Characterization of enzymatically induced aggregation of casein micelles in natural concentration by in situ static light scattering and ultra low shear viscosimetry

The aggregation of casein micelles in undiluted skim milk after the additio n of chymosin was studied by static light scattering and ultra low shear vi scometry, The static light scattering measurements were made with two diffe rent sample thicknesses, 72 and 16 mu m The scattering data were analyzed b y indirect Fourier transformation and by the polydispersity inversion techn ique which led to pair distance distribution functions and size distributio n function, respectively. The minimum scattering angle was 1 degrees, which allows for the determination of particle sizes up to a maximum diameter of 12 mu m. The fractal dimension determined from double logarithmic plots of intensity versus scattering vector resulted in values between 1.9 and 2.0, The influence of multiple scattering was determined by comparison of the m easurements with the different sample thicknesses. The measurements show no significant influence of multiple scattering when the transmission is abov e 0.85, Due to the very complex and porous structure of the casein aggregat es the Rayleigh-Debye-Gans scattering theory has been used in the data anal ysis. Measurements with a new instrument using ultra low shear showed good agreement with theory. (C) 1999 Academic Press.