Non-migratory bioactive polymers(NMBP)in food packaging 73 0 80 Fig 5.2 Activity of PEG-conjugated chymotrypsin and native chymotrypsin held at 45C. Activity is expressed in percent relative to the initial activity of each enzyme preparation. Adapted from Topchieva et al.(1995) colleagues(1995)demonstrated improved thermal stability of chymotrypsin when conjugated to poly(ethylene glycol)(PEG)(see Fig 5.2). Appendini and Hotchkiss (2001) similarly demonstrated the thermal stability of a small antimicrobial peptide when covalently attached to a PEG-grafted poly (styrene) (PS) support. The immobilised peptide remained active when dry-heated to 200C for 30 minutes and when autoclaved at 121C for 15 minutes. Polymers are often processed at temperatures that would denature native proteins thermally stable protein-polymer conjugates will be resistant to high processing temperatures and suitable for polymer extrusion and other high temperature polymer and food processing applications Appendini(1999)also demonstrated the improved activity of the conjugated peptide over a range of pH(see Fig 5.3). Note that although there is some loss of activity caused by attaching the peptide to the surface (this will be discussed in section 5.3 below), the residual activity is retained over a broader ph range than for the native peptide. Other authors have also reported improved stability of polymer-conjugated enzymes to pH and temperature (Gaertner and Puigserver, 1992; Yang et al., 1996; Yang et al, 1995a, Yang et al, 1995b Zaks and Klibanov, 1984). The extended range of pH stability will provide activity in a broader range of food products than would be the case for the native The stability of proteins to inimical media, such as organic solvents, supercritical fluids and gases, is often improved by polymer conjugation and applications have developed to exploit this in non-aqueous enzymologycolleagues (1995) demonstrated improved thermal stability of chymotrypsin when conjugated to poly(ethylene glycol) (PEG) (see Fig. 5.2). Appendini and Hotchkiss (2001) similarly demonstrated the thermal stability of a small antimicrobial peptide when covalently attached to a PEG-grafted poly(styrene) (PS) support. The immobilised peptide remained active when dry-heated to 200ºC for 30 minutes and when autoclaved at 121ºC for 15 minutes. Polymers are often processed at temperatures that would denature native proteins; thermally stable protein-polymer conjugates will be resistant to high processing temperatures and suitable for polymer extrusion and other high temperature polymer and food processing applications. Appendini (1999) also demonstrated the improved activity of the conjugated peptide over a range of pH (see Fig. 5.3). Note that although there is some loss of activity caused by attaching the peptide to the surface (this will be discussed in section 5.3 below), the residual activity is retained over a broader pH range than for the native peptide. Other authors have also reported improved stability of polymer-conjugated enzymes to pH and temperature (Gaertner and Puigserver, 1992; Yang et al., 1996; Yang et al., 1995a; Yang et al., 1995b; Zaks and Klibanov, 1984). The extended range of pH stability will provide activity in a broader range of food products than would be the case for the native compound. The stability of proteins to inimical media, such as organic solvents, supercritical fluids and gases, is often improved by polymer conjugation and applications have developed to exploit this in non-aqueous enzymology Fig. 5.2 Activity of PEG-conjugated chymotrypsin and native chymotrypsin held at 45ºC. Activity is expressed in percent relative to the initial activity of each enzyme preparation. Adapted from Topchieva et al. (1995). Non-migratory bioactive polymers (NMBP) in food packaging 73