Effect of calcium on microstructure and meltability of part skim mozzarella cheese

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.     

Effect of manufacturing factors,composition, and proteolysis on the functional characteristics of mozzarella cheese

Shredding and melting characteristics are vital to the function of low‐moisture Mozzarella cheeses that are used as ingredients for pizza and related foods. Newly manufactured Mozzarella melts to a tough, extremely elastic, and somewhat granular consistency with limited stretch that is unacceptable for pizza. However, during the first few weeks of refrigerated storage, a dramatic transformation occurs as the unmelted cheese becomes softer and the melted cheese becomes more viscous, less elastic, and highly stretchable. Thus, the cheese attains optimal functionality for pizza. Over longer periods, Mozzarella becomes excessively soft and fluid when melted and is no longer acceptable for pizza. Low‐moisture Mozzarella is correctly viewed as a cheese that requires aging.

The functional characteristics of low‐moisture Mozzarella are due initially to the chemical composition, including fat, moisture, NaCl, and mineral contents, and the structure of the paracasein curd matrix that is established during manufacture. Changes in functional characteristics during aging are directly related to proteolysis rate and possibly proteolytic specificity. Proteolysis during aging is influenced by manufacturing factors such as starter culture, coagulant, and stretching temperature, and possibly to indigenous proteases in the cheesemilk such as plasmin.     

干酪融化性测量方法及其研究进展

当干酪作为辅料应用在快餐食品中时,融化性是其主要评价指标之一。因此建立统一的融化性测量技术是十分重要的。本文介绍了测量干酪融化性的两类测量方法,即传统测量法和客观测量法,阐述了各种方法的优缺点及发展情况,并对干酪融化性测量技术的发展进行了展望。     

Effect of different manufacturing parameters on the characteristics of Graviera Kritis cheese

The objective of the present study was to improve the characteristics of Graviera Kritis cheese. The influence of lactic acid and propionic acid starters was studied and then the effect of washing and salting the curd combined with the use of starters was investigated. Although the traditional technology without starters resulted in the highest organoleptic characteristics, it was shown that the use of starters could improve texture characteristics of the cheeses if it is combined with a curd wash to control acidity development. Lower pH values and higher contents of low molecular weight nitrogenous substances were consistent with texture defects. Moreover, the ripening at higher temperatures increased proteolysis levels and decreased cheese quality.     

Rheology of mozzarella cheese

The rheological properties of mozzarella cheese were studied by using a parallel plate, a sliding plate, an extensional and a capillary rheometer over a temperature range of 25–60 °C. While mozzarella cheese behaves as a semisolid at room temperature, it behaves mostly as a liquid at higher temperatures (typically greater than 40 °C). The rheological data obtained from the various pieces of rheometers were compared. Differences among the various data sets were observed and these were demonstrated to be due to the inherent changes to the material structure during testing and to the changes in the physical properties of the cheese at different temperatures. Mozzarella cheese is a viscoelastoplastic material at room temperature, which becomes viscoelastic at about 60 °C. Its yield stress gradually decreases with increase of temperature pointing to structural changes that occur at elevated temperatures. A Herchel–Buckley viscoplastic rheological model was found to describe adequately its rheology.     

Effect of pH and calcium concentration on proteolysis in mozzarella cheese

Low-moisture Mozzarella cheeses (LMMC), varying in calcium content and pH, were made using a starter culture (control; CL) or direct acidification (DA) with lactic acid or lactic acid and glucono-delta-lactone. The pH and calcium concentration significantly affected the type and extent of proteolysis in Mozzarella cheese during the 70-d storage period at 4 degrees C. For cheeses with a similar pH, reducing the calcium-to-casein ratio from -29 to 22 mg/g of protein resulted in marked increases in moisture content and in primary and secondary proteolysis, as indicated by polyacrylamide gel electrophoresis and higher levels of pH 4.6- and 5%-PTA-soluble N. Increasing the pH of DA cheeses of similar moisture content, from approximately 5.5 to 5.9, while maintaining the calcium-to-casein ratio almost constant at approximately 29 mg/g, resulted in a decrease in primary proteolysis but had no effect on secondary proteolysis. Comparison of CL and DA cheeses with a similar composition showed that the CL cheese had higher levels of alpha(s1)-CN degradation, pH 4.6- and 5%-PTA-soluble N. Analysis of pH 4.6-soluble N extracts by reverse-phase HPLC showed that the CL cheese had higher concentrations of compounds with low retention times, suggesting higher concentrations of low molecular mass peptides and free amino acids.     

Effect of electron beam irradiation on the shelf life of mozzarella cheese

The effectiveness of electron beam irradiation on the shelf life of mozzarella cheese was evaluated using five different irradiation doses and a control cheese. Shelf life tests were run at 10 °C by determining the cell load of spoilage micro‐organisms monitored on the consecutive days during storage. By fitting the experimental data through a modified version of the Gompertz equation, the shelf life of samples irradiated to the different doses was calculated. Results show significant increases in the shelf life of the investigated cheese. There were slight differences in the functional properties such as stretching, oiling off, melting between irradiated and unirradiated cheeses at 260 °C in oven. Our results indicated that the electron irradiation at the dose of 2.0 kGy may inhibit the growth of spoilage micro‐organisms such as coliforms and Pseudomonas sp. without affecting the sensorial characteristics of the product.     

莫扎雷拉干酪的工艺介绍

探讨制作莫扎雷拉干酪的制作工艺及拉伸工艺中的影响因素。经过试验,发现要获得优良的拉延特性,干酪凝块的最佳pH应控制在5.2~5.4,产品的钙/非脂乳固体比例约为3.1%±0.1%,水分含量为55%±2%,无脂干酪的水分含量为70%±3%,残糖含量按半乳糖计为7 g/kg,无乳糖残留。     

Vatless manufacturing of low-moisture part-skim mozzarella cheese from highly concentrated skim milk microfiltration retentates

Low-moisture, part-skim (LMPS) Mozzarella cheeses were made from concentration factor (CF) 6, 7, 8, and 9, pH 6.0 skim milk microfiltration (MF) retentates using a vatless cheese-making process. The compositional and proteolytic effects of cheese made from 4 CF retentates were evaluated as well as their functional properties (meltability and stretchability). Pasteurized skim milk was microfiltered using a 0.1-microm ceramic membrane at 50 degrees C to a retentate CF of 6, 7, 8, and 9. An appropriate amount of cream was added to achieve a constant casein:fat ratio in the 4 cheesemilks. The ratio of rennet to casein was also kept constant in the 4 cheesemilks. The compositional characteristics of the cheeses made from MF retentates did not vary with retentate CF and were within the legal range for LMPS Mozzarella cheese. The observed reduction in whey drained was greater than 90% in the cheese making from the 4 CF retentates studied. The development of proteolytic and functional characteristics was slower in the MF cheeses than in the commercial samples that were used for comparison due to the absence of starter culture, the lower level of rennet used, and the inhibition of cheese proteolysis due to the inhibitory effect of residual whey proteins retained in the MF retentates, particularly high molecular weight fractions.     

Effect of formulation and manufacturing parameters on process cheese food functionality--I. Trisodium citrate

The objective of this research was to use a Rapid Visco Analyzer to study the effect of natural cheese age, trisodium citrate (TSC) concentration, and mixing speed on process cheese food (PCF) functionality. In this study 3 replicates of natural cheese were manufactured, and a portion of each cheese was subjected to 6 different PCF manufacturing treatments at 2, 4, 6, 12, and 18 wk of ripening. These treatments were factorial combinations of 3 levels of TSC (i.e., 2.0, 2.5, and 3.0%) and 2 mixing speeds during manufacture (450 and 1,050 rpm). Functional properties of the PCF evaluated included manufacturing properties [apparent viscosity after manufacture (VAM)], unmelted textural properties (firmness), melted cheese flow properties [hot apparent viscosity (HAV)], and cheese thickening during cooling [time at 5000 cP (T5)]. All 4 parameters (VAM, firmness, HAV, and T5) were significantly affected by natural cheese age and mixing speed, whereas VAM, HAV, and T5 were also significantly influenced by the amount of TSC. The VAM and firmness decreased as cheese age increased, whereas T5 values increased as cheese age increased. Similarly, VAM, HAV, and firmness values increased because of the increased mixing speed, whereas T5 values decreased. The age × mixing speed interaction was significant for VAM and firmness. The age × concentration of the TSC interaction term was significant for VAM, whereas the age × age × TSC concentration term was significant for HAV. The results demonstrate that natural cheese age, mixing speed during manufacture, and concentration of TSC have a significant impact on process cheese functionality.     

Mozzarella干酪提取液的抗菌活性

Mozzarella干酪中酪蛋白抗菌肽对人体有非常重要的作用。为了研究酪蛋白提取液的抑菌作用,对成熟期为40 d、50 d和60 d的Mozzarella干酪,分别用无菌蒸馏水、醋酸-醋酸钠缓冲溶液和TCA提取法制备干酪提取液,探讨了干酪提取液对大肠杆菌、枯草芽孢杆菌、酵母菌和黑曲霉的抑制作用。结果显示,不同成熟期Mozzarella干酪的提取液对大肠杆菌、枯草芽孢杆菌和酵母菌均有一定的抑制作用。成熟期为40 d的Mozzarella干酪,用无菌蒸馏水提取出的提取液对大肠杆菌的抑菌性最强;成熟期为60 d的Mozzarella干酪,用TCA提取法提取出的提取液对枯草芽孢杆菌、酵母菌和黑曲霉的抑菌性最强。     

Evaluation of cheese meltability using convection and conduction melt profilers

The University of Wisconsin (UW) Melt Profiler was operated under convection and conduction heating modes for evaluating the melt/flow properties of cheese. Five processed cheeses, each with a different solid fat index (SFI = 1+, 5?, 5+, 6? and 8+), were tested. In general, the higher the SFI of the cheese, the lower the time and temperature at the softening point. Similar trends were also observed between the cheese SFI values and the time and temperature at the rapid flow point. As conduction heating is more effective than convection heating, the heating method affected the cheese melt/flow parameters remarkably. Furthermore, T_SP and T_RF tended to be higher when the cheeses were tested at higher temperatures.     

Rheology of mozzarella cheese: Extrusion and rolling

A capillary rheometer was used to determine the processability and rheology of mozzarella cheese over the temperature range of 25–60 °C. End pressure corrections, which are corrections associated with the entry and exit of the mozzarella cheese in and out of the capillary die, were found to be significant. Surprisingly, wall slip was found to be insignificant up to shear stress values of 30 kPa. Capillary extrusion at low temperatures (<50 °C) resulted in extrudates that were distorted, while at higher temperatures (>50 °C), the extrudates were fairly smooth. Rolling experiments at 25 °C indicated that rolling can be used to shape mozzarella cheese (at a reduction ratio <2.1) without fracturing. Based on the extrusion and rolling experiments, mozzarella cheese can be described as a power law fluid with an index of about 0.24, while at higher temperatures (30 °C<T<60 °C), the power law index is about 0.4, indicating its increased flowability.     

Effect of pH and calcium concentration on some textural and functional properties of mozzarella cheese

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.     

Reversibility of the temperature-dependent opacity of nonfat mozzarella cheese

Salted and unsalted nonfat mozzarella cheese was made by direct acidification and stored at 4 degrees C over 60 d. Changes in cheese opacity were measured by using reflectance L* values while the cheese was heated from 10 to 90 degrees C, then cooled to 10 degrees C, and reheated to 90 degrees C. A characteristic opacity transition temperature (T(OP)) was obtained for each cheese. Both salt content and storage time influenced T(OP). Opacity during heating, cooling, and reheating formed a hysteresis. At d 1, the unsalted cheese became opaque when heated to 20 degrees C, but the salted cheese required heating to 40 degrees C. As the salted cheese was aged, its T(OP) increased so that by 60 d the cheese did not become opaque until it was heated to 70 degrees C.     

Temperature effect on structure-opacity relationships of nonfat mozzarella cheese

Our objective was to determine the effect of heating on the structure of nonfat Mozzarella cheese and then to relate changes in structure to changes in cheese opacity. Cheese was made according to a direct-acid, stirred-curd procedure. Cheese samples, at 4 degrees C, were taken on d 1 and placed into glass bottles, which were sealed and heated. Once the cheese reached 10 degrees C or 50 degrees C, the bottles were placed on a scanner and color values measured. Samples were also taken on d 1 for chemical, micro, and ultrastructural analyses. Applying heat increased cheese opacity. At 50 degrees C the cheese was more opaque than at 10 degrees C. The increase in temperature induced changes in cheese structure. Larger high-density protein aggregates and increased protein concentration in the protein matrix were observed in cheese at 50 degrees C. Applied heat would favor hydrophobic interactions, and possibly, re-association of beta-casein and calcium with the protein matrix, promoting protein-to-protein interactions. Thus, the protein matrix contracts, occupying less cheese matrix area, and microphase separation occurs, causing serum pockets to grow in size, and microstructural heterogeneity to increase. It is proposed that the increased size of aggregates and heterogeneity of the cheese at 50 degrees C promote light reflection, thus increasing cheese opacity. We concluded that applying heat alters protein interactions in the cheese matrix, manifested as changes in cheese structure. Such changes in structure help provide an understanding of changes in cheese opacity.     

Effect of milk preacidification on low fat mozzarella cheese. I. Composition and yield

The effect of milk preacidification with acetic or citric acid on the composition and yield of low fat Mozzarella cheese was determined. Two cheese manufacturing trials were conducted. In trial 1, three vats (230 kg of milk per vat) of cheese were made in 1 d using no preacidification (control) and preacidification to pH 6.0 and pH 5.8 with citric acid. In trial 2, four vats (230 kg of milk per vat) of cheese were made in 1 d using no preacidification (control), preacidification to pH 6.0 and 5.8 with acetic acid, and preacidification to pH 5.8 with citric acid. Cheese manufacture was repeated on three different days in trial 1 and four different days in trial 2 using a randomized-complete block design. Preacidification to pH 5.8 with citric acid decreased cheese calcium more than preacidification to pH 5.8 with acetic acid. Preacidification with citric acid in trial 1 decreased protein recovery in the cheese, and there was a trend for decreased protein recovery in the cheese for trial 2. Differences in fat recovery due to preacidification varied, sometimes being lower than the control other times being higher than the control. The reduction in calcium and protein recovery in the cheese caused by preacidification lowered composition adjusted cheese yield and yield efficiency. Yield efficiency was reduced by about 2.5 and 5.5%, respectively, with preacidification to pH 6.0 and 5.8 with citric acid. Yield efficiency was reduced by about 2.2 and 3.4%, respectively, with preacidification to pH 6.0 and pH 5.8 with acetic acid.     

Evaluation of mozzarella cheese stretchability by the ring-and-ball method

The functional quality of Mozzarella cheese is defined by its ability to melt and stretch. Currently used methods to evaluate the stretchability of Mozzarella cheese are empirical and lack control of moisture loss and temperature. The typical fork test, the imitative tensile stretch test, and the 3-pronged-hook probe tensile test all expose the test samples to ambient conditions during stretching and thus give poorly reproducible results. An objective method developed in our laboratory to evaluate stretchability of cheese is based on the principle of the Ring-and-Ball method used to measure the softening point of polymers. This technique, which controls temperature and moisture loss, was used to quantify the stretchability of Mozzarella cheese. Average stretch length varied between 4 to 9 cm between the youngest and the oldest cheese samples. The method was found to be sensitive enough to discriminate between cheeses of different ages. The results showed that the technique is reproducible and gives reliable stretch length and stretch length vs. time data, which was further used to estimate extensional viscosity of the test sample. Age-related differences were reflected in extensional viscosity that decreased from 17.4 to 13.6 kPa.s with increase in age.