Leticia Martínez González

Enzymatic activity of lactic acid bacteria (with antimicrobial properties) isolated from a traditional Spanish cheese

Twenty-four strains of lactic acid bacteria (LAB) isolated from a traditional Spanish cheese (Genestoso cheese) were evaluated for their enzymatic activities (acidifying and proteolytic abilities and carboxypeptidase, aminopeptidase, dipeptidase, caseinolytic and esterase activities), in order to select indigenous strains of technical interest for the manufacture of cheese. These strains were selected on the basis of their antimicrobial activity relative to five reference strains and were identified as Lactococcus lactis subsp. lactis (thirteen strains), Leuconostoc mesenteroides (two strains), Leuconostoc pseudomesenteroides (one strain), Lactobacillus paracasei (two strains), Lactobacillus plantarum (one strain) and Enterococcus faecalis (five strains). Lactococcus strains were those that showed the greatest degree of acidifying and proteolytic activity. The cell-free extracts (CFE) of L. paracasei exhibited the highest level of aminopeptidase activity. The highest level of caseinolytic activity was shown by the CFE of one strain of L. lactis. High values were also obtained with the CFE of Lactobacillus and of several Leuconostoc. The highest level of dipeptidase activity was found amongst the strains of L. lactis. Carboxypeptidase activity was generally very low or undetectable for the majority of strains. The greatest degree of esterolytic activity was detected for Enterococcus.

Microbiological and physico-chemical changes in Genestoso cheese, a Spanish acid curd variety, throughout ripening

Abstract The aim of this work was to study the microbiological and physico-chemical changes in four batches of Genestoso cheese (two ripened in autumn–winter and the other two in spring–summer) throughout manufacture and ripening. In general, the pH decreased more quickly in the cheeses manufactured in spring which, moreover showed values lower in aw and higher in salt/moisture content. The highest counts of aerobic mesophilic bacteria, presumptive lactococci and presumptive leuconostoc were reached in 2 day old cheeses. Lactobacilli and fungic flora became predominant with ripening. The counts of enterococci differed between the batches, but in general the maximum counts in kanamycin aesculin azide were obtained after ripening for 2 or 7 days. The counts on mannitol salt agar were very low and disappeared in the first days of ripening. Enterobacteriaceae were not detected after 15 days of ripening in the cheeses manufactured in spring nor in the 7 day old cheeses of an autumn batch.

Technological characterization of Geotrichum candidum strains isolated from a traditional Spanish goats' milk cheese.

Forty-one strains of Geotrichum candidum isolated from Armada cheese, Sobado variety, were screened for their enzymatic activities, including proteolytic and lipolytic activities and aminopeptidase activity. The highest extracellular proteolytic activity was detected for 8 strains with values ranging between 2.086 and 4.685 mM Gly L⁻¹ of milk. Extracellular lipolytic activity was high for all but one of the G. candidum strains, with values ranging between 67 and 131 μmol oleic mL⁻¹. Cell-bound lipase activity showed values which were considerably lower than those for extracellular activity, ranging between 32.50 and 42.50 μmol oleic mL⁻¹ and falling below 20 μmol oleic mL⁻¹ in 28 strains. Aminopeptidase activity was not very high in the cell-free extract (CFE) of any of the strains, showing the highest values toward the substrate Lys-p-nitroanilide, with levels of activity ranging between 6.12 and 10.05 UE mg⁻¹ protein in 8 strains. In accordance with the results obtained, four G. candidum strains were selected as co-cultures in order to study their role in the ripening of a semi-hard goats milk cheese.

Compositional and biochemical changes in Genestoso cheese, a Spanish raw cow's milk variety, during ripening

BACKGROUND Physicochemical characteristics, proteolysis and lipolysis were studied throughout the ripening of eight batches of a traditional Spanish variety made from raw cows milk, in order to establish a basis for its industrial production. RESULTS The main compositional characteristics of this cheese after 60 days of ripening were its high proportion of total solids (TS; 752 g kg⁻¹ of cheese), an average content of protein (452.8 g kg⁻¹ TS) and fat (475.1 g kg⁻¹ TS) and the presence of residual lactose (12.5 g kg⁻¹ TS). Its pH value (4.04) was extremely low. Phosphorus (5.13 g kg⁻¹ TS) and sodium (8.29 g kg⁻¹ TS) were the most abundant mineral elements in cheese, whereas calcium levels (1.92 g kg⁻¹ TS) were very low. Proteolysis extension and depth were very low, which resulted in almost zero degradation of αs1- and β-casein. Fat acidity increased during ripening, reaching final values of 50.1 mg KOH kg⁻¹ of fat. The main free fatty acid was C16:0, followed by C18:1 and C14:0. CONCLUSION These results suggest that this variety undergoes a limited proteolysis and moderate lipolysis during ripening. The low pH, low calcium content and limited proteolysis led to a crumbly texture in this cheese variety.