Reduced fat process cheese made from young reduced fat Cheddar cheese manufactured with exopolysaccharide-producing cultures.

In a previous study, exopolysaccharide (EPS)-producing cultures improved textural and functional properties of reduced fat Cheddar cheese. Because base cheese has an impact on the characteristics of process cheese, we hypothesized that the use of EPS-producing cultures in making base reduced fat Cheddar cheese (BRFCC) would allow utilization of more young cheeses in making reduced fat process cheese. The objective of this study was to evaluate characteristics of reduced fat process cheese made from young BRFCC containing EPS as compared with those in cheese made from a 50/50 blend of young and aged EPS-negative cheeses. Reduced fat process cheeses were manufactured using young (2 d) or 1-mo-old EPS-positive or negative BRFCC. Moisture and fat of reduced fat process cheese were standardized to 49 and 21%, respectively. Enzyme modified cheese was incorporated to provide flavor of aged cheese. Exopolysaccharide-positive reduced fat process cheese was softer, less chewy and gummy, and exhibited lower viscoelastic moduli than the EPS-negative cheeses. The hardness, chewiness, and viscoelastic moduli were lower in reduced fat process cheeses made from 1-mo-old BRFCC than in the corresponding cheeses made from 2-d-old BRFCC. This could be because of more extensive proteolysis and lower pH in the former cheeses. Sensory scores for texture of EPS-positive reduced fat process cheeses were higher than those of the EPS-negative cheeses. Panelists did not detect differences in flavor between cheeses made with enzyme modified cheese and aged cheese. No correlations were found between the physical and melting properties of base cheese and process cheese.

Effect of vacuum-condensed or ultrafiltered milk on pasteurized process cheese.

Milk was concentrated by ultrafiltration (UF) or vacuum condensing (CM) and milks with 2 levels of protein: 4.5% (UF1 and CM1) and 6.0% (UF2 and CM2) for concentrates and a control with 3.2% protein were used for manufacturing 6 replicates of Cheddar cheese. For manufacturing pasteurized process cheese, a 1:1 blend of shredded 18- and 30-wk Cheddar cheese, butter oil, and disodium phosphate (3%) was heated and pasteurized at 74 degrees C for 2 min with direct steam injection. The moisture content of the resulting process cheeses was 39.4 (control), 39.3 (UF1), 39.4 (UF2), 39.4 (CM1), and 40.2% (CM2). Fat and protein contents were influenced by level and method of concentration of cheese milk. Fat content was the highest in control (35.0%) and the lowest in UF2 (31.6%), whereas protein content was the lowest in control (19.6%) and the highest in UF2 (22.46%). Ash content increased with increase in level of concentration of cheese milk with no effect of method of concentration. Meltability of process cheeses decreased with increase in level of concentration and was higher in control than in the cheeses made with concentrated milk. Hardness was highest in UF cheeses (8.45 and 9.90 kg for UF1 and UF2) followed by CM cheeses (6.27 and 9.13 kg, for CM1 and CM2) and controls (3.94 kg). Apparent viscosity of molten cheese at 80 degrees C was higher in the 6.0% protein treatments (1043 and 1208 cp, UF2 and CM2) than in 4.5% protein treatments (855 and 867 cp, UF1 and CM1) and in control (557 cp). Free oil in process cheeses was influenced by both level and method of concentration with control (14.3%) being the lowest and CM2 (18.9%) the highest. Overall flavor, body and texture, and acceptability were higher for process cheeses made with the concentrates compared with control. This study demonstrated that the application of concentrated milks (UF or CM) for Cheddar cheese making has an impact on pasteurized process cheese characteristics.

Bioavailability of vitamin D from fortified process cheese and effects on vitamin D status in the elderly.

We conducted 2 studies to determine the effect of vitamin D-fortified cheese on vitamin D status and the bioavailability of vitamin D in cheese. The first study was designed to determine the effect of 2 mo of daily consumption of vitamin D3-fortified (600 IU/d) process cheese on serum 25-hydroxyvitamin D (25-OHD), parathyroid hormone (PTH), and osteocalcin (OC) concentrations among 100 older (> or =60 yr) men and women. Participants were randomized to receive vitamin D-fortified cheese, nonfortified cheese, or no cheese. Serum levels of 25-OHD, PTH, and OC were measured at the beginning and end of the study. There were no differences in 25-OHD, PTH, or OC after 2 mo of fortified cheese intake. The vitamin D-fortified cheese group had a greater decrease in 25-OHD than other groups, due to higher baseline 25-OHD. A second study was conducted to determine whether the bioavailability of vitamin D2 in cheese (delivering 5880 IU of vitamin D2/56.7-g serving) and water (delivering 32,750 IU/250 mL) is similar and whether absorption differs between younger and older adults. The second study was a crossover trial involving 2 groups of 4 participants each (younger and older group) that received single acute feedings of either vitamin D2-fortified cheese or water. Serial blood measurements were taken over 24 h following the acute feeding. Peak serum vitamin D and area under the curve were similar between younger (23 to 50 yr) and older (72 to 84 yr) adults, and vitamin D2 was absorbed more efficiently from cheese than from water. These studies demonstrated that vitamin D in fortified process cheese is bioavailable, and that young and older adults have similar absorption. Among older individuals, consuming 600 IU of vitamin D3 daily from cheese for 2 mo was insufficient to increase serum 25-OHD during limited sunlight exposure.

Comparison of effect of vacuum-condensed and ultrafiltered milk on cheddar cheese.

The objective of this study was to compare the effects of vacuum-condensed (CM) and ultrafiltered (UF) milk on some compositional and functional properties of Cheddar cheese. Five treatments were designed to have 2 levels of concentration (4.5 and 6.0% protein) from vacuum-condensed milk (CM1 and CM2) and ultrafiltered milk (UF1 and UF2) along with a 3.2% protein control. The samples were analyzed for fat, protein, ash, calcium, and salt contents at 1 wk. Moisture content, soluble protein, meltability, sodium dodecyl sulfate-PAGE, and counts of lactic acid bacteria and nonstarter lactic acid bacteria were performed on samples at 1, 18, and 30 wk. At 1 wk, the moisture content ranged from 39.2 (control) to 36.5% (UF2). Fat content ranged from 31.5 to 32.4% with no significant differences among treatments, and salt content ranged from 1.38 to 1.83% with significant differences. Calcium content was higher in UF cheeses than in CM cheeses followed by control, and it increased with protein content in cheese milk. Ultrafiltered milk produced cheese with higher protein content than CM milk. The soluble protein content of all cheeses increased during 30 wk of ripening. Condensed milk cheeses exhibited a higher level of proteolysis than UF cheeses. Sodium dodecyl sulfate-PAGE showed retarded proteolysis with increase in level of concentration. The breakdown of alphas1- casein and alphas1-I-casein fractions was highest in the control and decreased with increase in protein content of cheese milk, with UF2 being the lowest. There was no significant degradation of beta-casein. Overall increase in proteolytic products was the highest in control, and it decreased with increase in protein content of cheese milk. No significant differences in the counts of lactic starters or nonstarter lactic acid bacteria were observed. Extent as well as method of concentration influenced the melting characteristics of the cheeses. Melting was greatest in the control cheeses and least in cheese made from condensed milk and decreased with increasing level of milk protein concentration. Vacuum condensing and ultrafiltration resulted in Cheddar cheeses of distinctly different quality. Although both methods have their advantages and disadvantages, the selection of the right method would depend upon the objective of the manufacturer and intended use of the cheese.

Reduction of salt (NaCl) losses during the manufacture of cheddar cheese.

The objective of this study was to evaluate the effects of cheese-making technologies, including homogenization of cream, ultrafiltration, and vacuum condensing of milk, on the retention of salt in Cheddar cheese. One part of pasteurized, separated milk (0.58% fat) was ultrafiltered (55 degrees C, 16.0% protein), another vacuum condensed (12.5% protein), and the third was not concentrated. Cheddar cheese was manufactured using 6 treatments by standardizing unconcentrated milk to a casein-to-fat ratio of 0.74 with unhomogenized 35% fat cream (C), homogenized (6.9 MPa/3.5 MPa) 35% fat cream (CH), ultrafiltered milk and unhomogenized cream (UF), ultrafiltered milk and homogenized cream (UFH), condensed milk and unhomogenized cream (CM), and condensed milk and homogenized cream (CMH). Treatments C and CH had 3.7% fat and 3.5% protein, and the respective values for the remaining treatments were 4.9 and 4.6. The milled curd was dry salted at 2.7% by weight. The salt content of the cheeses receiving homogenization treatment was higher at 1.83 and 1.70% for CH and UFH, respectively, compared with their corresponding controls at 1.33%. The salt content in cheeses from CMH was 1.64% and was not affected by homogenization. Salt retention in C increased from 41.7 to 59.2% in CH, and in UF it increased from 42.5 to 54.5% in UFH. There was a corresponding decrease in the salt content of whey from these cheeses.

Estimation and fortification of vitamin D3 in pasteurized process cheese.

The objective of this study was to develop methods for the estimation and fortification of vitamin D3 in pasteurized Process cheese. Vitamin D3 was estimated using alkaline saponification at 70 degrees C for 30 min, followed by extraction with petroleum ether:diethyl ether (90:10 vol/vol) and HPLC. The retention time for vitamin D3 was approximately 9 min. A standard curve with a correlation coefficient of 0.972 was prepared for quantification of vitamin D3 in unknown samples. In the second phase of the study, pasteurized Process cheeses fortified with commercial water- or fat-dispersible forms of vitamin D3 at a level of 100 IU per serving (28 g) were manufactured. There was no loss of vitamin D3 during Process cheese manufacture, and the vitamin was uniformly distributed. No losses of the vitamin occurred during storage of the fortified cheeses over a 9-mo period at 21 to 29 degrees C and 4 to 6 degrees C. There was an approximately 25 to 30% loss of the vitamin when cheeses were heated for 5 min in an oven maintained at 232 degrees C. Added vitamin D3 did not impart any off flavors to the Process cheeses as determined by sensory analysis. There were no differences between the water- and fat-dispersible forms of the vitamin in the parameters measured in fortified cheeses.

Influence of salt on the quality of reduced fat cheddar cheese.

Cream was homogenized in a two-stage homogenizer (17.25 MPa in the first stage and 3.43 MPa in the second stage); blended with skim milk to produce milk containing 1.25% fat, which was pasteurized (63 degrees C for 30 min); and then manufactured into reduced fat Cheddar cheese. After milling, the curd was divided into three equal portions of 13 kg each. Three salting rates, 2.3, 3.8, and 5%, yielded cheeses with 1.3, 1.7, and 2.0% salt and 2.7, 3.7, and 4.5% salt in the moisture phase. Cheese moisture contents ranged from 45% (2.0% salt) to 47.7% (1.3% salt), and fat contents ranged from 14.6 to 15.1%. In the texture profile analysis, the hardness and fracturability of the cheeses increased as the salt content increased. Both parameters decreased during ripening, but cheeses with 4.5% salt in the moisture phase remained the hardest. Cheeses with the most salt had the least desirable body characteristics, but there were no differences in flavor. Intensity of bitterness was lowered as the amount of salt in cheese increased. During ripening, the number of lactic acid bacteria decreased more slowly in cheese with 2.7% salt in the moisture phase than in those with 3.7 or 4.5% salt in the moisture phase. As the salt content increased, proteolysis and the general rate of ripening decreased. Degradation of alpha s-casein was reduced by higher percentages of salt, but no differences were found in the degradation of beta-casein.

Growth characteristics of bifidobacteria in infant formulas.

Four species of bifidobacteria, Bifidobacterium bifidum (ATCC 15696), Bifidobacterium breve (ATCC 15700), Bifidobacterium infantis (ATCC 15697), and Bifidobacterium longum (ATCC 15708), were grown anaerobically at 37 degrees C in lactobacilli MRS broth with 0.5% cysteine-HC1 and inoculated at 2.5% into three types of infant formula (based on soy, or milk, or casein hydrolysate) and in nonfat milk followed by incubation at 37 degrees C for 24 h. In most cases, the logarithmic phase of growth for all species varied from the first 8 to 12 h postinoculation. Generation times for B. longum and B. breve were similar, and times for B. infantis were shortest, in all of the formulas. Trends for lactic acid production for all species in all the formulas were similar to trends for acetic acid production. Counts for formulas based on soy or milk were similar for all species except B. bifidum, and those for casein-hydrolyzed formula were always lowest for all species except B. bifidum, for which count was maximal with the formula based on soy. Results suggest that growth characteristics of bifidobacteria in infant formula were species specific and formula dependent and that growth was maximal in the formula based on milk.

Effect of bifidogenic factors on growth characteristics of bifidobacteria in infant formulas.

A bifidogenic factor, lactulose or fructooligosaccharides, was added (0.5%) into infant formula based on soy or infant formula with hydrolyzed casein. The infant formulas were then inoculated (2.5%) with Bifidobacterium bifidum (ATCC 15696), Bifidobacterium breve (ATCC 15700), Bifidobacterium infantis (ATCC 15697), or Bifidobacterium longum (ATCC 15708) or their mixture (mixed culture) and incubated at 37 degrees C for 24 h. Lactulose did not influence maximal counts or generation times in either formula for any species except B. infantis, which had lower counts. Trends of developed acidity and pH of the mixed culture in the infant formulas with or without lactulose were similar to those for B. breve. Maximal counts and generation times remained unchanged with or without fructooligosaccharides for all species and the mixed culture, except for B. bifidum in the formula based on soy, for which maximal counts did not occur. Growth in either formula was inhibited for B. infantis with lactulose and B. breve with fructooligosaccharides past 8 h of inoculation.

Growth and viability of Bifidobacterium bifidum in cheddar cheese.

Bifidobacterium bifidum (ATCC 15696) was grown in MRS broth containing cysteine.HCl at 37 degrees C, and the cells were harvested by centrifuging at 1300 x g for 15 min at 4 degrees C. Equal volumes of the cell slurry and a 2.5% solution of kappa-carrageenan were mixed and transferred by drops into a solution of .3 M KCl at 20 degrees C under an atmosphere of nitrogen. The gelled beads were separated, frozen, and lyophilized immediately. This preparation and a commercial powder preparation were added to Cheddar cheese curd at milling as two treatments. Treatments did not affect cheese composition. Soluble protein increased during ripening at 7 degrees C but without differences between treatments; SDS-PAGE patterns of proteolysis were also similar. Lactic acid content of cheeses increased during ripening, but differences between treatments were minor. Acetic acid and ethanol, common metabolites of bifidobacteria, were not detected during ripening. Bifidobacteria remained viable and increased in numbers in cheese during this 24-wk study but did not affect the flavor, flavor intensity, texture, or appearance of the cheese compared with that of the control.

Growth characteristics of bifidobacteria in ultrafiltered milk.

Five replicates of raw skim milk were ultrafiltered at 54 degrees C to total protein concentration ratios of 2:1, 3:1, 4:1, and 5:1. Bifidobacterium bifidum and Bifidobacterium longum were inoculated at 5% into skim milk that was not ultrafiltered (1:1) and into ultrafiltered skim milks followed by incubation at 37 degrees C. The mean maximum bacterial count (colony-forming units per milliliter) range and protein concentration ratio were from 6.25 x 10(8) to 1.69 x 10(9), skim milk; 4.42 x 10(8) to 3.56 x 10(9), 2:1; 2.62 x 10(8) to 3.94 x 10(9), 3:1; 6.67 x 10(8) to 1.88 x 10(9), 4:1; and 2.90 x 10(9) to 3.59 x 10(9), 5:1. The mean developed acidity at maximum B. bifidum population in skim milk was .16%, and pH was 5.55. The 5:1 concentrate had a higher mean developed acidity of .57% at pH 5.35, which was similar to that of the skim milk. Trends were similar for B. longum. Because of the increased buffering capacity of highly concentrated ultrafiltered milks, pH 5.5 or higher was maintained longer, along with high developed acidity. Scanning electron micrographs showed distinct morphological variations between bifidobacteria grown in broth versus those grown in the milks.

Manufacture of nonfat yogurt from a high milk protein powder.

Nonfat yogurts were manufactured from skim milk fortified with a new high milk protein powder. The powder, containing approximately 84% milk protein, was added to skim milk to obtain 5.2 to 11.3% total protein, 11.1 to 15% total solids, and 1.6 to 7.9% lactose in the yogurt mix. Mixes were homogenized, pasteurized at 90 degrees C for 10 min, and fermented with a yogurt culture at 42 degrees C to pH 4.6. Controls were made from the same skim milk fortified with NDM to approximately 14% total solids. Yogurts made with the protein powder and containing 5.6% protein were similar in firmness to the control and had good flavor when fresh and after 2 wk of storage. Yogurts with more than 5.6% protein were too firm and had an astringent flavor. Acetaldehyde content of all yogurts was comparable with that of the control, and fat content ranged from .18 to .33%. As the protein content of yogurts increased, the porosity of yogurts, as seen by scanning electron microscopy, decreased. Good quality nonfat yogurts can be produced by supplementing skim milk with a high milk protein powder up to 5.6% protein. The added protein assists in providing a firm body and minimal whey separation without the use of stabilizers.

Influence of milk ultrafiltration on bacteriophages of lactic acid bacteria.

Bacteriophages added to whole milk were partially concentrated during ultrafiltration. At 4:1 retentate, phage had concentrated 2.4:1. Thermal destruction at 54 degrees C followed first order kinetics up to 6% protein, whereafter it deviated. When allowed to grow in retentate in the presence of appropriate host, 3.5 generations of phage appeared after 12 h at 22 degrees C compared with four generations in skim milk. In the presence of phage, lactic acid bacteria population increased to only 10(7) cfu/ml compared with 3 X 10(9) in their absence. Retentate starter prepared in the presence of phage was as active as skim milk starter prepared in the presence of phage.

Growth of lactic acid bacteria in highly concentrated ultrafiltered skim milk retentates.

Buffer capacity of ultrafiltered skim milk retentates at various protein concentrations and growth of direct set, frozen concentrated lactic starter cultures in such retentates were studied. Maximum buffering occurred at approximately pH 5.1 to 5.3. An average .48% lactic acid concentration was required to reduce the pH of plain skim milk to 4.6 compared with 1.01% for skim milk retentates concentrated 2.3:1 and 1.14% for skim milk retentate concentrated 2.6:1. Skim milk retentates concentrated 4.3:1 and 5.8:1 were unable to attain pH 4.6 even when titratable acid was greater than 1.8%. Lactic acid required to reduce pH to 4.6 for the two lower concentrated retentates (2.3:1 and 2.6:1) were 1.85 and 2.45%. Time to attain pH 4.6 was a function of the bacterial cell concentration of the cultures and the total protein level of retentates. Starter organism growth was unaffected by high total solids or ash of retentates. Growth rate and lactose metabolism decreased markedly below pH 5.2 at which point bacterial population was 10(9) cfu/ml.

Use of Time-Temperature Indicators as Quality Control Devices for Market Milk.

i-Point TTM and 3M Monitormark time-temperature indicators were evaluated for their use as quality monitors for market milk. i-Point indicators exhibiting a life span of 10 d at 4.4°C. 8 d at 6.8°C and 6.5 d at 10°C and 3M Monitormark having a response temperature of 5°C and a 14 d maximum exposure time were selected. Fresh HTST pasteurized commercial market milk was stored at 4.4,6.8 or 10°C. Time temperature indicators, activated at the time of storage of milk were followed daily at the three storage temperatures for color development in i-Point TTM and index number in 3M Monitormark. Milks were evaluated for bacterial numbers and acceptability at selected time intervals. Milks generally remained acceptable approximately 4 d after the end of the life span of i-Point indicators at 10°C and more than 10 d at 4.4 °C. 3M Monitormark exhibited insensitivity in the temperature range of 4-10°C. This integration of time as well as temperature makes it possible to replace the sell-by-date on market milk with i-Point TTM indicator to more effectively monitor quality.