Structural, topographical, and shear characteristics of milk protein and monoglyceride monolayers spread at the air-water interface.
In this contribution we are concerned with the study of structure, topography, and surface rheological characteristics under shear conditions of monoglyceride (monopalmitin and monoolein) and milk protein (beta-casein, kappa-casein, caseinate, and WPI) spread monolayers at the air-water interface. Combined surface chemistry (surface film balance and surface shear rheometry) and microscopy (Brewster angle microscopy: BAM) techniques have been applied in this study to pure emulsifiers (proteins and monoglycerides) spread at the air-water interface. To study the shear characteristics of spread films, a homemade canal viscometer was used. The experiments have demonstrated the sensitivity of the surface shear viscosity (eta(s)) of protein and monoglyceride films at the air-water interface, as a function of surface pressure (or surface density). The surface shear viscosity was higher for proteins than for monoglycerides. In addition, eta(s) was higher for the globular WPI than for disordered beta-casein and caseinate due to the strong forces acting on spread globular proteins. This technique makes it possible to distinguish between beta-casein and caseinate spread films, with the higher eta(s) values for the later due to the presence of kappa-casein. The eta(s) value varies greatly with the surface pressure (or surface density). In general, the greater the surface pressure, the greater the values of eta(s). Finally, the eta(s) value is also sensitive to the monolayer structure, as was observed for monoglycerides with a rich structural polymorphism (i.e., monopalmitin).
Patino
Juan M Rodríguez
JM
Departamento de Ingeniería Química, Facultad de Química, Universidad de Sevilla, C/. Prof García González 1, 41012-Seville, Spain. jmrodri@us.es
Sánchez
Cecilio Carrera
CC
D000388:Air; D000818:Animals; D002364:Caseins / Q000737:chemistry; D002417:Cattle; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000737:chemistry*; D050178:Monoglycerides / Q000737:chemistry*; D012212:Rheology; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry*; D000067816:Whey Proteins
D002364:Caseins; D008894:Milk Proteins; D050178:Monoglycerides; D000067816:Whey Proteins; D014867:Water