Degradation of methylcellulose during ultra-high pressure homogenisation

Initially developed for the dairy industry, the very high pressure homogenisation (>100 MPa) is now also applied in the pharmaceutical sector and in biotechnology (breaking cells for biomass extraction). The use of this technology to make fine food emulsions and to modify functional properties of macromolecules seems to be promising. Thus the objective of this study was to understand the effect of homogenisation forces on the mechanical degradation of a model polymer extensively used in food, cosmetic and pharmaceutical preparations: the methylcellulose. Degradation of the polymer was studied in a pressure range in the homogenising valve from 20 to 350 MPa. It was observed that as the pressure imposed by the homogeniser increased, the intrinsic viscosity decreased. Intrinsic viscosity decrease was correlated to apparent changes in the average molecular weight of the polymers obtained by size exclusion chromatography coupled on-line with multiangle laser light scattering and refractive index detection (SEC/MALLS/RI). The strong elongational flow encountered by the polymer at the entrance of the valve of the high pressure homogeniser device may bring sufficient energy to disrupt covalent bonds. Consequently, as shown by flow behaviour the thickening properties of this polymer were also reduced. (C) 2001 Published by Elsevier Science Ltd.