Production of whey protein aggregates with controlled end-use properties

We studied the structural behaviour and foaming properties of whey proteins under the effects of spray-drying in a co-current configuration. We used two different inlet/outlet air temperatures (170/85 degrees C or 260/138 degrees C, respectively), the other operating conditions being unchanged. Using different characterisation techniques, we showed that both whey proteins (WP-P-85 and WP-P-138) which were submitted to hydro-thermal treatments under mild and high air processing conditions behaved differently from untreated proteins (WP-L). As expected, WP-P-138 powder exhibited lower moisture and free lactose contents, a higher particle internal porosity, and a thinner particle wall thickness than the WP-P-85 powder. The conformational stability of whey proteins, obtained by dilution of untreated whey proteins (WP-L) and dispersions of the two spray-dried powders (WP-P-85 and WP-P-138), were compared. Whey proteins in the WP-P-138 powder showed a red- shift in the tryptophan emission wavelength, the appearance of a newly created fluorescent compound at 420 nm, contrary to untreated and WP-P85 whey proteins. In addition, we observed formation of a higher proportion of covalently-bound aggregates (11% in WP-P-138, instead of 5% in WP-P-85) and a decrease in conformational stability against re-heating (similar to 50% s in WP-P-138, instead of similar to 30% in WP-P-85) compared with untreated WP-L solution. Finally, combination of continuous measurements of foam volume (by an on-line video camera) and liquid (by conductivity) entrained in a column foam during its formation by air injection, in parallel with automatic acquisition of video-foam images during the destabilisation step, showed that solution of WP-P-138 spray-dried powder, obtained using the highest air temperature conditions, has higher foaming properties than WP-P-85 and WP-L solutions.