Cheese-making Plants Research Articles

Environmental monitoring of Listeria monocytogenes contamination in dairy processing facilities combining culturing technique and molecular methods

Objectiveof the present study was to investigate Listeria contamination in Sardinian sheep cheese-making plants using culture and DNA-based methods. Food and environmental samples were collected from different surfaces of 14 facilities. Samples were collected using pre-moistened sponge swabs. Each site was sampled using two sponges used one for microbiological detection and the other for extraction of total DNA. The DNA was submitted to real time PCR targeting the prs gene for Listeria spp., the gene inlA for Listeria monocytogenes and the gene iap for Listeria innocua. DNA metabarcoding was also conducted on the total DNA. Overall were collected 254 environmental and 36 food samples. The prevalence of Listeria spp. and Listeria monocytogenes was 18.6% and 10.0%, respectively. Samples enrichment coupled with quantitative PCR (qPCR) showed a greater sensitivity than the conventional culture method with an overall prevalence of 12.1% for L. monocytogenes. Both, qPCR and ribosomal DNA-metabarcoding conducted on total DNA extracted from the sponges performed poorly in comparison to the culture-based method detecting the presence of Listeria genus in as little as 7 (2.4%) and 4 (1.4%) samples respectively. The present study supports the use of a culture enrichment coupled with qPCR for routine monitoring of contamination in food premises.

Traceability, virulence and antimicrobial resistance of Yersinia enterocolitica in two industrial cheese-making plants

Between 2018 and 2019, 309 environmental and food samples were collected from two industrial cheese-making plants located in Sardinia, in order to investigate Y. enterocolitica presence and to characterize the isolates. Y. enterocolitica isolates were further compared with isolates detected during a previous investigation from sheep and goat raw milk samples. Y. enterocolitica was detected in 7.4 % of the samples and the prevalence was higher, even if not significantly (P > 0.05) higher in non-food contact surface samples (10.2 %) than in food contact surface samples (3.8 %). The highest prevalence was detected in floor samples (13.5 %), followed by drain samples (7.2 %), which might serve as main harborage sites for further contamination. Y. enterocolitica was also detected in food contact surfaces, namely shelves of the Ricotta cooling room and packaging room, one cheese cutting machine surface and one raw milk filter sample. The biotype 1A isolates identified in this study were classified into six different serotypes. Additionally, a bioserotype 2/O:5,27 isolate was identified in one goat milk sample. All 1A isolates possessed the virulence genes invA and ystB while the 2/O:5,27 isolate showed the presence of ail, ystA, invA and yadA genes, thus confirming a pathogenic potential. The isolates showed intrinsic resistance to amoxicillin-clavulanic acid, ticarcillin and cefoxitin due to the presence of the blaA gene. Whole genome sequencing allowed to identify seven different sequence types among the 1A isolates, thus showing a high genetic diversity. The same Y. enterocolitica sequence type (ST3) was detected from three different areas of the same cheese-making plant, indicating a possible transfer of the microorganism along the processing lines. Y. enterocolitica contamination in cheese-making plants can pose a risk to human health. Preventive measures include the hygienic design of the plant layout and equipment, in association with proper cleaning and disinfection programmes.

Комплексная биологическая очистка сточных вод предприятий мясо-молочной промышленности

About 200 enterprises producing meat product and more than 50 enterprises of the dairy industry operate in the Republic of Belarus. Up to 70 % of the water used in these industries is contaminated with fatty substances. At present, physicochemical methods (coagulation and flocculation) and biological treatment using microorganisms-destructors of fats and oils are most widely used for the treatment of fat-containing wastewater, it is advisable to use these treatment methods in combination. Recently, more and more attention has been paid to the complete or partial replacement of chemical flocculants by biological or microorganisms with flocculating ability. In this paper, the process of wastewater treatment of meat and dairy industry enterprises was studied using a consortium of flocculant microorganisms and the microbial preparation Antoil. The investigated microbial consortium was shown to be as active as the most common polyacrylamide-based synthetic flocculants used for wastewater treatment. The flocculating activity was 92-98 %. It has been established that the process of purification of the studied wastewater with the help pf the consortium of microorganisms used depends on the temperature and pH value of the effluents. Dairy and meat industry wastewater was treated with an efficiency of 60.9-98.0 % in 7 days in the temperature range of 10-40 °C and pH 4-9. It is shown that the use of a consortium of flocculant microorganisms makes it possible to achieve high rates of wastewater treatment of a cheese-making plant and a poultry farm not only in terms of suspended solids, but also in terms of COD. The effectiveness of the combined use of a consortium of flocculant microorganisms and the microbial preparation Antoil for the treatment of wastewater from poultry farms and maintaining the treatment efficiency at a high level (86.5-92.9 %) during burst discharges has been practically confirmed.

Use of commercial protective cultures in portioned sheep milk cheeses to control Listeria monocytogenes.

The main objective of this study was to innovate soft and semi-cooked sheep milk cheese production processes with the use of a commercial protective culture able to control Listeria monocytogenes growth. A freeze-dried commercial culture of Lactobacillus plantarum was tested in DS cheese and PS cheese, two types of pasteurized sheep milk, raw-paste cheeses aged for no less than 20 and 30 days respectively. In the first step, in vitro tests were conducted to identify the most suitable matrix for the growth of L. plantarum in order to create a subculture that could be used at industrial cheese-making plants. During the second phase of the study, L. plantarum culture was introduced in the manufacturing process of the cheeses in a production plant. Finally, a challenge test was conducted on portioned DS and PS cheeses in order to evaluate the activity of the protective culture against L. monocytogenes: the cheeses were portioned, experimentally contaminated with L. monocytogenes strains, vacuum packed and stored at +4°C (correct storage conditions) and at +10°C (thermal abuse). Cheeses were analysed at the end of the shelf-life to evaluate the presence and growth of L. monocytogenes, to enumerate lactic acid bacteria and determine chemicalphysical features. The results confirmed that protective cultures are a useful technological innovation to control L. monocytogenes growth during cheese storage without altering composition, microflora and chemical- physical characteristics of the product. However, the use of protective cultures should be applied as an integration of risk control measures and not as a substitute for preventive actions.

Detection of Arcobacter spp. in environmental and food samples collected in industrial and artisanal sheep's milk cheese-making plants

The genus Arcobacter include species considered as human foodborne enteropathogens. In recent years, Arcobacter spp. have been frequently isolated from various food of animal origin such as meat, fish and dairy products. However, there is still little information on the occurrence of Arcobacter spp. in the dairy sheep chain. The present study was aimed to assess the prevalence of Arcobacter spp. in the processing environment of 10 industrial and 10 artisanal cheese making plants using sheep milk. A total of 250 samples were collected including food contact and non-food contact surfaces, cheeses, water and wastewater samples. Species identification of isolates was conducted by multiplex PCR and PCR-RFLP. Arcobacter spp. were isolated in 11 out of 20 cheese-making plants (55.0%) with an overall prevalence of 19.2%. Of Arcobacter positive samples 32 (66.6%) were detected from environmental surfaces, 11 (22.9%) from food samples and 5 from wastewater (10.4%). Arcobacter was never recovered from water samples. No differences were observed between industrial and artisanal cheese-making plants. Of 48 isolated strains, 39 (81.3%) were A. butzleri, 5 (10.4%) A. cryaerophilus and 4 (8.3%) A. skirrowii. This is the first investigation reporting the detection of A. cryaerophilus and A. skirrowii from both environmental surfaces and cheeses in dairy plants using sheep milk. Contamination was observed respectively in 6 ricotta (20.0%) and in 3 fresh cheeses (23.1%). The present study indicates the potential risk for human health associated to cheese obtained with pasteurized milk due to cross contamination originating from the processing environment. To minimize the risk of transmission of Arcobacter spp. to consumers through the ingestion of contaminated foods it is essential the implementation of environmental monitoring programs to collect samples from food processing surfaces and to detect the presence of this potential human pathogen.

Heat-resistance of suspect persistent strains of Escherichia coli from cheesemaking plants

Besides its health and spoilage hazards, Escherichia coli is a process hygiene indicator for cheeses made from milk that has undergone heat treatment. Hence, its ability to persist in cheesemaking plant environment and equipment is important. In total, 120 samples from two producing plants were analysed and 72 E. coli isolates were obtained. The target was to find out whether there is a difference in heat-resistance between persistent and non-persistent E. coli strains. The strains were selected using macrorestriction analysis and recurrent detection in cheesemaking plants hereby: one strain persisting in brine for blue-veined cheeses, two strains persisting in brine for hard cheeses and one non-persistent strain from raw material. Their D(50)-values were 196; 417; 370 and 182 min, respectively, D(59)-values ranged from 20 to 32 min and z-values were 7.5; 6.6; 8.1 and 9.0 °C, respectively. The non-persistent strain was the least resistant to heating to 50 °C but it was not the least resistant generally. All tested strains were highly heat-resistant and carried genes of the heat resistance locus LHR1 and/or LHR2. Our results emphasise the need to screen for the presence of LHR genes and the occurrence of heat-resistant E. coli in cheese production where they could survive sub-pasteurisation temperatures and contaminate the manufacturing environment and finished products.

Integrating reverse osmosis to reduce water and energy consumption in dairy processing: a predictive analysis for Cheddar cheese manufacturing plants

Reverse osmosis (RO) is essential for dairy processors to reduce their water input and the energy dedicated to dewatering processes such as evaporation. Indeed, water can be reclaimed by RO from numerous dairy fluids (e.g., milk, cheese whey, UF permeates, condensing water), but these applications may have different effects on plant efficiency in terms of water and energy use. Consequently, this study uses predictive analysis to evaluate the impact of performing RO at different steps in the process flow chart of an industrial cheesemaking plant. The hypothesis that preconcentrating milk by RO at the entry-gate of the plant (on skim milk) would reduce the volume of by-products to be processed, and the resources used, was not valid. Instead, the most efficient way to reduce the amount of resources consumed was to perform RO on the cheese whey and milk UF permeate prior evaporation. Preconcentrating these by-products to a total solids content of 20% and 22%, respectively, reduced the entire natural gas consumption by 36% and the electricity consumption by 10%, compared to a scenario where only condensing water was reclaimed.

Business social responsibility. Search for assessment methods

Purpose of the study. The research materials continue the author's series of articles devoted to the problems of the stakeholder approach. The social responsibility of business acts as a launching pad for fruitful cooperation and interaction between business structures and authorities. The concept of corporate social responsibility is very dynamic, characterized by constant transformation, change and enrichment with new ideas. So, if in the middle of the XX century it developed rather slowly, not finding a response in the business environment, then in the XXI century it is “preached” as the main business philosophy by most of the advanced countries. At the same time, a characteristic feature of existing scientific approaches is the emphasis on technocratic and economic positions and the complete absence of approaches based on the relationship between business and stakeholders. However, such approaches from the author's point of view are insufficient for the entire range of requirements imposed by the external and internal environment on modern business. The ambiguity of the interpretation of the concept under study made it possible to state the complexity of this category and its multidimensional nature. In this regard, there is a need for a comprehensive statistical assessment of the degree of business socialization and the choice of appropriate tools for this.Materials and methods. The statistical assessment of the degree of business social responsibility is based on local criteria, combined into five blocks. The presented system of criteria characterizes the activities of the business taking into account the requirements of the stakeholders. At the same time, the list of criteria can be adjusted when socio-economic trends and problems of society change. The information base of the study was the annual and financial reports of regional enterprises, the results of expert assessments. The hierarchy analysis method and the graphical polygon (radar) method were used as a tool for assessing the degree of business socialization.Results. The article concretizes the concept of social and economic responsibility of business. The author's approach covers the idea of a responsible partnership based on the interaction of business with a wide range of interested groups involved in active and passive forms of participation in its operations. The variety of interests of stakeholders representing various subjects of market interaction emphasizes the multi-criteria nature of the category of “social and economic responsibility of business”. Statistical tools are fully capable of providing an assessment of the entire spectrum of signs of corporate social responsibility. The integral indicator of the degree of social responsibility, built on the basis of the hierarchy analysis method, made it possible to distinguish four degrees of business socialization: low, moderate, noticeable and high. For each degree of socialization, characteristic features are determined. The results of the study showed that as the degree of social responsibility grows, business performance indicators increase and its well-being in the long term depends on the coordination of the interests of key participants in corporate relations. An integral assessment of the degree of business socialization was carried out according to twenty-six local criteria. As a result of calculating the private and local ranks of the values of the corresponding criteria, fifteen polygons of the degree of socialization of the regional business were built, included in the sample. The results obtained make it possible to ascertain the existence of a high degree of heterogeneity of regional enterprises in terms of the investigated integral indicator. The leaders in terms of social responsibility are JSC “Teplichnoye”, OJSC “Mordovcement”, OJSC “Elektrovypryamitel”, OJSC “Lato”. Outsiders include OJSC Cheese-Making Plant “Ichalkovsky”, Ltd “Lisma”, OJSC “Stankostroitel”, OJSC “RubEx”. Among the features of regional enterprises, one can single out the heterogeneity in the distribution of indicators along the radial straight lines. JSC “Teplichnoye” is characterized by sharp fluctuations in rank values, which is most active in interaction with consumers, its own personnel, but also stands out as one of the smallest values of the block associated with relationships with business partners. A similar situation is observed among outsider enterprises. The proposed methodology can be used as a tool for a comprehensive study of existing trends in the practice of socially responsible business behavior, characteristics of the results achieved, as well as identifying problem areas that focus additional attention.

DEVELOPMENT OF THE RECIPE OF THE CHEESE OF FUNCTIONAL PURPOSE

For the first time, the company Experimental Cheese-Making Plant LLC, the city of Barnaul, Altai Territory, developed a recipe for the production of functional cottage cheese, taking into account organoleptic, physico-chemical indicators and the shelf life of the finished product. The results of marketing research and respondents’ answers about the possibility of fortification of food products, in particular dairy products, showed the feasibility of developing recipes for functional cottage cheese. It was established that for its production it is advisable to use cottage cheese obtained by the acid method, since the product has a consistency, moisture content corresponding to GOST 31453–2013 Cottage cheese. Technical conditions Fermentation must be carried out at a temperature of 40 °C, and boiling at 65 °C. Under these conditions, the ripening time will be minimal and the yield of the finished product maximum. Experimentally established the optimal dose of making egg shell powder in cottage cheese with a mass fraction of fat 5 %, corresponding to 0.5 %. The introduction of egg shell powder allows to reduce the acidity of cottage cheese, increase the shelf life of the finished product, and expand the product range.

On the Use of Ultrafiltration or Microfiltration Polymeric Spiral-Wound Membranes for Cheesemilk Standardization: Impact on Process Efficiency.

Ultrafiltration (UF) and microfiltration (MF) are widely-used technologies to standardize the protein content of cheesemilk. Our previous work demonstrated that protein retention of a 0.1-µm MF spiral-wound membrane (SWM) was lower, but close to that of a 10 kDa UF one. Considering that the permeability of MF membranes is expected to be higher than that of UF ones, it was hypothesized that the former could improve the efficiency of the cheesemaking process. Consequently, the objectives of this work were to compare 0.1-µm MF and 10 kDa UF spiral-wound membranes in terms of (1) hydraulic and separation performance, (2) energy consumption and fouling behavior, (3) cheesemaking efficiency of retentates enriched with cream, and (4) economic performance in virtual cheesemaking plants. This study confirmed the benefits of using MF spiral-wound membranes to reduce the specific energy consumption of the filtration process (lower hydraulic resistance and higher membrane permeability) and to enhance the technological performance of the cheesemaking process (higher vat yield, and protein and fat recoveries). However, considering the higher serum protein retention of the UF membrane and the low price of electricity in Canada, the UF scenario remained more profitable. It only becomes more efficient to substitute the 10 kDa UF SWM by the 0.1-μm MF when energy costs are substantially higher.

Shelf Life Evaluation of Ricotta Fresca Sheep Cheese in Modified Atmosphere Packaging.

Ricotta fresca cheese is the product of Sardinian dairy industry most exposed to microbial post-process contamination. Due to its technological characteristics, intrinsic parameters, pH (6.10-6.80) and water activity (0.974-0.991), it represents an excellent substrate for the growth of spoilage and pathogenic microorganisms, which are usually resident in cheese-making plants environments. Generally, ricotta fresca has a shelf life of 5-7 days. For this reason, at industrial level, modified atmosphere packaging (MAP) is used to extend the durability of the product. However, few investigations have been conducted to validate the use of MAP in ricotta fresca. The aim of this work is to evaluate the shelf life of ricotta fresca under MAP. A total of 108 samples were collected from three Sardinian industrial cheese-making plants and analysed within 24 h after packaging and after 7, 14 and 21 days of refrigerated storage. Aerobic mesophilic bacteria, mesophilic and thermophilic cocci and lactobacilli, Enterobacteriaceae and E. coli, L. monocytogenes, Pseudomonas spp, Bacillus cereus, yeasts and moulds, and the chemical-physical parameters and composition of the product were determined. At the end of the shelf life, Pseudomonas spp. and Enterobacteriaceae reached high concentrations, 5 to 7 and 3 to 6 log10 colony forming unit g–1, respectively. The presence of environmental contaminants indicates that the use of MAP without the appropriate implementation of prerequisite programmes is not sufficient to extend the durability of ricotta fresca. Gas mixture and packaging material should be selected only on the basis of scientific evidence of their effectiveness.

Occurrence and traceability of Listeria monocytogenes strains isolated from sheep's milk cheese-making plants environment

Abstract The aim of the study was to conduct an extensive survey on Listeria monocytogenes and Listeria spp. environmental contamination in 13 cheese-making plants. A total of 409 environmental and food samples were collected during years 2011–2013. Listeria spp. contamination was observed in all the facilities, while L. monocytogenes was recovered from 12 facilities with a prevalence ranging between 3.0% and 22.6%. Floor drains were the most contaminated sampling sites (48.8% of positive samples), serving as harbourage site for subsequent contamination. Out of 616 isolates, 277 (45.0%) were Listeria innocua , 274 (44.5%) L. monocytogenes , 41 (6.6%) Listeria ivanovii , 14 (2.3%) Listeria welshimeri and 10 (1.6%) Listeria gravyi . Serotyping carried out by PCR and agglutination method for L. monocytogenes revealed that 169 strains (61.7%) were serotype 1/2a, 65 (23.7%) 4b, 20 (7.3%) 1/2b, 10 (3.6%) 3a, 7 (2.5%) 1/2c and 3 (1.1%) 3b. PFGE conducted on L. monocytogenes isolates using Asc I and Apa I restriction enzymes, yielded 6 clusters. Two predominant PFGE clusters were observed including respectively 36 and 32 strains. Within cheese-making plants, L. monocytogenes showed wide variability with strains distributed up to 4 different clusters. Pulsotypes isolated from raw milk filter were never detected in the processing environment, indicating that the contamination originated from sources other than raw milk. The isolation of strains with similar profile from different sampling sites, within and among cheese-making plants, indicated the possible transfer of L. monocytogenes contamination along production lines and from one facility to another. Strains recovered from food were confirmed as originating from the processing environment.

Exo-metabolites of mycelial fungi isolated in production premises of cheese-making and meat-processing plants

Data were obtained on the species composition of mycelial fungi isolated from the air of workrooms and production premises in cheese-making and meat-processing plants. The strains studied were shown to be capable of producing various low molecular weight compounds. Many of them are mycotoxins such as α-cyclopiazonic acid (CPA), mycophenolic acid (MPA), citrinin, cladosporin, roquefortine and ergot alkaloids. The profiles of the secondary metabolites were used to elucidate the species’ names of the isolated strains.

Hygienic and sensory quality factors affecting the shelf-life of Fruhe (Casu axedu) traditional Sardinian fresh cheese

A study was conducted to evaluate the dura- bility of the traditional fresh soft cheese Fruhe manufactured in Sardinia either from goats’ or sheep’s milk. Four farmstead cheese-making plants were visited three times during the Fruhe cheese-making season. During each visit environmental samples were collected from food contact and non-food contact sur- faces in order to evaluate the presence of Enterobacteriaceae , Escherichia coli , Pseudomonas spp. and Listeria spp. In a total of 60 environmental samples, Escherichia coli and Listeria spp. were never detected, while contamination with Enterobacteriaceae and Pseudomonas spp. was observed respectively in 48% and 43% of samples. The microbiological profile of 48 Fruhe cheese samples was assessed at different time points during the product shelf-life. Aerobic mesophilic bacteria, Enterobacteriaceae , E. coli , Pseudomonas spp., Bacillus cereus and Listeria monocytogenes were investigated at 0, 7, 14 and 21 days after production. E. coli , L. monocytogenes and B. cereus were never detected in the product. Enterobacteriaceae contamination was observed, showing decreasing levels over time. Pseudomonas spp. was recovered in only two Fruhe samples (3.3%) at day 0. Sensory analysis was also conducted using a triangle test to determine whether a difference between Fruhe samples at 14 and 21 days of shelf-life exists. Based on the evolution of the microbiological profile and the sensory attributes observed in the present study, it is reasonable to assume that the product shelf-life can be feasibly extended up to 21 days.

Listeria monocytogenes contamination in dairy plants: evaluation of Listeria monocytogenes environmental contamination in two cheese-making plants using sheeps milk

Listeria monocytogenes harbouring niches established in the processing plant support post-process contamination of dairy products made from pasteurised or thermised milk. The present study investigated L. monocytogenes environmental contamination in two sheep’s milk cheese-making plants. Persistence of contamination in the area at higher risk was also investigated. During a one-year survey 7 samplings were carried out in each dairy plant, along the production lines of Pecorino Romano and ricotta salata cheese. A total of 613 environmental samples collected from food contact and non-food contact surfaces were analysed according to ISO 11290-1:2005 standard method. Identification of the isolated strains was carried out by polymerase chain reaction. L. monocytogenes prevalence was 23.2% in dairy A and 13.1% in dairy B, respectively. The higher prevalence rate was found in the following areas: salting, products washing, packaging, ricotta salata storage and Pecorino Romano ripening rooms. L. monocytogenes was never found in the cheese-making area. The probability of observing samples positive for the presence of L. monocytogenes was asso- ciated with dairy plant, sampling area and the period of cheese-making (P<0.001). The greater persistence of contamination over time was observed in the washing, salting, and Pecorino Romano ripening areas. The control of persistent environmental contamination relies on the identification of L. monocytogenes niches within the processing environment and the prevention of harborage sites formation. The importance of strict cleaning and sanitising procedure in controlling L. monocytogenes environmental contamination is confirmed by the lower level of contamination observed after these procedures were correctly implemented.

Facility-Specific “House” Microbiome Drives Microbial Landscapes of Artisan Cheesemaking Plants

Cheese fermentations involve the growth of complex microbial consortia, which often originate in the processing environment and drive the development of regional product qualities. However, the microbial milieus of cheesemaking facilities are largely unexplored and the true nature of the fermentation-facility relationship remains nebulous. Thus, a high-throughput sequencing approach was employed to investigate the microbial ecosystems of two artisanal cheesemaking plants, with the goal of elucidating how the processing environment influences microbial community assemblages. Results demonstrate that fermentation-associated microbes dominated most surfaces, primarily Debaryomyces and Lactococcus, indicating that establishment of these organisms on processing surfaces may play an important role in microbial transfer, beneficially directing the course of sequential fermentations. Environmental organisms detected in processing environments dominated the surface microbiota of washed-rind cheeses maturing in both facilities, demonstrating the importance of the processing environment for populating cheese microbial communities, even in inoculated cheeses. Spatial diversification within both facilities reflects the functional adaptations of microbial communities inhabiting different surfaces and the existence of facility-specific "house" microbiota, which may play a role in shaping site-specific product characteristics.

Quantifying energy savings during cheese ripening after implementation of sequential air ventilation in an industrial cheesemaking plant

The main objective of this work was to determine the highest energy savings that could be made by implementing sequential air ventilation strategy in an industrial large-scale ripening room, without affecting the final cheese quality. Six ripening trials were run corresponding to different ventilation strategies: continuous air ventilation taken as reference, time-based sequential air ventilation, and temperature-based sequential air ventilation. The results showed that ripening caused substantial cheese respiratory activity that was not significantly affected by either continuous or sequential room ventilation. It was also shown that sequential ventilation had no significant effect on the evolution of cheese ripening microbial flora, biochemical characteristics, or appearance, and thus on the final cheese quality. In the conditions of this study, a specific energy consumption of 3.6 MJ per kg of cheese was estimated, and for the ripening room investigated, mean electrical energy savings ranged from 41 kWh per day to 170 kWh per day, depending on the strategy implemented. Industrial operators could usefully study how to generalize these results to the ripening rooms used in cheese production worldwide.

Conjugated linoleic acid content and isomer distribution during ripening in three varieties of cheeses protected with designation of origin

Cheeses have been identified as important sources of conjugated linoleic acid (CLA), a mixture of positional and geometric isomers with potential anticarcinogenic activity and other beneficial properties. The objectives of this study were to examine the effects of ripening on the overall CLA content as well as on the isomers profile using GC and Ag +-HPLC. Three Spanish cheeses Protected with Designation of Origin (Mahón, Manchego and Cabrales) were manufactured in different cheesemaking plants and monitored at different times during the ripening period. Total CLA content varied from 3 to 9 mg/g of total fatty acids and rumenic acid (9- cis, 11- trans C18:2, RA) represented more than 75% of total CLA. After RA, 7–9 ( cis/ trans plus trans/ cis), 11- trans, 13- trans and 11- trans, 13- cis C18:2 were the main CLA isomers. The results achieved confirm that the effect of ripening on the total CLA concentration and isomer distribution was negligible.

Impacts of feeding system and season on milk composition and Cheddar cheese yield in a subtropical environment

Milk obtained from cows on 2 subtropical dairy feeding systems were compared for their suitability for Cheddar cheese manufacture. Cheeses were made in a small-scale cheesemaking plant capable of making 2 blocks (about 2 kg each) of Cheddar cheese concurrently. Its repeatability was tested over 10 separate cheesemaking days with no significant differences being found between the 2 vats in cheesemaking parameters or cheese characteristics. In the feeding trial, 16 pairs of Holstein–Friesian cows were used in 2 feeding systems (M1, rain-grown tropical grass pastures and oats; and M5, a feedlot, based on maize/barley silage and lucerne hay) over 2 seasons (spring and autumn corresponding to early and late lactation, respectively). Total dry matter, crude protein (kg/cow.day) and metabolisable energy (MJ/cow.day) intakes were 17, 2.7, and 187 for M1 and 24, 4, 260 for M5, respectively. M5 cows produced higher milk yields and milk with higher protein and casein levels than the M1 cows, but the total solids and fat levels were similar (P > 0.05) for both M1 and M5 cows. The yield and yield efficiency of cheese produced from the 2 feeding systems were also not significantly different. The results suggest that intensive tropical pasture systems can produce milk suitable for Cheddar cheese manufacture when cows are supplemented with a high energy concentrate. Season and stage of lactation had a much greater effect than feeding system on milk and cheesemaking characteristics with autumn (late lactation) milk having higher protein and fat contents and producing higher cheese yields.

Determination of aflatoxin M 1 in ewe's milk samples and the produced curd and Feta cheese

Ewe's milk and the produced curd and Feta cheese samples were examined for the presence of aflatoxin M 1, using an enzyme-linked immunoassay. A total of 162 samples of the aforementioned materials was analyzed originating from traditional cheese-making plants of the West side of Thessaloniki Province. Levels of aflatoxin M 1 in milk were found far below the tolerance level (highest value 18.2 ng/l). In curd samples higher levels of aflatoxin M 1 were detected giving a mean enrichment factor of 4.9. On the contrary, the final ripened cheese was found to be free of aflatoxin M 1.