平成30年度 研究成果

福田央、山田修、韓錦順

伊豆諸島で生産されている焼酎の成分の特徴を把握するため、84種類の揮発性成分をSPME法とヘッドスペース法を用いて分析した。甘藷焼酎に関して伊豆諸島と本格焼酎鑑評会出品酒では44成分に有意差があった。ステップワイズ法で4成分(1-オクテン-3-オール、酪酸エチル、エナント酸エチル及びバニリン)の変数を選択し、判別分析を行ったところ、すべての試料が適切に判別され、判別精度を検討したところ、100%であった。麦焼酎に関して伊豆諸島と本格焼酎鑑評会出品酒では29成分に有意差があった。ステップワイズ法で4成分(ノナナール、酢酸エチル、酪酸エチル及びDMTS)の変数を選択し、判別分析を行ったところ、68点の試料中67点が適切に判別され、判別精度を検討したところ、98.5%であった。また、伊豆諸島で生産される甘藷焼酎と麦焼酎の混和焼酎と、甘藷焼酎、麦焼酎とでは42成分に有意差があり、ステップワイズ法で8成分(シトロネロール、イソ酪酸エチル、カプロン酸エチル、カプロン酸イソアミル、カプリン酸エチル、桂皮酸エチル、コハク酸ジエチル及びグアヤコール)の変数を選択し、判別分析を行ったところ、33点の試料中30点が適切に判別された。

飯塚幸子、磯谷敦子、神田涼子、藤井力

近年、全国新酒鑑評会出品酒に「マスカット様」、「ライチ様」、「柑橘様」の指摘がある。これらの香り特性にはチオール類が関与していると仮定し、チオール類の一つである4-mercapto-4-methylpentan-2-one(4MMP)について、2015年の出品酒を試料として分析を行った。試料25点の4MMP含量は、5～14 ng/Lで、いずれも以前に報告した清酒における4MMPの検知閾値（1.2 ng/L）酒よりも高かった。清酒の香り特性に対する4MMPの影響を調べるため、4MMPを添加した清酒の官能評価試験を行ったところ、8.0 ng/L 以上の4MMPの添加により、「硫黄系」の香り特性が有意に増強された。また、16.0 ng/L 以上の4MMPの添加により、香味評価が有意に低くなったものの、カプロン酸エチルや酢酸イソアミルの香りとは異なる「果実様」の香り特性が有意に増強された。

Fumikazu Akamatsu, Yasuhisa Tsuchida, Takaaki Oe, Yuri Hisatsune, Yukari Igi, Tomokazu Hashiguchi, Tsutomu Fujii

The carbon stable isotopic composition (δ¹³C) is often analyzed to quantify the addition of acidulants to Japanese apricot liqueur, but little is known about the variation in theδ¹³C values of the main organic acids arising from differences in the ripeness of Japanese apricots. We show that in Japanese apricot liqueur prepared using fruits at different stages of ripeness, theδ¹³C values of citric acid and malic acid ranged from -25.1‰ to -23.7‰ and from -22.3‰ to -19.7‰, respectively, and theδ¹³C values decreased as the fruit ripened. The averageδ¹³C value of citric acid from liqueurs was 0.7‰ higher than that from fresh fruits, whereas theδ¹³C values of malic acid showed no isotope discrimination. The variation inδ¹³C values of the main organic acids in Japanese apricot liqueurs will help detect acidulant addition and control authenticity.

Sharon Marie Bahena-Garrido, Tomoko Ohama, Yuka Suehiro, Yuko Hata, Atsuko Isogai, Kazuhiro Iwashita, Nami Goto-Yamamoto and Kazuya Koyama

BACKGROUND

Koshu, a hybrid of Vitis vinifera L. and V. davidii Foex, is the most popular indigenous cultivar for wine production in Japan. However, little is known about the potential aroma compounds it contains and how environmental factors affect these. In this study, we obtained comprehensive profiles of the volatile (both glycosidically bound and free) and phenolic compounds that occur in koshu berries, and compared these with similar profiles for V. vinifera cv. chardonnay. We then compared the response of these two cultivars to bunch shading and the ripening-related phytohormone abscisic acid (ABA).

RESULTS

Koshu berries contained significantly higher concentrations of phenolic compounds, such as hydroxycinnamic acid derivatives, and some volatile phenols, such as 4-vinyl guaiacol and eugenol, than chardonnay berries, which are thought to contribute to the characteristics of koshu wine. In addition, koshu berries had a distinctly different terpenoid composition from chardonnay berries. Shading reduced the concentration of norisoprenoid in both cultivars, as well as several phenolic compounds, particularly their volatile derivatives in koshu berries. The exogenous application of ABA induced ripening and increased the concentrations of lipid derivatives, such as hexanol, octanol, 1-nonanol, and 1-octen-3-ol. Multivariate and discriminant analyses showed that the potential aroma and flavor compounds in the berries could be discriminated clearly based on cultivar and environmental cues, such as light exposure.

CONCLUSION

The unique secondary metabolite profiles of koshu and their different responses to environmental factors could be valuable for developing various types of koshu wines and new cultivars with improved quality and cultural characteristics.

Hitoshi Shimoi, Yuta Hanazumi, Natsuki Kawamura, Miwa Yamada, Shohei Shimizu, Taro Suzuki, Daisuke Watanabe, and Takeshi Akao

Sake yeast strains are classified into Saccharomyces cerevisiae and have a heterothallic life cycle. This feature allows cross hybridization between two haploids to breed new strains with superior characteristics. However, cross hybridization of sake yeast is very difficult because only a few spores develop in a sporulation medium, and most of these spores do not germinate. We hypothesized that these features are attributable to chromosome recombination defect in meiosis, which leads to chromosome loss. To test this hypothesis, we examined meiotic recombination of sake yeast Kyokai no. 7 (K7) using the following three methods: (i) analysis of the segregation patterns of two heterozygous sites in the same chromosome in 100 haploid K7 strains; (ii) sequencing of the whole genomes of four haploid K7 strains and comparison of the bases derived from the heterozygosities; and (iii) construction of double heterozygous disruptants of CAN1 and URA3 on the chromosome V of K7 and the examination of the genotypes of haploids after sporulation. We could not detect any recombinant segregants in any of the experiments, which indicated defect in meiotic recombination in K7. Analyses after sporulation of the same double heterozygous disruptants of K6, K9, and K10 also indicated meiotic recombination defect in these strains. Although rapamycin treatment increased the sporulation efficiency of K7, it did not increase the meiotic recombination of the double heterozygous K7. Moreover, the spo13 disruptant of the K7 derivative produced two spore asci without meiotic recombination. These results suggest that sake yeasts have defects in meiotic recombination machinery.

Daisuke Watanabe, Takuma Kajihara, Yukiko Sugimoto, Kenichi Takagi, Megumi Mizuno, Yan Zhou, Jiawen Chen, Kojiro Takeda, Hisashi Tatebe, Kazuhiro Shiozaki, Nobushige Nakazawa, Shingo Izawa, Takeshi Akao, Hitoshi Shimoi, Tatsuya Maeda, Hiroshi Takagi.

Saccharomyces cerevisiae sake yeast strain Kyokai no. 7 (K7) and its relatives carry a homozygous loss-of-function mutation in the RIM15 gene, which encodes a Greatwall-family protein kinase. Disruption of RIM15 in non-sake yeast strains leads to improved alcoholic fermentation, indicating that the defect in Rim15p is associated with the enhanced fermentation performance of sake yeast cells. In order to understand how Rim15p mediates fermentation control, we here focused on target-of-rapamycin protein kinase complex 1 (TORC1) and protein phosphatase 2A with the ^B55δ regulatory subunit (PP2A^B55δ), complexes that are known to act upstream and downstream of Rim15p, respectively. Several lines of evidence, including our previous transcriptomic analysis data, suggested enhanced TORC1 signaling in sake yeast cells during sake fermentation. Fermentation tests of the TORC1-related mutants using a laboratory strain revealed that TORC1 signaling positively regulates the initial fermentation rate in a Rim15p-dependent manner. Deletion of the CDC55 gene encoding ^B55δ abolished the high fermentation performance of Rim15p-deficient laboratory yeast and sake yeast cells, indicating that PP2A^B55δ mediates the fermentation control by TORC1 and Rim15p. The TORC1-Greatwall-PP2A^B55δ pathway similarly affected the fermentation rate in the fission yeast Schizosaccharomyces pombe, strongly suggested that the evolutionarily conserved pathway governs alcoholic fermentation in yeasts.

It is likely that elevated PP2A^B55δ activity accounts for the high fermentation performance of sake yeast cells. Heterozygous loss-of-function mutations in CDC55 found in K7-related sake strains may indicate that the Rim15p-deficient phenotypes are disadvantageous to cell survival.

IMPORTANCE

The biochemical processes and enzymes responsible for glycolysis and alcoholic fermentation by the yeast S. cerevisiae have long been the subject of scientific research. Nevertheless, the factors determining fermentation performance in vivo are not fully understood. As a result, the industrial breeding of yeast strains has required empirical characterization of fermentation by screening numerous mutants through laborious fermentation tests. To establish a rational and efficient breeding strategy, key regulators of alcoholic fermentation need to be identified. In the present study, we focused on how sake yeast strains of S. cerevisiae have acquired high alcoholic fermentation performance. Our findings provide a rational molecular basis to design yeast strains with optimal fermentation performance for production of alcoholic beverages and bioethanol. In addition, as the evolutionarily conserved TORC1-Greatwall-PP2A^B55δ pathway plays a major role in the glycolytic control, our work may contribute to research on carbohydrate metabolism in higher eukaryotes.

Haruno Murayama, Yusuke Yamamoto, Misaki Tone, Takayuki Hasegawa, Moemi Kimura, Tamao Ishida, Atsuko Isogai, Tsutomu Fujii, Mitsutaka Okumura, Makoto Tokunaga

Gold (Au) nanoparticles (NPs) supported on SiO₂ (Au/SiO₂) were prepared by a practical impregnation method and applied as an adsorbent for 1,3-dimethyltrisulfane (DMTS), which is responsible for an unpleasant odour in drinks, especially Japanese sake. Compared with a conventional adsorbent, activated carbon, Au/SiO₂ selectively reduced the DMTS concentration in Japanese sake without decreasing the concentrations of other aromatic components. DFT calculations revealed that the selective adsorption of DMTS occurred through the formation of a stable intermediate. The size of the supported Au NPs was controlled by the preparation conditions and determined from TEM observations and XRD measurements, and the size was ranged from 2.4 nm to 30 nm. Au/SiO₂ having Au NPs with a diameter of 2.4 nm adsorbed DMTS the most efficiently. Smaller Au NPs showed better DMTS adsorption capabilities because larger amounts of Au atoms were exposed on their surfaces in the size range of this study. Langmuir-type monolayer adsorption and one-to-one binding of Au-S are proposed to occur based on an adsorption isotherm experiment. Even though significant differences of the fruity aroma score were not observed in the sensory evaluation between Au/SiO₂ and activated carbon for this less aromatic Japanese sake, Au/SiO₂ selectively decreased the DMTS concentration in the instrumental analysis.

赤尾健、周延、渡辺大輔、岡崎直人、下飯仁

先行研究において、代表的な清酒酵母であるきょうかい7号(K7)は3つの機能欠失変異（rim15^5067insA、msn4^C1540T、Δppt1::Ty2）を有し、これらがK7の高発酵性の原因を成すことが明らかにされている。約30株菌株ずつの調査では、これら変異のいずれもK7と近縁株（K6、K9、K10及びこれらの派生株）に共通かつ特異的であることから、優良きょうかい清酒酵母とその他の菌株を判別するためのDNAマーカーとして有用と期待された。本研究では、迅速かつ高精度な遺伝型タイピング法としてHRM解析を採用し、RIM15^5067ins及びMSN4¹⁵⁴⁰のそれぞれのタイピングの最適化を行った。続いて、これらDNAマーカーをより広範な菌株（98菌株134ストック）に拡張して適用し、これらの菌株がK7の系統に属するかか否かを推定した。

Yoshifumi Takao, Toshinari Takahashi, Tasuku Yamada, Tetsuya Goshima, Atsuko Isogai, Kazuo Sueno, Tsutomu Fujii, and Takeshi Akao

For several decades, almost all sake has been brewed with sake yeast Saccharomyces cerevisiae Kyokai no. 7 (K7) group strains. Although the widespread use of these strains has contributed to sake quality improvement, it may have lessened the diversity of sake gustatory properties brought about by house sake yeast (indigenous yeast of sake brewery). Sake yeast S. cerevisiae strain Km67 derives from the house yeast strain of Kiku-masamune Sake Brewing Co., Ltd., and it has been playing a central role in industrial sake brewing for decades. By using DNA sequencing, we revealed that strain Km67 does not possess specific loss-of-function mutations of stress response-related genes, which are characteristic of K7 group strains. Km67 had higher stress tolerance than K7 group strains likely because of the more efficient function of the stress response and heat shock elements in this strain. Sensory evaluation and taste sensor analysis demonstrated that sake brewed with Km67 had characteristically thicker body than sake brewed with K7 group strains. Chemical analysis suggested that unique sensory properties of the sake brewed with Km67 were due to high citramalic acid concentration. Taken together, these results revealed that strain Km67 differs from K7 group strains by genetic background and confers unique chemical composition and taste qualities upon sake it generates. It is expected that sake quality and gustatory properties will be diversified by utilizing house yeast such as strain Km67.

藤井力、磯谷敦子、飯塚幸子、伊豆英恵、神田涼子、橋口知一、後藤奈美

平成28酒造年度全国新酒鑑評会（第105回鑑評会）は、当該年度生産清酒を全国的に調査研究することにより、製造技術と酒質の現状及び動向を明らかにし、もって清酒の品質及び酒造技術の向上に資するとともに、国民の清酒に対する認識を高めることを目的として、日本酒造組合中央会との共催により実施した。

審査は、酒類総合研究所において、平成29年4月25日（火）から27日（木）の3日間に予審を行い、5月9日（火）及び10日（水）に決審を行った。また、5月24日（水）に東広島運動公園体育館で製造技術研究会を開催するとともに、6月17日（土）に日本酒造組合中央会主催の東京池袋のサンシャインシティ・文化会館展示ホールでの公開きき酒会を後援した。

出品は860点であった。審査の結果、優秀と認められた437点を入賞酒とし、さらに、決審において特に優秀と認められた242点に金賞を授与した。また、出品酒を公開する製造技術研究会及び公開きき酒会には、全国からそれぞれ、1,480人及び3,255人が来場した。

出品酒については、審査に加え酒質の現状及び動向を調査研究するため、出品者の記載による「全国新酒鑑評会出品酒調査表」（以下、「調査表」という。）の内容を集計するとともに、成分分析（「老ねやすさ」の受託分析を含む。）を行った。

向井伸彦、金井宗良、髙橋正之、西堀奈穂子、武藤彰宣、芳村俊広、後藤奈美

単式蒸留焼酎の品質を全国的に調査研究することにより、製造技術と酒質の現状及び動向を把握するとともに製造業者の参考とするため、第40 回本格焼酎・泡盛鑑評会を日本酒造組合中央会と共催で開催した。審査は平成29 年6月 1日（木）及び6月2日(金)に行い、単式蒸留焼酎の製造に関与している者等が出品酒をきき酒する製造技術研究会は6月23日（金）に当研究所で開催し92名が参加した。

開催にあたり、開催要領について日本酒造組合中央会と事前に検討し、今回は、（1）名称（旧称：本格焼酎鑑評会）、（2）出品酒の規格、（3）出品点数の制限、（4）成績上位酒の選定及び製造技術研究会における成績上位酒の展示、を変更した。

なお、輸出促進等に資する品質確保のために、第37回から分析を希望する出品者に対して有料でメタノールの受託分析を実施している。

出品状況、審査及び分析結果の概要について報告する。

日下一尊、神本真紀、武藤彰宣

全国地ビール品質審査会2018（以下、「審査会」という。）は、地ビールの醸造技術向上及び品質改善を目的として、全国地ビール醸造者協議会（Japan Brewers Association、以下、「JBA」という。）の主催により、平成30年3月6日(火)に、旧醸造試験所第一工場（通称「赤レンガ酒造工場」）（東京都北区滝野川）（以下、「赤レンガ酒造工場」という。）において実施された。審査会には46社から83点の出品があり、79点が官能評価による審査に供された。出品酒については、事前に独立行政法人酒類総合研究所（以下、「酒総研」という。）において成分分析及び微生物検査が実施された。

本報では、出品酒の成分分析、微生物検査及び官能評価の結果について報告する。

岡崎直人、野呂二三、稲橋正明、中原克己、蓮田寛和、武藤貴史、村上智子、五島徹也、赤尾健、木崎康造、石川雄章

日本醸造協会の頒布する清酒酵母株24種類について、過去から2014年度までの頒布保存株、合計385株について酵母種を目的変数として醸造特性値を説明変数とするパーティション分析を実施し、20醸造特性値が、統計的に有意な変数として選択された。20説明変数を用いたクラスター分析により、全酵母種ごとに単独のクラスターに分類することができ、また、クラスターから外れた一部 41 株を除いた344株に絞り込むことができた。24種類の酵母344株に対して、18説明変数を用いて判別分析を実施した場合の誤判別酵母株が7株であったのに対し、アミノ酸組成を除いた16説明変数によって判別分析を行った場合の誤判別酵母株が10株であり、アミノ酸組成を除いても判別に及ぼす影響は小さかったので、アミノ酸組成を分析項目から除くこととした。

選定後の344株からK-7のみを抽出し、クラスター解析を行った結果、大きく3クラスターに分割でき、その内、最近の頒布株のグループは、日本酒度、アルコールが高く、発酵性のよいグループであったが、この3クラスターとも他の酵母種のクラスターとは明確に分割されていることから、頒布の新旧にかかわらず、K-7の醸造特性が保たれていた。2003年以降の選定候補株24種、1250株について11醸造特性値によりクラスター分析を行ったところ、高香気生成酵母株のクラスター76株が選別され、その構成酵母種は、K-1601、K-1701、K-1801のみであった。また、K-1801のクラスターには、2006 年から2014年のすべてのK-1801頒布株が含まれ、K-1801株間の醸造特性値は安定していた。

Satoshi SEINO, Hitoshi KURIHARA, Ryosuke MATSUOKA, Yohei OKUYAMA, Masaaki KUNOU, Hanae IZU, Yongqiang CHENG, Yanxiang GAO, Beizhong HAN

The effect of ingestion of acetic acid bacteria on alcoholic liver injury was evaluated. C57BL/6J mice (8 weeks old, male, 22-27 g) were divided into three groups: the control group (without ethanol), ethanol group (ethanol 2.5 g/kg), and ethanol + acetic acid bacteria group (ethanol 2.5 g/kg + acetic acid bacteria 10 mg). The mice were given three times per day for 14 consecutive days in each group. Then the serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels and liver lipids of the mice were measured. As a result, AST and ALT levels, liver triglyceride and cholesterol levels were significantly higher in the ethanol group than those in the control group (P＜0.05). The ethanol + acetic acid bacteria group had significantly lower levels than those in the ethanol group(P＜0.05). These results suggested that the ingestion of acetic acid bacteria might alleviate alcoholic liver injury.

Hideaki SHIMIZU, Fumikazu AKAMATSU, Aya KAMADA, Kazuya KOYAMA, Masaki OKUDA, Hisashi FUKUDA, Kazuhiro IWASHITA, Nami GOTO-YAMAMOTO

Differences in mineral concentrations were examined among three types of wine in the Japanese market place: Japan wine, imported wine, and domestically produced wine mainly from foreign ingredients (DWF), where "Japan wine" has been recently defined by the National Tax Agency as domestically produced wine from grapes cultivated in Japan. The main objective of this study was to examine the possibility of controlling the authenticity of Japan wine. The concentrations of 18 minerals (Li, B, Na, Mg, Si, P, S, K, Ca, Mn, Co, Ni, Ga, Rb, Sr, Mo, Ba, and Pb) in 214 wine samples were determined by inductively coupled-plasma mass spectrometry (ICP-MS) and ICP-atomic emission spectrometry (ICP-AES). In general, Japan wine had a higher concentration of potassium and lower concentrations of eight elements (Li, B, Na, Si, S, Co, Sr, and Pb) as compared with the other two groups of wine. Linear discriminant analysis (LDA) models based on concentrations of the 18 minerals facilitated the identification of three wine groups: Japan wine, imported wine, and DWF with a 91.1% classification score and 87.9% prediction score. In addition, an LDA model for discrimination of wine from four domestic geographic origins (Yamanashi, Nagano, Hokkaido, and Yamagata Prefectures) using 18 elements gave a classification score of 93.1% and a prediction score of 76.4%. In summary, we have shown that an LDA model based on mineral concentrations is useful for distinguishing Japan wine from other wine groups, and can contribute to classification of the four main domestic wine-producing regions of Japan.

Yuriko IKEDA, Atsuko ISOGAI, Yuta MORIYOSHI, Ryoko KANDA, Kazuhiro IWASHITA, Tsutomu FUJII

Dimethyl trisulfide (DMTS) is the primary component responsible for "hineka", the stale aroma of Japanese sake. Deletion of the MRI1 or MDE1 gene of sake yeast, encoding 5'-methylthioribose-1-phosphate isomerase and 5'-methylthioribulose-1-phosphate dehydratase, respectively, has been reported to greatly reduce the amount of DMTS precursor (DMTS-P1) in sake and to suppress the formation of DMTS during storage. In this study, we constructed sake yeast strains lacking MRI1 gene function by a self-cloning method. Two methods were applied: in one, a stop codon was introduced in the MRI1 ORF by point mutation; in the other, the entire MRI1 ORF was deleted from the genome. In both methods, a plasmid vector containing drug-resistance and counter-selectable markers was used to introduce the mutation. We successfully obtained the strains, which did not contain the plasmid sequences, by both methods. Small-scale sake brewing tests using these SC strains (strains obtained by the self-cloning method) found that DMTS-P1 was hardly detected in sake brewed with SC strains, and DMTS production after sake storage was greatly reduced as compared with the parent strain. The components of brewed sake were almost the same between the SC and parent strains. These results suggest that SC strains can produce sake with higher flavor stability without changing the sake brewing properties.

Kiminori MATSUBARA, Mayumi OKUDA, Sachi SHIBATA, Shigeru MIYAKI, Takeshi OHKUBO, Hanae IZU, Tsutomu FUJII

Administration of alpha-glycerophosphocholine (GPC), a choline compound in food, is expected to contribute to human health. In this study, we evaluated its effect on aging in senescence-accelerated mouse prone 8 (SAMP8) mice. Male SAMP8 mice had free access to a commercial stock diet and drinking water with or without GPC (0.07 mg/ml). Mice in the GPC group had significantly lower total senescence grading score than that of the control group at 36 weeks of age. Administration of GPC decreased the deposition of transthyretin (TTR), an amyloidogenic protein, in the brain. Aggregated TTR activated microglia and led to neuroinflammation. Thus, GPC would protect the brain by reducing TTR deposition and preventing neuroinflammation. In a histological study of knee joints, it was found that SAMP8 mice administered GPC showed decreased joint degeneration. These results suggest that GPC delays the aging process and may be a useful compound in anti-aging functional food development.

Takumi OHDATE, Fumihiko OMURA, Haruyo HATANAKA, Yan ZHOU, Masami TAKAGI, Tetsuya GOSHIMA, Takeshi AKAO, Eiichiro ONO

For maltose fermentation, budding yeast Saccharomyces cerevisiae operates a mechanism that involves transporters (MALT), maltases (MALS) and regulators (MALR) collectively known as MAL genes. However, functional relevance of MAL genes during sake brewing process remains largely elusive, since sake yeast is cultured under glucose-rich condition achieved by the co-culture partner Aspergillus spp.. Here we isolated an ethyl methane sulfonate (EMS)-mutagenized sake yeast strain exhibiting enhanced maltose fermentation compared to the parental strain. The mutant carried a single nucleotide insertion that leads to the extension of the C-terminal region of a previously uncharacterized MALR gene YPR196W-2, which was renamed as MAL73. Introduction of the mutant allele MAL73L with extended C-terminal region into the parental or other sake yeast strains enhanced the growth rate when fed with maltose as the sole carbon source. In contrast, disruption of endogenous MAL73 in the sake yeasts decreased the maltose fermentation ability of sake yeast, confirming that the original MAL73 functions as a MALR. Importantly, the MAL73L-expressing strain fermented more maltose in practical condition compared to the parental strain during sake brewing process. Our data show that MAL73(L) is a novel MALR gene that regulates maltose fermentation, and has been functionally attenuated in sake yeast by single nucleotide deletion during breeding history. Since the MAL73L-expressing strain showed enhanced ability of maltose fermentation, MAL73L might also be a valuable tool for enhancing maltose fermentation in yeast in general.

奥田将生、上用みどり、福田央

本研究では、アルカリ/尿素崩壊性試験による蒸米酵素消化性の推定方法について検討した。目視で判定した米試料のアルカリ/尿素溶液の崩壊濃度はDSCの糊化温度、蒸米の酵素消化性、蒸米の老化性と有意な相関関係を示した。尿素崩壊・ヨウ素染色後の吸光度値も、蒸米の酵素消化性や蒸米の老化性と有意な相関関係を示した。従ってアルカリ/尿素溶液による崩壊濃度判定や尿素崩壊後のヨウ素染色液の吸光度によって簡便に蒸米の酵素消化性を推定できる可能性が示唆された。しかしながら、崩壊濃度に関して心白の有無は影響しなかったものの、精米歩合や米の水分は影響を及ぼした。従って、精米歩合や米の水分に応じた推定基準を設けることにより、本法は蒸米の酵素消化性の推定に有効なものになると考えられる。

Thongekkaew J, Fujii T, Masaki K, Koyama K

Important 'floral' aromas naturally occur in grapes predominantly as flavourless glycoconjugate precursors. Since these aroma compounds can be released by hydrolysis, different glycosidase enzymes can potentially contribute different aromas to wines. In this paper, the effects of crude and purified Candida easanensis JK8 β-glucosidases on wine aroma precursors of Muscat of Alexandria grape powder were investigated by GC/MS combined with stir bar sorptive extraction (SBSE). A total of 19 bound volatile compounds were identified, including phenols, terpenes, aldehyde, ester and alcohols. The concentrations of terpenes especially nerol and geraniol, and β-Damascenone, a C13-norisoprenoid, contributes flowery and slightly fruity aromas were signiflcantly increased in enzyme treated. These results suggest the potential application of this yeast β-glucosidase as an aroma-enhancing enzyme in winemaking.