Jean Crouzet

Identification of the aroma components of acerola (Malphigia glabra L.) : Free and bound flavour compounds

Abstract Free and glycosidically-bound flavour compounds of acerola fruit were isolated and identified by GC and GC–MS analysis. Among the 46 compounds identified in the volatile fraction, the alcohols (3-methyl-but-3-en-1-ol, 3-methyl-butan-1-ol and 2-methyl-butan-1-ol) were predominant. Two other classes, aromatic compounds and esters, can participate in the fruity and fresh aroma of acerola. Among the 42 aglycones identified for the first time in this fruit, aliphatic alcohols and norisoprenoids were the main components. The latter were present in free form and only in traces. The hydrolysis of these aglycones could increase the fruity aroma of acerola. Four glucosides and one rutinoside were charaterized by GC–EIMS of their TFA derivatives.

6-O-α-L-arabinopyranosyl-β-D-glucopyranosides as aroma precursors from passion fruit

Abstract The 6-O-α- l - Arabinopyranosyl -β- d - glucopyranosides of linalool, benzyl alcohol and 3-methyl-but-2-en-1-ol were isolated from passion fruit ( Passiflora edulis ) by adsorption chromatography on XAD-2 resin, then further extracted on the same resin after partial enzymic hydrolysis and semi-preparative chromatography on RP-18 phase by HPLC. Their structures were identified by 1 H NMR spectroscopy and mass spectral analysis and by methylation analysis of the carbohydrate moieties.

Enzymatic hydrolysis of edible Passiflora fruit glycosides

The combined action of Hemicellulase REG 2 and sweet almond glucosidase containing β-d-glucopyranosidase, α-l-rhamnopyranosidase, α-l-arabinopyranosidase and α-l-arabinfuranosidase activities allowed release of most of the volatile compounds bound as aglycones in edible Passiflora fruits. Great variability between the four species studied, P. edulis, P. edulis f falvicarpa, P. ligularis, P. molissima, was noticed. 2,5-Dimethyl-4-hydroxy-3-(2H) furanone (furaneol) was identified for the first time in bound form in purple and yellow passion fruit. Only geraniol was identified as the aglycone in P. molissima. and no terpenol is present in the hydrolysate obtained from P. ligularis. Several terpene diols: 2,6-dimethyl-1,8-octanediol, (E)- and (Z)-2,6-dimethylocta-2,7-diene-1,6-diol, 2,6-dimethylocta-3,7-dien-2,6-diol and 2,6-dimethylocta-1,7-dien-3,6-diol have been identified in both purple and yellow passion fruit and small amounts of (Z)-2,6-dimethylocta-2,7-diene-1,6-diol are present in P. molissima. α-Ionol derivatives oxygenated in position 3 seem to be characteristic of purple passion fruit whereas β-ionol compounds oxygenated in position 3 are the major norisoprenoids identified as the aglycone in yellow passion fruit. The bound norisoprenoid content of P. ligularis and P. molissima is low. Important concentrations of bound aromatic alcohols are found in purple and yellow passion fruit whereas phenolics can be considered as characteristic of purple varieties. ©

Eggplant polyphenol oxidase: Purification, characterisation and properties

Abstract The isolation and purification of polyphenol oxidase from purple eggplant ( Solanum melongena L.) is described. A 15-fold purified preparation has been obtained with 15% yield by a procedure involving (NH 4 ) 2 SO 4 precipitation, DEAE cellulose chromatography and Sephadex G 100 gel filtration. The enzyme has an optimum pH of 6·4 and a molecular weight of 79 000 ± 5000. Inhibition studies with sodium diethyl dithiocarbamate and potassium cyanide and dialysis against the latter show that the enzyme requires copper. Eggplant polyphenol oxidase exhibits only a catecholase activity and presents a great affinity for catechol and caffeic acid. This latter compound is no doubt its natural substrate. These results show that conversely to tomato, where a polyphenol oxidase activity was tightly bound to the peroxidase, in the case of eggplant there is a true polyphenol oxidase enzyme.

Tomato volatile components: Effect of processing

Abstract The effect of processing on the volatile components present in tomato products has been studied by combined gas chromatography-mass spectrometry. The conditions involved in the preparation of canned juice do not seriously affect the heavy components, while the most volatile (hexanal, hexenal, hexenols) decrease or disappear. After a prolonged treatment (of tomato paste) these components also disappear and heat-induced products are found (aromatic compounds and furan byproducts). Three compounds (furfural, linalyl acetate and 6 -methyl- 5 -hepten- 2 -one) are more important. Some of the volatile compounds of the fresh fruit are present, along with heat-induced products, in water condensed from the evaporator. These results are confirmed by the study of the compounds isolated from fresh juice heated at 100°C in a closed system. The increase of trans-2 -hexenal and decrease of trans-2 -hexen- 1 -ol are discussed on the basis of possible pathways by which these products are formed in tomato.

Free and bound flavour components of Amazonian fruits : 3-glycosidically bound components of cupuacu

Abstract The total quantity (11.7 mg/kg of pulp) of aglycones released by enzymatic hydrolysis of the glycosidic extract indicates a significant aroma potential for cupuacu. Among the 47 aglycones identified, 24 are not present in the free volatile fraction, among them, 4-methylguaiacol, 4-propylguaiacol, 2,6-dimethyl-octa-1,7-dien-3,6-diol, 2,6-dimethyl-oct-7-en-1,6-diol, homovanillic acid, 2-methyl-but-3-en-1-ol and acetic acid. The quantitatively most important aglycones are 3-methyl-butan-1-ol, 2-phenylethanol, linalol, (Z)-2,6-dimethyl-octa-2,7-dien-1,6-diol, butan-1-ol and hexan-1-ol. The methylated alditol acetates analysis of monosaccharides released by acid hydrolysis of the heterosidic extract, indicates that glucose is involved in glucosidic and glycosidic structures. Moreover, rhamnopyranose and xylopyranose units, bound in the terminal position, suggest the presence of rutinosides and small amounts of primeverosides. Six glucosides, hexyl, benzyl, 2-phenylethyl, (R) and (S)-linalyl and geranyl β- d -glucopyranosides, five rutinosides, benzyl, (R) and (S)-linalyl, α-terpineyl and 2-phenylethyl rutinosides and 3-methyl-but-2-enyl vicianoside were identified by GC–EIMS after TFA derivatization of the crude heterosidic fraction. Moreover, four linalol oxides, octyl, 3-methyl-butyl β- d -glucopyranosides and hexyl, octyl, two linalol oxides and 3-methyl-butyl rutinosides, have been tentatively identified from their TFA mass spectra. Some glucosides are probably substituted by malonyl and unidentified acyl residues.

A cyanogenic glycoside from Passiflora edulis fruits

Cyanogenic β-rutinoside ((R)-mandelonitrile α-L-rhamnopyranosyl-β-d-glucopyranoside) was isolated from fruits of Passiflora edulis. Its structure was elucidated mainly by enzymatic hydrolysis using a specific enzyme, GC-mass spectrometric analysis of trifluoroacetyl derivatives, and NMR spectroscopy.

Partial purification and properties of plantain polyphenol oxidase

Abstract Free and bound polyphenol oxidase activities were identified in plantain; the soluble form increases with the maturity of the fruit. No difference was found between the two fractions during the purification process. An eight-fold partially purified preparation was obtained after gel filtration and ion-exchange chromatography. The enzyme has an optimum pH of 6.5. The apparent molecular weights, 30 000 ± 5000 and 70 000 ± 500, estimated by gel filtration are indicative of the presence of multiple forms. The thermal inactivation pattern agrees with the presence of two isoenzymes with different thermal stabilities, the values obtained for E A being 18 kJ/mol for the heat-resistant form. The greatest activity was found when 4-methyl catechol, catechol, pyrogallol, dopamine and L -dopa were used as substrates. The presence of trace quantities of dopamine in plantain pulp (2 μg/g of fresh matter) was established by high-performance liquid chromatography (HPLC). The plantain-polyphenol oxidase is inhibited by copper complexing agents and by reducing agents. One-hundred per cent inhibition was noted in the presence of sodium diethyl dithiocarbamate, L -cysteine, sodium metabisulphite and ascorbic acid (10 −3 M). At this concentration only 40% of inhibition was obtained with potassium cyanide. Determination of browning during flour preparation shows that the enzyme may be efficiently inactivated using sodium metabisulphite. This compound also prevents non-enzymatic browning during the slicing and drying steps of preparation of plantain flour.

Free and bound flavour components of Amazonian fruits: 2. Cupuaçu volatile compounds.

Forty-five volatile compounds were identified and 14 tentatively identified in cupuacu (Theobroma grandiflorum) pulp using solid phase extraction on XAD-2 and simultaneous distillation extraction. Among them, 35 compounds were reported for the first time in this fruit. The olfactive characteristics of several compounds, separated after solid phase extraction, and their odour activity values showed that linalol, α-terpineol, 2-phenylethanol, myrcene, and limonene were contributors of the cupuacu pleasant, floral flavour. Ethyl 2-methylbutanoate, ethyl hexanoate and butyl butanoate were involved in the typical fruity characteristics of cupuacu. Diols (2,6-dimethyl-oct-7-en-2,6-diol. (E)-2,6-dimethyl-octa-2,7-dien-1,6-diol, and its (Z) isomer) and methoxy-2,5-dimethyl-3(2H)-furanone were possible contributors of the typical exotic odour. Moreover, hexadecanoic acid can be considered as a contributor of the grassy, heavy odour of cupuacu. Copyright

Free and bound flavour components of amazonian fruits. 1: Bacuri

The free and bound flavour components of bacuri fruits were analysed by capillary GC and GC–MS following XAD-2 separation. Seventy-five components were identified in the free volatile fraction; the most abundant were terpene alcohols, among them, linalol and related compounds, linalol furanoxides and pyranoxides, hotrienol and several dimethyl-octadiendiols. Abundant amounts of 4-methoxy-2,5-dimethyl-3(2H)-furanone were also found. Seven glucosides and three rutinosides were identified by GC–MS of their TFA derivatives for EI–MS and NCI–MS, in agreement with quantitative data obtained for enzymatically released aglycones and saccharidic moieties structure; the most important glycosides were benzyl, 2-phenylethyl, (E)-linalol furanoxide and (S)-linalol glucosides and benzyl, 2-phenylethyl, and (S)-linalol rutinosides. Glycosides possessing ‘unusual’ saccharidic moieties remained unidentified. Copyright