IONIZATION BEHAVIOUR OF HOP COMPOUNDS AND HOP-DERIVED COMPOUNDS

The ionization behaviour of colupulone, (?)-humulone, trans-isohumulone and trans-humulinic acid was investigated using a number of techniques. When a potentiometric technique was employed, precise estimates of pKa could not be obtained for any of the compounds, since a drift in the observed pKa values occurred during the titrations. Approximate, or equilibrium pKa values for the most acidic function of each of the compounds were: colupulone, 6.1; (?)-humulone, 5.0; trans-isohumulone, 3.1; trans-humulinic acid, 2.7. Evidence from spectroscopic measurements (UV, ¹H-NMR, ¹³C-NMR), conductiometric experiments and measurements of the pH dependency of solvent partition behaviour and aqueous solubility of the compounds is consistent with the possibility that, in aqueous solution, compounds such as trans-isohumulone are present as covalent hydrates. It is likely that reversible hydration occurs at one or more carbonyl groups. As a consequence of this behaviour, no single pKa value is sufficient to describe the behaviour of any one hop compound or hop-derived compound. The potential significance of this phenomenon is discussed.     

PHENOLIC COMPOUNDS IN RUM

SUMMARY— A study was made of the phenolic fraction of a Jamaica rum containing 75% ethanol. Identification of the phenols was performed by coupled gas chromatography and mass spectrometry and further by infrared spectrometry and thin layer chromatography. Phenol, p-ethylphenol, o-cresol, p-cresol, guaiacol, p-ethylguaiacol and dihydroeugenol were found in Jamaica rum for the first time; the presence of p-methylguaiacol and eugenol was confirmed.     

VARIETAL AROMA COMPOUNDS OF VITIS VINIFERA CV. KHAMRI GROWN IN TUNISIA

ABSTRACT

The aroma composition of the grape juice of Khamri, a native variety of Vitis vinifera grown in Tunisia, was investigated for the first time. A total of 27 free and 20 glycosidically bound compounds were identified by gas chromatography‐mass spectrometry. According to the obtained results, the aroma compounds were C6 alcohols, benzene compounds, terpenes, acids and norisoprenoids. On the basis of gas chromatography‐olfactometry, these compounds were grouped, according to volatiles exhibiting the identical odor quality, into 10 groups of the same character (aromatic series) as a way of establishing an aroma profile for the studied variety. The high glycosidically bound norisoprenoid concentrations and the absence of the bound form of the acids were a positive factor for the Khamri variety potential aroma.

PRACTICAL APPLICATIONS

This article aimed on the identification of the unknown Tunisian grapevine varieties that are very well adapted to the arid conditions and that could have a good quality. The discovery of unknown autochthonous grapevine varieties with good aroma and pomological characteristics could be of great importance for the agriculture sector all over the world especially the arid regions.

     

NITROGEN COMPOUNDS IN RUM AND WHISKEY

SUMMARY— The nitrogen compounds from a Jamaica rum and a Scotch blended whiskey were isolated and identified by gas chromatography and mass spectrometry. In both spirits were found: pyridine, α-picoline, β-picoline, thiazole, methylpyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-methyl-6-ethy/pyrazine, 2-methyl-5-ethylpyrazine, trimethylpyrazine and 2.5.dimethyl-3-ethylpyrazine. 2.Methyl-6-vinylpyrazine was detected only in rum. Nine compounds in whiskey and eleven in rum have not previously been reported as constituents of these drinks or fusel oils.     

EVOLUTION OF VOLATILE COMPOUNDS DURING WORT-BOILING

Pilot scale trials have been carried out to determine the nature and patterns of evolution of compounds present in condensates obtained from boiling worts at atmospheric pressure. Analytical procedures involving gas chromatography and gas chromatography-mass spectrometry have been used to identify 70 compounds in condensates from unhopped ale worts. Over 30 of these volatile compounds have been classified according to one of three patterns of evolution. The rate of evolution for one class remained constant throughout the boiling period, for the second class decreased gradually towards the end of boiling, and for the third was sufficiently rapid to lead to the removal of most of a component during the early stages of boiling. Many of the compounds identified in the condensates are highly flavour-active.     

甘薯渣中多酚类化合物的分离与结构鉴定

用高速逆流色谱（HSCCC），结合薄层层析（TLC）和颜色反应，对甘薯渣中多酚类化合物进行分离纯化，结果表明：分离得到的3种化合物均为多酚类化合物。根据MS（质谱）、^1H NMR（核磁共振氢谱）和^13C NMR（核磁共振碳谱）谱图分析结果，上述3种化合物分别为阿魏酸、绿原酸、异鼠李素。     

酱油香气成分GC/MS分析

用无水乙醚提取酱油中香气成分，GC／MS分离鉴定其化学组成，以面积归一化法测定其相对含量。酱油乙醚萃取物中鉴定出32种化合物，其中对酱油香气成分贡献最大的是HEMF（4-羟基-2（5）-乙基-5（2）-甲基-3（2H）-映喃酮）、4-乙基愈创木酚、香茅醇、5-甲基-2-糖醛及3-甲巯基丙醇等。     

PHENOL COMPOUNDS IDENTIFIED IN SELECTED LIQUID SMOKES

Liquid smokes including mesquite, hardwood blend, hickory (aqueous), and hickory-oil (oil-based) were subjected to direct ether extraction; phenolic components were separated and identified using gas chromatography/mass spectrometry (GC/MS). A solution containing 1,250 μg/ml each of phenol, isoeugenol, o -cresol, m -cresol, 4-allylsyringol, catechol, 4-methylcatechol, 2,6-dimethoxy-phenol, 2-methoxyphenol, 4-ethylphenol, and 2,3-dimethylphenol was injected directly or ether extracted prior to GC/MS separation for quantification of phenols in smokes and for recovery calculations. Phenol, guaiacol, syringol, and catechol in ether and ether extracted from oil were used as standards for oil-based smoke. The total amount of phenols in the smokes was similar but the proportions of individual phenols differed. Hickory smoke contained more syringol and its derivatives (4-allysyringol and 4-methylsyringol) than mesquite; mesquite contained more phenol, o-cresol, catechol and 4-methylcatechol than hickory.     

THE PRODUCTION OF AROMA COMPOUNDS BY YEAST

The yeast plasma membrane regulates the movement of compounds into the yeast cell and of yeast metabolites from the cell into the medium. The rate of penetration of organic acids into the yeast cell depends on their lipophilic nature, and on their molecular size and degree of branching. During fermentation yeast synthesizes a vast number of aroma compounds. The numerically and quantitatively largest groups of aroma compounds include fusel alcohols, fatty acids and fatty acid esters. The yeast used and the fermentation conditions can influence the formation of aroma compounds. The yeast also has a profound effect on the formation of other aroma compounds, such as sulphur compounds and phenols. In addition to fermentation, the maturing of a beverage can also influence the aroma. During the maturing lactones, phenols and other compounds are extracted from the oak casks in which the beverage is aged. The presence of the so-called “whisky lactone”, β-methyl-γ-octalactone, is characteristic of a beverage that has been matured in oak.     

THE IDENTIFICATION OF CARBONYL COMPOUNDS IN BEER

Carbonyl compounds were separated from bottom-fermented lager beer by extraction with a diethylether-pentane mixture and precipitation from the extract with 2,4-dinitrophenylhydrazine. The diketones, diacetyl and 2,3-pentanedione, were identified as bishydrazones by thin-layer chromatography with benzene-petroleum ether-ethyl acetate (34:5:1) as solvent and Silica Gel HF₂₅₄ as adsorbent. For the identification of the aldehydes, the hydrazone precipitate was treated with ozone in formic acid solution and the aldehydes were determined as their corresponding carboxylic acids by iso-thermal gas chromatography on a NEGS column. Aldehydes were found in the following order of magnitude: acetaldehyde, isobutyraldehyde, isovaler- and/or opt.act.valeraldehyde (2-methylbutyraldehyde), valeraldehyde and butyraldehyde.     

ANTIFUNGAL ACTIVITY OF MONOLAURIN AND RELATED COMPOUNDS

Lauricidin^R (monolaurin) and related compounds were tested against 16 fungi belonging to different groups and having different cell wall composition. Lauricidin Plus F (a combination of monolaurin, butylated hydroxy anisole and ethylenediaminetetraacetic acid) was the most effective agent and inhibited the growth of all fungi tested at a concentration of 0.1%. Lauribic (a combination of monolaurin and sorbic acid) also exhibited strong antifungal activity but was less effective than Lauricidin Plus F. In most cases Lauricidin showed antifungal activity at a concentration of 0.5%. Other commercial samples of monolaurin, e.g. Lauricidin 812 (A), Lauricidin 802 (B), and Lauricidin 112 (C), showed higher antifungal activity than Lauricidin. Tests comparing Lauricidin Plus F with sorbic acid, K sorbate and propionic acid, showed that Lauricidin Plus F has higher antifungal activity except when sclerotia of Sclerotium rolfsii were used for inoculation. Lauricidin Plus F was fungistatic and maintained its activity in a semi-synthetic medium for at least 21 days at 26°C.