MUSTAPHA NEDJMA (1), Lucie Hazelwood (2), Huu Vang Nguyen (3)
(1) nedjman@aol.com; (2) NIZO Food Research BV, Netherlands; (3) INRA, AgroParisTech, Thiverval-Grignon, France
Maltose (60–70%), maltotriose (14–20%), and glucose (10–15%) are the
most abundant fermentable sugars in wort. In case of incomplete
fermentation, maltotriose can cause a range of detrimental qualitative
problems in beer and ethanol loss. Furthermore, yeast which comes
pre-grown on glucose biomass cannot fully adapt itself to wort
composition during beer fermentation. The development and production of
selected beer yeast for a fast and complete metabolization of these
three main fermentable sugars in wort has been considered. The
performance of fermentation was followed through the optimization of the
culture medium, reproducing accurately the wort composition by
monitoring yeast growth, ethanol synthesis, original gravity and
attenuation, and sugar consumption during the fermentative process. Beer
flavor was evaluated through the content of fusel alcohols, volatile
esters, and aroma compounds. The expression of AGT1 (MAL11) – MTT1
(MAL31-like) is a limiting step in the fermentation of maltotriose in
the beer yeast actually used. The selected strains expressing a
maltotriose transporter show a significant difference in kinetic
fermentation and metabolization of sugars. The MTT1 transporter has a
high affinity toward maltotriose. The presence of MTT1 in the selected
strains and its induction by the composition of the medium during
propagation leads to a higher efficiency in maltotriose consumption. The
medium constitution for the biomass production of the selected yeast
strains CBS 1513 (ex Saccharomyces carlsbergensis) and CBS 1503 (ex S. monacensis)
“traditional medium” showed better gene expression in the maltose
medium. The results obtained confirmed that the same strain produced on
maltose medium gave more capacity to metabolize maltose and maltotriose.
Mustapha Nedjma was the director of the Research and Development
Department within AEB Group and was in charge of biotechnologies since
1997 in the facility based in Ile de France (near Paris). He received
two postdoctoral positions specializing in microbiology, enzymology, and
fermentation. He has published several papers, reviews, and patents for
the beverage industry, especially in the beer, wine, and juice fields.
His current research activities include beer fermentation and production
of enzymes under solid-state fermentation.
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