Hidehiko Wakabayashi

Action of transglucosidase from Aspergillus niger on maltoheptaose and [U–13C]maltose

Oligosaccharides synthesized from a mixture of maltoheptaose and [U-(13)C]maltose with transglucosidase [EC 2.4.1.24] from Aspergillus niger were investigated. When the reaction mixture was incubated at 15 degrees C for 1h, several types of oligosaccharides with DP (degree of polymerization) 2 to DP8 containing alpha-D-Glcp-(1-->6)-maltoheptaose were detected by liquid chromatography-mass spectrometry (LC-MS) and methylation analysis. Most of these compounds consisted of alpha-(1-->4) linkages in the main chain and alpha-(1-->6) linkages at the non-reducing ends. However, when the reaction mixture was incubated for 96h, most of these products were converted into oligosaccharides with DP2 to DP5 consisting of only alpha-(1-->6) linkages. These results suggested that A. niger transglucosidase rapidly transferred glucosyl residues to maltooligosaccharides, and gradually hydrolyzed both alpha-(1-->4) linkages and alpha-(1-->6) linkages at the non-reducing end, and transformed these into smaller molecules of mainly alpha-(1-->6) linkages.

Characterization of the key aroma compounds in beef extract using aroma extract dilution analysis.

Aroma extract dilution analysis (AEDA) of an ether extract prepared from beef extract (BE) and subsequent identification experiments led to the determination of seven aroma-active compounds in the flavor dilution (FD) factor range of 32-128. Omission experiments to select the most aroma-active compounds from the seven aroma compounds suggested that 2,3,5-trimethyl pyrazine, 1-octen-3-ol, 3-methylbutanoic acid, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone were the main active compounds contributing to the aroma of BE. Aroma recombination, addition, and omission experiments of the four aroma compounds in taste-reconstituted BE showed that each compound had an individual aroma profile. A comparison of the overall aroma between this recombination mixture and BE showed a high similarity, suggesting that the key aroma compounds had been identified successfully.

Characterization of the key aroma compounds in pork soup stock by using an aroma extract dilution analysis

The aroma extract dilution analysis of an extract prepared from pork stock and subsequent experiments led to the identification of 15 aroma-active compounds in the flavor dilution factor range of 64–2048. Omission experiments to select the most aroma-active compounds from the 15 odor compounds suggested acetol, octanoic acid, δ-decalactone, and decanoic acid as the main active compounds contributing to the aroma of pork stock. Aroma recombination, addition, and omission experiments of these four aroma compounds in taste-reconstituted pork stock showed that each compound had an individual aroma profile. A comparison of the overall aroma between this recombined mixture and pork stock showed strong similarity, suggesting that the key aroma compounds had been successfully identified. Graphical Abstract Most aroma-active compounds contributing to the aroma of clear type pork stock detected by AEDA and subsequent omission and addition experiments.

Structural analysis and taste evaluation of γ-glutamyl peptides comprising sulfur-containing amino acids

Abstract The structures, flavor-modifying effects, and CaSR activities of γ-glutamyl peptides comprising sulfur-containing amino acids were investigated. The chemical structures, including the linkage mode of the N-terminal glutamic acid, of γ-L-glutamyl-S-(2-propenyl)-L-cysteine (γ-L-glutamyl-S-allyl-L-cysteine) and its sulfoxide isolated from garlic were established by comparing their NMR spectra with those of authentic peptides prepared using chemical methods. Mass spectrometric analysis also enabled determination of the linkage modes in the glutamyl dipeptides by their characteristic fragmentation. In sensory evaluation, these peptides exhibited flavor-modifying effects (continuity) in umami solutions less pronounced but similar to that of glutathione. Furthermore, the peptides exhibited intrinsic flavor due to the sulfur-containing structure, which may be partially responsible for their flavor-modifying effects. In CaSR assays, γ-L-glutamyl-S-methyl-L-cysteinylglycine was most active, which indicates that the presence of a medium-sized aliphatic substituent at the second amino acid residue in γ-glutamyl peptides enhances CaSR activity. Structural analyses and taste evaluations of g-L-glutamyl-S-(2-propenyl)-L-cysteine and its sulfoxide isolated from garlic and related peptides were performed using authentic chemically synthesized samples.

Changes in the Volatile Compounds related to Deterioration of Crushed Dried Bonito During Storage.

かつお節粉砕後の密閉保存におけるカルボニル化合物などの劣化臭成分の変化について検討し,以下の結果を得た.(1) 条件を変えて保存した場合,-20℃ (24日間)で強い酸敗臭が発現したが,70℃ (4時間)では酸敗臭は弱く,弱い焦げ臭が発現した.25℃ (12日間)では酸敗臭が発現したが,その程度は-20℃の場合と比べて弱かった.(2) -20℃ (24日間),25℃ (12日間)および70℃ (4時間)のいずれの条件において保存してもカルボニル化合物が増加したが,組成は異なっていた.-20℃ではヘキサナールなどの直鎖アルデヒド類が増加したが,70℃では直鎖アルデヒド類は検出されず,分枝鎖アルデヒド類やケトン類が増加した.25℃ではそれらの中間的な組成を示した.これは,保存中に脂質の酸化分解(一次反応)と共存成分との反応(二次反応)が同時に起こり,温度によってそれぞれの反応の起こりやすさが異なるためと考えられた.(3) 保存中に生成した主な劣化臭成分は,酸素分子あるいは水分子中の酸素を取り込んで生成することを,18Oを使用した実験より確認した.(4) 保存中に増加した各種カルボニル化合物の標準物質を粉砕直後のかつお節に添加して,香気特性への影響をみた結果,ヘキサナールなどの直鎖アルデヒド類により酸敗臭的香りが発現することを確認した.また,分枝鎖アルデヒド類やケトン類の影響は少ないと考えられた.