Abstract
Knowledge of particle size is important in the food industry because it affects the production and handling of ingredients and the formulation, processing, and quality control of food and beverage products. Particle size affects reactivity, solubility, and flowability of ingredients and the texture, mouthfeel, and processing of products.
Particle size analysis has been applied to a wide variety of ingredients and products, including coffee, sugar, salt, flour, chocolate, milk powder, spices, and flavors. Analytical techniques for measuring particle size range from traditional sieving and sedimentation to use of modern automated imaging and laser-based instruments.
Sieving
Sieving is the traditional method for determining the size distribution of a sample of solid material. A dry sample is placed in the top sieve of a stack of sieves of decreasing aperture sizes, and the stack is vibrated to separate the different sizes by gravity. Then the sieves are weighed to determine the size distribution. Sieving is commonly used with relatively large materials, greater than 63 microns in diameter.Sedimentation
Sedimentation velocity of suspended particles can be obtained by measuring the concentration of particles remaining in suspension with time. Sedimentation can be either gravitational or centrifugal. Gravitational sedimentation is normally limited to particles of relatively large size because the rate of sedimentation for small particles is too low to give a practical analysis time and because Brownian motion of small particles becomes too large to allow effective settling. In this method, also called integral sedimentation, a beam of light or X-rays is passed through a fluid sample at a known distance from the fluid surface to measure particle concentration. As particles settle through the fluid, the concentration of particles remaining in the dispersion falls, and the intensity of light or X-rays that reaches the detector increases. Stokes’ law is used to calculate the size of particles that settle out of the fluid as a function of time, and a particle size distribution is generated by plotting the measured concentration of particles against the calculated particle diameter. In centrifugal sedimentation, also called differential centrifugal sedimentation, a sample is placed on top of a column of clear liquid in an optically clear rotating disc and forms a thin film that spreads radially over the surface of the liquid due to centrifugal force. As the particles reach the edge of the disc, they block the beam of light. The change in light intensity is recorded and converted into a particle size distribution.>> Download the full Application Note as PDF
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