Characterization of the consistency of gruels consumed by infants in developing countries: assessment of the Bostwick consistometer and comparison with viscosity measurements and sensory perception.

Standardized techniques are still needed to characterize the consistency of gruels for infants in developing countries. The aim of this study was to evaluate the interest of the use of the Bostwick consistometer. Bostwick flow was measured on gruels prepared with different flours, at low or high energy density (i.e. without or with amylase). The range of Bostwick flow, from 0 to 240 mm/30 sec, adequately described a wide range of gruel consistencies from completely liquid to almost solid. However, the temperature of the gruel must be carefully controlled during measurements as Bostwick flow is highly temperature dependent, especially in the case of gruels with high energy density. The relationship between Bostwick flow and apparent viscosity proved to depend on the type of gruel: at an apparent viscosity of 1 Pa.sec, gruels prepared from maize, rice, millet or multicomponent flours had different Bostwick flow values of, respectively, 20, 35, 75 and 55 mm/30 sec. Sensory analysis was then performed with a panel of mothers of infants and young children in Ouagadougou (Burkina Faso). Gruels of similar apparent viscosity and different Bostwick flow distances or of inversely similar Bostwick flow distances and different apparent viscosities were prepared by adding carob seed flour, and differentiation and ranking tests were then carried out. Both types of test revealed that mothers differentiated similar gruels having different Bostwick flow distances more easily than gruels having different apparent viscosities. It can thus be concluded that Bostwick flow, which is an empirical multi-criteria parameter, conveys the sensory perception of gruel consistency better than apparent viscosity.