Aroma extract dilution analysis (AEDA) revealed 13 compounds as important contributors to the aroma of roasted coffee (powder): 2-methyl-3-furanthiol (I), 2-furfurylthiol (II), methional (III), 3-mercapto-3-methylbutylformate (IV), 3-isopropyl-2-methoxypyrazine (V), 2-ethyl-3,5-dimethylpyrazine (VI), 2,3-diethyl-5-methylpyrazine (VII), 3-isobutyl-2-methoxy-pyrazine (VIII), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon, IX), 4-ethylguaiacol (X), 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone (XI), 4-vinylguaiacol (XII), and (E)-β-damascenone (XIII). A comparative AEDA of the coffee powder and brew showed in the brew an increase of III, IX, vanillin and 4-hydroxy-2,5-dimethyl-3(2H)-furanone and a decrease of I, II, IV, V, VII, and VIII.

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Potent odorants of the roasted powder and brew of Arabica coffee

Four samples of neutral fractions of protein hydrolysates were separated by gas chromatography and the individual components were identified from the mass spectra obtained. Some of the identified compounds were not previously reported as volatile components of foodstuffs. Three of these compounds namely 3-chloropropan-1-ol, 2,3-dichloropropan-1-ol, and 1,3-dichloropropan-2-ol, were toxic chlorohydrins. 1,3-Dichloropropan-2-ol was present in samples in concentrations 0.17 to 0.94 mg/kg. To check the possibilities of the formation of these chlorohydrins and to find their precursor, glycerol, and hydrochloric acid mixtures were heated under conditions of producing protein hydrolysates. All three chlorohydrins, formerly found in protein hydrolysates have been identified.

Chlorohydrins in protein hydrolysates.

Recent developments in studies of the maillard reaction

Three closely related 4-hydroxy-3(2H)-furanones have been found in a range of highly cooked foodstuffs where they are important flavour compounds with aroma threshold values as low as 20 micrograms kg-1 water (approximately 0.14 mumol l-1). The compounds are formed mainly as a result of the operation of the Maillard reactions between sugars and amino acids during heating but one compound, 5-(or 2)-ethyl-2-(or 5)-methyl-4-hydroxy-3(2H)-furanone, appears in practice to be produced by yeast, probably from a Maillard intermediate, during the fermentation stages in the production of soy sauce and beer. The compounds are also important in the flavour of strawberry, raspberry, pineapple and tomato but the route of biosynthesis is unknown. Two 3-hydroxy-2(5H)-furanones, emoxyfuranone and sotolon, which are produced spontaneously from amino acids such as threonine and 4-hydroxy-L-leucine are major contributors to meaty and spicy/nutty flavours in foods. The biosynthesis of 5-(1,2-dihydroxyethyl)-3,4-dihydroxy-2(5H)-furanone (ascorbic acid, vitamin C) and 5-hydroxymethyl-3,4-dihydroxy-2(5H)-furanone (erythroascorbic acid) from sugars in plants and yeast, respectively, has been characterized to the enzymic level. After treatment with chlorine, humic waters contain a range of chloro-furanones, some of which, particularly 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), are powerful mutagens. The furanones which occur in foods are also mutagenic to bacteria and cause DNA damage in laboratory tests. However, these compounds are, in practice, very effective anti-carcinogenic agents in the diets of animals which are being treated with known cancer-inducing compounds such as benzo[alpha]pyrene or azoxymethane. Two of the food-derived furanones have antioxidant activity comparable to that of ascorbic acid. A biological function has been discovered for some of the furanones besides vitamin C. 5-Methyl-4-hydroxy-3(2H)-furanone is a male pheromone in the cockroach Eurycolis florionda (Walker) and the 2,5-dimethyl derivative deters fungal growth on strawberries and is an important component of the attractive aroma of the fruit. The red seaweed Delisea pulchra (Greville) Montagne produces a range of brominated furanones which prevent colonisation of the plant by bacteria by interfering with the acylated homoserine lactone (AHL) signalling system used by the bacteria for quorum sensing. In addition, these compounds can deter grazing by marine herbivores. It is proposed here that the evolved biological function of a number of furanones is to act as inter-organism signal molecules in several different systems. This has resulted in two coincidental effects which are important for humans. Firstly, the easily oxidized nature of the furanones in general, which is likely to be an important property in their functioning as signal molecules, results in both mutagenic and anti-carcinogenic activity. The balance of these two effects from compounds in the diet has yet to be fully established. Secondly, and more specifically, the 4-hydroxy-3(2H)-furanones associated with fruit aromas act to attract animals to the fruit, which ensures seed dispersal. In the case of humans, the coincidental synthesis of some of these compounds in foods during preparation results in these foods appearing particularly attractive through the transferred operation of the original signalling mechanisms.

The naturally occurring furanones: formation and function from pheromone to food.

Current information relating to the chemical composition of both natural and simulated meat flavors is presented, with particular reference to beef flavor. The origin of natural meat flavor is described in terms of the nature of the precursors and the formation pathways of volatile components contributing to meat flavor. A table listing the aroma components of natural beef is included and their relative contributions to the overall flavor is considered. The historical development of commercial meat flavorings is traced from the early spice blends and meat extracts to the thermally produced imitation meat flavors (processed meat flavorings) including “reaction products” and flavorings derived from natural meat. Some G.B. and U.S. “reaction products” patents and meat flavor contributing compounds patented since 1960 are summarized in tabular form.

Natural and simulated meat flavors (with particular reference to beef)

SUMMARY— The characteristic seasoning flavor of hydrolyzed vegetable proteins has previously been attributed to α-ketobutyric acid formed from threonine under the conditions of acid-hydrolysis. However, pure α-ketobutyric acid is virtually odorless and tasteless, and it develops the characteristic flavor only upon ageing. The true flavoring principle is probably α-hydroxy-β-methyl-Δ.α,β-γ-hexenolactone, which is formed from the acid by dimerization, lactonization, and decarboxylation. This conversion occurs spontaneously, but is greatly accelerated under acidic conditions.

J. DePIZZOL

Papers

A Probable Flavoring Principle in Vegetable‐Protein Hydrolysates