Effect of β-lactoglobulin A and B whey protein variants on cheese yield potential of a model milk system

Cheese yield mainly depends on the amount and proportion of milk constituents; however, genetic variants of the proteins present in milk may also have an important effect. The objective of this research was to study the effect of the variants A and B of β-lactoglobulin (LG) on cheese yield using a model system consisting of skim milk powder fortified with different levels of a mixture containing α-lactalbumin and β-LG genetic variants (A, B, or A-B) in a 1:2 ratio. Fortified milk samples were subjected to pasteurization at 65°C for 30 min. Miniature cheeses were made by acidifying (pH = 5.9) fortified milk and incubating with rennet for 1 h at 32°C. The clot formed was cut, centrifuged at 2,600 × g for 30 min at 20°C and drained for determining cheese yield. Cheese-yielding capacity was expressed as actual yield (grams of cheese curd per 100 g of milk) and dry weight yield (grams of dried cheese curd per 100 g of milk). Free-zone capillary electrophoresis was used for determining β-LG A or B recovery in the curd during rennet-induced coagulation. The presence of β-LG variant B resulted in a significantly higher actual and dried weight cheese yield than when A or A-B were present at levels ≤0.675% of whey protein (WP) addition. Results of free-zone capillary electrophoresis allowed us to infer that β-LG B associates with the casein micelles during renneting, as shown by an increase in the recovery of this variant in the curd when β-LG B was added up to a maximum at 0.45% (equivalent to 0.675% WP). In general, actual or dried weight cheese yield increased as WP addition was increased from 0.225 to 0.675%. However, when WP addition ranged from 0.675 to 0.90%, a drastic drop in cheese yield was observed. This behavior may be because an increase in the aggregation of casein micelles with a concomitant inclusion of whey protein in the gel occurs at low levels of WP addition, whereas once the association of WP with the casein micelles reach a saturation point at addition levels higher than 0.675%, rearrangements of the gel network result in larger whey expulsion and syneresis. This knowledge is expected to be useful to maximize cheese yield and optimize processing conditions during cheese and cheese analogs manufacturing.     

Effect of somatic cell count on Prato cheese composition

The objective of this research was to evaluate the effect of 2 levels of somatic cell counts (SCC) in raw milk on Prato cheese composition, protein and fat recovery, cheese yield, and ripening. A 2 × 6 factorial design with 3 replications was performed in this study: 2 levels of SCC and 6 levels of storage time. Initially, 2 groups of dairy cows were selected to obtain low (<200,000 cells/ mL) and high (>600,000 cells/mL) SCC in milks that were used to manufacture 2 vats of cheese: 1) low SCC and 2) high SCC. Milk, whey, and cheese compositions were evaluated; clotting time was measured; and cheese yield, protein recovery, and fat recovery were calculated. The cheeses were evaluated after 5, 12, 19, 26, 33, and 40 d of ripening according to pH, moisture, pH 4.6 soluble nitrogen, 12% trichloroacetic acid soluble nitrogen as a percentage of total nitrogen, and firmness. High-SCC milk presented significantly higher total protein and nonprotein nitrogen and lower true protein and casein concentrations than did low-SCC milk, indicating an increased whey protein content and a higher level of proteolysis. Although the pH of the milk was not affected by the somatic cell level, the cheese obtained from high-SCC milk presented significantly higher pH values during manufacture and a higher clotting time. No significant differences in cheese yield and protein recovery were observed for these levels of milk somatic cells. The cheese from high-SCC milk was higher in moisture and had a higher level of proteolysis during ripening, which could compromise the typical sensory quality of the product.     

Standardization of milk using cold ultrafiltration retentates for the manufacture of Swiss cheese: effect of altering coagulation conditions on yield and cheese quality

Fortification of cheesemilk with membrane retentates is often practiced by cheesemakers to increase yield. However, the higher casein (CN) content can alter coagulation characteristics, which may affect cheese yield and quality. The objective of this study was to evaluate the effect of using ultrafiltration (UF) retentates that were processed at low temperatures on the properties of Swiss cheese. Because of the faster clotting observed with fortified milks, we also investigated the effects of altering the coagulation conditions by reducing the renneting temperature (from 32.2 to 28.3°C) and allowing a longer renneting time before cutting (i.e., giving an extra 5 min). Milks with elevated total solids (TS; ∼13.4%) were made by blending whole milk retentates (26.5% TS, 7.7% CN, 11.5% fat) obtained by cold (<7°C) UF with part skim milk (11.4% TS, 2.5% CN, 2.6% fat) to obtain milk with CN:fat ratio of approximately 0.87. Control cheeses were made from part-skim milk (11.5% TS, 2.5% CN, 2.8% fat). Three types of UF fortified cheeses were manufactured by altering the renneting temperature and renneting time: high renneting temperature = 32.2°C (UFHT), low renneting temperature = 28.3°C (UFLT), and a low renneting temperature (28.3°C) plus longer cutting time (+5 min compared to UFLT; UFLTL). Cutting times, as selected by a Wisconsin licensed cheesemaker, were approximately 21, 31, 35, and 32 min for UFHT, UFLT, UFLTL, and control milks, respectively. Storage moduli of gels at cutting were lower for the UFHT and UFLT samples compared with UFLTL or control. Yield stress values of gels from the UF-fortified milks were higher than those of control milks, and decreasing the renneting temperature reduced the yield stress values. Increasing the cutting time for the gels made from the UF-fortified milks resulted in an increase in yield stress values. Yield strain values were significantly lower in gels made from control or UFLTL milks compared with gels made from UFHT or UFLT milks. Cheese composition did not differ except for fat content, which was lower in the control compared with the UF-fortified cheeses. No residual lactose or galactose remained in the cheeses after 2 mo of ripening. Fat recoveries were similar in control, UFHT, and UFLTL but lower in UFLT cheeses. Significantly higher N recoveries were obtained in the UF-fortified cheeses compared with control cheese. Because of higher fat and CN contents, cheese yield was significantly higher in UF-fortified cheeses (∼11.0 to 11.2%) compared with control cheese (∼8.5%). A significant reduction was observed in volume of whey produced from cheese made from UF-fortified milk and in these wheys, the protein was a higher proportion of the solids. During ripening, the pH values and 12% trichloroacetic acid-soluble N levels were similar for all cheeses. No differences were observed in the sensory properties of the cheeses. The use of UF retentates improved cheese yield with no significant effect on ripening or sensory quality. The faster coagulation and gel firming can be decreased by altering the renneting conditions.     

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.     

Heating of milk alters the binding of curcumin to casein micelles. A fluorescence spectroscopy study

Curcumin, a polyphenolic compound present in turmeric, is a hydrophobic molecule that has been shown to bind to casein micelles. The present work tested the hypothesis that surface changes in the casein micelles caused by heat-induced interactions with the whey proteins would affect the binding of curcumin. Binding was quantified by direct and tryptophan quenching fluorescence spectroscopy. Curcumin binds to the hydrophobic moieties of the casein proteins, with a 10 nm blue shift in its fluorescence emission peak, and causes quenching of the intrinsic fluorescence spectra of the proteins. The fluorescence intensity of curcumin increased after heating of milk at 80 °C for 10 min; a similar trend in the binding constants was also observed with casein micelles separated from the soluble proteins by centrifugation. There was an increase in the non-specific interactions with heating milk at 80 °C for 10 min, both in milk as well as in casein micelles separated from the serum proteins. The increased capacity of milk proteins to bind curcumin after heat treatment can be attributed to whey protein denaturation, as whey proteins bind to the surface of casein micelles with heating.     

High-pressure homogenization of raw and pasteurized milk modifies the yield, composition, and texture of queso fresco cheese

High-pressure homogenization (HPH) of milk was studied as an alternative processing operation in the manufacturing of queso fresco cheese. Raw and pasteurized (65°C for 30 min) milks were subjected to HPH at 0, 100, 200, and 300 MPa and then used to manufacture queso fresco. The cheeses were evaluated for yield, moisture content, titratable acidity, nitrogen content, whey protein content, yield force, yield strain, and tactile texture by instrumental or trained panel analyses. The combination of HPH and thermal processing of milk resulted in cheeses with increased yield and moisture content. The net amount of protein transferred to the cheese per kilogram of milk remained constant for all treatments except raw milk processed at 300 MPa. The highest cheese yield, moisture content, and crumbliness were obtained for thermally processed milk subjected to HPH at 300 MPa. The principal component analysis of all measured variables showed that the variables yield, moisture content, and crumbliness were strongly correlated to each other and negatively correlated to the variables yield strain, protein content (wet basis), and sensory cohesiveness. It is suggested that the combination of thermal processing and HPH promotes thermally induced denaturation of whey protein, together with homogenization-induced dissociation of casein micelles. The combined effect results in queso fresco containing a thin casein-whey matrix that is able to better retain sweet whey. These results indicate that HPH has a strong potential for the manufacture of queso fresco with excellent yield and textural properties.     

Yield and sensory properties of cheese made with milk from Holstein or Montbéliarde cows milked twice or once daily

The aim of this study was to evaluate the milk properties and the yield and sensory properties of Cantal cheese made with milk from Holstein or Montbéliarde cows milked once or twice daily. Sixty-four grazing cows [32 Holstein (H) and 32 Montbéliarde (M) cows] in the declining phase of lactation (157 d in milk) were allocated to 1 of 2 equivalent groups milked once daily (ODM) or twice daily (TDM) for 7 wk. The full-fat raw milk collected during 24 h from the 4 groups of cows (M-TDM, M-ODM, H-TDM, and H-ODM) was pooled and processed into Cantal cheese 4 times during the last 4 wk of the experimental period. In all, 16 cheeses were made (2 milking frequencies × 2 breeds × 4 replicates) and analyzed after a ripening period of 15 and 28 wk. The results showed that for both breeds, the pooled milk content of fat, whey protein, casein, total protein, and phosphorus as well as rennet clotting time and curd firming time were significantly higher with ODM cows, whereas the casein-to-total protein ratio was lower, and lactose, urea, calcium, and free fatty acids contents of milk remained unchanged. The acidification and draining kinetics of the cheese as well as cheese yields and the chemical and rheological properties of the ripened cheese were not significantly modified by milking frequency. For both breeds, the cheeses derived from ODM cows had a slightly yellower coloration but the other sensory attributes, except for pepper odor, were not significantly affected by milking frequency, thereby demonstrating that ODM does not have an adverse effect on the sensory properties of Cantal cheese. Compared with that of Holstein cows, milk from Montbéliarde cows resulted in a higher cheese yield (+1.250 kg/100 kg of milk) and ripened cheeses with lower pH, dry matter, calcium, sodium chloride, and water-soluble nitrogen concentrations. These cheeses had also a less firm and more elastic texture, a more acidic taste, and a yogurt/whey aroma.     

Valuation of milk composition and genotype in cheddar cheese production using an optimization model of cheese and whey production

A mass balance optimization model was developed to determine the value of the κ-casein genotype and milk composition in Cheddar cheese and whey production. Inputs were milk, nonfat dry milk, cream, condensed skim milk, and starter and salt. The products produced were Cheddar cheese, fat-reduced whey, cream, whey cream, casein fines, demineralized whey, 34% dried whey protein, 80% dried whey protein, lactose powder, and cow feed. The costs and prices used were based on market data from March 2004 and affected the results. Inputs were separated into components consisting of whey protein, ash, casein, fat, water, and lactose and were then distributed to products through specific constraints and retention equations. A unique 2-step optimization procedure was developed to ensure that the final composition of fat-reduced whey was correct. The model was evaluated for milk compositions ranging from 1.62 to 3.59% casein, 0.41 to 1.14% whey protein, 1.89 to 5.97% fat, and 4.06 to 5.64% lactose. The κ casein genotype was represented by different retentions of milk components in Cheddar cheese and ranged from 0.715 to 0.7411 kg of casein in cheese/kg of casein in milk and from 0.7795 to 0.9210 kg of fat in cheese/kg of fat in milk. Milk composition had a greater effect on Cheddar cheese production and profit than did genotype. Cheese production was significantly different and ranged from 9,846 kg with a high-casein milk composition to 6,834 kg with a high-fat milk composition per 100,000 kg of milk. Profit (per 100,000 kg of milk) was significantly different, ranging from $70,586 for a high-fat milk composition to $16,490 for a low-fat milk composition. However, cheese production was not significantly different, and profit was significant only for the lowest profit ($40,602) with the κ-casein genotype. Results from this model analysis showed that the optimization model is useful for determining costs and prices for cheese plant inputs and products, and that it can be used to evaluate the economic value of milk components to optimize cheese plant profits.     

Available lysine and fluorescence in heated milk proteins/dextrinomaltose or lactose solutions

In order to predict and compare the effects of dextrinomaltose and lactose on available lysine loss by the Maillard reaction, six model systems were prepared by mixing casein, laboratory whey protein or commercial whey protein with dextrinomaltose or lactose. The solutions were prepared at concentrations similar to those used in enteral and infant formula processing and were heated at 100, 120 or 140 °C for 0–30 min. The progress of the Maillard reaction in these model systems was followed by monitoring free fluorescence intermediary compounds. Model systems with lactose showed higher available lysine less than the model systems with dextrinomaltose; linear lysine losses were obtained between 0 and 20 min at 100 and 120 °C. At sterilization temperature and time (120 °C/10 min), lysine losses of milk proteins with dextrinomaltose as reducing sugar were 6.1% for casein, 4.1% for laboratory whey protein and 13.4% for commercial whey protein. Available lysine showed correlation with furosine in model systems prepared with lactose and casein or laboratory but not commercial whey protein at 100 and 120 °C. The initial fluorescence value obtained by mixing casein or laboratory whey protein with lactose or dextrinomaltose was low (between 3.8 and 5.7), whereas the value obtained when commercial whey proteins were used was close to 9. At 120 °C/10 min, there was only a small increase of fluorescence in casein and laboratory whey protein but a large increase in commercial whey protein (threefold the initial value). Fluorescence measurement is useful for finding the extent of the Maillard reaction in commercial whey protein (thermally damaged protein). An absolute value greater than 10 may indicate that products were prepared with thermally damaged proteins.     

Effect of type of concentrated sweet cream buttermilk on the manufacture, yield, and functionality of pizza cheese

Sweet cream buttermilk (SCB) is a rich source of phospholipids (PL). Most SCB is sold in a concentrated form. This study was conducted to determine if different concentration processes could affect the behavior of SCB as an ingredient in cheese. Sweet cream buttermilk was concentrated by 3 methods: cold ( < 7°C) UF, cold reverse osmosis (RO), and evaporation (EVAP). A washed, stirred-curd pizza cheese was manufactured using the 3 different types of concentrated SCB as an ingredient in standardized milk. Cheesemilks of casein:fat ratio of 1.0 and final casein content ∼2.7% were obtained by blending ultrafiltered (UF)-SCB retentate (19.9% solids), RO-SCB retentate (21.9% solids), or EVAP-SCB retentate (36.6% solids) with partially skimmed milk (11.2% solids) and cream (34.6% fat). Control milk (11.0% solids) was standardized by blending partially skimmed milk with cream. Cheese functionality was assessed using dynamic low-amplitude oscillatory rheology, UW Meltprofiler (degree of flow after heating to 60°C), and performance of cheese on pizza. Initial trials with SCB-fortified cheeses resulted in ∼4 to 5% higher moisture (51 to 52%) than control cheese (∼47%). In subsequent trials, procedures were altered to obtain similar moisture content in all cheeses. Fat recoveries were significantly lower in RO- and EVAP-SCB cheeses than in control or UF-SCB cheeses. Nitrogen recoveries were not significantly different but tended to be slightly lower in control cheeses than the various SCB cheeses. Total PL recovered in SCB cheeses (∼32 to 36%) were lower than control (∼41%), even though SCB is high in PL. From the rheology test, the loss tangent curves at temperatures > 40°C increased as cheese aged up to a month and were significantly lower in SCB cheeses than the control, indicating lower meltability. Degree of flow in all the cheeses was similar regardless of the treatment used, and as cheese ripened, it increased for all cheeses. Trichloroacetic acid-soluble N levels were similar in the control and SCB-fortified cheese. On baked pizza, cheese made from milk fortified with UF-SCB tended to have the lowest amount of free oil, but flavor attributes of all cheeses were similar. Addition of concentrated SCB to standardize cheesemilk for pizza cheese did not adversely affect functional properties of cheese but increased cheese moisture without changes in manufacturing procedure.     

Physical properties of pizza Mozzarella cheese manufactured under different cheese-making conditions

The effect of manufacturing factors on the shreddability and meltability of pizza Mozzarella cheese was studied. Four experimental cheeses were produced with 2 concentrations of denatured whey protein added to milk (0 or 0.25%) and 2 renneting pH values (6.4 or 6.5). The cheeses were aged 8, 22, or 36 d before testing. Shreddability was assessed by the presence of fines, size of the shreds, and adhesion to the blade after shredding at 4, 13, or 22°C. A semi-empirical method was developed to measure the matting behavior of shreds by simulating industrial bulk packaging. Rheological measurements were performed on cheeses with and without a premelting treatment to assess melt and postmelt cheese physical properties. Lowering the pH of milk at renneting and aging the cheeses generally decreased the fines production during shredding. Adding whey protein to the cheeses also altered the fines production, but the effect varied depending on the renneting and aging conditions. The shred size distribution, adhesion to the blade, and matting behavior of the cheeses were adversely affected by increased temperature at shredding. The melting profiles obtained by rheological measurements showed that better meltability can be achieved by lowering the pH of milk at renneting or aging the cheese. The premelted cheeses were found to be softer at low temperatures (<40°C) and harder at high temperatures (>50°C) compared with the cheeses that had not undergone the premelting treatment. Understanding and controlling milk standardization, curd acidification, and cheese aging are essential for the production of Mozzarella cheese with desirable shreddability and meltability.     

Yield and aging of Cheddar cheeses manufactured from milks with different milk serum protein contents

Whey proteins in general and specifically β-lactoglobulin, α-lactalbumin, and immunoglobulins have been thought to decrease proteolysis in cheeses manufactured from concentrated retentates from ultrafiltration. The proteins found in whey are called whey proteins and are called milk serum proteins (SP) when they are in milk. The experiment included 3 treatments; low milk SP (0.18%), control (0.52%), and high milk SP (0.63%), and was replicated 3 times. The standardized milk for cheese making of the low milk SP treatment contained more casein as a percentage of true protein and more calcium as a percentage of crude protein, whereas the nonprotein nitrogen and total calcium content was not different from the control and high SP treatments. The nonprotein nitrogen and total calcium content of the milks did not differ because of the process used to remove the milk SP from skim milk. The low milk SP milk contained less free fatty acids (FFA) than the control and high milk SP treatment; however, no differences in FFA content of the cheeses was detected. Approximately 40 to 45% of the FFA found in the milk before cheese making was lost into the whey during cheese making. Decreasing the milk SP content of milk by 65% and increasing the content by 21% did not significantly influence general Cheddar cheese composition. Higher fat recovery and cheese yield were detected in the low milk SP treatment cheeses. There was more proteolysis in the low milk SP cheese and this may be due to the lower concentration of undenatured β-lactoglobulin, α-lactalbumin, and other high molecular weight SP retained in the cheeses made from milk with low milk SP content.     

Microbial and sensory changes throughout the ripening of Prato cheese made from milk with different levels of somatic cells

The objective of this research was to evaluate the effects of 2 levels of raw milk somatic cell count (SCC) on the composition of Prato cheese and on the microbiological and sensory changes of Prato cheese throughout ripening. Two groups of dairy cows were selected to obtain low-SCC (<200,000 cells/mL) and high-SCC (>700,000 cells/mL) milks, which were used to manufacture 2 vats of cheese. The pasteurized milk was evaluated according to the pH, total solids, fat, total protein, lactose, standard plate count, coliforms at 45°C, and Salmonella spp. The cheese composition was evaluated 2 d after manufacture. Lactic acid bacteria, psychrotrophic bacteria, and yeast and mold counts were carried out after 3, 9, 16, 32, and 51 d of storage. Salmonella spp., Listeria monocytogenes, and coagulase-positive Staphylococcus counts were carried out after 3, 32, and 51 d of storage. A 2 × 5 factorial design with 4 replications was performed. Sensory evaluation of the cheeses from low- and high-SCC milks was carried out for overall acceptance by using a 9-point hedonic scale after 8, 22, 35, 50, and 63 d of storage. The somatic cell levels used did not affect the total protein and salt:moisture contents of the cheeses. The pH and moisture content were higher and the clotting time was longer for cheeses from high-SCC milk. Both cheeses presented the absence of Salmonella spp. and L. monocytogenes, and the coagulase-positive Staphylococcus count was below 1 × 10² cfu/g throughout the storage time. The lactic acid bacteria count decreased significantly during the storage time for the cheeses from both low- and high-SCC milks, but at a faster rate for the cheese from high-SCC milk. Cheeses from high-SCC milk presented lower psychrotrophic bacteria counts and higher yeast and mold counts than cheeses from low-SCC milk. Cheeses from low-SCC milk showed better overall acceptance by the consumers. The lower overall acceptance of the cheeses from high-SCC milk may be associated with texture and flavor defects, probably caused by the higher proteolysis of these cheeses.     

Influence of brine concentration and temperature on composition, microstructure, and yield of feta cheese

The protein matrix of cheese undergoes changes immediately following cheesemaking in response to salting and cooling. Normally, such changes are limited by the amount of water entrapped in the cheese at the time of block formation but for brined cheeses such as feta cheese brine acts as a reservoir of additional water. Our objective was to determine the extent to which the protein matrix of cheese expands or contracts as a function of salt concentration and temperature, and whether such changes are reversible. Blocks of feta cheese made with overnight fermentation at 20 and 31°C yielded cheese of pH 4.92 and pH 4.83 with 50.8 and 48.9 g/100 g of moisture, respectively. These cheeses were then cut into 100-g pieces and placed in plastic bags containing 100 g of whey brine solutions of 6.5, 8.0, and 9.5% salt, and stored at 3, 6, 10, and 22°C for 10 d. After brining, cheese and whey were reweighed, whey volume measured, and cheese salt, moisture, and pH determined. A second set of cheeses were similarly placed in brine (n = 9) and stored for 10 d at 3°C, followed by 10 d at 22°C, followed by 10 d at 3°C, or the complementary treatments starting at 22°C. Cheese weight and whey volume (n = 3) were measured at 10, 20, and 30 d of brining. Cheese structure was examined using laser scanning confocal microscopy. Brining temperature had the greatest influence on cheese composition (except for salt content), cheese weight, and cheese volume. Salt-in-moisture content of the cheeses approached expected levels based on brine concentration and ratio of brine to cheese (i.e., 4.6, 5.7 and 6.7%). Brining at 3°C increased cheese moisture, especially for cheese with an initial pH of 4.92, producing cheese with moisture up to 58 g/100 g. Cheese weight increased after brining at 3, 6, or 10°C. Cold storage also prevented further fermentation and the pH remained constant, whereas at 22°C the pH dropped as low as pH 4.1. At 3°C, the cheese matrix expanded (20 to 30%), whereas at 22°C there was a contraction and a 13 to 18 g/100 g loss in weight. Expansion of the protein matrix at 3°C was reversed by changing to 22°C. However, contraction of the protein matrix was not reversed by changing to 3°C, and the cheese volume remained less than what it was initially.     

Fate of lysostaphin in milk from individual cows through pasteurization and cheesemaking

Transgenic cows secreting over 3 μg of lysostaphin/ mL of milk are protected against mastitis caused by Staphylococcus aureus, but it is unknown if active lysostaphin persists through dairy processing procedures or affects the production of fermented dairy foods. The objective of this study was to determine the fate of lysostaphin as milk was pasteurized and then processed into cheese. Raw milk from transgenic cows was heat treated at 63°C for 30 min, 72°C for 15 s (high temperature, short time), or 140°C for 2 s (UHT). Portions of the high temperature, short-time milk were manufactured into semi-hard cheeses. Aliquots taken at each processing step were assayed to determine the quantity (ELISA) and activity (ability to inhibit S. aureus growth) of lysostaphin. Results indicated that most of the lysostaphin was present in the aqueous portion of the milk and was not affected by pasteurization, although UHT treatment reduced enzyme concentration by 60%. The quantity and activity of the lysostaphin decreased during cheesemaking. Based on the amount of lysostaphin present in the starting cheesemilk, 10 to 15% of the lysostaphin was recovered in the whey, 21 to 55% in the cheese curd at d 1, and 21 to 36% in cheese stored at 4°C for 90 d. Enough of the lysostaphin secreted into milk by transgenic cows survived typical dairy processing conditions to impart potential value as a bioprotective agent against staphylococci in dairy foods.     

Mexican Queso Chihuahua: functional properties of aging cheese

Queso Chihuahua, a semi-hard cheese manufactured from raw milk (RM) in northern Mexico, is being replaced by pasteurized milk (PM) versions because of food safety concerns and the desire for longer shelf life. In this study, the functional traits of authentic Mexican Queso Chihuahua made from RM or PM were characterized to identify sources of variation and to determine if pasteurization of the cheese milk resulted in changes to the functional properties. Two brands of RM cheese and 2 brands of PM cheese obtained in 3 seasons of the year from 4 manufacturers in Chihuahua, Mexico, were analyzed after 0, 4, 8, 12, and 16 wk of storage at 4°C. A color measurement spectrophotometer was used to collect color data before and after heating at 232°C for 5 min or 130°C for 75 min. Meltability was measured using the Schreiber Melt Test on samples heated to 232°C for 5 min. Sliceability (the force required to cut through a sample) was measured using a texture analyzer fitted with a wire cutter attachment. Proteolysis was tracked using sodium dodecyl sulfate-PAGE. Compared with PM cheeses, RM cheeses showed less browning upon heating, melted more at 232°C, and initially required a greater cutting force. With aging, cheeses increased in meltability, decreased in whiteness when measured before heating, and required less cutting force to slice. Seasonal variations in the cheesemilk had minimal or no effect on the functional properties. The differences in the functional properties can be attributed, in part, to the mixed microflora present in the RM cheeses compared with the more homogeneous microflora added during the manufacture of PM cheeses. The degree of proteolysis and subsequent integrity of the cheese matrix contribute to melt, slice, and color properties of the RM and PM cheeses. Understanding the functional properties of the authentic RM cheeses will help researchers and cheesemakers develop pasteurized versions that maintain the traditional traits desired in the cheeses.     

Yield,changes in proteolysis,and sensory quality of Prato cheese produced with different coagulants

The objective of this research was to compare the effect of 2 fungal proteases, one that is already commercially established as a milk-clotting agent and another produced at the laboratory scale, on Prato cheese composition, protein and fat recovery, yield, and sensory characteristics. Cheeses were produced according to the traditional protocol, using protease from the fungus Thermomucor indicae-seudaticae N31 and commercial coagulant from Rhizomucor spp. as clotting agents. A 2 × 6 factorial design with 3 replications was performed: 2 levels of coagulants and 6 levels of storage time. After 5, 12, 19, 33, 43, and 53 d of refrigerated storage (12°C), cheeses were monitored for proteolysis, firmness, and casein degradation by capillary electrophoresis. Sensory acceptance was evaluated after 29 d of manufacturing. The different coagulants did not statistically affect Prato cheese composition, protein and fat recovery, and yield. Both cheeses presented good sensory acceptance. Proteolysis increased and firmness decreased for both cheeses during the storage time, as expected for Prato cheese. Caseins were well separated by capillary electrophoresis and the results showed, with good resolution, that the cheeses exhibited similar protein hydrolysis profile. Both cheeses presented good sensory acceptance. The gathered data showed that the protease from T. indicae-seudaticae N31 presented similar action compared with the commercial enzyme, indicating its efficiency as clotting agent for Prato cheese manufacture.     

Rheology and melt characterization of low-fat and full fat Mozzarella cheese made from microfluidized milk

Microfluidization of cheese milk at different temperatures and pressures altered the meltability and rheological properties of Mozzarella cheese. Pasteurized milks, standardized to 1.0 (low-fat (LF)) or 3.2 (full fat (FF)) g fat/100 g milk, heated to 10, 43, or 54 °C, and then microfluidized at pressures of 34, 103, or 172 MPa, were used to manufacture Mozzarella cheese. Cheeses made from nonmicrofluidized milks served as controls. During the hot water step, only control cheeses and cheeses made with milk microfluidized at 10 °C could be stretched while all others had short curds that did not fuse together. Cheese responses to different stresses (heat, compression, torsion, and oscillatory shear) were measured after 1 and 6 weeks of storage. FF cheeses made with the control milks and milks processed at 10 °C/34 MPa or 10 °C/103 MPa were softer and less rigid, and had the lowest visco-elastic properties and the highest meltabilities of all the cheeses. Microfluidization of the cheese milk did not improve the melt or rheology of LF cheeses. Microfluidization of milk with fat in the liquid state at higher pressures resulted in smaller lipid droplets that altered the component interactions during the formation of the cheese matrix and resulted in LF and FF Mozzarella cheeses with poor melt and altered rheology.