Hydrolyzed whey proteins as emulsifiers and stabilizers in high-pressure processed dressings

Thirty-eight model dressings were produced according to a fractional factorial design. Dressings prepared with hydrolysed whey protein concentrate (DH 1 with Corolase PN-L from RohmGmbH) were compared to dressings produced with whey protein concentrate (WPC) and purified beta-lactoglobulin (beta-LG) as emulsifiers. The dressings were produced in a high-pressure homogeniser at similar to70 kPa pressure. The factors varied were protein%, oil%, pH, process temperature, and in addition NaCl, CaCl2 and sucrose. The dressings were evaluated with regard to textural and structural properties by emulsion stability (ES), rheological measurements, scanning electron microscopy (SEM) and image analysis. The dressings produced spanned from thin milk-like liquids to thick pastes. WPC formed mainly thin dressings, while dressings produced by hydrolysate and beta-LG were mainly creamy. None of the dressings showed separation of the oil phase, however some syneresis of water was observed. Variation in protein and oil content affected the stability of the dressings. When the protein content was increased from 2 to 4% and the oil content from 5 to 30%, the hydrolysate and beta-LG dressings became more stable, in contrast to WPC dressings, which became less stable. Addition of sucrose increased the stability and the phase angle of all protein types. High processing temperature (75 degreesC) affected the dressings differently. A positive effect was observed on the stability of WPC and beta-LG dressings, while hydrolysate dressings showed reduced stability, except for the combination of low pH (4.0), high protein (4%) and fat content (30%). This dressing was highly stable at high processing temperature. SEM-images revealed that the fat globule size was smallest for WPC (0.1-0.9 mum) and increased in the order WPC < hydrolysate < beta-LG. The microstructure of WPC dressing showed homogenous, non-aggregated structure in contrast to hydrolysate and beta-LG dressing, which showed highly ordered, aggregated structure which supports the rheological measurements for gel formation. Image analysis indicated that the microstructure of the dressings made with different protein types were special and identifiable. (C) 2003 Elsevier Ltd. All rights reserved.