Lactic acid and mineral salts give goat cheese its distinctive taste.
AROMAS ARE THE STARS OF THE FOOD INDUSTRY: Many firms produce and sell them to the large food processing conglomerates that make yogurts, soups, sauces, and so on. Nonetheless, foods that are aromatic and little else please only the nose, for they are lacking in taste—hence the interest in taste molecules, still poorly understood. Do these molecules exert the same effect in foods as in water solution, where their properties have long been studied? At the Institut National de la Recherche Agronomique Laboratoire de Recherches sur les Arômes, in Dijon, Christian Salles, Erwan Engel, and Sophie Nicklaus studied this question in connection with goat cheese.
As food is chewed, saliva conveys taste molecules to receptors in the papillae. The Dijon physical chemists sought to analyze the behavior of these molecules in water-soluble compounds, which is to say in the aqueous part of foods. In the case of cheese this phase consists chiefly of lactose (a sugar), lactic acid (formed from lactose by microorganisms in the course of fabrication), mineral salts, amino acids, and peptides (short chains of amino acids). Although the taste of most of these compounds is known, their effects in combination are not. Some of the compounds in the aqueous part of the milk used to make cheese mask the effect of other sapid molecules; others (known as enhancers) augment their effect.
Salles and his colleagues first tested solutions containing only compounds whose presence had been detected in the aqueous phase of goat cheese. Because peptides cannot easily be identified, the chemists isolated them from the hydrosoluble part yielded by 20 kilograms (44 pounds) of cheese. After centrifugation they separated out the juice by a series of ultrafiltrations using membranes permeable by molecules of a mass lower than 10,000, then lower than 1,000, and finally lower than 400. The unfiltered residue was peptides.
All Except One
To evaluate the effect of the various compounds on each of the five basic tastes, a jury of sixteen judges compared the reconstituted aqueous part to a solution with the same components except for one or more compounds that were deliberately omitted. These omission tests were performed under rigorous conditions, with anonymous products, individual booths, red light to prevent bias due to color, and so on. Each taster was equipped with a nose clip in order to eliminate the perception of odors. After training the tasters were instructed to rank each of the five tastes by comparison with a specific reference solution for each sample presented.
Salts, Not Peptides
The first sensory evaluations came as a surprise. Although many studies had offered glimpses of the sapid properties of peptides, suggesting that they have a bitter taste, the peptides in goat cheeses turned out to have no discernible effect on taste, direct or indirect, regardless of their molecular mass. Though not excluding the possibility that these compounds might one day be shown to have a sapid effect in the case of other cheeses, the Dijon team discounted an effect by peptides on the taste of goat cheese.
Comparing solutions containing lactose with ones from which it had been removed, the researchers found that this compound had no effect on the sapidity of the model solutions either. The amino acids likewise turned out to be tasteless. However, lactic acid and mineral salts were found to powerfully contribute to taste. The acidity of the cheese resulted principally from hydrogen ions released by the phosphorus and lactic acids, an effect enhanced by sodium chloride. In the presence of salt, then, the sour note is pronounced. Why? The question has yet to be answered.
The salt taste resulted from the effect of sodium, potassium, calcium, and magnesium chlorides as well as of sodium phosphate. A part of the bitter taste came from calcium and magnesium chlorides, although it was partially masked by sodium chloride mixtures and by phosphates. As for the sweet and umami tastes (the latter caused by monosodium glutamate, widely used in commercial soups and sauces), they were so weak that the researchers were unable to associate them with any of the hydrosoluble compounds tested.
An Overall Taste
The main conclusion to be drawn from these studies, apart from the detailed information they yield regarding the various compounds contained in the hydrosoluble part of the cheeses, is that no taste can be attributed to the action of a single compound. Further complicating matters is the fact that the different sapid compounds have both inhibiting and enhancing effects on one another. On the other hand, we now know which compounds must be added to cheeses in order to reinforce certain tastes or to mask others. Producers may find it difficult to incorporate such compounds, however, not only for legal reasons but also because a large proportion of the molecules dissolved in the milk would be lost during drainage. Nonetheless, gourmets may now amuse themselves by sprinkling their cheeses with various salts and raising toasts. To your chlorides! To your phosphates! To your tartaric acid!