Ewe's Milk Cheese Research Articles

Identification and characterization of proteolytic activity of Enterococcus spp. isolated from milk and Roncal and Idiazábal cheese

Roncal and Idiazábal cheeses are manufactured from ewe's milk in the Autonomous Region of Navarre in Spain. Levels of enterococci are high in these cheeses and in other types of ewe's-milk cheeses. The present study has identified enterococci present in the milk used and in the Roncal and Idiazábal cheeses after 120 days of ripening. A total of 282 strains were isolated and identified, and the cytoplasmic and extracellular enzymatic activities of some of the strains were assessed. The dominating species were Enterococcus faecalis, which accounted for 85% of the total both in the milk as well as in the two types of cheese, and Enterococcus faecium, Enterococcus durans, and Enterococcus avium which were present in lower proportions. Aminopeptidase and proteinase activity levels in enterococci were low, and considerable variation between strains of the same species was recorded, highlighting the need to study individual strains when selecting the most suitable bacteria as a starter culture. Aminopeptidase activity levels for the enterococci were appreciably higher at pH 7 than at pH 5.5, hence aminopeptidase activity by enterococci would appear to be less significant in the normal manufacturing conditions of the two cheeses.

Hygienic Conditions and Microbial Contamination in Six Ewe's-Milk-Processing Plants in Sardinia, Italy

In Sardinia, ewe's milk is almost exclusively used for cheese manufacture, and it is usually processed in small dairies which do not have sufficient technical and scientific knowledge for largescale controlled production. This study was carried out to identify the sources of contamination and the kinds of contaminating microorganisms present in six ewe's milk processing plants in Sardinia. Samples were collected during production hours three times over a period of 6 months. Raw milk, heat-treated milk, curd, 30-day-old cheese, lactic culture, rennet, and water used in processing lines were analyzed and the microbial contamination of air and surfaces was evaluated. Total mesophilic aerobic counts, coliforms, Escherichia coli, gram-negative psychrotrophs, Staphylococcus aureus, Salmonella spp., Listeria spp., yeasts, and molds were determined. Our survey confirmed that the production offood of high microbiological quality is strictly dependent on the microbiological quality of the raw material, optimization of the parameters for the heat treatment, water of potable quality, well-defined cleaning and disinfection procedures, and properly hygienic processing conditions. In fact, only plants characterized by raw milk and rennet of acceptable quality, generally clean work surfaces, and low microbial counts in the air of working areas made finished products of high microbiological quality. Standardization of technological parameters and achievement of properly hygienic processing conditions will help minimize the risk of developing food-safety problems, in compliance with public health regulatory requirements. These actions would help guarantee an adequate quality of Sardinian ewe's milk cheeses and might also lead to access to the international market.

Effects of processing conditions on the caseinolytic activity of crude extracts of Cynara cardunculus L/Efectos de las condiciones de extracción sobre la actividad caseinolítica de los extractos de Cynara cardunculus L

Four processing parameters (time of grinding, pH of buffer, salt concentration of buffer, and homogenization time) involved in the liquid extraction of proteinases from flowers of the wild thistle ( Cynara cardunculus), were studied for their effects on final caseinolytic activity by a surface response method. The caseinolytic activity was assayed spectrophotometrically using o-phthal dialdehyde. An empirical quadratic model was applied to experimental data pertaining to the average enzymatic activity and equations describing the optimal conditions were obtained. Simultaneous solution of these equations for the local maxima indicated that, within the range tested, the maximum (estimated) specific caseinolytic activity (around 9.5 μmol of equivalent leucine/min.g of thistle flower) was obtained by grinding the flowers for 36 s, using an extrac tion buffer with a pH of 5.9 and a salt content of 0% (w/w), and homogenizing the ground flower/buffer suspension for 15 min. These data are of use in the optimization of extraction proce dures, which are of relevance to the production of standardized plant rennets suitable for the large scale manufacture of ewe's milk cheese.

Effects of freezing and frozen storage on the microstructure and texture of ewe's milk cheese

Semi-hard ewe's milk cheeses, frozen immediately after manufacture either slowly at −35 °C or rapidly at −80 °C and stored at −20 °C for 4 months were studied for microstructural and textural characteristics during subsequent ripening. Two control groups were used to establish the effect of freezing: the fresh unfrozen cheese and cheese thawed immediately after freezing. Freezing proper did not result in any marked changes in the textural parameters of the cheeses, but considerable changes were found in slowly frozen cheeses after 4 months of frozen storage. Shear strength values were lower in all frozen and stored cheeses, particularly in cheese samples frozen slowly compared to those in the unfrozen control batch. This parameter and firmness values were significantly lower in both slowly and rapidly frozen cheeses at the completion of ripening. Ripening tended to offset differences in elasticity, noticeable in the cheeses during the first 30 days of ripening. Light microscopy and electron microscopy revealed small cracks and ruptures in the cheeses which could not be observed by the naked eye. More extensive damage to the cheese microstructure was found in slowly frozen cheese samples stored frozen for 4 months.

The effects of freezing and frozen storage of ewe's milk cheese on the viability and proteolytic activity of lactococci used as a starter

A study has been conducted on the effect of two freezing conditions (slow and fast) and frozen storage of ewe's milk cheese (−20 °C for 4 months) on the viability and the proteolytic (cascinolytic and aminopeptidase) activity ofLactococcus lactis subsp.lactis andL. lactis subsp.cremoris used as starters in the manufacture of cheese. The study was carried out on the lactococci subjected to freezing and frozen storage, either in the cheeses or in curds simulating a model system. As well as other parameters used to quantity microbial activity, the total viable counts during the subsequent cheese ripening have been analysed in the frozen cheeses. Frozen storage of the investigated lactococci, either in the cheese or in model systems, gave rise to significant decreases in the caseinolytic and aminopeptidase activities greater than did freezing alone. No clear differences were found in enzymatic activity values when using slow or fast freezing conditions. Storage of the cheeses under frozen conditions also affected microbial viability and consequently caused a greater decrease of the viable flora during subsequent ripening of the frozen stored cheeses.

Biochemical characteristics of a semi-hard ewe's-milk cheese

Physicochemical, organoleptic and microbiological characteristics of three batches of industrial semihard ewe's milk cheeses were studied over a 90-day ripening period. Cheeses were made with a selected starter containingLactococcus lactis subsp.lactis and subsp.cremoris. The total microbial count was normal throughout manufacture and the ripening period. The level of noncasein nitrogen (NCN) was moderate (23.8% of the total nitrogen, TN) but non-protein nitrogen and amino-acid nitrogen were high: 73.6 (% NCN) and 1.92 (% TN) respectively. Breakdown ofα s-(66%) andβ-caseins (17%) at 90 days provided the cheeses with excellent textural and sensory characteristics.

Effect of Technological Parameters on Electrophoretic Detection of Cow's Milk in Ewe's Milk Cheeses

Electrophoretic analysis of whey proteins was used to determine the presence and amount of cow's milk in ewe's milk cheeses. Various combinations of types of whey proteins were compared; using the ratio of cow's β-lactoglobulin A and B to bovine serum albumin was most accurate. The influence of various technological parameters was studied. Vegetable rennet exerted greater proteolytic action on whey proteins than did animal rennet but did not influence the level of detection. Type of pressing had no effect, There was no influence of aging on the level of detection in either Manchego cheese or Roquefort cheese. When silver nitrate was used for staining, quantities of cow's milk at levels of 1% or more were detectable in various types of cheese. Heating of the cow's milk to 90°C for 30min denatured the whey proteins and gave negative results when cow's milk was added to sheep's milk for cheese making. This method has the advantage that whey proteins are less susceptible to proteolysis than caseins and is a simple procedure and of low cost.

Some interesting figures

Electrophoretic analysis of whey proteins was used to determine the presence and amount of cow's milk in ewe's milk cheeses. Various combinations of types of whey proteins were compared; using the ratio of cow's β-lactoglobulin A and B to bovine serum albumin was most accurate. The influence of various technological parameters was studied. Vegetable rennet exerted greater proteolytic action on whey proteins than did animal rennet but did not influence the level of detection. Type of pressing had no effect, There was no influence of aging on the level of detection in either Manchego cheese or Roquefort cheese. When silver nitrate was used for staining, quantities of cow's milk at levels of 1% or more were detectable in various types of cheese. Heating of the cow's milk to 90°C for 30 min denatured the whey proteins and gave negative results when cow's milk was added to sheep's milk for cheese making. This method has the advantage that whey proteins are less susceptible to proteolysis than caseins and is a simple procedure and of low cost.

Sixteenth-century Ewe's milk cheese in Essex

Sixteenth-century Ewe's milk cheese in Essex