Reaction F Aldol Condensation

Aldehydes can arise by Reactions C, D, and E, and they can then react with each other by the aldol condensation. Amines (and particularly their salts), including peptones and egg albumin, are effective catalysts. Additional carbonyl compounds which can participate in the condensation may be derived by the oxidation of lipids. 

Browning has been demonstrated for 2-oxopropanal alone, furfurals, and 2-oxo-propanoate plus furfural. Less browning occurs with sugars or with aldol itself. 

Benzoquinones can act as dicarbonyl components of the Strecker reaction, readily form imines in the cold, and can be involved in the production of melanoidins. Benzoquinones in plant systems are usually derived from polyphenols and constitute well known intermediates in enzymic browning. They are also involved in the formation of melanin in animals, including humans. 

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