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 CONTRIBUTION OF HERBS TO THE ACCUMULATION OF HISTAMINE IN "OTLU" CHEESE

The aim of this study was to determine the effect of herbs and the use of raw milk on histamine accumulation in “Otlu” (Herby) cheese during ripening. Cow's milk was used for the cheese production. The milk was divided into two main groups: one was used raw and the other was pasteurized at 65C for 30 min. Each group was further divided into two subparts, one of which was used as control (without herbs), while 2% (w/v) of the herbs were added into the other to produce Herby cheese. All cheeses were ripened at 7C for 90 days. The cheese samples were analyzed in terms of histamine content, titratable acidity, dry matter, salt and degree of ripening on days 5, 30, 60 and 90. Total mesophilic aerobic bacteria (MAB) were also counted during ripening. The use of raw milk and the addition of herb both increased histamine formation in Otlu cheeses (P < 0.05). Moreover, higher water‐soluble nitrogen values, as degree of ripening, were obtained from both raw milk and herb‐added cheeses. The number of MAB was higher in raw cheeses (P < 0.05) and also herb‐added cheeses. The study suggests that the addition of herbs may facilitate histamine formation in Herby cheese.     

Angiotensin‐converting enzyme‐inhibitory and antithrombotic activities of soluble peptide extracts from buffalo and cow milk Cheddar cheeses

The aim of the study was to evaluate potential role of a water‐soluble peptide (WSP) extracts derived from buffalo and cow milk Cheddar cheeses with special reference to their antihypertension and antithrombotic activities. The WSP fractions collected at different stages of ripening were tested to assess their degree of proteolysis, their peptides were profiled by RP‐HPLC and in vitro assays for potential bioactivity were conducted. The peptide peak development was observed with slight differences in peaks number, area and height. Both angiotensin‐converting enzyme‐inhibitory and antithrombotic activities increased progressively during ripening. In comparison, the highest activities were observed in peptide extracts obtained from buffalo milk Cheddar cheese, in a dose‐dependent fashion.     

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.     

Effect of standardization of ewes'' milk for casein/fat ratio on the composition, sensory and rheological properties of Feta cheese

Ewes' milk standardized to four different casein/fat (C/F) ratios (0·80, 0·72, 0·67, 0·62) was used for Feta cheese manufacture. Cheese made from the low C/F ratio (0·62) milk had higher fat, fat in dry matter (FDM) and lower moisture and protein content than cheese made from the high C/F ratio (0·80) milk. With increase in C/F ratio, a significant decrease in fat, and FDM content and increase in protein content of Feta cheese was observed. The other components of cheese were not significantly affected by the C/F ratio of milk used. Also, the yield of cheese, expressed as kg of cheese/100 kg milk, decreased with increase in the C/F ratio of milk. On the other hand, yield expressed as kg of cheese with 56% moisture/kg milk fat increased with increasing C/F ratio. The sensory and rheological properties of cheese were not affected by the four C/F ratios of milk. Conclusions are drawn on the application of these results to Feta cheese manufacture.     

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.     

Survival of micro‐organisms and organic acid profile of probiotic Cheddar cheese from buffalo milk during accelerated ripening

The study aimed to assess the impact of ripening at elevated temperatures on the survival of probiotic micro‐organisms and production of organic acids in Cheddar cheese. Cheese was manufactured from buffalo milk using lactococci starters along with different probiotic bacteria (Lactobacillus acidophilus LA‐5, Bifidobacterium bifidum Bb‐11 and Bifidobacterium longum BB536) as adjunct cultures. The cheeses were ripened at 4–6 °C or 12–14 °C for 180 days and examined for composition, organic acids and microbial survival. The production of organic acids was accelerated at 12–14 °C when compared to normal ripening temperatures. The probiotic bacteria increased production of lactic and acetic acids, compared to cheese made with lactococci alone. The survival of the mesophilic starters was significantly (P < 0.05) reduced in all the cheese samples ripened at the higher temperature. However, the probiotic bacteria remained viable (>7.0 log₁₀ cfu/g) throughout the 180 days of ripening, irrespective of temperature. It was concluded that Cheddar containing additional probiotic cultures can effectively be ripened at elevated temperatures without any adverse effects.     

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.     

The effects of using a starter culture,lipase, and protease enzymes on ripening of Mihalic cheese

The purpose of this study was to determine the effects of fungal lipase from Mucor miehei and a bacterial neutral protease from Bacillus subtilis alone and combined with a starter culture on ripening properties of traditional Turkish Mihalic cheese. The use of protease with lipase (Cult + Prot + Lip) resulted in better flavour and texture with accelerated ripening. The obtained results pointed out that the gross compositions of the cheeses were changed by the type of enzymes and ripening time (P < 0.01). The acid degree value (ADV) of all cheeses showed a linear increase with ripening. The highest lipolysis rate was noted in lipase‐added cheese batch (as 5.56 ADV) with highest γ‐CN ratio and β‐CN degradation. At the end of ripening time, it was observed that αs‐CN ratios decreased in starter‐added (Cult), starter + protease–added (Cult + Prot), and protease‐added (Prot) cheese batches. The use of protease with lipase (Cult + Prot + Lip) resulted in better flavour and texture with accelerated ripening. Protease‐added cheeses, which were characterized by bitterness and crumbly textural properties owing to the intense breakdown of β‐casein, scored lower than lipase‐added cheeses. It was determined that the use of mesophilic aromatic starter culture with lipase and protease could be used to accelerate ripening of Mihalic cheese made from pasteurised milk.     

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.     

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.     

Effects of standardization of whole milk with dry milk protein concentrate on the yield and ripening of reduced-fat cheddar cheese

Commercial milk protein concentrate (MPC) was used to standardize whole milk for reduced-fat Cheddar cheesemaking. Four replicate cheesemaking trials of three treatments (control, MPC1, and MPC2) were conducted. The control cheese (CC) was made from standardized milk (casein-to-fat ratio, C/F approximately 1.7) obtained by mixing skim milk and whole milk (WM); MPC1 and MPC2 cheeses were made from standardized milk (C/F approximately 1.8) obtained from mixing WM and MPC, except that commercial mesophilic starter was added at the rate of 1% to the CC and MPC1 and 2% to MPC2 vats. The addition of MPC doubled cheese yields and had insignificant effects on fat recoveries (approximately 94% in MPC1 and MPC2 vs. approximately 92% in CC) but increased significantly total solids recoveries (approximately 63% in CC vs. 63% in MPC1 and MPC2). Although minor differences were noted in the gross composition of the cheeses, both MPC1 and MPC2 cheeses had lower lactose contents (0.25 or 0.32%, respectively) than in CC (0.60%) 7 d post manufacture. Cheeses from all three treatments had approximately 10(9) cfu/g initial starter bacteria count. The nonstarter lactic acid bacteria (NSLAB) grew slowly in MPC1 and MPC2 cheeses during ripening compared to CC, and at the end of 6 mo of ripening, numbers of NSLAB in the CC were 1 to 2 log cycles higher than in MPC1 and MPC2 cheeses. Primary proteolysis, as noted by water-soluble N contents, was markedly slower in MPC1 and MPC2 cheeses compared to CC. The concentrations of total free amino acids were in decreasing order CC > MPC2 > MPC1 cheeses, suggesting slower secondary proteolysis in the MPC cheeses than in CC. Sensory analysis showed that MPC cheeses had lower brothy and bitter scores than CC. Increasing the amount of starter bacteria improved maturity in MPC cheese.     

Microbiological changes throughout ripening of goat cheese made from raw,pasteurized and high-pressure-treated milk

The bacteriological quality during ripening of raw (RA), pasteurized (PA; 72°C, 15 s) and pressure-treated (PR; 500 MPa, 20°C, 15 min) goat milk assessed by enumeration of total bacteria, psychrotrophic bacteria, Enterobacteriaceae, lactobacilli, enterococci, Micrococcaceae and lactococci was evaluated. The high pressure treatment applied was as efficient as pasteurization in reducing the bacterial population of milk. Experimental cheeses were made from RA, PA and PR milks to study the microbial population during ripening. Lactobacilli and lactococci were the predominant microbiota present during ripening in all the cheeses. There were no differences in numbers of starter bacteria during ripening. However, lactobacilli counts for RA milk cheese were significantly higher than for PA and PR cheeses in all the ripening stages studied. Micrococcaceae and enterococci remained at a secondary level, and no differences were observed between cheeses at the end of ripening. On the other hand, the number of Enterobacteriaceae decreased during ripening, but faster in PR milk cheese than in PA and RA milk cheeses. The results of this study suggest that goat cheese made from PR milk had similar microbiological characteristics to PA milk cheeses.     

Triacylglycerol composition of protected designation of origin cheeses during ripening. Authenticity of milk fat

Triacylglycerol (TAG) composition by carbon number in 2 protected designation of origin cheeses, Mahón (cheese from cow milk) and Manchego (cheese from ewe milk) that were manufactured by 3 different producers was analyzed during cheese ripening using gas chromatography with a short capillary column. The TAG composition at different times during cheese ripening was also analyzed in cheeses from different batches produced at the same plant. Lipolysis levels in the Mahón and Manchego cheeses during ripening were low; free fatty acid values ranged from 2,500 to 4,000 ppm at the end of ripening. The TAG composition did not change significantly during ripening. The TAG values obtained from each cheese sample were substituted into the multiple regression equations that have been proposed to detect foreign fats in milk fat. The values obtained using the equations for bovine (proposed by the European Union) and ovine milk (proposed by our laboratory) were within the normal range. Accordingly, these equations can be considered useful for detecting foreign fat in these cheeses during the ripening period contemplated during this study.     

Characterization of major and trace minerals,fatty acid composition,and cholesterol content of Protected Designation of Origin cheeses

Cheese provides essential nutrients for human nutrition and health, such as minerals and fatty acids (FA). Its composition varies according to milk origin (e.g., species and breed), rearing conditions (e.g., feeding and management), and cheese-making technology (e.g., coagulation process, addition of salt, ripening period). In recent years, cheese production has increased worldwide. Italy is one of the main producers and exporters of cheese. This study aimed to describe mineral, FA, and cholesterol content of 133 samples from 18 commercial cheeses from 4 dairy species (buffalo, cow, goat, and sheep) and from 3 classes of moisture content (hard, <35% moisture; semi-hard, 35–45%; and soft, >45%). Mineral concentrations of cheese samples were determined by inductively coupled plasma optical emission spectrometry, and FA and cholesterol contents were determined by gas chromatography. Moisture and species had a significant effect on almost all traits: the highest levels of Na, Ca, and Fe were found in cheeses made from sheep milk; the greatest level of Cu was found in cow milk cheese, the lowest amount of K was found in buffalo milk cheese, and the lowest amount of Zn was found in goat cheeses. In all samples, Cr and Pb were not detected (below the level of detection). In general, total fat, protein, and minerals significantly increased when the moisture decreased. Buffalo and goat cheeses had the highest saturated FA content, and sheep cheeses showed the highest content of unsaturated and polyunsaturated FA, conjugated linoleic acid, and n-3 FA. Goat and sheep cheeses achieved higher proportions of minor FA than did cow and buffalo cheeses. Buffalo cheese exhibited the lowest cholesterol level. Our results confirm that cheese mineral content is mainly affected by the cheese-making process, whereas FA profile mainly reflects the FA composition of the source milk. This study allowed the characterization of mineral and FA composition and cholesterol content and revealed large variability among different commercial cheeses.     

Effect of activating lactoperoxidase system in cheese milk on the quality of Saint‐Paulin cheese

Saint‐Paulin cheese was made from cow’s milk refrigerated at 4 °C for 72 h and preserved by the lactoperoxidase (LP) system. The effect of the LP system on the microbiological, physicochemical and biochemical properties of cheese over a ripening period of 23 days was investigated, using a control (C0), refrigerated LP‐inactivated cow’s milk (C1) and refrigerated LP‐activated cow’s milk (LPA). The LPA treatment showed the least contamination in flora count, particularly salt‐tolerant bacteria at the end of the ripening period. LPA cheese had significantly lower coliform, yeasts and mould counts (P < 0.05) than the other cheeses; this demonstrated the bacteriostatic effect of the LP system. The proteolysis results showed the least value for LPA cheese as compared with the two other samples, as determined by using sodium dodecyl sulphate‐polyacrylamide gel electrophoresis of casein fractions extracted from the three samples. The findings indicated that the preservation of cow’s cheese milk by the LP system can be used to improve the microbiological quality, inhibit psychotropic germs, correct the losses of soluble nitrogen fractions in the whey and conserve the cheese yield affected by refrigeration.     

Characteristics of Miniature Cheddar‐Type Cheese Made by Microbial Rennet from Bacillus amyloliquefaciens: A Comparison with Commercial Calf Rennet

Miniature Cheddar‐type cheeses were produced using microbial rennet from Bacillus amyloliquefaciens (milk‐clotting enzyme [MCE]) or calf rennet (CAR). With the exception of pH, there were no significant differences in gross composition between MCE‐cheese (MCE‐C) and CAR‐cheese (CAR‐C). The pH value of CAR‐C was significantly higher than that of MCE‐C at 40 and 60 d of ripening. The total nitrogen content of the pH 4.6‐soluble fraction obtained from MCE‐C was higher than that obtained from CAR‐C. However, nitrogen content of the 12% TCA‐soluble fraction was similar between CAR‐C and MCE‐C. The extent of α_s1‐casein and β‐casein hydrolysis, measured by urea‐PAGE, was similar in both cheese samples. The hydrolysis of β‐casein was lower than that of α_s1‐casein. Different reverse phase‐high‐performance liquid chromatography peptide profiles of ethanol‐soluble and ethanol‐insoluble fractions were obtained from CAR‐C and MCE‐C. The peptide content in the 2 cheese samples increased throughout ripening; the ratio of hydrophobic to hydrophilic peptides was lower in MCE‐C than in CAR‐C. Compared with CAR‐C, MCE‐C was softer as a result of higher protein hydrolysis. Microbial rennet from B. amyloliquefaciens contributed to higher proteolytic rates, which reduced ripening time.     

Proteolysis texture and microstructure of low‐fat Tulum cheese affected by exopolysaccharide‐producing cultures during ripening

The objective of the study was to determine the effects of exopolysaccharide (EPS)‐producing or non‐EPS‐producing starters on proteolysis, physical and microstructural characteristics of full‐fat or low‐fat Tulum cheeses during ripening. For this purpose, Tulum cheese was manufactured using full‐ or low‐fat milk with EPS‐producing and non‐EPS‐producing starter cultures. Chemical composition, proteolysis, texture profiles and microstructure of the cheeses were studied during 90 days of ripening. Urea‐PAGE of water‐insoluble and RP‐HPLC peptide profiles of water‐soluble fractions of the cheeses showed that the use of starters resulted in different degradation patterns in all cheeses during ripening. Although β‐casein exhibited similar degradation patterns in all cheeses, small differences are present in α_s1‐casein degradation during ripening. Reducing fat in Tulum cheese changed the RP‐HPLC peptide profile of the cheeses. The use of EPS‐producing cultures improved the textural characteristics and changed the microstructure and proteolysis of low‐fat Tulum cheese.     

Effects of Penicillium roqueforti and whey cheese on gross composition,microbiology and proteolysis of mould‐ripened Civil cheese during ripening

Four different types of mould‐ripened Civil cheese were manufactured. A defined (nontoxigenic) strain of a Penicillium roqueforti (SC 509) was used as the secondary starter with and without addition of the whey cheese (Lor); in parallel, secondary starter‐free counterparts were manufactured. Chemical composition, microbiology and proteolysis were studied during the ripening. The incorporation of whey cheese in the manufacture of mould‐ripened Civil cheese altered the gross composition and adversely affected proteolysis in the cheeses. The inoculated P. roqueforti moulds appeared to grow slowly on those cheeses, and little proteolysis was evident in all cheese treatments during the first 90 days of ripening. However, sharp increases in the soluble nitrogen fractions were observed in all cheeses after 90 days. Microbiological analysis showed that the microbial counts in the cheeses were at high levels at the beginning of ripening, while their counts decreased approximately 1–2 log cfu/g towards the end of ripening.     

Influence of ovine milk in mixture with bovine milk on the quality of reduced fat Muenster-type cheese

Reduced fat Muenster-type cheeses were manufactured from a mixture of bovine skim milk and ovine whole milk and from bovine milk only (control). Cheeses were evaluated at 15, 30, 60, 90, 120, and 180 d of age for numbers and type of microflora, casein hydrolysis, and amounts of free fatty acids. alpha(s1)-Casein degradation was similar for both cheeses during the aging period, but beta-casein degradation proceeded at a faster rate in the control cheese. The total amounts of free fatty acids remained constant throughout the ripening time; however, the cheeses produced with bovine/ovine milk yielded a significantly larger amount of caprylic (C8:0) and capric (C10:0) acids compared with the bovine milk cheeses. Lactobacilli increased during the aging period, while the populations of lactic acid bacteria, yeast and molds, and lipolytic organisms did not increase. Both cheeses had comparable cheese flavor intensity, but the bovine/ovine milk cheese had a greater occurrence of off flavors. The bovine/ovine milk cheeses were firmer than the bovine cheeses throughout the aging period.