Effects of protein and fat levels in milk on cheese and whey compositions

Bulk tank milk was standardised to six levels of fat (3·0, 3·2, 3·4, 3·6, 3·8, 4·0%) and similarly to six levels of protein, thus giving a total of 36 combinations in composition. Milk was analyzed for total solids, fat, protein, casein, lactose and somatic cell count and was used to make laboratory-scale cheese. Cheese samples from each batch were assayed for total solids, fat, protein and salt. Losses of milk components in the whey were also determined. Least squares analysis of data indicated that higher protein level in milk was associated with higher protein and lower fat contents in cheese. This was accompanied by lower total solids (higher moisture) in cheese. Inversely, higher fat level in milk gave higher fat and lower protein and moisture contents in cheese. Higher fat level in milk resulted in lower retention of fat in cheese and more fat losses in the whey. Higher protein level in milk gave higher fat retention in cheese and less fat losses in the whey. Regression analysis showed that cheese fat increased by 4·22%, while cheese protein decreased by 2·61% for every percentage increase in milk fat. Cheese protein increased by 2·35%, while cheese fat decreased by 6·14% per percentage increase in milk protein. Milk with protein to fat ratio close to 0·9 would produce a minimum of 50% fat in the dry matter of cheese.     

Effects of protein and fat levels in milk on Cheddar cheese yield

Over a 14-month period, bulk tank milk was collected twice a week and was adjusted with cream and skim milk powder to provide six levels each of fat and protein varying from 3·0 to 4·0%. Milk samples were analyzed for total solids, fat, protein, casein, lactose and somatic cell count and were used for laboratory-scale cheesemaking. Data obtained from the milk input and the cheese output were used to determine actual, moisture adjusted, theoretical yield, and efficiency of yield. Least squares analyses of data indicated that higher cheese yields were obtained from higher fat and protein contents in milk. Higher yield efficiency was associated with higher ratios of protein to fat and casein to fat. Regression analysis indicated that a percentage increase in fat content in milk resulted in an increase of 1·23–1·37% in moisture adjusted yield in the different protein levels. For a similar increase of protein in milk, there were 1·80–2·04% increase in moisture adjusted yields in different fat levels.     

Accelerated ripening of low fat Ras cheese by attenuated lactobacilli cells

Thirteen Ras cheese were made from 4% fat raw milk; 3% raw and heat treated; 2% raw and heat treated milks in order to study the effect of freeze-shocked or heat-shocked L. casei NIH 334 or L. helveticus CNRZ 53 on the quality of the resultant cheeses. The soluble nitrogen, soluble tyrosine, soluble tryptophan, total volatile fatty acids, titratable acidity and organoleptic evaluation scores increased as ripening period progressed, while moisture decreased. Neither strain nor the heated lactobacilli had significant effects on moisture content of cheeses, while increasing their acidity. Cheeses with freeze-shocked L. casei or L. helveticus had higher titratable acidity than cheeses in which heat-shocked cells were added. However, cheeses added L. helveticus had higher acidity than those with L. casei. Ripening indices (soluble nitrogen, soluble tyrosine, soluble tryptophan and total volatile fatty acids) and organoleptic evaluation scores had similar trends. Cheeses with attenuated lactobacilli had higher ripening indices and cheese scores than cheeses without lactobacilli. Addition of either freeze-shocked L. casei or L. helveticus yielded cheeses having higher ripening indices and organoleptic scores than cheeses made with heat-shocked lactobacilli. The best cheeses were made from 3% fat milk heated to 70 °C, and containing freeze-shocked L. helveticus followed by cheeses made from 2% fat milk heated to 75 °C and containing freeze-shocked L. helveticus.     

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.     

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.     

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.     

Effect of protein-to-fat ratio of milk on the composition, manufacturing efficiency, and yield of cheddar cheese

Twenty-three Cheddar cheeses were prepared from milks with a protein content of 3.66% (wt/wt) and with different protein-to-fat ratio (PFR) in the range 0.70 to 1.15; the PFR of each milk differed by 0.02. For statistical analysis, the 23 cheeses were divided into 3 PFR groups: low (LPFR; 0.70 to 0.85), medium (MPFR; 0.88 to 1.00) and high (HPFR; 1.01 to 1.15), which were compared using ANOVA. The numbers of PFR values in the LPFR, MPFR, and HPFR groups were 9, 7, and 7, respectively. Data were also analyzed by linear regression analysis to establish potentially significant relationships among the PFR and response variables. Increasing PFR significantly increased the levels of cheese moisture, protein, Ca, and P, but significantly reduced the levels of moisture in nonfat substances, fat-in-DM, and salt-in-moisture. The percentage of milk fat recovered in the LPFR cheese was significantly lower than that in the MPFR or HPFR cheeses. In contrast, the recovery of water from milk to the LPFR cheese was significantly higher than that in the MPFR or HPFR cheeses. Increasing the PFR led to a significant decrease in the actual yield of cheese per 100 kg of milk but a significant increase occurred in the normalized yield of cheese per 100 kg of milk with reference values of fat plus protein (3.4 and 3.3%, wt/wt, respectively). The results demonstrate that alteration of the PFR of cheese milk in the range 0.70 to 1.15 has marked effects on cheese composition, component recoveries, and cheese yield.     

The potential of immobilized cell technology to produce freeze-dried, phage-protected cultures of Lactococcus lactis

Lactococcus lactis cells were immobilized in calcium alginate beads and added to growth media to enable biomass production in the gel. The immobilized population was then freeze-dried. Survival during freeze-drying (FD), stability upon high-temperature storage and residual humidity were evaluated. This culture was compared to a classical liquid starter and fresh beads of immobilized L. lactis in simulated quarg manufacture. Acidifying characteristics, proteolytic activity, sensitivity to bacteriophage and sensory properties of quarg products were evaluated.

The population in the beads prior to FD was 7 × 10¹⁰ CFU/g. The best survival rate to FD (62–79%) was obtained when the beads were mixed with a milk-based protective solution. In the absence of protective ingredients (milk solids, sucrose and vitamin C) the alginate beads had high water content following FD. Survival of the immobilized cells during FD was as high for immobilized cells as that of free cells. Stability of the immobilized cells at high-temperature storage (45–55°C) was higher than for the free cells. Quarg cheese was succesfully produced in 5 h with the immobilized freeze-dried (IFD) culture, but sensory evaluation confirmed a significant texture difference between cheeses made with free or IFD cultures. Higher inoculation rates were required with the IFD culture to obtain the same acidifying activity as classical fresh liquid starters. The IFD culture performed well under phage contamination; following a 6-h fermentation, 30% of the cells remained viable and active in the phage-contaminated sample. Increase in non-protein amino compounds (0·2 g/100 g cheese) over a 30-day storage period at 4°C was similar in quarg cheeses made with fresh or IFD starters, despite the higher inoculation rate used with the IFD culture.     

Composition, yield, and functionality of reduced-fat Oaxaca cheese: effects of using skim milk or a dry milk protein concentrate

The effect of adding either skim milk or a commercial dry milk protein concentrate (MPC) to whole milk on the composition, yield, and functional properties of Mexican Oaxaca cheese were investigated. Five batches of Oaxaca cheeses were produced. One batch (the control) was produced from whole milk containing 3.5% fat and 9% nonfat solids (SNF). Two batches were produced from milk standardized with skim milk to 2.7 and 1.8% fat, maintaining the SNF content at 9%. In the other 2 batches, an MPC (40% protein content) was used to standardize the milk to a SNF content of 10 and 11%, maintaining the milk fat content at 3.5%. The use of either skim milk or MPC caused a significant decrease in the fat percentage in cheese. The use of skim milk or MPC showed a nonsignificant tendency to lower total solids and fat recoveries in cheese. Actual, dry matter, and moisture-adjusted cheese yields significantly decreased with skim milk addition, but increased with MPC addition. However, normalized yields adjusted to milk fat and protein reference levels did not show significant differences between treatments. Considering skim milk-added and control cheeses, actual yield increased with cheese milk fat content at a rate of 1.34 kg/kg of fat (R = 0.88). In addition, cheese milk fat and SNF:fat ratio proved to be strong individual predictors of cheese moisture-adjusted yield (r² ≈ 0.90). Taking into account the results obtained from control and MPC-added cheeses, a 2.0-kg cheese yield increase rate per kg of milk MPC protein was observed (R = 0.89), with TS and SNF being the strongest predictors for moisture adjusted yield (r² ≈ 0.77). Reduced-fat Oaxaca cheese functionality differed from that of controls. In unmelted reduced-fat cheeses, hardness and springiness increased. In melted reduced-fat cheeses, meltability and free oil increased, but stretchability decreased. These changes were related to differences in cheese composition, mainly fat in dry matter and calcium in SNF.     

PRELIMINARY OBSERVATIONS ON EFFECTS OF FAT CONTENT AND DEGREE OF FAT EMULSIFICATION ON THE STRUCTURE-FUNCTIONAL RELATIONSHIP OF CHEDDAR-TYPE CHEESE

Cheddar type cheeses of different fat contents were produced and denoted: full-fat (FFC), 306g/kg; half-fat (HFC), 174 g/kg; and low fat (LFC, 13 g/kg). Full-fat Cheddar cheese (FFCH) was also prepared from milk which had been homogenized at first and second stage pressures of 25 and 5 MPa, respectively. The cheeses were held at 4C for 30 days and at 7C for the remainder of the 190-day ripening period. Reducing the fat level from 174 to 13 g/kg resulted in decreases in contents of moisture in nonfat substance and pH 4.6 soluble N as a percentage of total N (pH4.6SN), and increases in the contents of moisture, protein and intact casein. Homogenization of cheesemilk resulted in a slight increase in moisture content and an increase in pH4.6SN. Confocal laser scanning microscopy revealed that the extent of fat globule clumping and coalescence in both the unheated and heated (to 95C) cheeses decreased with homogenization of the cheesemilk and with fat reduction. Homogenization of the cheesemilk and reducing the fat content of the cheese resulted in a decrease in the flowability and stretchability of the melted cheese. Dynamic measurement of the viscoelastic changes on heating the cheese from 20 to 90C showed that reduction of fat content resulted in a decrease in the magnitude of the phase angle, δ, at temperatures >50C. At temperatures<∼60C, the storage modulus, G', increased on reducing the fat content from 306–174 g/kg to 13 g/kg. Homogenization resulted in a marked decrease in δ at temperatures>45–50C, with δ_max typically decreasing from ∼65–70° in the FFC to ∼35° in the FFCH.     

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.     

Evaluation of iron‐fortified Feta cheese for physicochemical and sensory properties

Standardised cow's milk (fat 3 g/100 g) was used to manufacture Feta cheese fortified with 40, 60 and 80 mg of iron/kg cheese using ferrous sulphate (FeSO₄), ferric chloride (FeCl₃), ferric pyrophosphate (Fe₄ (P₂O₇)₃) and microencapsulated ferrous sulphate. Chemical composition and sensory characteristics of fortified cheeses were determined after 60 days of ripening, during which the iron content and thiobarbituric acid (TBA) values were measured. The metallic taste, colour, flavour, overall score and TBA values were statistically (P < 0.05) affected by the source and concentration of iron. The best quality was found in cheeses fortified with 40 mg/kg of microencapsulated ferrous sulphate.     

Short communication: Effects of milk fat depression induced by a dietary supplement containing trans-10, cis-12 conjugated linoleic acid on properties of semi-hard goat cheese

Dietary supplements of conjugated linoleic acid (CLA) containing trans-10, cis-12 CLA reduce milk fat synthesis in lactating goats. This study investigated effects of milk fat depression induced by dietary CLA supplements on the properties of semi-hard goat cheese. Thirty Alpine does were randomly assigned to 1 of 3 groups and fed diets with lipid-encapsulated CLA that provided trans-10, cis-12 CLA at 0 (control), 3 (CLA-1), and 6 g/d (CLA-2). The experiment was a 3 × 3 Latin square design. Periods were 2 wk in length, each separated by 2-wk periods without CLA supplements. Bulk milk was collected on d 3 and 13 of each of 3 periods for cheese manufacture. The largest decrease (23.2%) in milk fat content, induced by the high dosage (6 g/d per doe) of trans-10, cis-12 CLA supplementation at d 13 of treatment, resulted in decreases of cheese yield and moisture of 10.2 and 10.0%, respectively. Although CLA supplementation increased the hardness, springiness, and chewiness, and decreased the cohesiveness and adhesiveness of cheeses, no obvious defects were detected and no significant differences were found in sensory scores among cheeses. In conclusion, milk fat depression induced by a dietary CLA supplement containing trans-10, cis-12 CLA resulted in changes of fat-to-protein ratio in cheese milk and consequently affected properties of semi-hard goat cheese.     

Short communication: Norbixin and bixin partitioning in Cheddar cheese and whey

The Cheddar cheese colorant annatto is present in whey and must be removed by bleaching. Chemical bleaching negatively affects the flavor of dried whey ingredients, which has established a need for a better understanding of the primary colorant in annatto, norbixin, along with cheese color alternatives. The objective of this study was to determine norbixin partitioning in cheese and whey from full-fat and fat-free Cheddar cheese and to determine the viability of bixin, the nonpolar form of norbixin, as an alternative Cheddar cheese colorant. Full-fat and fat-free Cheddar cheeses and wheys were manufactured from colored pasteurized milk. Three norbixin (4% wt/vol) levels (7.5, 15, and 30 mL of annatto/454 kg of milk) were used for full-fat Cheddar cheese manufacture, and 1 norbixin level was evaluated in fat-free Cheddar cheese (15 mL of annatto/454 kg of milk). For bixin incorporation, pasteurized whole milk was cooled to 55°C, and then 60 mL of bixin/454 kg of milk (3.8% wt/vol bixin) was added and the milk homogenized (single stage, 8 MPa). Milk with no colorant and milk with norbixin at 15 mL/454 kg of milk were processed analogously as controls. No difference was found between the norbixin partition levels of full-fat and fat-free cheese and whey (cheese mean: 79%, whey: 11.2%). In contrast to norbixin recovery (9.3% in whey, 80% in cheese), 1.3% of added bixin to cheese milk was recovered in the homogenized, unseparated cheese whey, concurrent with higher recoveries of bixin in cheese (94.5%). These results indicate that fat content has no effect on norbixin binding or entrapment in Cheddar cheese and that bixin may be a viable alternative colorant to norbixin in the dairy industry.     

Influence of rate of inclusion of microalgae on the sensory characteristics and fatty acid composition of cheese and performance of dairy cows

Modification of milk and cheese fat to contain long-chain n-3 fatty acids (FA) by feeding microalgae (ALG) to dairy cows has the potential to improve human health, but the subsequent effect on the sensory attributes of dairy products is unclear. The objective was to determine the effect of feeding dairy cows different amounts of ALG that was rich in docosahexaenoic acid (DHA) on milk and cheese FA profile, cheese sensory attributes, and cow performance. Twenty Holstein dairy cows were randomly allocated to 1 of 4 dietary treatments in a 4 × 4 row and column design, with 4 periods of 28 d, with cheddar cheese production and animal performance measurements undertaken during the final 7 d of each period. Cows were fed a basal diet that was supplemented with ALG (Schizochytrium limancinum) at 4 rates: 0 (control, C), 50 (LA), 100 (MA), or 150 g (HA) of ALG per cow per day. We found that both milk and cheese fat content of DHA increased linearly with ALG feed rate and was 0.29 g/100 g FA higher in milk and cheese from cows fed HA compared with C. Supplementation with ALG linearly reduced the content of saturated FA and the ratio of n-6:n-3 FA in milk and cheese. Supplementation with ALG altered 20 out of the 32 sensory attributes, with a linear increase in cheese air holes, nutty flavor, and dry mouth aftertaste with ALG inclusion. Creaminess of cheese decreased with ALG inclusion rate and was positively correlated with saturated FA content. We also observed a quadratic effect on fruity odor, which was highest in cheese from cows fed HA and lowest in LA, and firmness and crumbliness texture, being highest in MA and lowest in HA. Supplementation with ALG had no effect on the dry matter intake, milk yield, or live weight change of the cows, with mean values of 23.1, 38.5, and 0.34 kg/d respectively, but milk fat content decreased linearly, and energy-corrected milk yield tended to decrease linearly with rate of ALG inclusion (mean values of 39.6, 38.4, 37.1, and 35.9 g/kg, and 41.3, 41.3, 40.5, and 39.4 kg/d for C, LA, MA, and HA, respectively). We conclude that feeding ALG to high-yielding dairy cows improved milk and cheese content of DHA and altered cheese taste but not cow performance, although milk fat content reduced as inclusion rate increased.     

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.     

Effects of fat on the properties of halloumi cheese

Halloumi cheese was produced from 11 bovine milks with fat contents of 1.61–4.04%, giving a range of 32–53% fat in dry matter (FDM) in the cheeses. Starter culture and/or microparticulated whey protein (Simplesse ^® 100(E)) was also added to selected batches of milk. Hardness decreased with increasing FDM, with increase in moisture and with lower pH. On sensory evaluation, there was an increase in preference score with FDM ( R ²   = 0.8). Inclusion of microparticulated whey protein may have had a fat mimetic effect, as preference scores otherwise decreased with increasing protein levels ( R ² = 0.75).     

Transglutaminase-mediated incorporation of whey protein as fat replacer into the formulation of reduced-fat Iranian white cheese: physicochemical,rheological and microstructural characterization

The effects of transglutaminase treatment (0–2 units/g milk protein) on the chemical composition, textural characteristics, proteolysis and yield of reduced-fat Iranian white cheese (milk fat: 0.4–1.4% w/w) incorporated with whey proteins (0–6 g/L milk) were investigated. Enzyme-mediated inclusion of whey proteins in the reduced-fat cheese caused a noticeable increase in moisture to protein (M:P) ratio with concomitant decease in the hardness rheological parameters of fracture stress and Young’s and storage (G’) moduli. However, increase in concentrations of whey proteins or/and transglutaminase enzyme above a critical level led to formation of a cheese matrix with lower moisture content and greater values of hardness indices. Whey protein addition and transglutaminase treatment resulted in the same trends of changes in proteolysis rate and cheese yield as in cheese softness. Response surface method (RSM) suggested that the enzymatic incorporation of 4.2 g deliberately added whey proteins to 1 L of milk (1.04% w/w fat) into the cheese matrix using 0.833 unit transglutaminase per gram milk protein would provide a reduced-fat product with the softest texture and the highest yield. The scanning electron micrographs showed formation of honeycomb structures in the protein matrix of the reduced-fat sample with optimum formulation.     

Fate of Aflatoxin M1 during Manufacture and Storage of Feta Cheese

ABSTRACT:  The effect of feta cheese manufacture on aflatoxin M₁ (AFM₁) content was studied using an enzyme immunoassay technique. Feta cheese was made from milk spiked with 1 and 2 μg AFM₁ per kilogram milk. Pasteurization at 63 °C for 30 min caused <10% destruction of AFM₁. During cheese making, the remaining AFM₁ in milk was partitioned between curd and whey with two-thirds retained in the curd and one-third going into the whey. Cheeses were then stored for 2 mo in 8%, 10%, and 12% brine solutions at 6 and 18 °C. There was a 22% to 27% reduction of AFM₁ during the first 10 d of storage, with slightly more loss as salt concentration increased and when the cheese was stored at 18 °C. Further storage caused only slight decrease in AFM₁ and after 30 d of brining there was no difference in AFM₁ content of the cheese based upon salt concentration of the brine. At 18 °C, no further losses of AFM₁ occurred after 30 d, and at 6 °C, there was continued slight decrease in AFM₁ levels until 50 d. After 60 d of brining, there was a total loss of 25% and 29% of the AFM₁ originally present for cheese brined at 6 and 18 °C, respectively. Thus, the combination of pasteurization, conversion of milk into feta cheese, and at least 50 d storage of cheese in brine caused a total loss of about 50% of the AFM₁ originally present in the raw milk.     

Use of an exopolysaccharide-producing strain of Streptococcus thermophilus in the manufacture of Mexican Panela cheese

An exopolysaccharide (EPS) producing strain of Streptococcus thermophilus was evaluated for the production of Panela cheese using two total solids milk (TSM) concentrations (12.5 and 17.5 g/100 mL). This ropy strain increased cheese yield; nevertheless, with 12.5 TSM the increment was higher than with 17.5 TSM. Analysis of cheese composition showed that with 12.5 TSM, the ropy strain increased moisture, but did not change the fat or non fat solids on dry weight basis (dwb), suggesting that the increment of the yield is only due to water retention. In 17.5 TSM cheeses the ropy strain caused an increase in the moisture and fat (dwb), suggesting that besides water retention, fat also contributed to the yield. The difference in yield increment could be explained by cheese composition: higher fat content creates a more hydrophobic environment, which would expel more water than the cheese with lower fat content. Electron microscopy showed EPS attached to the protein matrix of the cheeses. In 17.5 TSM cheeses EPS was observed around the milk fat globules (MFG), confirming that higher TSM causes EPS to bind the MFG besides binding the protein matrix, retaining fat within the cheese. Sensory evaluation demonstrated that ropy cheeses were softer and creamier.