Effect of protein–polysaccharide mixtures on the continuous manufacturing of foamed food products

The aim of this work is to understand the effects of protein and polysaccharide interactions on the physicochemical properties of highly viscous Newtonian model foods and their impact on continuous foaming operation in laminar flow conditions. Model foods consisted of modified glucose syrups. Foaming was carried out at constant gas-to-liquid flow rate ratio as a function of rotation speed. Overrun, mean bubble diameter d32 and stability over time were used to characterize foams. Results showed that blow-by occurred during foaming of models including either 0.1% guar or xanthan without proteins, while 0.1% pectin allowed a total incorporation of the gas phase with large bubbles. For proteins, models with 2% whey protein isolate (WPI) were able to form foams with the desired overrun and small bubbles, while foaming was less effective with 2% Na-caseinates. With WPI, guar addition did not improve significantly foam properties. Overrun was reduced in WPI–xanthan mixtures, probably because the matrix exhibited viscoelastic trends even though xanthan decreased d32. WPI–pectin mixtures provided abundant and stable foams with the smallest d32 and the best stability because WPI reinforced the time-dependent behaviour of pectin recipes. However, blow-by was observed with 0.1% pectin when WPI was replaced by Na-caseinates, which demonstrates the key role of specific protein–polysaccharide interactions on overrun. Conversely, bubble diameters in foams were governed by process parameters and could be adequately described using a laminar Weber number based on foam viscosity measured during foaming for all model foods that provided stable foams.