Sekvenace genomu spodní pivovarské kvasinky Klíčová slova: genom, kvasinka, Saccharomyces pastorianus ■ ■ 1 ÚVOD Pivovarské kvasinky se dělí do dvou skupin: na svrchně kvasící kmeny, používané pro výrobu piv typu ale, a na spodně kvasící kmeny, produkující piva typu ležák. Obě skupiny se řadí do druhu Saccharomyces. Kmeny spodních a svrchních kvasinek se však vzájemně liší fyziologickými a genetickými vlastnostmi a jedná se tedy o dva rozdílné druhy rodu Saccharomyces. Svrchní kvasinky jsou geneticky blízké rodu Saccharomyces cerevisiae, zatímco spodní kvasinky tvoří heterogenní druh a jsou jedním z nejlepších příkladů přirozených hybridů kvasinek (Saerens et al ., 2010). Kvůli jejich odlišnosti od svrchních kvasinek byly spodní kvasinky Hansenem nazvány Saccharomyces carlsbergensis (Saerens et al ., 2010). Později byly spodní kvasinky zařazeny do rodu Saccharomyces pastorianus (Martini a Martini, 1987). Studie založené na hybridizaci dvou molekul DNA ukázaly, že S. pastorianus obsahuje dva typy chromozomů, které byly označeny jako S. cerevisiae-typ a S. bayanus-typ (Tamai et al ., 1998; Yamagishi a Ogata, 1999). Jak bylo u mezidruhového hybridu předpokládáno, byly u S. pastorianus nalezeny dva rozdílné ortology u téměř všech testovaných genů. Jednotlivé geny spodních kvasinek byly skutečně velmi podobné buď genům S.
Cejnar R., Mestek O., Dostálek P. (2013): Determination of silicon in Czech beer and its balance during the brewing process. Czech J. Food Sci., 31: 166-171.Inductively coupled plasma mass spectrometry was used for the determination of silicon in beer samples from the Czech market and in brewing raw materials and semiproducts. The content of silicon in barley malt depended on the barley variety and growing region. The goal was to establish silicon concentration in Czech beer and to find out which processes are the most significant in terms of silicon concentration in beer. The silicon concentration in Czech beer ranged from 16 mg/l to 113 mg/l depending especially on two factors. Firstly, the silicon content in beer increased as the original wort concentration and increased secondly, during decoction mashing, silicon from malt was leached to a much greater extent than in the case of infusion mashing.
Compared to most other alcoholic beverages, the shelf life of beer is much more limited due to its instability in the bottle. That instability is most likely to appear as turbidity (haze), even sedimentation, during storage. The haze in beer is mostly caused by colloidal particles formed by interactions between proteins and polyphenols within the beer. Therefore, beers are usually stabilized by removing at least one of these components. We developed and constructed a Saccharomyces cerevisiae strain with a proline-rich QPF peptide attached to the cell wall, using the C-terminal anchoring domain of α-agglutinin. The QPF peptide served to bind polyphenols during fermentation and, thus, to decrease their concentration. Strains displaying QPF were able to bind about twice as much catechin and epicatechin as a control strain displaying only the anchoring domain. All these experiments were done with model solutions. Depending on the concentration of yeast, uptake of polyphenols was 1.7-2.5 times higher. Similarly, the uptake of proanthocyanidins was increased by about 20 %. Since the modification of yeasts with QPF did not affect their fermentation performance under laboratory conditions, the display of QPF appears to be an approach to increase the stability of beer.
Since modification of yeasts with ALDC variants did not affect their fermentation performance, the display of α-acetolactate decarboxylase activity is an effective approach to decrease the formation of diacetyl during beer fermentation.
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