Screening of Lactobacillus spp. and Pediococcus spp. for glycosidase activities that are important in oenology

The definitive version is available at www.blackwell-synergy.comAims: To assess glycosidase activities from a range of Lactobacillus and Pediococcus species and characterize these activities under conditions pertinent to the wine industry. Methods and Results: Lactic acid bacteria were cultured in MRS broth supplemented with apple juice before being harvested, washed and assayed for glycosidase activity using ρ-nitrophenol-linked substrates. All strains exhibited a detectable capacity for the hydrolysis of the β- and α-D-glucopyranosides. The magnitude of these activities and their response to the physico-chemical parameters investigated varied in a strain-dependent manner. The use of an assay buffer with a pH below 4 generally resulted in a reduced hydrolysis of both substrates while temperature optima ranged between 35 and 45°C. The effect of the inclusion of ethanol in the assay buffer (up to 12%, v/v) ranged from near complete inhibition to increases in activity approaching 80%. With the clear exception of a single strain, glucose and fructose (0•1–20 g l⁻¹) acted as inhibitors. An assessment of glycosidase activity during simultaneous exposure to glucose and ethanol at a pH of 3•5 suggested that ethanol decreased loss of activity under these wine-like conditions. Conclusions: Lactobacillus spp. and Pediococcus spp. possess varying degrees of β- and α-D-glucopyranosidase activities, which in turn are influenced differently by exposure to ethanol and/or sugars, temperature and pH. Several strains appeared suited for further evaluation under winemaking conditions. Significance and Impact of the Study: This work highlights the fact that strains of Lactobacillus and Pediococcus have the potential to influence the glycoside composition of wine. Tailoring of wine may therefore be possible through selective application of strains or enzymatic extracts thereof

On the persuasiveness of visual arguments in mathematics

Two experiments are reported which investigate the factors that influence how persuaded mathematicians are by visual arguments. We demonstrate that if a visual argument is accompanied by a passage of text which describes the image, both research-active mathematicians and successful undergraduate mathematics students perceive it to be significantly more persuasive than if no text is given. We suggest that mathematicians' epistemological concerns about supporting a claim using visual images are less prominent when the image is described in words. Finally we suggest that empirical studies can make a useful contribution to our understanding of mathematical practice