ワイン醸造におけるキラー酵母の利用

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Because grape musts are usually not pasteurized before fermentation in wine making, many wild yeasts from natural grapes are brought into fermenting musts, resulting in inferior products. Therefore, for producing a good wine with pure cultures, we bred a useful killer wine yeast (2HY-1) of Sacharomyces cerevisiae by back-crossing KL-88,a wild killer sake yeast (K_1 type), with a repetitive parent, OC-2,one of the best wine yeasts. In the same way, useful cryophilic killer wine yeasts (2HYL-2,2HYG-1) were also bred. Furthermore, we obtained a useful killer sherry hybrid (SK-4) by protoplast fusion using polyethylene glycol between an S. cerevisiae killer wine yeast (2HY-1) and S. bayanus, a useful sherry yeast (SN).The hybrids (K_1 type killer) were highly tolerant of SO_2 and killed only Saccharomyces yeasts in grape must. Especially, they could kill Saccharomyces killer yeasts except K_1 type killers, that is, K_2 or K_3 killer type yeast strains (NCYC 738 or NCYC 761) and 3 nesw killer type yeast strains (Y-1,Y-6,and Y-9) belonging to S. cerevisiae, which were isolated from musts or pomaces in Japanese wineries. Y-1 killer type strains were isolated with high frequency and the molecular weight of the killer plasmid (M-dsRNA) of this type was larger than that of the killer plasmids of K_1,K_2,and K_3,which had been described previously. On the other hand, no killer plasmid (M-dsRNA) was detected in the Y-6 or Y-9 strains. In winemaking using the useful killer wine hybrid as starter, no sensitrive yeasts were detected in the last stage of fermenting must, because they were killed by the killer hybrid. Most of the neutral yeasts such as Kloeckera and Torulopsis that were abundant in the grape juice before the addition of the starter yeast disappeared in the middle stage, because they were markedly inhibited by the SO_2 added and the alcohol formed. In sherry making using the useufl killer sherry hybrid as starter, it grew in the wine, and a film formed of a single killer strain on the surface of the wine, even if many wild yeasts belonging to pseudo-film-forming yeasts (non-killer) were in the wine.These results show the possibility of fermenting musts or film formation with only a single strain of useufl killer yeasts without contamination by other yeast strains.In addition, we found that killer yeasts of the genus Hansenula were distributed on line 1 and line 2 of the phylogenetic lines proposed by Wickerham. Especially, the killer yeasts with saturn-shaped ascospores (line 1a) such as H. beijerinckii, H. saturnus, and H. mrakii showed very strong killer activity against yeasts belonging to various genera, including all Saccharomyces species. The killer toxin of H. mrakii was stable against heat treatment (boiling for 3 min at pH 4.0) and in a wide pH range (4〜11), while it was pronase sensitive. H. mrakii will be useufl for breeding of killer wine yeasts possessing much stronger killer activity than K_1 type killer yeasts for winemaking, and the killer toxins will have a wide application as antibiotics.
1984-09-25

著者

原昌道
大阪国税局鑑定

ワイン醸造におけるキラー酵母の利用

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