francis, John Wiley & Sons, K,1437-1448,
2000.
LaPorte, T.L.,Shevitz, J., Kim,Y.and Wang, S.S. Long term shear effects
on a hybridoma cell line by dynamic perfusion devices,
Bioprocess Engineering, 15. 1-7, 1996.
Wang, S.S. and Zheng, X., Tribological Shear Conversion of Starch,
Journal of Food Science 60(2) 201-204, 1995.
Kim, I.H. and S.S. Wang, Measurement of Hydrodynamic Shear Using
a Dissolved Oxygen Probe, Biotech and Bioeng. 41, 296-302, 1993.
Wang, S.S., W.C. Chiang, B.L. Zhao, and I.K. Kim. Experimental
Analysis and Computer Simulation of Starch-Water Interactions During
Phase Transition, J. Food Science, 56(1), 121 (1991).
|
