Hisao Kuroda

Characterization of Factors Involved in the Production of 2(E)-Nonenal during Mashing

To characterize the factors involved in the production of volatile aldehydes during mashing, a model mashing experiment was done. After we inactivated the endogenous lipoxygenase (LOX) activity in the mash by mashing at 70°C for 30 min, further incubation with recombinant barley LOX-1 stimulated the accumulation of 2(E)-nonenal; however, this effect was significantly reduced by boiling the mash sample. The result suggests that both LOX-1 and a heat-stable enzymatic factor are involved in the production of 2(E)-nonenal during mashing. Malt contained fatty acid hydroperoxide lyase-like activity (HPL-like activity) that transformed 9-hydroperoxy-10(E),12(Z)-octadecadienoic and 13-hydroperoxy-9(Z),11(E)-octadecadienoic acid into 2(E)-nonenal and hexanal, respectively. Proteinase K sensitivity tests showed that they are distinct factors. 9-HPL-like activity survived through the mashing at 70°C for 30 min but was inactivated by boiling, suggesting it will be the heat-stable enzymatic factor found in the model mashing experiment.

Identification and Functional Analyses of Two cDNAs That Encode Fatty Acid 9-/13-Hydroperoxide Lyase (CYP74C) in Rice

Fatty acid hydroperoxide lyase (HPL), a member of cytochrome P450 (CYP74), produces aldehydes and oxo-acids involved in plant defensive reactions. In monocots, HPL that cleaves 13-hydroperoxides of fatty acids has been reported, but HPL that cleaves 9-hydroperoxides is still unknown. To find this type of HPL, in silico screening of candidate cDNA clones and subsequent functional analyses of recombinant proteins were performed. We found that AK105964 and AK107161 (Genbank accession numbers), cDNAs previously annotated as allene oxide synthase (AOS) in rice, are distinctively grouped from AOS and 13-HPL. Recombinant proteins of these cDNAs produced in Escherichia. coli cleaved both 9- and 13-hydroperoxide of linoleic and linolenic into aldehydes, while having only a trace level of AOS activity and no divinyl ether synthase activity. Hence we designated AK105964 and AK107161 OsHPL1 and OsHPL2 respectively. They are the first CYP74C family cDNAs to be found in monocots.

Behavior of mono-, di-, and trihydroxyoctadecenoic acids during mashing and methods of controlling their production.

The behavior of mono-, di-, and trihydroxyoctadecenoic acids was investigated during laboratory-scale mashing under various conditions with a view to controlling their production. Using a malt in which the lipoxygenase activity was at only a trace level (less than 0.01 U/g) or starting the mashing at a higher temperature than that conventionally used (65 degrees C instead of 48 degrees C) significantly decreased the production of these hydroxy fatty acids. Lowering the pH of the mash to inhibit lipoxygenase activity and preventing O2 uptake by the mash using carbon dioxide were also effective in reducing the amounts of these acids produced during mashing. From the viewpoint of industrial-scale beer production, the prevention of O2 uptake by the mash was selected as an appropriate method for reducing oxidation during wort production without affecting the subsequent brewing process or the taste of the finished beer. After introducing oxidation prevention procedures, the content of trihydroxyoctadecenoic acids decreased by about 30% and the foam stability and taste were improved in commercial products brewed using less than 25% malts.

Oral Administration of a Hop Water Extract Ameliorates the Development of Dermatitis Induced by the Periodical Topical Application of a Mite Antigen in Atopic Dermatitis Model NC/Nga Mice

We investigated the inhibitory effect of an oral administration of a hop water extract (HWE) on the development of dermatitis by using NC/Nga atopic dermatitis model mice. The induction of allergic dermatitis was conducted by tape-stripping and topical application of a mite antigen (Dermatophagoides farinae) on to the ear once a week for 10 weeks. HWE was orally administered at a dose of 100 or 500 mg/kg. The total immunoglobulin E (IgE) concentration in serum and the ear thickness were periodically examined. Finally, the antigen-specific IgE level in the serum and the production of interleukin (IL)-4, IL-12 and interferon (IFN)-γ from splenocytes and cervical lymph node cells were measured. The oral administration of HWE significantly inhibited the increase of total IgE production and ear swelling throughout the experimental period. The production of IL-12 was significantly lower in the HWE administered group than in the control group. The results suggest that the intake of HWE may be effective in preventing and alleviating the development of atopic dermatitis-like skin disease.

Characterization of 9-fatty acid hydroperoxide lyase-like activity in germinating barley seeds that transforms 9(S)-hydroperoxy-10(E),12(Z)-octadecadienoic acid into 2(E)-nonenal.

Previously, we reported that 2(E)-nonenal, having a low flavor threshold (0.1 ppb) and known as the major contributor to a cardboard flavor (stale flavor) in stored beer, is produced by lipoxygenase-1 and a newly found factor named 9-fatty acid hydroperoxide lyase-like (9-HPL-like) activity in malt. To assess the involvement of 9-HPL-like activity in beer staling, we compared the values of the wort nonenal potential, an index for predicting the staleness of beer, with the lipoxygenase and 9-HPL-like activity of 20 commercial malts. There was a significant correlation between the malt 9-HPL-like activity and the values of wort nonenal potential (r=0.53, P<0.05), while the correlation between malt lipoxygenase activity and the wort nonenal potential was statistically insignificant. Analysis of the partially purified 9-HPL-like activity from embryos of germinating barley seeds indicated that 9-HPL-like activity consisted of fatty acid hydroperoxide lyase and 3Z:2E isomerase.