Production of whey protein aggregates with controlled end-use properties

Abstract

-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• C or 260/138• 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-P 85 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 (∼50% s in WP-P 138 , instead of ∼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 videofoam 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. • C et 260/138• C, respectivement), les autres conditions opératoires étant inchangées. Par application de différentes techniques de caractérisa-tion, nous avons montré que les protéines (WP-P 85 et WP-P 138 ) qui ont subi des traitements hydrothermiques à température d'air modérée et sévère, respectivement, se comportent différemment des protéines (WP-L) contenues dans les solutions avant séchage. Comme attendu, la poudre contenant les protéines WP-P 138 présente des taux d'humidité et de lactose libre plus faibles, un taux de porosité interne plus important, et une épaisseur de paroi plus faible. L'étude spectrofluorimétrique des protéines, contenues dans des dispersions dans l'eau distillée des poudres issues des deux conditions de séchage, indique que pour les protéines WP-P 138 , et contrairement aux protéines WP-L et WP-P 85 , la longueur d'onde maximum d'émission de fluorescence du tryptophane présente un déplacement vers le rouge, ainsi que l'apparition de nouveaux composés qui fluorescent avec une longueur d'onde maximum d'émission à 420 nm. D'autre part, nous avons observé une plus forte proportion d'agrégats covalents (11 % pour WP-P 138 au lieu de 5 % pour WP-P 85 ), ainsi qu'...

Enhancement of protein structure-forming properties in liquid foams by spray drying

“…Spray drying of a whey product (pH 6.7) prepared by ultrafiltration of skimmed milk (Ingredia-Arras, France) was performed in a pilot-scale dryer (Niro Minor pilot, GEA, Niro Atomiser, Bochum, Germany), with an atomiser rotary disc type, and feeding in drying air in a co-current configuration, as described previously [3,34]. In the present study, we report results obtained by spray drying at four air inlet temperatures (170, 217, 247 and 260…”

“…In the literature [21], the particle shrinkage effect under spray drying of a whey protein concentrate containing 30% dry matter was assumed to be accompanied by a 15% decrease in particle average size. Considering that the shrinkage of a liquid droplet under evaporation increases with decreasing dry matter content (Pierre Schuck, personal communication), we supposed that for whey protein samples containing 22% dry matter content, initial d p values are 20% higher than average diameter values evaluated from corresponding powders [3,34] .…”

“…The different powders were characterised through their particle median diameter (d 50 ) and density (ρ p ) values, as described in a previous paper [34]. The volume particle size repartition was determined by using light-scattering equipment (Malvern Mastersizer -MS 1000 -Malvern Instruments, Orsay, France).…”

“…Some authors have also considered the effects of heat-treatments applied before dryer feeding on protein aggregation or denaturation [29,38]. Most of the studies relating spray-drying parameters to quality of powders focused on characteristics such as density, average particle diameter, flowability or surface composition, but a few studies were performed on protein structural changes during their resident conditions (hydro-thermal pathway) inside the spray-dryer [1,3,34].…”

“…The predicted air and product temperature and water content will be compared with measured values, using recently published results [34] obtained from drying experiments performed at 170/85…”