Effect of the formulation on the continuous manufacturing of foamed products
Special Symposium - Innovations in Food Technology (LMC Congress)
Flexible Production, PAT & Modelling (Food-3a)
Keywords: food foam, foaming process, foam formulation, polysaccharides, proteins
Foaming is a unit operation that consists in dispersing and stabilizing a gas phase in the form of bubbles into a continuous solid or semi-solid matrix, in order to confer a porous structure. It is frequently used in the food industry. Most common examples of foamed food are “sweet foams” (dairy desserts…), “acid foams” (textured cheese, fruit fools…) and “salted foams” (fish foams, pâtés...).
The aim of this work is to study the effect of formulation on the properties of the continuous phase and of the gas/liquid interfaces, while a continuous foaming process in laminar flow conditions. The continuous phase was a Newtonian glucose syrup (1 Pa.s) in which additives were varied to optimise rheological and interfacial properties. Thus, three polysaccharides were studied at 0.1% in all formulations: xanthan, LM pectin and guar. The effect on gas/liquid interfaces was investigated by adding 2% of two kinds of proteins: sodium caseinate and whey proteins. The combined effect of polysaccharide and proteins was studied by using formulations containing a mixture of both components. Rheological and interfacial properties of the continuous phase were measured using a stress-controlled rheometer and a static tensiometer. Foaming was studied by varying gas to liquid flow ratio at constant liquid flow rate (30 mL/min) and rotation speed between 400 and 1600 rpm. At the exit of the column, foams were characterized by their overrun and their bubble size distribution using image analysis. The average size was defined using Sauter mean diameter (d32).
Results showed that the formulations containing 0.1% xanthan or guar without proteins, did not allow the gas incorporation because of the blow-by phenomenon. On the other hand, the formulation containing 0.1% of pectin allowed the incorporation up to 100% of the gas phase with a gas flow rate of 10 mL/min for all rotation speeds. However, the bubble diameter in these foams was about 50µm ± 10. In regard to the results on proteins, the formulation containing 2% Na-caseinate without polysaccharides allowed the incorporation of only 72% of the gas phase with a gas flow rate of 10 mL/min and 400 rpm. This value decreased to 60% when the rotation speed increased and at 1600 rpm, blow-by appeared. Conversely, experiments on the formulation containing 2% of whey proteins showed their positive role on foaming. For all process conditions, abundant foam with an interesting stability in time was obtained. The average bubble diameter was about 20 µm ± 2 with a homogeneous size distribution. About formulations containing 2% whey proteins with one of the three polysaccharides (0.1%), the formulation containing pectin gave abundant and very stable foam. The mixture of whey proteins and xanthan allowed the incorporation up to 100 % gas with a gas flow rate of 10 mL/min and for all rotation speeds. Bubbles were very small, about 13 µm ± 1. The formulation with 0.1% guar exhibited also a total incorporation of the gas phase, but with a slightly wider bubble size distribution and d32 about 17 µm ± 3.
These results can be analysed as follows: guar addition changes only slightly the rheological properties of the continuous phase, while pectin addition doubles the viscosity. Both maintain a Newtonian behaviour. Conversely, xanthan provides a highly shear-thinning behaviour and measurable first normal-stress difference. Without proteins, all formulations present interfacial properties close to those of water. Additionally, gas dispersion experiments with a 2 Pa.s glucose syrup solution without pectin exhibited only blow-by. This demonstrates that pectin presents specific interactions with the glucose syrup that favour gas dispersion and stabilisation. In the presence of proteins, their interfacial properties stabilize gas/liquid interfaces. Stabilisation is also enhanced by proteins exhibiting high interfacial elasticity, such as whey proteins. As surface tension is not affected by polysaccharides, the non-Newtonian viscoelastic behaviour of the xanthan/whey proteins mixture seems responsible for the more homogeneous bubble size distributions in comparison to guar/whey protein mixtures. However, only the specific interactions described above between pectin and glucose syrup, but also the known interactions between pectin and whey proteins, can explain the remarkable foamability and stabilisation ability of pectin/whey proteins mixtures. As a conclusion, LM pectin seems an interesting additive for food processors involved in food foam manufacturing.
See the full pdf manuscript of the abstract.
Presented Wednesday 19, 15:35 to 15:50, in session Flexible Production, PAT & Modelling (Food-3a).
