Its aromatic qualities depend on its texture.
THE FOOD INDUSTRY IS FOREVER LOOKING for ways to make its products lighter by reducing lipid content and increasing water or air content, without the taste suffering as a result. Even liver mousse, renowned for its sturdy lipidic constitution, has not been spared. Michel Laroche and his colleagues in the Laboratoire d’Étude des Interactions des Molécules Alimentaires at the Institut National de la Recherche Agronomique (INRA) station in Nantes studied liver mousses to which a large amount of starch had been added, in order to determine by how much the fat content of such products can be reduced without affecting flavor. Physicochemical measurements and sensory analyses showed that the attractiveness of lighter versions depends principally on their meltability, that the sensation of fattiness does not depend on the quantity of lipids substituted for by starch, and that the perception of flavor depends on their consistency.
Making a low-fat liver mousse is particularly tricky because one wants it to be easily spread on toast, a property that in classic mousses seems to result from their high lipidic concentration (as much as 50%). Earlier, in 1985, two other researchers from the Nantes station, René Goutefongea and Jean-Paul Semur, showed that this property could be preserved by adding hydrocolloids, which is to say dispersions of long molecules in water. The recent experiments tested the partial or complete substitution of lipids by starch paste obtained from fava beans, the seeds of a leguminous plant (Vicia faba) cultivated in France, which preliminary studies suggested might be a suitable candidate.
In a liver mousse prepared in the classic fashion, by grinding up pork livers with egg whites, lactoserum, gelatin, sodium nitrite, salt, pepper, onions, shallots, and cognac, the Nantes researchers replaced the various quantities of lipids with fava bean starch paste (15% starch in water) for a first batch of samples and with a fixed quantity of paste having variable concentrations of starch for a second batch (so that the result would be 50% lighter but with different starch concentrations). These preparations were compared with liver mousse prepared by traditional methods that was purchased at a local grocery store.
Various mechanical measurements were made to characterize these different mousses, which were then tasted by ten trained judges. In a room dimly illuminated by red light, the tasters were instructed to evaluate four sensory elements: meltability (defined as the ease with which a sample melts between the tongue and palate), fattiness, granular texture (defined as the perception of particulate matter), and intensity of flavor. Finally, they gave an ordered ranking of these elements with respect to their relative contribution to the overall perception of quality.
First, meltability was found to increase with the quantity of starch in the first batch of substituted products but to diminish in the second. The perception of granular texture was not changed by the amount of starch unless it was very large. And the sensation of fattiness, which was independent of the actual quantity of fat for the batch with variable lipid content, diminished by contrast when the starch content was increased in the second batch. An analogous variation was observed for the perception of flavor, which increased for the first batch but diminished with the quantity of starch in the second batch.
The four sensory indices turned out to be strongly correlated, but the relationship between meltability and the perception of flavor is the most interesting: The increase in the quantity of starch in the second batch was associated with diminished meltability and a diminished perception of flavor. Should it be concluded, then, that the aromatic compounds were adsorbed by the starch? Or that they were adsorbed by the water? No; both of these conclusions are invalidated by the results obtained for the first batch, where an increase in the quantity of starch went hand in hand with an increase in the water content of the mousse and a notable increase in meltability.
Because the composition of the samples does not explain the relationship between meltability and aromatic quality, it seems either that the increase in meltability, which is associated with a more even distribution of the mousse in the mouth, improved the perception of flavor, or that the less smooth the texture, the more trouble the tasters had perceiving the other elements.
Meltability was well correlated with high marks for the other sensory indices, in order of importance for the overall impression of quality: meltability, fattiness, flavor, and granular texture. These four parameters were in turn strongly correlated with the measurements of hydration and mechanical resistance. What is the optimal proportion of starch? Using a 15% starch solution, one can replace two-thirds of the lipids without diminishing the overall quality of the mousse; at higher concentrations, however, the mousse becomes too soft.
These studies lead us to conclude three things. First, meltability is the chief factor in determining the overall quality of a liver mousse. Second, the sensation of fattiness is independent of the quantity of lipids that are replaced. Third, the perception of flavor depends on texture. This final result calls to mind the finding of Patrick Étiévant and his colleagues at the INRA station in Dijon, in 1990, that the addition of pectins to strawberry jam firmed up the texture while also reducing its aromatic qualities.