Behavior of Escherichia coli O157:H7 during the manufacture and ripening of feta and telemes cheeses

Pasteurized whole ewe's and cow's milk was used in the manufacture of Feta end Telemes cheeses, respectively, according to standard procedures. In both cases, the milk had been inoculated with Escherichia coli O157:H7 at a concentration of ca. 5.1 log CFU/ml and with thermophilic or mesophilic starter cultures at a concentration of ca. 5.3 to 5.6 log CFU/ml. In the first 10 h of cheesemaking, the pathogen increased by 1.18 and 0.82 log CFU/g in Feta cheese and by 1.56 and 1.35 log CFU/ g in Telemes cheese for the trials with thermophilic and mesophilic starters, respectively. After 24 h of fermentation, a decrease in E. coli O157:H7 was observed for all trials. At that time, the pH was reduced to 4.81 to 5.10 for all trials. Fresh cheeses were salted and held at 16 degrees C for ripening until the pH was reduced to 4.60. Cheeses were then moved into storage at 4 degrees C to complete ripening. During ripening, the E. coli O157:H7 population decreased significantly (P < or = 0.001) and finally was not detectable in Feta cheese after 44 and 36 days and in Telemes cheese after 40 and 30 days for the trials with thermophilic and mesophilic starters, respectively. The estimated times required for one decimal reduction of the population of E. coli O157:H7 after the first day of processing were 9.71 and 9.26 days for Feta cheese and 9.09 and 7.69 days for Telemes cheese for the trials with thermophilic and mesophilic starters, respectively.     

The effect of varying casein/fat ratio on physicochemical and sensory qualities of Feta‐type cheese made using buffalo milk

The Feta‐type cheese was prepared with different casein/fat (C/F) ratios of buffalo milk using microbial rennet. The manufactured Feta cheeses were subjected to physicochemical and sensory quality at 15‐day interval up to 60 days of ripening. Sensory analysis discriminated the different level of C/F ratio of buffalo milk cheeses predominantly by age. There was no significant difference (P < 0.01) observed in cheese made from C/F ratio of 0.6–0.7 in terms of flavour. The titratable acidity (TA), soluble protein and free fatty acid appear to be age‐dependent and increased throughout the ripening in all experimental cheeses.     

Probiotic cheese production using Lactobacillus casei cells immobilized on fruit pieces

Lactobacillus casei cells were immobilized on fruit (apple and pear) pieces and the immobilized biocatalysts were used separately as adjuncts in probiotic cheese making. In parallel, cheese with free L. casei cells and cheese only from renneted milk were prepared. The produced cheeses were ripened at 4 to 6°C and the effect of salting and ripening time on lactose, lactic acid, ethanol concentration, pH, and lactic acid bacteria viable counts were investigated. Fat, protein, and moisture contents were in the range of usual levels of commercial cheeses. Reactivation in whey of L. casei cells immobilized on fruit pieces after 7 mo of ripening showed a higher rate of pH decrease and lower final pH value compared with reactivation of samples withdrawn from the remaining mass of the cheese without fruit pieces, from cheese with free L. casei, and rennet cheese. Preliminary sensory evaluation revealed the fruity taste of the cheeses containing immobilized L. casei cells on fruit pieces. Commercial Feta cheese was characterized by a more sour taste, whereas no significant differences concerning cheese flavor were reported by the panel between cheese containing free L. casei and rennet cheese. Salted cheeses scored similar values to commercial Feta cheese, whereas unsalted cheese scores were significantly lower, but still acceptable to the sensory panelists.     

Migration of di-(2-ethylhexylexyl)adipate plasticizer from food-grade polyvinyl chloride film into hard and soft cheeses

Food-grade polyvinyl chloride (PVC) film containing 28.3% di-(2-ethylhexylexyl)adipate (DEHA) plasticizer was used to wrap three different types of cheese (Kefalotyri, Edam, and Feta). Samples were split into two groups and stored at 5+/-0.5 degrees C. One group was analyzed for DEHA content at intervals between 1 and 240 h of contact (kinetic study), and a second group was cut into slices (1.2 mm thick) after 240 h of cheese/PVC contact and was analyzed for DEHA content (penetration study). The DEHA was determined by indirect gas chromatography. Statistically significant differences in migration of DEHA were observed between the cheese types. Migration of DEHA depended on contact time, fat, and moisture contents, and consistency of cheese samples. Equilibrium conditions were approached after approximately 100 h of contact for Edam and 150 h for Kefalotyri cheese. Equilibrium conditions were not reached for Feta cheese, even after 240 h of contact. After 240 h of contact under refrigeration, the migration of DEHA was approximately 345.4 mg/kg (18.9 mg/dm2) for Kefalotyri, 222.5 mg/kg (12.2 mg/dm2) for Edam, and 133.9 mg/kg (7.3 mg/dm2) for Feta. The loss of DEHA from the PVC film into the three cheese types was 37.8, 24.3, and 14.6%, respectively. These values, with the exception of Feta, were higher than the upper limit for global migration from plastic packaging materials into food and food stimulants set by the European Union (EU) (10 mg/dm2 or 60 mg/kg). After 240 h of cheese/film contact, DEHA was detected in the first three slices beneath the cheese surface (3.6 mm total depth) of Edam cheese and in the first two slices (2.4 mm total depth) of Kefalotryi and Feta cheeses. DEHA was not detected in subsequent layers. The effect of cheese rind on migration of DEHA was studied in Edam and Kefalotyri cheeses. The DEHA migration after 240 h into the first 1 mm beneath the surface of Kefalotyri cheese was 22.4 mg/kg, while DEHA was not detected in Edam cheese.     

RHEOLOGICAL PROPERTIES OF UF-FETA CHEESE DETERMINED BY UNIAXIAL COMPRESSION AND DYNAMIC TESTING

Rheological characteristics of three Feta cheeses produced from ultrafiltered milk (UF-Feta cheeses) with different textures were evaluated using uniaxial compression and dynamic testing (strain and frequency sweeps). Stress at fracture was 20–46 kPa, Hencky strain at fracture was 0.20–0.35, modulus of deformability was 176–465 kPa, and work up to fracture was 4.4–6.7 kj/m³, depending on the type of cheese and the strain rate. Stress at a given strain, and stress at fracture increased with strain rate: the slope of the log (stress at fracture) versus log(in-itial Hencky strain rate) plot was 0.06–0.21, indicating a partially viscous behavior. Stress at fracture discriminated between all three Feta textures, and Hencky strain at fracture discriminated a Tin Feta texture from two Brick Feta textures at every compression rate. In dynamic testing the complex modulus was 40–173 kPa, and tan (δ) was 0.17–0.25 depending on the type of cheese and the frequency of oscillation. The slope of log(complex modulus) or log(storage modulus) versus log (frequency) was 0.12–0.14, and the slope of log(loss modulus) versus log (frequency) was 0.07–0.11 for all three types of cheese. The complex modulus from strain and frequency sweeps in the dynamic testing distinguished the Tin Feta texture from the Brick Feta textures, and the phase angle (δ) measured in strain sweep could differentiate the Blue Brick Feta texture from the Red Brick Feta texture in the strain interval 0.0003–0.024.     

Evolution of lipolysis during the ripening of traditional Feta cheese

Lipolysis was studied during ripening of traditional Feta cheese produced in two small dairies, A and B. The cheeses were made from a thermized mixture of ewes’/goats’ milk by using yoghurt as starter and artisanal rennet from lambs’ and kids’ abomasa (cheese A) or mixed artisanal rennet with calf rennet (cheese B).The acid degree value and the free fatty acids (FFA) contents in both cheeses increased sharply up to 18 d (pre-ripening period at 15 °C) and continued to increase throughout ripening. In both mature cheeses, acetic acid was found at high levels (13–18% of the total FFAs). However, except for this, all FFA contents differed significantly (P < 0.05) between the two cheeses throughout ripening. The levels of individual and total C2:0–C8:0, C10:0–C14:0 and C16:0–C18:2 fatty acids were significantly higher (P < 0.05) in cheese A than in cheese B. Presumably the difference, especially in the C2:0–C8:0 content, was due mainly to the type of the rennet used. Butyric acid was the dominant FFA in cheese A (20% of the total FFAs at 120 d), while the most abundant FFAs in cheese B were capric (18%) and lauric acid (18%). In general, the lipolysis degree of the two cheeses was higher than those reported for the industrially-made Feta cheese.In organoleptic evaluation, cheese A had a piquant taste that was attributed to its high content of butyric acid and showed a significantly (P < 0.05) higher total score than cheese B.     

Effects of starter level, draining time and aging on the physicochemical, organoleptic and rheological properties of feta cheese

Feta cheese was made from ewe's milk using three different levels of starter (0.20, 0.50 and 0.75%) and two draining times (6 and 20 h). Cheese made with addition of 0.75% starter had a lower pH and moisture content than the cheeses made with 0.20 and 0.50% starter. With the increase in starter level there was also an increase in cheese fat content, although the fat in dry matter remained almost constant. The lower level of starter resulted in cheese with lower protein content, while other cheese components were not significantly affected by the starter levels used. The yield of cheese made with addition of 0.75% starter was significantly lower than the yield of cheeses made with the other levels. Also, the yield of cheeses made with 6 h drainage was greater than the yield of cheeses made with 20 h drainage. In general, the organoleptic and rheological properties of cheeses were not affected by the three levels of starter used for feta cheese manufacture.     

Proteolysis in reduced sodium Feta cheese made by partial substitution of NaCl by KCl

Feta cheeses (five trials) of different sodium content were made, using ewes’ milk, from split lots of curd by varying the salting procedure, i.e. dry salting with NaCl (control) or mixtures of NaCl/KCl (3:1 or 1:1, w/w basis) and filling the cans with brine made with NaCl or the above NaCl/KCl mixtures, respectively, in order to study the influence of the partial substitution of NaCl by KCl on the proteolysis during cheese ripening. The extent and characteristics of proteolysis in the cheeses were monitored during aging by using Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen, trichloroacetic acid-soluble nitrogen, phosphotungstic acid-soluble nitrogen), the cadmium–ninhydrin method for the determination of total free amino acids (FAA), urea–polyacrylamide gel electrophoresis of cheese proteins followed by densitometric analysis of the α_s1- and β-casein fractions, reverse-phase HPLC analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCl in the manufacture of Feta cheese had no significant effect on the extent and characteristics of proteolysis during cheese aging.     

Microflora of Feta cheese from four Greek manufacturers

The components of the microflora of four Feta cheeses, produced by different Greek manufacturers, were determined by culture dependent and independent techniques. Isolates from microbiological media were first grouped by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) and then representatives of each DGGE group were sequenced for identification purposes. DNA and RNA, extracted directly from the cheese, were subjected to PCR-DGGE. Moreover, Feta cheeses were subjected to FISH analysis in order to identify viable bacterial populations. The microbial ecology, as represented by the Lactic Acid Bacteria (LAB) and yeast populations, was different for the four cheeses. The main LAB species isolated were Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus coryniformis and Lactobacillus fermentum. However, some inconsistencies were observed between the results obtained with the culture dependent and the culture independent approach. In the case of the yeasts, the results obtained by PCR-DGGE compared very well with those obtained by the conventional microbiological analysis and the main species found were Kluyveromyces lactis, Pichia fermentans and C. zeylanoides. FISH analysis highlighted viable but not culturable populations of Streptococcus thermophilus and Lactococcus spp. RAPD-PCR performed on the L. plantarum isolates revealed a cheese specific distribution and a temperature dependent clustering.     

Study of organic acids, volatile fraction and caseins of a new Halloumi-type cheese during ripening in whey brine

Organic acids, fat hydrolysis, volatile compounds and sensory characteristics of a new brine cheese which combines characteristics of Halloumi and Feta cheeses during its ripening in whey brine (100g NaCl L⁻¹) were studied. Thermotolerant protease of Mucor miehei as a coagulant enzyme and a mixture of thermotolerant starter cultures Enterococcus faecium 0165 (0.5% w/w) and Lactobacillus casei 80 10D were used. Good quality new Halloumi-type cheese was produced with higher proteolysis than traditional Halloumi cheese kept in whey brine. The volatile compounds identified comprised alcohols, aldehydes, ketones, acids, esters, hydrocarbons and sulphur compounds. Ethanol was the dominant volatile compound determined. Lactic acid was the dominant acid produced; its concentration increased during ripening, reaching a maximum value of 9929 mg kg⁻¹ at day 30. Acetic acid was also found in high amounts, which increased during cheese ripening. Lipolysis of cheese was not intense. The most abundant acids of the mature cheese were palmitic, oleic and acetic acid. The Halloumi-type cheese scored higher in the sensory analysis when fresh than did the mature cheese.     

Feta cheese texture: the effect of caprine and ovine milk concentration

Feta cheese was produced commercially with different caprine to ovine milk ratios. Milk fat concentrations, moisture and salt contents were similar for all the batches. However, the hardness and adhesive characteristics of the cheeses differed in relation to the milk ratio. The hardness of the cheese appeared to be correlated to increased goat milk content. Cryo-scanning electron microscopy (cryo-SEM) of the cheese samples showed that feta cheese with a higher proportion of caprine milk had a more compact and less porous appearance than feta produced from purely ovine milk. This difference in cheese structure helps to explain the difference in hardness between the samples.     

Effect of supplementation of brine with calcium on the Feta cheese ripening

Feta blocks ripened in plain or calcium‐supplemented brine were analysed with respect to biochemical characteristics, proteolysis and inorganic fractions; moreover, the inorganic and N content of the respective brines was estimated. The acidification of Feta in supplemented brine was faster, the moisture content was lower, secondary proteolysis was more extended, and the organoleptic scores were higher compared to control Feta ripened in plain brine. The TCASN fraction of cheeses contributed more than that of WSN to the N enrichment of brine. It was concluded that calcium supplementation of the brine retarded the diffusion of cheese N and Ca into the brine.     

Pressing technique and its effect on the quality of Dhaka cheese

Dhaka cheese is a semihard artisanal variety made mainly from bovine milk, using very simple pressing methods. Experimental cheeses were pressed at gauge pressures up to 31 kPa for 12 h at 24 °C and 70% RH. These cheeses were subsequently examined for their compositional, textural and rheological properties plus their microstructures investigated by confocal laser microscopy. The cheese pressed at 15.6 kPa was found to have the best compositional and structural properties.     

Analysis of Selected Volatile Organic Compounds in Split and Nonsplit Swiss Cheese Samples Using Selected‐Ion Flow Tube Mass Spectrometry (SIFT‐MS)

Splits/cracks are recurring product defects that negatively affect the Swiss cheese industry. Investigations to understand the biophysicochemical aspects of these defects, and thus determine preventive measures against their occurrence, are underway. In this study, selected‐ion, flow tube mass spectrometry was employed to determine the volatile organic compound (VOC) profiles present in the headspace of split compared with nonsplit cheeses. Two sampling methodologies were employed: split compared with nonsplit cheese vat pair blocks; and comparison of blind, eye, and split segments within cheese blocks. The variability in VOC profiles was examined to evaluate the potential biochemical pathway chemistry differences within and between cheese samples. VOC profile inhomogeneity was most evident in cheeses between factories. Evaluation of biochemical pathways leading to the formation of key VOCs differentiating the split from the blind and eye segments within factories indicated release of additional carbon dioxide by‐product. These results suggest a factory‐dependent cause of split formation that could develop from varied fermentation pathways in the blind, eye, and split areas within a cheese block. The variability of VOC profiles within and between factories exhibit varied biochemical fermentation pathways that could conceivably be traced back in the making process to identify parameters responsible for split defect.     

Lipolysis,proteolysis and sensory properties of ewe’s raw milk cheese (Idiazabal) made with lipase addition

In this paper, we describe the effect of the addition of pregastric lipase on the composition and sensory properties of Idiazabal cheese. Free fatty acids (FFA), partial glycerides, free amino acids (FAA), gross composition and sensory characteristics were determined at different ripening times in cheeses manufactured with three different amounts of commercial animal lipase or with lipase-containing artisanal lamb rennet paste. The addition of lipase increased the content of total FFA, particularly of short-chain FFA, and that of total partial glycerides in cheeses. Unexpectedly, lipase utilization significantly affected total FAA concentration, which decreased in cheeses elaborated with high lipase amount. In general, Val, Glu and Leu were the major FAA, and their concentrations depended, mainly, on ripening time. Lipase addition had significant influence on the sensory characteristics of the cheeses, increasing scores for most of the flavour and odour attributes of the cheese. Principal component analysis (PCA) was done including dry matter, FFA, FAA, partial glycerides and odour and flavour attributes of the cheeses. It indicated that aroma and flavour parameters of Idiazabal cheese and the content of short-chain FFA and diglycerides were highly correlated to first principal component (PC1), while texture parameters, compositional variables and FAA were correlated to the second principal component (PC2).     

Assessment of aflatoxin M1 levels in selected dairy products in north‐western Iran

The purpose of this survey was to evaluate the natural occurrence and content of aflatoxin M_1, AFM_1, in dairy products marketed in Urmia. During September 2007, 40 samples of pasteurised milk, 40 samples of ultra high temperature‐treated (UHT) milk, 40 samples of creamy cheese and 40 samples of Iranian Feta cheese were collected from different supermarkets in Urmia city. AFM₁ contents were determined by the competitive enzyme‐linked imunosorbent assay (ELISA) technique. All milk samples analysed showed a mean of AFM₁ concentrations lower than the permissible level of 50 ng/kg in Iran (23.22 and 19.53 ng/kg in pasteurised milk and UHT milk respectively). The mean levels of AFM₁ contamination were 43.31 ng/kg in Feta cheeses and 21.96 ng/kg in creamy cheeses. The potential risk of human exposure to aflatoxin M₁ via consumption of milk and milk products is well known. Dairy products must therefore be evaluated for aflatoxin and kept free from fungal contamination as much as possible.     

From milk to cheese: Evolution of flavor fingerprint of milk,cream, curd,whey, ricotta,scotta, and ripened cheese obtained during summer Alpine pasture

The role of each step of cheese and ricotta making in development of flavor of cheese and other dairy products is not yet well known. The objectives of this study were to characterize volatile organic compounds (VOC) in cheese and ricotta making with bulk milk from cows grazing in a highland area and to evaluate their evolution in the various dairy products and by-products obtained during the production processes. A group of 148 cows was grazed day and night on pasture from June to September. A total of 7 cheese-making sessions were carried out using the bulk milk collected every 2 wk during summer pasturing according to the artisanal procedure used for Malga cheese production. All milks, products, and by-products were sampled, and the VOC content of milk, cream, whey, ricotta, scotta (residual liquid), fresh cheeses, and cheeses ripened for 6 and 12 mo was determined by solid-phase microextraction gas chromatography–mass spectrometry. Forty-nine compounds were identified belonging to the following chemical families: alcohols (13), aldehydes (9), esters (8), free fatty acids (6), ketones (5), lactones (2), sulfurs (2), terpenes (2), phenol (1), and benzene (1). The results showed that the amounts of VOC in the various dairy products differed significantly. Comparisons between the VOC of 4 types of milk (whole evening, skim evening, whole morning, mixed in the vat) showed that the skimming process had the greatest effect, with about half of all the VOC analyzed affected, followed by time of milking (evening milking vs. morning milking) and mixing (skim evening milk mixed with whole morning milk). In general, among fresh products, cream had higher contents of fatty acids, sulfurs, and terpene volatile compounds than fresh cheese and ricotta, whereas ricotta showed a very high VOC amount compared with fresh cheese, probably due to its high processing temperature. The effects of the progressive nutrient depletion in milk during processing were investigated by comparing the amounts of VOC in vat milk, whey, and scotta. Although milk contained greater amounts of nutrients, whey and especially scotta had higher concentrations of VOC, with the exception of esters, sulfurs, terpenes, and phenolic compounds, as a result of physicochemical and microbial modifications during processing. Finally, the effect of ripening was tested by comparing the VOC of fresh and ripened cheeses (6 and 12 mo), revealing that VOC release increased dramatically during the first semester and further with increasing the ripening period to 1 yr. In particular, some alcohols (butan-2-ol), aldehydes (2-methylpropanal, hexanal, and heptanal), esters (ethyl butanoate and ethyl hexanoate), fatty acids (acetic, butanoic, and hexanoic acids), and ketones (butan-2-one, pentan-2-one, and heptan-2-one) showed a very large increase. In conclusion, according to the artisanal milk processing carried out for Malga cheese production, the quantity of VOC was shown to increase about 3 times during cheese making (from milk in vat to fresh cheese plus whey), almost 4 times during ricotta making (from whey to ricotta plus scotta), and about 16 times during 1 yr of ripening of cheese.     

Effects of salting method and storage time on composition and quality of feta cheese

Feta cheese was manufactured by using five different salting methods (dry salting for one day followed by addition of 6% NaCl brine, dry salting for 1,2 or 3 days followed by addition of 7% NaCl brine and dry salting for 3 days followed by addition of 8% NaCl brine). The effects of salting method and storage time on the composition, physicochemical, organoleptic and rheological properties of feta cheese were studied. It was found that moisture was not affected by salting method or storage time. The salting method but not the storage time had a significant effect on salt content. As the salt content of cheeses increased or the storage time was prolonged the moisture decreased. pH and cheese yield were not influenced by salting method but did decrease with storage time. Protein content was not affected by salting method or storage time, whereas fat content was affected by both factors. Proteolysis, lipolysis, organoleptic and rheological properties of cheeses were not influenced by the salting methods applied. On the other hand, storage time had a significant effect on proteolysis, lipolysis, cheese appearance, fracturability and percentage compression at the yield point. Dry salting of cheese for one day and preservation in 7% NaCl brine was considered as the most appropriate salting method for practical application.     

Objective assessment of cheddar cheese quality

Chemical and physical analyses of cheese are required to objectively assess cheese ripening. Statistical Multivariate Analysis of HPLC and free amino acid data for each of 60 Cheddar cheeses, varying in age and quality, were used to objectively classify the cheeses according to maturity, flavour quality (defective or not) and texture. Additional information was obtained from compositional analysis and gel electrophoresis. The total concentration of free amio acids was more effective than HPLC analysis for discriminating between mild, mature and extra-mature Cheddar cheeses whereas HPLC discriminated more effectively between defective and non-defective.