Mixing quality of powder-liquid mixtures studied by near infrared spectroscopy and colorimetry

• A new mixing process for inserting liquid into powders was evaluated.
• The liquid was mixed in a powdery state, as so called powder-liquids.
• The mixing quality was quantified by NIR spectroscopy and colorimetry.
• Both NIR spectroscopy and colorimetry showed similar mixing kinetics.
• Powder-liquids mixed faster and more homogeneously compared with sprayed liquid.

In many industries, mixing powder with a low amount of liquid is a frequently used process step, e.g. in order to generate agglomerate/granule product structures or for sintering and extrusion of wet powders or pastes. There are still great difficulties in achieving a homogeneous mixture due to local agglomeration and lump formation. A new mixing methodology has therefore been developed, in which the liquid is transformed into a solid powder by spray chilling, generating so-called powder-liquids. These powder-liquids are then mixed with other dry powders.An even liquid distribution, as well as the related even distribution of functional components in the final product is of high relevance. We thus aimed to evaluate the mixing quality of such powder/powder-liquid mixtures studied by near infrared (NIR) spectroscopy and colorimetry. For this purpose we quantified the homogeneity of fat based powder-liquids mixed with flour. NIRS is a well-recognized quantification method that successfully has been used to analyze powder mixtures before, while colorimetry is a method less used for such an application. The results demonstrated that both methods are applicable for quantifying the mixing behavior of such powder mixtures. We showed that cheap, easy and fast colorimetry is as reliable as NIRS measurements and hence can be a first choice validation method in industry. Comparing the powder-liquid mixing with spraying the liquid directly into the powders, the powder-liquids mixed faster and resulted in better homogeneity. Our results support the use of powder-liquids to process new highly homogeneous products required in functional foods or pharmaceutical products.

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