Functional Characteristics of Protein Stabilized Emulsions: Emulsifying Behaviour of Proteins in a Sonifier.

• Protein stabilized emulsions made up of 40% soybean oil by weight and protein dispersions of 2.5% (w/w) protein content have been prepared in an ultrasonic device. The emulsifying apparatus was incorporated into a recirculating system, where power input and number of passes were varied. The food proteins studied were a soy bean protein isolate, a whey protein concentrate (WPC), and a sodium caseinate. The emulsions obtained were characterized in terms of droplet size distribution and amount of protein adsorbed per unit fat surface area (protein load). The results were compared to the fat surface area and the protein load of emulsions made in different ways in a valve homogenizer. Flocculated emulsions, such as the types stabilized with soy protein and WPC (0.2–7), produced either in a sonitier or in a valve homogenizer, have larger fat surface areas and broader size distributions than nonflocculating systems. In the sonifier, overprocessing in terms of fat surface area occurs at high power inputs for all protein stabilized emulsions. Sonified emulsions have smaller droplet size and a broader spectrum of globule size than valve homogenized emulsions made with the same power input respectively, and number of passes. The protein load is largely determined by the protein/fat surface area ratio and by the type of protein used as an emulsifier, irrespective of the emulsifying conditions (emulsifying apparatus, intensity, and time). But the latter are dominating with regard to the final droplet size distribution of the emulsions, where the choice of protein is of minor importance. The relation between percentage protein adsorbed from the bulk phase as a function of the fat surface area suggests that the caseinates are mainly adsorbed from the bulk phase to the newly created interface up to a surface area of 8–9 m2/ml emulsion. For the soy protein (0–7) and WPC (0.2–7) stabilized emulsions spreading of already adsorbed molecules becomes more favorable than adsorption of proteins from the bulk at fat surface areas as low as ∼ 3 m2/ml emulsion. This change in the way of covering the interface occurs for WPC (0–7) stabilized emulsions at surface areas of about 4 m2/ml emulsion.

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TEKNIK OCH TEKNOLOGIER  -- Annan teknik -- Livsmedelsteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies -- Food Engineering (hsv//eng)

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