Akio Kobayashi

Volatile Components of Roasted Shrimp

The components of the strong and favorable aroma obtained from roasted shrimp were investigated. The aroma concentrate of roasted shrimp was isolated by combining the dichloromethane extract and carbon dioxide distillation methods. The concentrate was fractionated into acidic, basic and neutral fractions. Each fraction was analyzed by combined gas chromatography-mass spectrometry. Seventy-seven compounds were identified, among which isovaleric acid, alkyl pyrazines, isovaleramide, ketones and some sulfur-containing compounds were the main and characteristic constituents of the roasted shrimp aroma.These constituents were compared with those of the volatiles of boiled shrimp, which was prepared by using simultaneous distillation and extraction methods in a modified Likens and Nickerson’s apparatus.

Isolation of Some Glucosides as Aroma Precursors from Ginger

A glycosidically bound fraction was prepared by adsorbing a 80% methanol extract from fresh rhizomes of ginger onto a column of Amberlite XAD-2 resin and successively eluting with ethyl acetate or methanol. Enzymatic hydrolysis of this fraction with an acetone powder prepared from fresh ginger and commercial glycosidase liberated such alcohols as geraniol, 2-heptanol, α-terpineol, nerol, linalool, and citronellol, suggesting that fresh ginger included glycosides and glycosidase. The ethyl acetate eluate was chromatographed by an ODS flash column and then HPLC to isolate the β-glucopyranosides of 5-hydroxyborneol, 1,8-epoxy-p-menthan-3-ol, (2E, 6E)- and (2E, 6Z)-3,7-dimethyl-8-hydroxyoctadien-1-ol, 2-heptanol, geraniol, nerol, (R)-linalool, and citronellol. All the glucosides, except for 5-hydroxybornyl-O-β-D-glucopyranoside, were identified for the first time in the rhizome of ginger, and many of their aglycons were major constituents of the essential oil. The results indicate that these glucosides are aroma precursors of fresh ginger.

Flavor Components of Shoyu and Miso Japanese Fermented Soybean Seasonings

The name soybean come form “bean of soy” which is derived from Portuguese Soya. In the 16th century, Portuguese imported Japanese soy sauce u2028shoyu” and distributed it in the European countries. The name Soya is an alteration of the Japanese word “shoyu.” In this respect, shoyu has been an international food item since that time.

Amino acid precursors of the garlic-like odour in Scorodocarpus borneensis

Abstract Two new natural amino acids, (Rs)-3-[(methylthio)methylsulfinyl]- l -alanine and S-[(methylthio)methyl]- l -cysteine, were isolated from the fruit of Scorodocarpus borneensis which is known to have a garlic-like odour. C–S lyase-mediated enzymatic conversion showed that both amino acids play an important role in developing the main odorous components of methyl methylthiomethyl disulfide and bis(methylthiomethyl) disulfide.

Optical isomers of methyl jasmonate in tea aroma

Two epimers of methyl jasmonate were optically resolved by capillary gas chromatography, using heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin as the chiral stationary phase. In the tea volatile concentrates, both of these epimers were present as only one enantiomer, their absolute configurations being ascertained as (-)-(1R,2R)-methyl jasmonate and (+)-(1R,2S)-methyl epijasmonate. The thermal isomerization of methyl epijamonate to methyl jasmonate was also clarified by optically resolved gas chromatography to have occurred at the asymmetric carbon of the C-2 position that is connected to the carbonyl group.

First isolation of geranyl disaccharides from ginger and their relations to aroma formation.

Abstract Three geraniol glycosides were isolated from immature fresh ginger rhizomes (Zingiber officinale Roscoe). Their structures were identified as geranyl 6-O-α-L-arabinopyranosyl-β-D-glucopyranoside (1), geranyl 6-O-β-D-apiofuranosyl-β-D-glucopyranoside (2) and geranyl 6-O-β-D-xylopyranosyl-β-D-glucopyranoside (3) by spectrometric analyses. After incubating each glycoside with a crude enzyme solution prepared from ginger, geraniol was liberated in all of those fractions. This result indicates that the glycosides are related to the formation of geraniol-related compounds in ginger aroma.

Progress of Tea Aroma Chemistry

Over 60% (w/w), of the components of essential oils from tea were identified before 1960 by classical chemical methods. With the advent of GC and GC-MS, many new compounds were identified, compounds important in contributing to characteristic tea aromas even though present in small concentrations. Now 99.9% (w/w) of the components of essential oils from tea have been determined. With the identification of components and with further improvements in analytical methods, differences in different types of teas and detailed changes in the processing of teas were elucidated. Advanced analytical methods have also made possible the study of stereochemistry of tea aroma compounds. Some of the important optical isomers, such as the structures of linalool, linalool oxides and methyl jasmonate are discussed. Enzymatic studies showed that the main aroma components precursors of black tea are present as glycosides, some of which were separated and identified by the use of HPLC, NMR and FABMS. Synthetic glycosides are used as substrate of glycosidase prepared from fresh tea leaves and primeverosides are hydrolyzable by this enzyme system.

Flavor of Black Tea:Part V Comparison of Aroma of Various Types of Black Tea

In comparing the aroma concentrates from various types of black tea by the use of gas chromatography (GLC), differences of aroma pattern were recognized among these black tea of Ceylon, India, Peru, Formosa and Japan.One of the typical differences, by which the variety would be characterized, appeared in the proportion of linalool (include its oxides) to geraniol and phenylethanol. Furthermore the ratio of the total area of peaks before and after linalool seemed to have some relation with the variety of black tea.Also, top note of black tea aroma was compared by head space vapor analyses.

Studies on the Flavor of Green Tea:Part VII. Flavor Components of Manufactured Green Tea

The essential oil from manufactured green tea was separated into carboxylic, phenolic, carbonyl and alcoholic fractions and analysed by gas chromatography.Seventeen alchols, two carbonyls, seven acids and two phenolic compounds were identified on the basis of their relative retention times and aroma of effluents by comparing with authentic compounds.The quantities of these compounds were also determined by gas chromatography.Four alcohols (present in rather high amounts), two caronyls, three esters and two phenols have remained unidentified.

Flavor of Black Tea: Part II. Alcohols and Carbonyl Compounds

The neutral fraction of the essential oils from three kinds of black tea (same samples as described in the previous paper,1) i.e., Assam, Shan and Benihomare) was separated into carbonyl and carbonyl-free fractions and analysed by gas chromatography. On the basis of relative retentions and aroma of effluents with the references of the chromatographic data obtained by the previous works,2–4) the major alcohols were found to be cis-2-pentenol, n-hexanol, cis-3-hexen-1-ol, three isomers of linalooloxide, linalool, nerol, geraniol, benzylalcohol, and phenylethylalcohol. In the carbonyl fraction, phenylacetaldehyde was newly identified, and besides it, the presence of iso- and n-butyr-, iso- and n-valer- aldehyde, methylethylketone, trans-2-hexenal, benzaldehyde were recognized. There were no differences in the components among three kinds of black tea, but the relative quantity of each component in the essential oil was different among three varieties.