Sour-sweet reaction

Doctor Test A method which can be used to determine the sweet or sour nature of gasoline by treating gasoline with a solution of lead plumbite and sulfur. As an example, the reaction which occurs with methylmercaptan is as follows ... 

Cocaine and other local anesthetics abolish not only the sensation of pain, but other special sensations, if they are suitably applied. Here also there is some selection. In the skin, they paralyze first the vasoconstrictor reaction, then progressively the sensations of cold, warmth, touch, tickling, pressure, pain, and joint sense. In the nose, they abolish the olfactory sense. On the tongue, they destroy the taste for bitter substances but have less effect on sweet and sour taste and none on salty taste. When cocaine is applied to the appropriate nerves, it is found that the centrifugal vagus fibers are paralyzed before the centripetal, vasoconstrictor fibers before vasodilator, bronchial constrictors before the dilators, etc. (Sollmann, 1944). 

Proteases degrade the proteins to free amino acids and oligopeptides, thus imparting sweet, sour and mainly a bitter taste to the product. Further reactions lead to the corresponding Strecker aldehydes 2-methylbutanal and 3-methylbutanal with a pungent, malty, cocoa note. 

The sense of taste, also known as gustation, consists of taste receptors on the tongue, which then translate chemical reactions into electrical impulses that are transmitted by a series of nerves to the brain stem. The brain stem is located in the rear of the brain, and connects the brain to the spinal cord. The brain stem also regulates the central nervous system. The main taste sensations are sweet, sour, salty, and bitter, along with a newer sensation described as umami (Japanese for savory). These taste sensations, combined with olfactory input and touch sensations in our mouth, give us the sensory input that we describe as flavor [18]. 

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