Effect of the formulation on the continuous manufacturing of foamed products

The aim of this work is to understand the effects of the rheological and interfacial properties of a model food on continuous foaming operation in laminar flow conditions. The rheological properties of food model (glucose syrup) were adjusted using three polysaccharides: xanthan, LM pectin and guar. Interfacial properties were varied using two kinds of proteins: Na-caseinates and whey proteins (WPI). Foaming was studied in a narrow annular gap column at constant gas-to-liquid flow rate ratio as a function of rotation speed N. Overrun, bubble size distribution, average bubble diameter d32 and stability over time were used to characterize foams. Results showed that blow-by occurred during the foaming of formulations including either 0.1% xanthan or guar without proteins, while 0.1% pectin allowed the total incorporation of the gas phase for all N values with d32 about 50μm. This was related to the tendency of this formulation to solidify under shear flow. In the absence of polysaccharides, only syrups containing WPI were able to form foams with the desired overrun with d32 around 20μm. Indeed, blow-by was favoured for high N values with Nacaseinates. This confirmed the key role of interfacial elasticity and viscosity on the continuous foaming operation. For protein-polysaccharide mixtures, guar did not interact with proteins. As a result, the WPI-guar formulation exhibited nearly the same rheological properties and foaming ability as glucose syrup with WPI. Conversely, overrun was reduced in WPI-xanthan mixtures and high N values favoured blow-by, although d32 decreased to 15μm due to the higher viscosity of these formulations. This confirmed that a matrix exhibiting viscoelastic behaviour under shear flow played a negative role on gas dispersion during foaming. On the contrary, WPI-pectin mixtures provided abundant foams with d32 about 15μm and an improved stability due to the enhanced ability of WPI-pectin mixtures to solidify after foaming. While WPI reinforced the time-dependent behaviour of pectin in glucose syrup, Nacaseinates inhibited this effect and blow-by was reported when pectin and Nacaseinates mixtures were subjected to foaming. This highlighted the strong influence of protein-polysaccharide interactions on overrun. Conversely, bubble diameters in foams were less dependent on polysaccharides and could be adequately described using an approach involving a laminar Weber number based on the apparent viscosity of the foam during foaming.