Effect of pH on microstructure and characteristics of cream cheese.
ABSTRACT This study evaluated the effect of pH on the microstructure of cream cheese and compared pH-induced changes in its microstructure with concomitant changes in cheese firmness and meltability. On 4 different days, experimental batches of cultured hot pack cream cheese were manufactured and analyzed for initial chemical composition. The cheeses were then sectioned into samples that were randomly assigned to 7 different treatment groups. Three groups were exposed to ammonia vapor for 1, 3, and 5 min to increase the pH; 3 groups were exposed to acetic acid vapor for 30, 60, and 90 min to decrease the pH; and 1 unexposed group served as the control. After equilibration at 4 degrees C, samples were analyzed for pH, firmness, meltability, and microstructure by scanning electron microscopy. The effects of experimental treatments on cheese pH, firmness, and meltability were analyzed by randomized complete block analysis of variance (ANOVA). Relationships between cheese pH and firmness and meltability were evaluated by regression. Experimental treatments significantly affected cheese pH, firmness, and meltability. Cheese firmness decreased and meltability increased with increasing pH from about pH 4.2 to 6.8. Cheese microstructure also changed dramatically over the same approximate pH range. Specifically, the volume of the protein network surrounding the fat droplets increased markedly with increasing pH, presumably due to casein swelling. These data support the hypothesis that protein-to-water interactions increased as the cheese pH increased, which gave rise to progressive swelling of the casein network, softer texture, and increased meltability.
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ABSTRACT: The effect of milk preacidification on cheese manufacturing, chemical properties, and functional properties of low fat Mozzarella cheese was determined. Four vats of cheese were made in 1 d using no preacidification (control), preacidification to pH 6.0 and pH 5.8 with acetic acid, and preacidification to pH 5.8 with citric acid. This process was replicated four times. Modifications in the typical Mozzarella manufacturing procedures were necessary to accommodate milk preacidification. The chemical composition of the cheeses was similar among the treatments, except the calcium content and calcium as a percentage of protein were lower in the preacidified treatments. During refrigerated storage, the chemical and functional properties of low fat Mozzarella were affected the most by milk preacidification to pH 5.8 with citric acid. The amount of expressible serum, unmelted cheese whiteness, initial unmelted hardness, and initial apparent viscosity were lower with preacidification. The reduction in initial unmelted cheese hardness and initial apparent viscosity in the pH 5.8 citric treatments represents an improvement in the quality of low fat Mozzarella cheese that allows the cheese to have better pizza bake characteristics with shorter time of refrigerated storage.Journal of Dairy Science 07/2001; 84(6):1348-56. · 2.57 Impact Factor
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ABSTRACT: The role of calcium in the microstructure of part skim Mozzarella cheese was evaluated using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Part skim Mozzarella cheeses with 4 calcium levels (control 0.65%, T1 0.48%, T2, 0.42%, and T3 0.35%) were manufactured and stored at 4 degrees C. Microstructure and meltability of cheeses were studied on d 1 and 30. The micrographs were analyzed for numbers, area, perimeter, roundness, and size of the fat particles. Reduced calcium cheeses had greater meltability and more hydrated protein matrix with greater number of fat particles (control=125, T1=193, T2=184, and T3=215 with SEM and control = 86, T1=87, T2= 125, and T3= 140 with CLSM). Further, area and perimeter of these fat particles were also greater in reduced calcium cheeses. Area, perimeter, and size of fat particles increased and their roundness decreased upon storage of 30 d. Decrease in free serum in the protein matrix of all cheeses upon refrigerated storage was evident from the CLSM. Hydrated protein network and better emulsified fat in low calcium cheeses might have improved melt properties of Mozzarella cheese.Journal of Dairy Science 08/2004; 87(7):1975-85. · 2.57 Impact Factor
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ABSTRACT: The effects of Ca concentration and pH on the composition, microstructural, and functional properties of Mozzarella cheese were studied. Cheeses were made using a starter culture (control) or by direct acidification of the milk with lactic acid or lactic acid and glucono-delta-lactone. In each of three trials, four cheeses were produced: a control, CL, and three directly-acidified cheeses, DA1, DA2, and DA3. The cheeses were stored at 4 degrees C for 70 d. The Ca content and pH were varied by altering the pH at setting, pitching, and plasticization. The mean pH at 1 d and the Ca content (mg/g of protein) of the various cheeses were: CL, 5.42 and 27.7; DA1, 5.96 and 21.8; DA2, 5.93 and 29.6; DA3, 5.58 and 28.7. For cheeses with a high pH (i.e., approximately 5.9), reducing the Ca content from 29.6 to 21.8 mg/g of protein resulted in a significant decrease in the protein level and increases in the moisture content and mean level of nonexpressible serum (g/g of protein). Reducing the Ca concentration also resulted in a more swollen, hydrated para-casein matrix at 1 d. The decrease in Ca content in the high-pH cheeses coincided with increases in the mean stretchability and flowability of the melted cheese over the 70-d storage period. The fluidity of the melted cheese also increased when the Ca content was reduced, as reflected by a lower elastic shear modulus and a higher value for the phase angle, delta, of the melted cheese, especially after storage for <12 d. The melt time, flowability, and stretchability of the low-Ca, high-pH DA1 cheese at 1 d were similar to those for the CL cheese after storage for > or = 12 d. In contrast, the mean values for flowability and stretchability of the high-pH, high-Ca DA2 cheese over the 70-d period were significantly lower than those of the CL cheese. Reducing the pH of high-Ca cheese (27.7 to 29.6 mg/g of protein) from -5.95 to 5.58 resulted in higher flowability, stretchability, and fluidity of the melted cheese. For cheeses with similar pH and Ca concentration, the method of acidification had little effect on composition, microstructure, flowability, stretchability, and fluidity of the melted cheese.Journal of Dairy Science 07/2002; 85(7):1655-69. · 2.57 Impact Factor