N. Schamp

Production of flavours by microorganisms

Abstract Flavours and fragrances are extremely important for the food, feed, cosmetic, chemical and pharmaceutical industries. Most available flavour compounds are now produced via chemical synthesis or extraction. Drawbacks of such chemical processes are the formation of undesirable racemic mixtures and the growing aversion of the consumer towards chemicals added to his food, cosmetics and other household products. This has caused flavour companies to direct their attention towards flavour compounds of biological origin, so called natural- or bio-flavours. Up to now, plants were also an important source of essential oils and flavours: however, active components are often present in minor quantities or in bound form or are only found in exotic plants, making isolation difficult and the flavour products expensive. Apart from plant cell and tissue culture techniques (which still need further development) a directly viable alternative route for flavour synthesis is based on microbial processes, i.e. fermentation (=de novo) and bioconversion of appropriate precursor-compounds. This review presents the current state of the art of bioflavour-synthesis, based on microorganisms (bacteria, fungi, yeasts) and their enzymes, with emphasis on currently commercialised processes. It also comments on regulatory aspects of biotechnological production of aroma-compounds. A comprehensive referenced literature survey of de novo fermentation and of bioconversion processes for flavour-compound synthesis concludes this review.

Elimination of hydrogen sulphide from odorous air by a wood bark biofilter

Abstract Wood bark, used as biofilter material, gives less back pressure than fibre peat or household compost and is therefore cheaper in variable costs than the other materials. With a filter bed height of 0.9 m and with a surface load of 65 m 3 m −2 h −1 , 10 ppm hydrogen sulphide is efficiently eliminated from odorous air by a wood bark biofilter. The most important parameter for a good functioning of the filter is the water content of the filter material. The optimum for wood bark is about 65%. Unnecessarily high back pressures are recorded during sprinkling water on top of the filter. Therefore, it seems preferable to condition the relative humidity of air entering the filter. If absorption and adsorption were the only factors in the biofilter mechanism, hydrogen sulphide would, in the given circumstances, break through after about 7 h. It is shown that hydrogen sulphide is oxidized to sulphate. According to literature data, chemical oxidation is too slow and therefore hydrogen sulphide oxidation in the biofilter is attributed to microbiological action.

The essential oil of greater galanga (Alpinia galanga) from Malaysia

Abstract The essential oil of A. galanga, a common spice in Malaysia, was prepared from fresh and dried rhizomes and analysed by means of capillary GC and GC/MS. Forty components were identified (only three of which were previously reported), accounting for 83–93% of the oil, depending on its method of preparation. Apart from monoterpenes, monoterpene alcohols and esters, and sesquiterpenes, also methyleugenol, eugenol acetate, chavicol (4-allylphenol) and chavicol acetate were present. This is the first time the latter substance has been reported in nature. Standardization of GC is proposed and tentatively applied towards a more systematic use of the Kovats indices as an aid in the identification of the constituents of essential oils.

The essential oil of Nepeta nuda. Identification of a new nepetalactone diastereoisomer

Abstract The essential oils of nine specimens of N. nuda were prepared by steam distillation, and analysed by GC and GC/MS. Thirty-seven substances were identified, accounting for 91.6–99% of the oils. They all contained varying amounts of 1,8-cineole, a mixture of nepetalactones and germacrene-D as chief components. In seven samples the new 4aβ,7α,7aα-nepetalactone was found. It was isolated, and identified by 1 H and 13 C NMR.

The volatiles of Calamintha nepeta subsp. Glandulosa

Abstract The volatiles of C. nepeta subsp. glandulosa were studied by analysis of the essential oil and of the headspace (after concentration on Tenax GC). Amongst the 27 compounds identified in the essential oil, up to 92 % consisted of piperitone oxide and piperitenone oxide, the relative concentrations of which depended on the maturity of the plants. The weak fragrance of the intact plant originated mainly from limonene and piperitone oxide. During the preparation of the essential oil, trans -sabinene hydrate and piperitone oxide isomerized in part into terpinen-4-ol and 4-hydroxypiperitone, respectively.

Composition and variability of the branched-chain fatty acid fraction in the milk of goats and cows

Branched-chain fatty acids of the milk fat of goats were analyzed by high resolution gas chromatography-mass spectrometry. Iso- and anteiso-acids predominated, but a range of other monomethyl-branched components, mostly with methyl-substitution on carbons 4 and 6, was present. Analysis of the milk fat of cows revealed the presence of iso- and anteiso-fatty acid; other mono-methyl-substituted fatty acids, as found in the milk fat of the goat, were virtually absent. Only a trace amount of 6-methylhexadecanoate was detected. The difference between goats and cows in the effectiveness with which these animals metabolize propionyl-CoA and methylmalonyl-CoA is discussed.

Reactivity of α-chloro-aldimines☆

Abstract A series of secondary N-1-(2-chloroalkylidene)amines has been prepared by condensation of disubstituted acetaldehydes with primary amines followed by chlorination with N-chlorosuccinimide in carbontetrachloride. A study of the reactivity of these N-homologues of α-chloroaldehydes is described. Treatment of the title compounds with sodium methoxide in methanol gave high yields of α,β-unsaturated aldimines. However, N-1-(2-chloro-2-methylpropylidene)amines afforded a mixture of elimination and rearrangement products, which proceeded via an aziridine intermediate. On the other hand, α-phenyl-substituted α-chloro aldimines on treatment with methoxide in methanol underwent α-substitution, consistent with an S N 1 mechanism. Powerful nucleophiles such as sodium thiophenolate in methanol and sodium azide in acetone caused α-substitution. Reaction of α-chloro aldimines with Grignard reagents produced coupling of two aldimine units or α-alkylation. Finally the reactivity of α-chloro aldimines was compared with the reactivity of the corresponding oxygen-analogues, i.e. α-chloro aldehydes.

A Facile Synthesis of 1,2-Disubstituted Aziridines

Abstract In spite of the fact that a number of methods are available for the preparation of aziridines, general synthetic routes leading to 1,2-disubstituted aziridines remained laborious in most cases(2-6). A convenient and versatile synthesis is desirable in order to permit studies of this important biologically active heterocyclic system.

Aldehyde metabolism and the aroma quality of stored golden delicious apples

Abstract Aldehyde production by intact apples was monitored by reversed phase HPLC of headspace concentrates, after reaction with 2,4-dinitrophenylhydrazine. Depending on the degree of maturity and their storage history, Golden Delicious apples showed a variable headspace composition, differences being mostly of a quantitative nature. Whereas the headspace of pre-climacteric fruits was particularly rich in C 1 C 6 aldehydes, that of climacteric, ripening apples was greatly reduced, and some aldehydes were only present in trace amounts. Treatment of pre-climacteric or cold stored fruits with carboxylic acid vapours had a negligible effect on the aldehyde composition. Controlled atmospheric storage, however, led to a notable increase in the aldehydes derived from the added carboxylic acids or from those shortened by β-oxidation. This confirms the presence of a reductive path of carboxylic acids into aldehydes. Further results suggest that high carbon dioxide (CA-storage) interferes with carboxylic acid metabolism and alcohol dehydrogenase activity, leading to a deterioration of the aroma quality.

Synthesis of azetidines from β-chloro imines

Abstract The reaction of β-chloro imines 4 with potassium cyanide in methanol or with lithium aluminium hydride in dry ether gave rise to 2-cyanoazetidines 5 and azetidines 21 . The reaction proceeded by nucleophilic addition of cyanide or hydride across the carbon-nitrogen double bond, followed by ringclosure. The corresponding β-chloro tosylhydrazones, which could either give rise to a four- or five-membered heterocycle on treatment with potassium cyanide in methanol, were shown to afford N-tosylamino 2-cyanoazetidines, exclusively.