[Thickened infant formula, rheological study of the "in vitro" properties]

Thickened infant formulas, specially formulated to increase the viscosity, are commonly used in the treatment of regurgitation in the non-complicated gastroesophageal reflux.

To analyse viscosity and the rheological behaviour of different thickened standard formulas on the Spanish market compared to a standard formula with or without the addition of 10 g/100mL of gluten-free cereals.

Viscosity of the samples was evaluated in a Bohlim CS-1o controlled-stress rheometer and was performed at basal conditions (25 degrees C, pH 7) and at simulated gastric conditions (37 degrees C, pH 4 and 10 g/100mL of pepsin) at time 0, 30 and after 60 min of incubation. Values were expressed as centipoises (cp) (1 cp=1/100 p).

All formulas show a viscosity increase both in basal conditions and in gastric simulated conditions but the behaviour is very heterogeneous. Formulas containing bean gum (carob seed flour) with 2.9 g/100g and a protein ratio similar to cow's milk (80 casein/20 whey) showed the highest and consistent viscosity (70 cp and 90 cp), with significant differences compared to the standard formula in all the measurements. When this thickener is in formulas with a protein ratio similar to breast milk (40 casein/60 whey) the viscosity was lower and reached 50 cp only with the thickener at a concentration of 4.7 gr/100g, achieving significant differences versus standard formula. The formulas with starch thickeners (rice, potatoes and corn) achieved a lower and less consistent viscosity, with no significant difference. The viscosity reached after the addition of cereals both in basal conditions and in gastric simulated conditions was similar to that achieved with more effective thickeners. Lipid concentration is not involved in viscosity and rheological behaviour.

The viscosity of the thickened infant formula depends on the agent used, concentration and protein ratio. Not all reach a viscosity of 50 cp, hypothetical value to reach, since it doubles the viscosity of a standard formula. The ideal viscosity to be reached and the role of other components of the formula in the viscosity and rheological behaviour is still unclear.