No abstract

8The ultrasonic effect on the physicochemical and emulsifying properties of three animal proteins, 9 bovine gelatin (BG), fish gelatin (FG) and egg white protein (EWP), and three vegetable proteins, pea protein 10 isolate (PPI), soy protein isolate (SPI) and rice protein isolate (RPI), was investigated. Protein solutions (0.1 -11 10 wt. %) were sonicated at an acoustic intensity of ~34 W cm -2 for 2 minutes. The structural and physical 12 properties of the proteins were probed in terms of changes in size, hydrodynamic volume and molecular 13 structure using DLS and SLS, intrinsic viscosity and SDS-PAGE, respectively. The emulsifying performance of 14 ultrasound treated animal and vegetable proteins were compared to their untreated counterparts and Brij 97. 15Ultrasound treatment reduced the size of all proteins, with the exception of RPI, and no reduction in the 16 primary structure molecular weight profile of proteins was observed in all cases. Emulsions prepared with all 17 untreated proteins yielded submicron droplets at concentrations ≤ 1 wt. %, whilst at concentrations > 5 wt. % 18 emulsions prepared with EWP, SPI and RPI yielded micron sized droplets (> 10 μm) due to pressure 19 denaturation of protein from homogenisation. Emulsions produced with sonicated FG, SPI and RPI had the 20 similar droplet sizes as untreated proteins at the same concentrations, whilst sonicated BG, EWP and PPI 21 emulsions at concentrations ≤ 1 wt. % had a smaller droplet size compared to emulsions prepared with their 22 untreated counterparts. This effect was consistent with the observed reduction in the interfacial tension between 23 these untreated and ultrasound treated proteins.

Using a multitechnique approach, two temperature domains have been identified in agarose gelation. Below 35°C, fast gelation results in strong, homogeneous and weakly turbid networks. The correlation length, evaluated from the wavelength dependence of the turbidity, is close to values of pore size reported in the literature. Above 35°C, gelation is much slower and is associated with the formation of large‐scale heterogeneities that can be monitored by a marked change in the wavelength dependence of turbidity and visualised by transmission electron microscopy. Curing agarose gels at temperatures above 35°C, and then cooling them to 20°C, produces much weaker gels than those formed directly at 20°C. Dramatic reductions in the elastic modulus and failure strain and stress are found in this case as a result of demixing during cure. An interpretation, based on the kinetic competition between osmotic forces (in favor of phase separation) and elastic forces (that prevent it) is proposed. © 2001 John Wiley & Sons, Inc. Biopolymers 59: 131–144, 2001

No abstract

No abstract