Maltose Transport by Brewer's Yeasts in Brewer's Wort

Abstract

The kinetics of maltose transport by two industrial yeasts were studied. The ale and lager strain each showed both high and low affinity transport. For the lager strain, maltose transport was only weakly inhibited by maltotriose, sucrose and trehalose, suggesting that its dominant maltose transporter is the maltose-specific type coded by MALx1 genes. For the ale strain, maltose transport was strongly inhibited by maltotriose, sucrose and trehalose, suggesting that its dominant maltose transporter may be the AGT1-encoded type that also carries these sugars. Also glucose inhibited transport by the ale strain more than that by the lager strain. Instantaneous inhibition by ethanol at concentrations met in brewery fermentations was moderate (about 25% at 50 g ethanol · L -1 ). The apparent Vmax for high affinity transport increased about 100-fold between 0 and 30°C, whereas the Km (3 ± 1 mM) was constant. Standard activities of maltose transport and maltase were followed through pilot fermentations of 11-24°P worts. Rapid (20 s) measurements of the zero-trans-rate of maltose uptake were also made with each day's yeast (rapidly harvested and washed) in reaction mixtures containing the same day's wort labelled with tracer 14 C-maltose. Results suggested that maltose uptake is the dominant factor controlling the rate of maltose utilization in these wort fermentations.Key words: Brewing fermentation, catabolite inactivation, glucose repression, maltose transporters, transport inhibition. -2863(9'8-32The main fermentable sugars in brewing fermentation are maltose, glucose and maltotriose. These sugars interfere with each others' catabolism (reviewed by SpencerMartins et al. 23 ). Maltose transporters and ␣-glucosidases (maltases) are encoded, respectively, by MALx1 and MALx2 genes (x = 1-4 and 6, corresponding to different MAL loci, located on different chromosomes and each containing one or more copies of the different MAL genes). MALx3 produces an activator of the other two MAL genes. These genes are repressed by glucose and also by fructose and sucrose 5 . Especially during N-starvation 16 , glucose and maltose itself 9,21 induce catabolite inactivation of maltose transporters but not of maltase 6 . This inactivation involves the proteolysis of already existing transporter molecules. Ethanol is known to inhibit the endocytosis and subsequent proteolysis of maltose transporter, which could play a role in fermentations conditions where the ethanol concentration is high at the end of the process 2,15 .In addition, maltose and maltotriose compete for the same transporter in strains containing the AGT1-coded transporter, which carries several ␣-glucosides 8,24 , whereas glucose and maltose inhibit each other's transport in some strains, although they are not carried by the same transporters 3,23 . Jespersen et al. 11 screened 5 ale yeasts and 25 lager yeasts and found that all contained MALx1 genes and all but one also contained AGT1 genes.It has often been suggested that brewing fermentations could be accelerated if yeast...

Improved Fermentation Performance of a Lager Yeast after Repair of Its AGT1 Maltose and Maltotriose Transporter Genes

“…Transformants of strain A15 (integrants 1, 2, and 14) engineered in this way fermented 15 and 24°P worts faster and more completely than did strain A15, producing beers containing more ethanol and lower levels of residual maltose and maltotriose. This result confirms earlier findings (17,27) that the rate of ␣-glucoside uptake is a major factor limiting the rate of wort fermentation. The size of the changes was economically significant (Table 5): primary fermentation times for 15 and 24°P worts were decreased by 8 to 20% and 11 to 37%, respectively, which represents a marked increase in annual output from the same-size brew house and fermentor facilities, and for 25°P worts the final ethanol concentrations were increased by 2% (from about 93 to 95 g of ethanol ⅐ liter Ϫ1 ), giving a similar increase in yield from raw materials.…”

“…Maltose transport seems to have a high level of control over the fermentation rate. Thus, during the early and middle stages of fermentation of brewer's wort by a lager yeast, the specific rate of maltose consumption was the same as the specific zero-trans maltose uptake rate measured off line with each day's yeast in each day's wort spiked with [ 14 C]maltose (27). Furthermore, introducing a constitutive MAL61 (maltose transporter) gene into a brewer's yeast on a multicopy plasmid accelerated the fermentation of high-gravity worts (17).…”

“…The 16 and 25°P worts were oxygenated immediately before use to 10 and 12 mg of oxygen ⅐ liter Ϫ1 , respectively. Pitching yeasts were grown and fermentations were performed essentially as described earlier (27), except that main yeast growths and 24°P fermentations were at 18°C. The precultures of 100 ml of autoclaved YP containing 4% maltose in 250-ml Erlenmeyer flasks were inoculated with 500 l of glycerol stock (100 mg yeast) and grown overnight at 24°C to an OD 600 between 6 and 10 (series A) or 20 (series B).…”

Regulation of Saccharomyces cerevisiae maltose fermentation by cold temperature and CSF1

“…This probably is a consequence of a higher energy demand for maintenance under cold temperature, affecting maltose fermentation due to the further energy requirement for active maltose uptake by yeasts (16). Our results are also in agreement with a strong temperature dependence recently observed for maltose transport by yeast (10). The csf1∆ strain did not ferment or grow on maltose (Fig.…”

Application of Non-Saccharomyces Yeasts Isolated from Kombucha in the Production of Alcohol-Free Beer

“…Looking at the main sugars of wort, only the control strain WLP001 was able to ferment maltose and maltotriose. The disability to ferment maltose and maltotriose indicates the absence of a maltose transporter and the enzyme maltase [26,27]. The sugar fermentation patterns were confirmed by the sugar analysis of the final beers.…”