Studies on glass transition temperature of mono and bilayer protein films plasticized by glycerol and olive oil

摘要

Thermomechanical and thermal properties of whey protein, maize prolamin protein (zein), and the laminated whey protein-zein films were studied. The dynamic mechanical (thermal) analysis (DMTA) results showed that the single zein film had higher T-g than single whey protein and zein-whey laminated films. The shift in the T-g values of films from 31.2 degrees C in whey protein film and 88.5 degrees C in the zein film to 82.8 degrees C in the laminated whey protein-zein films may be implied some interaction formation between the two polymers. The small tan 6 peaks were observed at -50 degrees C in zein-glycerol films and at -22.37 degrees C in the whey protein films and can be related to beta-relaxation phenomena or presence of glycerol rich region in polymer matrix. Zein-olive oil and zein-whey protein-olive oil films showed tan 8 peaks corresponded the T-g values at 113.8, and 92.4 degrees C, respectively. Thus, replacing of glycerol with olive oil in film composition increased T-g. A good correspondence was obtained when DSC results were compared with the tan delta peaks in DMTA measurements. DSC thermograms suggested that plasticizers and biopolymers remained a homogeneous material throughout the cooling and heating cycle. The results showed that T-g of zein-glycerol films predicted by Couchman and Karasz equation is very close to value obtained by DSC experiments. (C) 2008 Wiley Periodicals, Inc.