Influence of lactic acid and cellulolytic bacteria on the physicochemical parameters of alfalfa silage

The study is aimed at studying the effect of a microbiological preparation consisting of lactic acid bacteria, thermophilic streptococci and cellulolytic bacteria on the quality of alfalfa silage with different dry matter content. Determined pH, content of organic acids, dry matter and nutrients, including carbohydrates. Inoculant application increased crude protein, crude fat and crude fiber and reduced water-soluble carbohydrates in silage. The preservation of nutrients in the test samples was higher than that of the control. pH corresponded to optimal values; however, lactic acid fermentation proceeded more intensively in the sample with an increased dry matter content.

Comparison of Statistical Methods for Identification ofStreptococcus thermophilus,Enterococcus faecalis, and Enterococcus faecium from Randomly Amplified Polymorphic DNA Patterns

ABSTRACT Thermophilic streptococci play an important role in the manufacture of many European cheeses, and a rapid and reliable method for their identification is needed. Randomly amplified polymorphic DNA (RAPD) PCR (RAPD-PCR) with two different primers coupled to hierarchical cluster analysis has proven to be a powerful tool for the classification and typing of Streptococcus thermophilus,Enterococcus faecium, and Enterococcus faecalis (G. Moschetti, G. Blaiotta, M. Aponte, P. Catzeddu, F. Villani, P. Deiana, and S. Coppola, J. Appl. Microbiol. 85:25–36, 1998). In order to develop a fast and inexpensive method for the identification of thermophilic streptococci, RAPD-PCR patterns were generated with a single primer (XD9), and the results were analyzed using artificial neural networks (Multilayer Perceptron, Radial Basis Function network, and Bayesian network) and multivariate statistical techniques (cluster analysis, linear discriminant analysis, and classification trees). Cluster analysis allowed the identification of S. thermophilus but not of enterococci. A Bayesian network proved to be more effective than a Multilayer Perceptron or a Radial Basis Function network for the identification of S. thermophilus, E. faecium, and E. faecalis using simplified RAPD-PCR patterns (obtained by summing the bands in selected areas of the patterns). The Bayesian network also significantly outperformed two multivariate statistical techniques (linear discriminant analysis and classification trees) and proved to be less sensitive to the size of the training set and more robust in the response to patterns belonging to unknown species.

Production and monomer composition of exopolysaccharides by yogurt starter cultures

As components of starter cultures for Bulgarian yogurt, Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus revealed extensive exopolysaccharide (EPS) production activity when cultivated in whole cow's milk. The polymer-forming activity of thermophilic streptococci was lower (230-270 mg EPS/L) than that of the lactobacilli (400-540 mg EPS/L). Mixed cultures stimulated EPS production in yogurt manufacture, and a maximum concentration of 720-860 mg EPS/L was recorded after full coagulation of milk. The monomer structure of the exopolysaccharides formed by the yogurt starter cultures principally consists of galactose and glucose (1:1), with small amounts of xylose, arabinose, and/or mannose.Key words: Streptococcus thermophilus, Lactobacillus bulgaricus, starter cultures, yogurt, exopolysaccharides.

FROZEN CONCENTRATED CULTURES OF LACTIC STARTER BACTERIA. A REVIEW1

Concentrated starter cultures are now used routinely in many food fermentations. Recent literature concerning preparation and performance of such cultures is reviewed. Batch procedures are preferred over continuous culture procedures for preparing concentrated cultures. Most attention has been focused on bacteria used to manufacture cultured milk products. Performances of concentrated cultures of lactic streptococci, leuconostocs, lactobacilli, and thermophilic streptococci in preparing cultured dairy products have compared favorably to those of traditionally prepared milk cultures. Storage in liquid nitrogen appears to be the best method for long term holding of concentrated cultures.