Diversity of Geotrichum candidum strains isolated from traditional cheesemaking fabrications in France

Characterization of Lactobacillus strains and monitoring by RAPD-PCR in controlled fermentations of “Almagro” eggplants

The characterization of 23 Lactobacillus strains was performed. The strains were assayed for biogenic amine-forming capacity, hydrogen peroxide production, pectin esterase, cellulase and polygalacturonase production, growth rate, acidifying capacity and salt tolerance. Three strains were selected which belonged to the species, Lactobacillus brevis, Lactobacillus plantarum and Lactobacillus fermentum. Different starter cultures prepared as combinations of these three strains were assayed in pilot scale fermentations and Randomly Amplified Polymorphic DNA (RAPD) analysis, using a previously selected random primer, was applied for monitoring the inoculated strains. The course of fermentations was similar in all batches but sensorial analysis of eggplants fermented using a mixed culture of the three strains displayed the best results, and no differences were obtained when compared with commercial eggplants.

Interests in Geotrichum candidum for cheese technology

The wide genotypic and phenotypic diversity of Geotrichum candidum strains does not facilitate its classification as yeast or a yeast-like fungus that is still a matter of debate. Whatever its classification, G. candidum possesses many different metabolic pathways that are of particular interest to the dairy industry. G. candidum is of importance in the maturation of cheese, and much is known about its direct contribution to cheese ripening and flavour formation. Its diverse metabolic potential means that G. candidum can play an important role in the ripening of many soft and semi-hard cheeses and make a positive contribution to the development of taste and aroma. It may also influence the growth of other microorganisms, both valuable and detrimental. The significance of the presence of G. candidum in cheese depends on the particular type of production and on the presence of biotypes featuring specific types of metabolism. However, in situ metabolic pathways involved in cheese ripening and their regulations are mainly unknown. The information available provides a good understanding of the potential of G. candidum strains that are used in cheese manufacture, and permits a better choice of strain depending on the characteristics required. The biochemical activities of G. candidum and its application in the dairy industry are presented in this review.

Phenotypic and genotypic characterization of lactobacilli isolated from Spanish goat cheeses

Lactic acid bacteria from 18 Spanish goat cheeses produced by seven dairies were isolated to evaluate the genetic diversity of this bacterial community. 136 representative isolates were characterized by phenotyping and Randomly Amplified Polymorphic DNA (RAPD-PCR) analysis. Ten species were identified with predominance of Lactobacillus paracasei subsp. paracasei. The presence of L. curvatus, L. pentosus, L. cellobiosus and L. rhamnosus has not hitherto been reported in Spanish goat cheeses. A high degree of genetic diversity was found for L. paracasei subsp. paracasei, L. curvatus and L. plantarum. Some of the identified strains displayed strong acidifying and proteolytic capacities.

Purification and properties of a novel glycine amino peptidase from Actinomucor elegans and its potential application

AIMS

To study the properties and show the potential application of a glycine aminopeptidase from Actinomucor elegans.

METHODS AND RESULTS

The enzyme was estimated to have molecular mass of 320 kDa by gel filtration and the subunit size of 56.5 kDa by SDS-PAGE. It hydrolysed glycine from substrate more efficiently than other amino acids. The optimal temperature for this enzyme was 40 degrees C and at pH 8.0 it showed its highest activity. The Km and Kcat of the enzyme for glycine-beta-naphthylamine was 0.24 mm and 100.8 s(-1), respectively. Zinc, copper, cadmium and o-phenanthrolin suppressed almost all enzyme activities at the concentration of 1.0 mm. In the process of hydrolysing proteins, it could improve the protease activity considerably.

CONCLUSIONS

It was a hexamer metalloenzyme which was specific for the substrates with glycinse residue at the N-terminal and some metal cations were needed to maintain its activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the properties of a novel aminopeptidase and shows its potential application in the process of the food industry.

Dual influence of the carbon source and L-methionine on the synthesis of sulphur compounds in the cheese-ripening yeast Geotrichum candidum

The effect of the carbon source and l-methionine on the ability of Geotrichum candidum to produce volatile sulphur compounds (VSC) was studied. This yeast was cultivated in a synthetic medium supplemented with various carbon sources and l-methionine at different concentrations. Both glycerol and glucose significantly increased VSC production by G. candidum. Unlike the effect on the l-methionine- and 4-methylthio-2-oxobutyric acid-demethiolating activities, the supply of a carbon source had a dramatic effect on the activity of aminotransferase, a key enzyme in l-methionine catabolism. An increase in the initial concentration of l-methionine resulted in a rise in the production of sulphur compounds (VSC, 4-methylthio-2-oxobutyric acid) but had limited effect on l-methionine-catabolising enzyme activities. Evidence for the existence of a dual effect of the carbon source and l-methionine on VSC biosynthesis was obtained in this study.

Genetic diversity among Geotrichum candidum strains from various substrates studied using RAM and RAPD-PCR

AIMS

Assessment of genetic diversity within the species Geotrichum candidum and development of tools to trace the strains that play an important role in the agro food industry.

METHODS AND RESULTS

RAM-PCR and RAPD-PCR techniques were assessed for their ability to discriminate 57 strains of various morphotypes, substrates and geographical origin. The techniques were complementary and, when combined, allowed us to discriminate isolates. Moreover, we established a link between a taxon and its occupation of an ecological niche, which should not be confused with the substrate of isolation.

CONCLUSIONS

We observed a high degree of diversity, which could be linked to the variety of the ecological niches chosen and to the high degree of morphological polymorphism encountered within the species.

SIGNIFICANCE AND IMPACT OF THE STUDY

Used in combination, RAM-PCR and RAPD-PCR permit traceability and monitoring systems for G. candidum strains during food processing.