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* Wisconsin Center for Dairy Research, and
Department of Food Science, University of Wisconsin-Madison, Madison 53706
1 Corresponding author: rani{at}cdr.wisc.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: buttermilk • functionality • cheese yield • phospholipid
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Sweet cream buttermilk has been used as an ingredient in baking applications (e.g., in pancake mixes); however, SCB is considered a low value-added material due to its limited uses in food products. One of the ways to increase the demand for buttermilk is to find attractive uses for it as a cheese ingredient. Sweet cream buttermilk has been used as an ingredient in cheese making, but currently in the United States it cannot be legally used in cheeses with a standard of identity. According to Codex regulations (Codex Alimentarius Commission, 2003), SCB can be used as an ingredient in cheese as it permits the use of "milk and/or products obtained from milk". It can be used in pizza cheese, a nonstandard of identity cheese. Pizza cheese is functionally and organoleptically similar to low moisture part-skim Mozzarella cheese but it is a nonpasta filata, stirred-curd cheese, manufactured using mesophilic cultures (Lactococcus lactis ssp. cremoris and lactis). This cheese does not produce brown blisters when heated due to the lack of residual sugar because of complete sugar fermentation by the starter culture and the altered manufacturing protocol in which a washing step is incorporated to reduce sugar level in the cheese. Pizza cheese is commonly manufactured from milk with CN:fat ratio of about 1.0 to 1.05 and can be standardized by cream removal or addition of condensed or UF skim milk or NDM. As condensed SCB is available commercially, it would provide another option for standardization of cheesemilk for pizza cheese manufacture. However, the cost of SCB vs. NDM fluctuates and if SCB is expensive compared with NDM, this would impede its use as an ingredient in cheese making.
Research had shown that the use of SCB might alter the physical and melting properties of cheese (Poduval and Mistry, 1999). Previous studies have shown that the addition of SCB lowered free oil formation in low-fat Cheddar cheese (Mistry et al., 1996). The use of SCB in low-fat Mozzarella cheese inhibited blister formation, but reduced meltability (Poduval and Mistry, 1999). Addition of SCB increased the moisture content of reduced-fat cheese (Madsen et al., 1966; Joshi and Thakar, 1993; Mayes et al., 1994; Mistry et al., 1996; Poduval and Mistry, 1999). Additionally, curd fusion was poor in cheeses manufactured with 10 to 25% UF SCB (Mistry et al., 1996). The use of condensed SCB to standardize cheesemilk could increase the lactose level in the serum phase of milk, which would increase the residual sugar content in cheese (unless water is added). This may result in an excessively low pH or discoloration of the cheese when baked.
In Wisconsin, regulations (ATCP 80:44, 2002) require that raw cream used for butter making must be given a minimum pasteurization treatment of 85°C for 15 s. The term "raw cream" refers to cream that the butter-making plant receives before butter making. The extent of heat treatment of this raw cream before arriving at the butter-making plant is not always known (it may have been heat-treated several times either as milk or cream). As a result of severe heat treatments there would be substantial denaturation of whey protein. Because denatured ß-lactoglobulin is mostly bound to CN micelles, it would effectively increase the CN content of the SCB. The measured CN content of SCB not only reflects the amount of CN present in the SCB samples but also the amount of denatured whey proteins associated with CN micelles.
There are 2 main obstacles in using SCB as an ingredient in cheese making: variability in composition and inconsistent quality of this product due to variations in the cream processing conditions. Thus, we investigated compositional changes in raw and pasteurized cream and fresh unconcentrated SCB, which were collected over a 1-yr period. The objective of this study was also to investigate the impact of using different levels of condensed SCB on pizza cheese manufacture including cheese yield, composition, proteolysis, and functional characteristics. We also wanted to identify any modifications during the manufacture of pizza cheese that may be necessary to successfully use condensed SCB for pizza cheese. Differences in cheese moisture contents also alter functional and ripening properties so modifications to cheese-making procedures will be used to attain SCB-fortified cheeses with similar moistures to control cheese. Little is known about the recovery of the PL present in SCB into cheese. We also wanted to determine how much of the PL were recovered during cheese making.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Standardization
Raw whole milk and cream were obtained from the University of Wisconsin-Madison dairy plant on the day before cheese making. Raw whole milk was partially skimmed (fat content 2.30 ± 0.05%). As dairy plant A did not concentrate SCB, we obtained commercial samples of condensed SCB from local dairy plant B, which was used in the cheese-making experiments. The composition of the condensed SCB used for cheese making is given in Table 1
. Four types of cheesemilks were prepared: control, and milks standardized with 3 levels of condensed SCB. Control milk was standardized by blending the part-skim milk with cream to an average of 11.20% (2.51 ± 0.08% CN) solids with a mean CN:fat ratio of ~1.0. The 3 SCB-standardized cheesemilks were prepared by the addition of condensed SCB at 2, 4, and 6% by weight basis of cheese milk (the levels were selected based on preliminary trials that covered a wider range of SCB additions) to part-skim milk and cream. The CN and fat content for all treatments was standardized to a CN:fat ratio of ~1.0. The cheese-making procedure was kept the same for all treatments and this set of cheese trials was repeated 3 times.
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Because the first cheese trials demonstrated that the use of SCB increased moisture content and decreased pH, a second set of trials was conducted. In the second set of cheese trials, the manufacturing procedure was modified to obtain similar cheese moisture contents in all cheeses. The SCB-fortified cheeses were subjected to a 20-min stir out during cooking, whereas control cheese had no stir out. The coagulum from the 6% SCB fortified milk was cut using 6.0-mm knives. The second set of cheese trials was repeated 3 times.
Compositional Analyses
All compositional analyses for each sample were carried out in triplicate. Sweet cream buttermilk, milk, whey, wash water, and press whey samples were analyzed for fat by Mojonnier (AOAC, 2000), protein (total percentage N x 6.35) by Kjeldahl (AOAC, 2000), CN (AOAC, 2000), lactose (AOAC, 2000), total solids (Green and Park, 1980), and NPN (AOAC, 2000). The amount of denatured protein from the pasteurization of raw cream was estimated using the method described by Guinee et al. (1995).
The cheeses were sampled after 1 wk for compositional analysis. At the time of sampling, a 2.5-cm slab was cut off from the block; this slab was further sampled for each analysis. The subsampled cheese sample was completely ground and used for analysis. Cheese samples were analyzed for moisture (Marshall, 1992), fat (AOAC, 2000), pH by the quinhydrone method (Marshall, 1992), protein by Kjeldahl (AOAC, 2000), and salt by chloride electrode method (model 926, Corning Glass Works, Medfield, MA; Johnson and Olson, 1985). Proteolysis was monitored during ripening by measuring the amount of 12% TCA-soluble nitrogen at 1, 2, and 4 wk (AOAC, 2000). Free oil formed in the pizza cheeses was analyzed at 1, 2, and 4 wk using the method described by Kindstedt and Rippe (1990). The results were expressed as both the percentage free oil in cheese and the percentage free oil in cheese fat.
Fat and Nitrogen Recovery and Yield
A mass balance was carried out for each vat of cheese. Milk, drain whey, wash water, and press whey were weighed to ± 0.1 kg and cheese was weighed to ±0.01 kg. The percentage of fat or N recovered in the cheese, drain whey, wash water, and press whey was calculated as the total amount of fat or N in each one of these products divided by the total amount of fat or N in the original standardized milk and multiplied by 100.
Actual yield was calculated for each vat of cheese as the weight of the cheese divided by the weight of the original standardized milk multiplied by 100. Actual cheese yield was also adjusted to the target cheese moisture content (46% for pizza cheese). The approach described recently by Govindasamy-Lucey et al. (2005) was used to determine the predictive cheese yield, and the recoveries of fat, CN, and other solids in cheese. The Van Slyke yield equation was initially developed for Cheddar cheese (Van Slyke and Price, 1936) and we determined what the RC, RF, and RS values would be for pizza cheese. Predictive cheese yields were calculated for each vat using the Van Slyke cheese yield model equation (Eq. 1 as shown below; Van Slyke and Price, 1936).
 | [1] |
where RF is fraction of fat recovered in cheese, RC is fraction of CN recovered in cheese, and RS reflects the proportion of other milk solids and salt recovered in cheese in relation to the amount of CN and fat in cheese. The RF values were determined experimentally as fat recovery for each cheese type during the cheese-making trials. The RC was calculated (Govindasamy-Lucey et al., 2005) using the following equation:
 | [2] |
where estimated percentage CN in cheese (*) = percentage N in cheese x 6.31 (van Boekel, 1993).
No correction factor was applied in the estimation of percentage CN in cheese because the amount of non-CN N will be very small (calculated as less than 1% of total N). However, in cheese with denatured serum protein attached to CN, the denatured whey protein is calculated as CN.
The following approach was used to calculate RS:
Fat in DM (FDM) in cheese was determined experimentally as follows:
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The percentage fat in cheese can be calculated as follows:
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The total solids in cheese can be calculated as follows:
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Substituting equations 4 and 5 into equation [3], we obtain the following equation:
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By rearranging equation 6 we obtain the following equation:
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Total PL analysis
The extraction of lipid was carried out using a modified Mojonnier procedure (AOAC, 2000). Depending on the concentration of PL, various amounts of samples were used in this procedure; 30 g for cheese milk, 10 g for condensed SCB, 30 g for drained whey and pressed whey, and 50 g for wash water. To improve recovery of PL, 1.5% (wt/wt) of NaCl was added to the sample (Walstra and de Graaf, 1962).
Digestion was applied to liberate phosphorus from the extracted fat using a modified method as described by Walstra and de Graaf (1962). The extracted fat was rinsed into a Kjeldahl digestion flask using ethyl ether. The solvent was evaporated by placing the digestion flask on a Kjeldahl Micro Digestor digestion unit (Labconco, Kansas City, MO) and heating it at 70°C until the fat sample was completely dried. Ten milliliters of concentrated HNO3 (16 M) and 5 mL of concentrated (18 M) H2SO4 were added to the flask. The flask was again heated on the heating unit at 250°C until the contents in the flask turned clear. Some HNO3 (10 to 15 mL) was added if the contents did not become clear after 1 h of digestion. At the end of the digestion, the solution in the flask was clear or slightly yellow. While heating, 30% of H2O2 (~1 mL) was added to remove excess HNO3. The total digestion time was about 2 to 4 h depending on the amount of fat being digested. The contents inside of the flask were rinsed into a 100-mL graduated flask and made up to volume with deionized water.
Phosphorus content was determined using the colorimetric method as described by Walstra and de Graaf (1962). A test was conducted to determine the recovery of PL using this method. A known amount of PL from soy lecithin was extracted and digested using the procedure described above. After the spectrophotometric test, it was found that the recovery of PL was ~93 ± 3%. This recovery test was repeated 6 times. The total PL recovery in cheese was determined by subtracting the total PL found in whey, press whey, and wash water from the total PL content in cheese milk.
Rheological Properties During Rennet Coagulation of Cheesemilks
Rennet-induced milk gels are viscoelastic and their small deformation rheological properties can be determined by dynamic low amplitude oscillatory rheometry by measuring storage modulus (G'), loss modulus (G''), and loss tangent (LT; Zoon et al., 1988; Van Vliet et al., 1989; Lucey, 2002). The rheological characteristics of the standardized cheesemilks, control, and cheese milk with added lecithin PL (ADM Ultralec, Decatur, IL) during renneting were measured at 34.4 ± 0.1°C in a UDS 200 Physica rheometer (Physica Messtechnik, D-70564 Stuttgart, Germany) operating in oscillation mode at a frequency of 0.1 Hz and a strain of 1%. This lecithin contained a mixture of phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidic acid. The amount of lecithin (~30 mg) added was estimated to be similar to the amount of PL found in cheese milk with 6% SCB addition. The measuring system consisted of 2 coaxial cylinders (diameters 25.0 and 27.5 mm). A profiled (serrated) bob was used in this couette-type fixture. Before testing, the milk sample was warmed to 34.4°C for about 30 min in a waterbath, and 100 µL of distilled water containing 1.77 µL of double-strength chymosin (Chymostar, Rhodia, Madison, WI) was added to the milk, and mixed thoroughly; then, approximately 13 mL of the mixture was immediately placed in the cup (maintained at 34.4°C) of the rheometer. Vegetable oil was layered onto the surface of the milk to prevent evaporation during coagulation. Measurements were started 120 s after rennet addition and were taken at 60-s intervals for 100 min.
Small Amplitude Oscillatory Rheology Tests on Cheese
Rheological properties of the cheeses were carried out using a UDS 200 Physica rheometer (Physica Messtechnik) as described by Lucey et al. (2005). At 1, 2, and 4 wk of ripening, cheeses were cut into smaller blocks (12 x 10 x 10 cm) and thin slices (~3.2 to 3.4 mm in width) were cut using a hand-operated slicer. Using a cylindrical cork borer, 50-mm diameter discs were cut from these cheese slices. The disc-shaped cheese samples were then transferred to plastic bags to prevent dehydration and stored at ~5 to 6°C for at least 2 h before testing. The cheese samples were glued to the bottom plate of the rheometer with cyanoacrylate to prevent slippage (Nolan et al., 1989). To help prevent slippage from the top plate during testing, a serrated plate measuring system (MP31, 50-mm diameter) was used (Rosenberg et al., 1995). The cheese sample was mounted carefully onto the rheometer using the normal force measurement so that the cheese sample was subjected to minimal deformation by the measuring system. The normal force of the rheometer at the start of the test was kept <1 N, to ensure that the sample was in good contact with the measuring system but was not excessively deformed. The test was not started until a constant normal force reading (~0.7 N) was obtained. Cheese samples were subjected to a heating profile in the rheometer. In this test, a strain of 0.2% was applied at a frequency of 0.1 Hz to the cheese samples. The cheese samples were heated at a constant rate of 1°C/min from 5 to 80°C and G' (or stiffness), G'', and LT parameters were measured as a function of temperature. The temperature where LT was equal to 1 (i.e., where G' = G'') was also calculated, because this indicates the transition from a solid to a liquid-like system (i.e., a crossover point).
Sensory Analysis
Each cheese was evaluated for bitterness, saltiness, acidity, oxidized flavor, other off-flavors, firmness, and smoothness on a scale from 0 to 7. Seven judges were trained to detect oxidized and off-flavors by sampling oxidized milk and rancid cream samples until their scores for these attributes were consistent. Cheeses were shredded on a pilot plant scale shredder (Urschel model CC, Alard Equipment Corp., Williamson, NY). The cheeses were baked on pizza in a forced-air commercial oven (Impinger Ovens, Lincoln Foodservice Products Inc., Ford Wayne, IN) at 260°C for 5 min and their performances (e.g., oiling-off, strand elasticity, flow-off crust, mouthfeel, chewiness, and flavor, such as acidity, saltiness) were subjectively evaluated by a panel of 6 to 8 panelists.
Experimental Design and Statistical Analyses
Three replicate cheese-making trials were carried out; in each trial, 4 standardized milks (i.e., part-skimmed milk or control, 2%-SCB, 4%-SCB, and 6%-SCB) were used to make pizza cheese. A 4 x 3 complete randomized block design, which incorporated all 4 treatments and 3 blocks (replicate trials), was used for analysis of the response variables relating to milk, cheese, and whey composition. A second set of experiments was performed in which specific steps were taken to maintain constant moisture content in all the cheeses. The ANOVA was carried out using the PROC GLM procedure of SAS (version 9.1; SAS Institute Inc., Cary, NC). In the ANOVA model, the 4 differently standardized milks (different treatments) were analyzed as a discontinuous variable, whereas cheese-making day (i.e., different batch of milk) was blocked. Scheffe’s multiple-comparison test was carried out to evaluate differences in the treatments means at a significance level of P < 0.05.
A split-plot design was used to monitor the effects of treatment and time of aging and their interactions on pH, proteolysis (12% TCA-soluble nitrogen expressed as a percentage of total nitrogen), maximum LT values, temperature at which LT was maximum, temperature of crossover point, the amount of free oil formed, and the sensory attributes during ripening. For the whole-plot factor, treatment was analyzed as a discontinuous variable, whereas cheese-making day was blocked. For the subplot factor analysis, age was treated as continuous variable. The interactive term treatment x cheese-making day was treated as the error term for the treatment effect. The ANOVA for the split-plot design was carried out using the PROC GLM procedure of SAS. Fisher’s least significant difference test was carried out to evaluate differences in the treatments means at a significance level of P < 0.05.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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). The composition of the raw cream, pasteurized cream, and unconcentrated SCB varied during the entire year. The fat and solids content of cream were lower in March and September samples compared with other months (results not shown). Unconcentrated SCB composition followed the same compositional trends as the seasonal variation in cream composition. Total PL composition in unconcentrated SCB ranged from 1.13 to 1.53 mg per g of sample (0.113 to 0.153%). The total PL values obtained in this study agree with those reported by McDowell (1958), who had obtained a mean value of 0.156% and a range of 0.103 to 0.191% for SCB obtained from 2 New Zealand dairy factories measured over a 13-mo period. Pasteurization of cream appeared to degrade some PL, especially phosphatidylethanolamine species (results not shown).
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). In the fall months, September, October, and December, the percentage denatured whey proteins was the highest; more than 50% of the whey proteins found in the cream were denatured after pasteurization. In the rest of the year, pasteurized cream contained less than 25% denatured whey proteins. The difference in percentage denatured whey proteins found in cream was probably due to the processing conditions at which the cream was pasteurized. Although the average pasteurization temperature and time reported by the local dairy was ~86°C for 18 s, there could be processing variations throughout the year. These variations could affect the composition and quality of SCB that is produced from the butter-making process. Another explanation for the variation in percentage denatured whey proteins in pasteurized cream could be the initial heat treatments given to the cream before the butter plant received the cream. As mentioned before, the "raw cream" that the creamery used for butter making is from different dairy plants and this raw cream probably already underwent heat treatments. Because the cream came from different dairy plants, it is not possible to tell the extent of heat treatment the raw cream received. The changes in percentage denatured whey proteins found in cream was probably due to the different sources of cream and the extent of heat treatment it received before its arrival at the local dairy.
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). At the fortification levels used, condensed SCB contributed from 6 to 20% of the total CN content of milk in the cheese vats fortified with SCB. All milks were standardized to a similar CN:fat ratio, 1.03 to 1.04 (Table 4) so that as the concentration of condensed SCB used in cheese making increased, there was more cream added during the blending for the standardized cheesemilks (Table 4). As expected, total solids, fat, total protein, true protein, and CN contents were significantly (P < 0.0001) higher in the milks standardized with condensed SCB than in control milks (Table 4). Lactose contents in the milk and in the serum phase in the SCB standardized milks were significantly higher than in the control milks; the lactose content in cheesemilks increased with the increasing amount of SCB added. Although there was no significant difference in the amount of whey protein in all cheesemilks, there was a slightly higher whey protein content in the 4%- and 6%-SCB cheesemilk compared with the other cheesemilks.
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). After changes were made to the manufacturing procedure, the moisture contents for the 4 treatments were not significantly different (P > 0.05) and there was no significant difference in the composition of cheeses once moisture was corrected (Table 4). There were 2 possible reasons why the addition of SCB increased the moisture content of pizza cheeses. First, the addition of condensed SCB would have introduced denatured whey proteins into the system. The cream that was used to produce the SCB was pasteurized at a high temperature (average ~85°C for 15 s). After butter making, the SCB underwent additional heat treatment to produce the condensed SCB. When the condensed SCB is added to cheesemilk, it must undergo another pasteurization. Denatured whey proteins, such as ß-lactoglobulin, interact with CN and form CN-whey protein complexes that impair the coagulation of milk and prevent the usual syneresis of the cheese curd. This complex formation slows down the enzymatic reaction by reducing the accessibility of 
-CN and the aggregation of rennet-altered CN micelles (Leaver et al., 1995; Lucey, 1995). The strength of the renneted milk gel is weaker due to disruption of the continuity of the gel network caused by attachment of denatured whey proteins to CN micelles (Lucey, 1995). After the rennet gel is cut, normal syneresis cannot take place due to the presence of whey proteins in the gel. Because syneresis is impaired, more moisture is retained in the cheese. Denatured whey proteins are also thought to have a high water-holding capacity. When they interact with the CN micelles and are incorporated into the CN matrix, they can further increase the moisture content of cheese (Lawrence, 1987). The presence of MFGM fragments and PL may also play a part in increasing the moisture content of cheeses. The addition of these PL may alter the structure of the rennet gel during the coagulation phase. Phospholipids could potentially interact with proteins and form lipoprotein complexes (Drake et al., 1996). These complexes may interfere with the normal structure of the gel and CN interactions (in an analogous way to the presence of denatured whey proteins). Any alteration of the gel can prevent normal syneresis from occurring and result in more moisture being retained in cheese. Laloy et al. (1998) reported that the addition of liposomes (composition was ~80% phosphatidylcholine) to Cheddar cheese greatly increased the moisture content and suggested that the presence of PL interfered with the syneresis process.
Coagulation Properties
The control gel had higher G' values than gels made with PL-fortified milks (Figure 1), which indicated that the control gel was stiffer. The addition of PL did appear to slightly weaken the rennet gel. Because the source and the type of PL from lecithin were very different than PL in SCB, the effect of PL from SCB on rennet gel structure might be different. This experiment showed that the addition of a soy-derived lecithin could slightly weaken a rennet gel. Further study is needed to examine how PL derived from SCB influence rennet gel formation.
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). The SCB-fortified cheeses did have significantly (P < 0.01) higher fat losses in the drain whey compared with control cheese (Table 5). The fat recovery in the control cheese exhibited considerable variation, possibly due to seasonal changes in milk or other sources of error; this reduced the likelihood of the control cheese having a statistically significant difference with the SCB-fortified cheeses. The amount of N recovered in the 4%- or 6%-SCB cheeses was significantly (P < 0.01) higher than in the control or 2%-SCB cheeses. Mistry et al. (1996) also reported slightly higher (but not significant) protein recovery in reduced-fat Cheddar cheese made with 5% UF SCB. It is possible that because there was some additional denatured whey protein associated with CN in SCB (due to heat treatments), there might have been a slight increase in N recovery in cheeses fortified with higher levels of SCB.
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). Overall recovery of PL in cheese was low (<40%); other studies have also reported low and variable recoveries of PL during cheese making (Sachdeva and Buchheim, 1997; Turcot et al., 2001). This low recovery of PL could be explained by the origin of the PL in milk. Only about 60% of the PL is present in the milk fat globules, and the rest is in the skim milk serum phase (Huang and Kuksis, 1967; Patton and Keenan, 1974). The PL in SCB were from both the disrupted MFGM materials and PL present in milk serum phase. It was unclear how much of the PL from SCB were recovered in the cheese (because there are PL in the milk as well).
Cheese Yield
As expected, actual and moisture-adjusted yields in the SCB cheeses increased (Table 6), due to the higher CN and fat content in the SCB-standardized milks (Table 4). Van Slyke cheese yield equations (equation 1) were developed for all 4 cheeses (Table 6). It has been our experience that an RC value of 0.96 perhaps reflects a maximum or ideal situation for CN recovery, and that, in practice, RC will be slightly lower. The RC values were calculated for control, 2%-, 4%-, and 6%-SCB cheeses using equation 2 and found to be 0.935, 0.940, 0.958, and 0.956, respectively. The calculated RC values were slightly higher for the SCB cheeses compared with the control cheeses, and increased with the increasing amount of SCB used (possibly due to some additional denatured whey proteins that were recovered along with CN in this cheese). Thus, all calculations were carried out using individual RC values for each cheese type as shown in Table 6. In this study, RF was determined experimentally from the cheese trials, and using the calculated values for RC, RS was calculated using equation 7. The developed Van Slyke cheese yield (Table 6) formula simultaneously predicted the experimentally obtained actual cheese yield and FDM (equation 6; results not shown).
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). The pH of all cheese slightly decreased with aging (Figure 2). As expected, the amount of 12% TCA-soluble nitrogen increased with age (Table 7). In our study, as the rennet:CN ratio was kept the same for both the control and experimental milk, there was no difference in the amount of 12% TCA-soluble nitrogen formed between any of the cheeses.
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70°C; results not shown). The maximum LT value and the temperature where this maximum occurred are shown in Figure 3. Cheeses from the control treatment tended to have the highest maximum LT values at all times studied compared with cheeses from SCB treatments; this became significantly (P < 0.05) different by wk 4 (Figure 3a). The value of LT at higher temperature has been used as index of meltability (Mounsey and O’Riordan, 1999). A high LT indicates a more liquid-like system, which could then flow and melt (Lucey et al., 2003). This result suggested that control cheeses were more meltable than cheeses with added SCB. The slightly lower maximum LT values in cheeses with added SCB could be due to the presence of denatured whey proteins (from SCB) complexed with CN, via disulfide bonds. This binding might hinder melting by cross-linking CN polymers and reduce the ability of the CN matrix to flow (Lelievre and Lawrence, 1988). A similar phenomenon also occurs in cheese made from severely heated milk (Banks et al., 1994; Lucey et al., 2003).
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, Table 7); the cheeses from 6% SCB treatment melted at lower temperature than other cheeses. The temperature at which maximum LT occurred decreased as a function of age (Figure 3b). This indicated that the older cheese melted at a lower temperature probably due to ongoing proteolysis and the shift from insoluble to soluble Ca; both of which occur during cheese ripening (Lucey et al., 2003, 2005). The crossover point (i.e., when LT = 1) has been used as another indicator of cheese meltability (Sutheerawattanonda and Bastian, 1998). There was no significant difference in the temperature of this crossover for any of the 4 cheese types (Table 7).
Free Oil Formation
The levels of free oil in cheese are shown in Figure 4. Free oil was expressed on a fat basis. The percentage free oil as a percentage of total cheese fat showed that addition of SCB significantly lowered (P < 0.05) free oil formation at wk 1 (Figure 4, Table 7), but there were no significant differences at wk 2 and 4. The free oil formed in all cheeses increased with time except in control cheese. Control cheese had relatively constant levels of free oil during ripening (Figure 4). Mistry et al. (1996) found that reduced-fat Cheddar cheeses made with added SCB also had lower free oil levels than cheeses without added SCB. Poduval and Mistry (1999) suggested that the emulsification properties of the MFGM materials could have helped to reduce free oil formation.
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. Judges did not detect any high levels of oxidized flavors or any other off-flavors in the unmelted SCB cheeses. Treatment did not significantly affect oxidized flavors or any other off-flavors in the unmelted cheeses (Table 8). Buttermilk contains a high concentration of polyunsaturated fatty acids that could make it susceptible to oxidative deterioration (O’Connell and Fox, 2000). Mistry et al. (1996) reported that the flavor and flavor intensity scores were not different among treatments but an off-flavor was noted occasionally by some panelists in cheeses made with 5% UF SCB. Drake et al. (1998) determined that granulated soy lecithin improved yields and the texture of 33% reduced-fat cheeses; however, at the concentrations studied (i.e., as little as 0.025% wt/wt), off-flavors occurred as a result of soy lecithin catalyzing lipid auto-oxidation reactions in cheeses. Soy lecithin contains phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol (Nawar, 1985). Because more than 50% of the fatty acid in granular soy lecithin is linoleic acid and as this unsaturated fatty acid is susceptible to lipid oxidation, linoleic acid may be a source of off-flavor (Drake et al., 1998).
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). Strand thickness and cohesiveness were significantly (P < 0.01) higher in control cheeses compared with cheeses made with SCB (Table 8). For cheeses with similar moisture, denatured whey proteins from SCB probably disrupted the CN network and inhibited stretch. As the cheeses aged, the strand length decreased for all cheeses, probably due to breakdown of the CN network by residual coagulant (Lucey and Fox, 1993).
Control cheeses were significantly (P < 0.05) chewier after baking compared with cheeses fortified with condensed SCB. The matrix in cheeses fortified with SCB may have been weaker, which could explain why these cheeses were less chewy. Mistry et al. (1996) reported that reduced-fat Cheddar cheese made with 5% UF SCB had lower hardness values after 4 wk of ripening than control cheese (cheeses had similar moisture contents). Control cheese exhibited more extensive flow compared with cheeses made with added SCB (results not shown). This finding agreed with the higher maximum LT results in control cheese (Figure 3a).
Cheeses from control treatment exhibited significantly (P < 0.05) more oiling-off on pizza than cheeses made with SCB (Table 8), especially at the 6% SCB level. As the cheeses aged, the amount of free oil did not significantly increase. This finding did not agree with the chemical analysis of free oil and suggested that the chemical extraction method may not be as useful (i.e., of practical value) for the determination of free oil for this type of cheese. The chemical method for the assessment of free oil was developed for Mozzarella cheese (Kindstedt and Rippe, 1990), which is known to exhibit considerable oiling-off during baking. The pizza cheese used in this experiment was not a stretched curd cheese and free oil formation on pizza was relatively low.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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6%) could adversely affect cheese texture, melt, and sensory properties. At low levels (~2%), however, the addition of condensed SCB improved cheese yield without adversely affecting the compositional, rheological, and sensory properties of pizza cheese (when the cheese moisture content was adjusted to be similar to that of the control cheese). Using very high levels of condensed SCB causes acid defects because of the high lactose content in the condensed SCB. This issue could be alleviated using UF or diafiltration to produce concentrated SCB with reduced lactose content.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Received for publication July 21, 2005. Accepted for publication September 22, 2005.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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) (means, n = 3). Rheological properties were measured by applying a constant strain of 1% at a frequency of 0.1 Hz. Vertical line indicates cutting time as reported in cheese-making experiments.
), and 6% SCB (
) cheeses made with different contents of SCB (wt/wt) using the modified manufacturing protocol to adjust for moisture in the SCB cheeses during 4 wk of ripening of pizza cheeses at 7°C. Vertical bars represent standard deviations.
