EVALUATION OF SPICES AND OLEORESINS — VIII — IMPROVED SEPARATION AND ESTIMATION OF PUNGENT AND RELATED COMPONENTS OF GINGER BY THIN-LAYER CHROMATOGRAPHY

A combination of the wedged-tip TLC technique and choice of solvent polarity has been used to clearly separate the pungent and weakly pungent homologs of gingerols and shogaols of ginger extracts. The quantitative estimation, of the separated components provides valid data for correlation with subjective pungency. By TLC analysis of the alkaline degradation products, the pungent fractions were shown to be the (6) — and the weakly pungent fractions to be (8) — (and possibly (10) —) gingerols and shogaols. Zingerone has not been found even in commercial samples stored over many years.     

GAS CHROMATOGRAPHY AND GAS CHROMATOGRAPHY-MASS SPECTROMETRY OF SOFT RESINS AND RELATED COMPOUNDS

The α-acids, β-acids, iso-α-acids, hulupones and humulinic acid have been separated by gas chromatography utilising the cool on-column injection technique on various bonded phase capillary columns. The α-acids were separated into cohumulone and humulone; the β-acids into colupulone and lupulone; and the hulupones into cohulupone and hulupone. Iso-α-acids were separated into four peaks; cis-isocohumulone, trans-isocohumulone, cis-isohumulone and trans-isohumulone. Flame ionization detection (FID) and chemical ionization mass spectrometry (CIMS) were used for chromatographic detection. Best results were achieved by employing a DB-1 fused silica capillary column with isooctane as the sample solvent .     

RAPID GAS CHROMATOGRAPHIC EXAMINATION OF BEER FLAVOUR

Gas chromatographic analysis of the headspace vapour of beer permits rapid measurement of the concentration of myrcene and the principal volatile alcohols, esters and carbonyl compounds in beer. In some cases the results obtained can be correlated with differences in flavour associated with changes in brewing procedure. The strength of the hop aroma of beers which had been dry-hopped, or to which hop oil had been added, was broadly reflected by the content of myrcene, which varied from 7 to 120 μg. per litre. A similar range was found in wort, the content depending on the conditions of boiling. However, the major part of this was lost during fermentation.     

ANALYSIS OF DIACETYL AND RELATED COMPOUNDS IN FERMENTATIONS

A number of British beers have been analysed for diacetyl, 2,3-pentanedione, and related compounds. Finished beers contained little or no α-acetohydroxyacids or diketone bisulphite addition compounds. Sources of error in measuring the diketones by g.l.c. or by the Institute of Brewing Recommended Methods are discussed, and a special study is made of methods of assaying for α-acetolactic acid. Even under oxidizing conditions some acetoin is formed from α-acetolactic acid.     

GAS CHROMATOGRAPHIC DETERMINATION OF TYROSOL AND TRYPTOPHOL IN WINES AND BEERS

A gas chromatographic method for the determination of tyrosol and tryptophol in wines and beers has been developed. The aromatic fusel alcohols are extracted with ether or ethyl acetate from a sample made alkaline with Na₂CO₃ and saturated with NaCl. In beer determinations the extraction is performed with ethyl acetate in order to avoid complications caused by emulsion. Most of the solvent is removed by distillation and the rest is cautiously allowed to evaporate. The gas chromatographic determination of tyrosol and tryptophol is performed in a 0·5-m. Apiezon M-DEGS column at 190°C. According to the infra-red spectra, both components are eluted without being decomposed at this temperature. In the grape wines investigated, tyrosol was found in amounts of 10–40 mg. per litre, in two Finnish berry wines 10–15 mg. per litre and in two different types of pale lager beers 5–10 mg. per litre. The same samples contained about 1–4 mg. tryptophol per litre. The two white grape wines and one red berry wine were exceptional, with only 0·2–0·3 mg. tryptophol per litre.     

QUANTITATIVE GAS CHROMATOGRAPHIC ANALYSIS OF AMINO ACIDS IN BEER AND WORT

Amino acids present in beer and wort samples were isolated using Dowex 50W-X8 ion exchange resin. These acids were converted to N-trifluoroacetyl methyl esters and were separated on a 10 ft. x 1/4 in. copper column packed with 3/4% Carbowax 1540 and 1/4% NPGS on Chromosorb W. Complete separation and quantitative estimation was obtained for eleven amino acids: valine, alanine, isoleucine, leucine, glycine, proline, aspartic acid, threonine, methionine, glutamic acid, and phenylalanine. Standards of the acids showed a relative standard deviation of 4% and less for nine acids while threonine and methionine gave deviations of 9% and 15% respectively. The other naturally-occurring amino acids did not interfere with the separation of the above eleven. Amino acid assimilation data is presented along with other beer and wort analyses.     

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.     

A GAS CHROMATOGRAPHIC METHOD FOR THE ACCURATE DETERMINATION OF LOW CONCENTRATIONS OF VOLATILE SULPHUR COMPOUNDS IN ALCOHOLIC BEVERAGES

By using a new sensitive method the contents of dimethyl sulphide, dimethyl disulphide and dimethyl trisulphide have been determined in beers and wines, and the contents of these sulphides and diethyl sulphite measured in distilled beverages. The head-space volatiles are swept out from the beverage in a stream of nitrogen and adsorbed in a tube containing porous polymer. The volatiles are desorbed directly onto the column of a gas chromatograph by connecting the tube to the column and sliding the free end of the tube into the hot injection block from the oven side. The sulphur-sensitive flame photometric detector is used and the peak areas and identifications are collected on cassette and processed by computer to give the content of volatile sulphur compounds directly in μg/litre beverage. The detection limits are 2 μg/litre for dimethyl sulphide, 0.1 μg/litre for dimethyl disulphide and trisulphide, and 5 μg/litre for diethyl sulphite. The analysis time for each sample is 30 min and the coefficient of variation is 5%.     

GAS AND HIGH-PERFORMANCE LIQUID CHROMATOGRAPHIC ANALYSES OF AMINO ACIDS IN SOYBEAN MEAL, CORN AND TRITICALE

Analyses of amino acids in six samples each of soybean meal, corn and triticale by high-performance liquid chromatography (HPLC) and gas chromatography (GC) were compared. Samples were hydrolyzed in 6N HC1, then phenylthiocarbamyl (for HPLC) and N-heptafluorobutyryl (for GC) derivatives of free amino acids were prepared and analyzed by the appropriate system. Coefficient of variation within each feedstuff for amino acids analyzed by HPLC ranged from 1.8 (leucine) to 23.5% (methionine) in soybean meal, 2.7 (leucine) to 14.7% (methionine) in corn and 1.7 (leucine) to 14.3% (cystine) in triticale. Corresponding figures from GC analysis were 0.7 to 22.4%, 1.4 to 14.3% and 1.6 to 12.1%, respectively. Linear regression of HPLC on GC values gave good fits with R² ranging from 0.86 for cystine and 0.99 for isoleucine, leucine, lysine, methionine, phenylalanine, threonine, alanine, aspartic acid and glycine. Although some differences between the two systems were evident, feedstuff amino acid values obtained by HPLC and GC analyses compare very well. Results of this study and consideration of such factors as ease of derivatization and length of time for analysis, in our opinion, make HPLC the system of choice.     

GAS CHROMATOGRAPHIC DETECTION OF DIACETYL IN ORANGE JUICE

A GLC method was developed for detection of diacetyl (2,3-butanedione) and acetoin (3-hydroxy-2-butanone) in orange juice. Retention times for diacetyl and acetoin were 2.8 ± 0.03 and 6.8 ± 0.02 min, respectively. Concentration by distillation was essential to detect small quantities by GLC of diacetyl but was ineffective for acetoin. A linear response of diacetyl concentration to peak area was observed between 0.05 and 0.5 ppm. The peak areas at 0.05 and 0.5 ppm diacetyl were 1242 ± 203 and 20142 ± 1120, respectively. Elevating the column temperature and decreasing the carrier gas flow rate, increased the limit of detection for acetoin from ≥ 100 ppm to ≥ 10 ppm, but diminished the resolution of the diacetyl peak from juice volatiles.     

GAS CHROMATOGRAPHIC DETERMINATION OF VOLATILE NITROSAMINES IN FOODS

Methods are presented for determination of certain volatile nitrosamines which have been reported to occur in foods. Nitrosamines were removed from foods using a Likens-Nickerson extractor; 60% of added dimethylnitrosamine and 70% of added diethyl-nitrosamine were recovered from 10 rig/g aqueous solutions. Potential gas chromatographic (GC) interferences were removed from the extract by a simple acid extraction step and, when needed, by liquid column chromatography. Dilute solutions containing nitrosamines were analyzed directly with a GC solvent stripping technique. Nitrosamines were detected with a Coulson electrolytic conductivity detector operated in the pyrolytic mode and with a flame ionization detector. Sensitivities of these detectors are compared for selected volatile alkyl and heterocyclic nitrosamines of potential significance in foods. The specificity of the Coulson detector is demonstrated for analysis of extracts of smoked fish and a number of processed meats. Additional clean-up of concentrates from foods is required to insure unambiguous identification of nitrosamines by combined GC-mass spectrometry.     

GAS CHROMATOGRAPHIC DETERMINATION OF TRIHYDROXYOCTADECENOIC ACIDS IN BEER

A rapid and quantitative method for measuring the content of trihydroxyoctadecenoic acids in beer is described. The acids are extracted from degassed beer with ethyl acetate and methylated with diazomethane. After washing, the methylated compounds are silylated and analysed by gas chromatography. The coefficient of variation of the method is 3·2%. The amounts of total trihydroxyoctadecenoic acids in commercial beer samples varied from 4 to 12 mg/litre. The effects of these acids on beer flavour and head retention are discussed.     

THE GAS CHROMATOGRAPHIC DETERMINATION OF TRACES OF HYDROGEN SULPHIDE AND ALKANE THIOLS IN BEER

By using lgepal CA 630 and didecyl phthalate as stationary phases on Chromosorb G-AW, DMCS, and a mixture of GE-SF 96 and Embaphase as stationary phases on Chromosorb W, gas chromatographic columns were obtained which were used for the analysis of volatile sulphur compounds. Applying a Melpar Flame Photometric detector, minute traces of hydrogen sulphide and alkane thiols in beer could be determined quantitatively. Threshold values of perception of different thiols and organic sulphides were also determined in beer. As levels of these values were in the same range as the sensitivity limit of the gas chromatographic system, organoleptic and gas chromatographic results could be compared.