The ability of lactic acid bacteria to grow in beer has been studied using 31 beers, 13 strains of Lactobacillus and 3 strains of Pediococcus isolated from wort or beer. In 3 beers all the micro organisms were able to grow, in 5 beers none of them developed and diverse results were obtained with the remaining 23 beers. Resistance of the beers to spoilage was not correlated with values of pH, specific gravity, total or free amino nitrogen, individual or total fermentable sugars, colour or levels of sulphur dioxide. Resistant beers became sensitive after certain filtration treatments and after heating at 80°for 15 minutes, but not after treatment at 60°. Resistance to spoilage is tenta tively attributed to the presence of a yeast metabolite which is heat-labile. The lactic acid bacteria varied in their ability to grow in beer but those possessing a broad range of biochemical abilities had the greater propensity to cause spoilage.
A commercially produced system for the identification of Lactobacillus, by which the reactions of concentrated cell suspensions towards 50 substrates may be determined, is useful for the characterization of strains of Pediococcus. Suitable conditions for inoculum preparation vary for slow and fast growing strains; the influence of cell concentration on the results is described. The reactions are classified in terms of their value for species characterization and the results are shown to agree well with those in other studies where classical procedures have been used.
A commercially-available antiserum for the identification of group D strains of Streptococcus contains antibodies which react with Pediococcus and Micrococcus, and provides a convenient method to detect these genera in yeast, wort and beer. After suitable adsorption it can be used to distinguish between Pediococcus and Micrococcus and, within each genus, to differentiate between groups normally found in a brewery environment and those from other sources.
Antisera have been prepared using Lactobacillus brevis, L. casei var. alactosus and L. casei var. rhamnosus. The interaction between these and the acid-soluble antigens of a range of Lactobacillus strains, most of which were isolated from beer, has been studied using a gel diffusion precipitin test; the fluorescent anti body staining technique was used to observe the reaction between whole cells and the antisera. Gel diffusion demonstrated the presence of specific, group and non-specific antibodies. Thus, each antiserum contained (i) a specific antibody towards the organism used to produce the antiserum and towards others in the same taxonomic unit and (ii) a non-specific antibody reacting with antigens from each of the strains of Lactobacillus and also with cells of Pediococcus cerevisiae and Saccharomyces cerevisiae. Additionally (iii) a serum prepared against L. casei var. rhamnosus contained a group antibody which reacted with an antigen present in Streptobacteria but not in Betabacteria, whilst an antiserum made using L. brevis contained group antibodies reacting with L. brevis and L. plantarum. Fluorescent antibody staining confirmed these distinctions and, using adsorbed sera, allowed the rapid identification of lactobacilli which cause beer spoilage.
Quantitative and semi-quantitative methods are given for estimating alginate, carrageenan and furcellaran at low concentrations in beer. A number of commercial beers and experimental beers known to have been brewed with either copper finings or auxiliary finings containing these acidic polysaccharides as active ingredients were analysed for alginate, carrageenan and furcellaran residues. The results show that alginate and carrageenan do not occur in finished beers at levels greater than 1 mg/litre. Using a serological technique which is more sensitive for furcellaran, it was found that levels of furcellaran in most finished beers were below 0 5 mg/litre, though a few beers contained this polysaccharide at about 0-5 mg/litre.
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