P.S. Kindstedt

Relationship between the yield of cheese (Chevre) and chemical composition of goat milk

Abstract The relationships between goat milk constituents and cheese (Chevre, a fresh goat’s milk cheese) yield were determined to develop formula for predicting the moisture-adjusted yield of Chevre. Samples of commingled goat milk shipped to a commercial manufacturer of Chevre were collected weekly over a 12-month period and analyzed for milk fat, crude protein (CP), casein, total solids (TS), and mineral contents. The yield of Chevre made from the sampled milk was measured and adjusted to a 60% moisture content. There was a definite trend in the 60% moisture-adjusted yield of Chevre during the year, which ranged from 14% in June to 20% in December and January. Milk TS and CP contents were the most significant predictors of Chevre yield ( Y ): Y=2.64 TS −15.48 ( r 2 =0.81, P Y=8.6116 CP −12.7598 ( r 2 =0.79, P

Factors Affecting the Functional Characteristics of Unmelted and Melted Mozzarella Cheese

Mozzarella is one of several pasta filata or stretched curd cheeses that originated in Italy. In the United States, Mozzarella cheese is classified by standards of identity into four categories based on moisture content and fat on a dry basis (FDB). The four categories are divided into two high moisture types and two low moisture types. The low moisture types, which are used predominantly in food service and processing as ingredients for pizza products, account for a large majority of the Mozzarella produced in the U.S. (Kindstedt, 1993b). This review will focus on low-moisture (LM) Mozzarella.

Heat-induced modifications of the functional properties of sodium caseinate

Abstract The effects of heating sodium casemate solutions (5–6%, w v , pH 7.0) at 120 or 132° C for 60 min on functionality were investigated by measuring solubility, viscosity, foaming and emulsifying properties. Solubility of the protein at pH 2.0–3.5 was increased markedly by the heat treatments, but there was little change at pH values above 5.5. The viscosity of Na casemate solution was decreased by the heat treatments. Heating reduced significantly the foaming and emulsifying capacity of Na casemate, but the foam stability appeared to be improved by the heating. The drainage of liquid from the foam appeared to follow first-order kinetics. The relative hydrophobicity also was reduced by the heat treatments.

Distribution of plasminogen activator in different fractions of bovine milk

The type and relative amounts of plasminogen activator (PA) in different fractions of bovine milk obtained from 15 Holstein cows were examined. Raw milk was centrifuged to separate skim milk and a somatic cell pellet. PA was mainly localized within the casein fraction, being 42 times that in the serum, and in association with somatic cells. The predominant form of PA in milk casein was isolated from SDS-PAGE gel extracts and had a molecular mass of approximately 75 kDa. Its activity was increased 4.1-fold (P < 0.01) in the presence of fibrin but was unaffected by the presence of amiloride, indicating that it was due to tissue-PA. The predominant forms of PA associated with milk somatic cells were isolated from SDS-PAGE gel extracts and had molecular masses of approximately 30 and approximately 50 kDa. The activity of both proteins was unaffected by the presence of fibrin but was dramatically reduced by the presence of amiloride, indicating that they represented urokinase-PA.

Effect of pH on microstructure and characteristics of cream cheese.

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.

Effect of pH on Characteristics of Low-Moisture Mozzarella Cheese during Refrigerated Storage

This study evaluated the effect of cheese pH on proteolysis, calcium distribution, and functional characteristics of Mozzarella cheese. On 4 occasions, cultured low-moisture part-skim Mozzarella cheeses were obtained from a commercial producer on the day after manufacture. Cheese blocks were randomly assigned to 2 groups. One group was shredded, subdivided, and exposed to either ammonia vapor to increase the pH or HCl vapor to decrease the pH. Samples were vacuum packaged, stored at 4 degrees C, and analyzed for pH 4.6 and 12% TCA soluble nitrogen, apparent viscosity, free oil, and water-soluble calcium on days 5, 12, 22, and 40. The 2nd group was sectioned into 23-mm thick slabs and similarly exposed to either ammonia vapor to increase the pH or HCl vapor to decrease the pH. The slabs were vacuum packaged, stored at 4 degrees C, and analyzed for pH 4.6 and 12% TCA soluble nitrogen, TPA hardness, springiness and cohesiveness, and meltability on days 17, 29, and 41. Data were analyzed by ANOVA according to a spilt-plot design. Experimentally induced pH differences persisted and significantly affected TPA hardness, apparent viscosity, meltability, and water-soluble calcium throughout 40 d of storage, but did not affect soluble nitrogen changes. Thus, cheese pH affected functional characteristics and calcium distribution but did not affect proteolysis rates. Higher cheese pH resulted in a harder cheese that required longer aging to develop desirable melting characteristics, whereas cheese with lower pH developed desirable melting characteristics more quickly but had a shorter functional shelf life.

Nitrogen and mineral distribution in infant formulae

Abstract Nitrogen and mineral distributions in infant formulae were compared to raw and pasteurized milk samples. The percentage of total nitrogen present in the fat fraction after centrifugation ranged from 20 to 50% among the infant formulae, whereas only 1.4% was found in the fat fraction of raw milk. Recovery of individual minerals from the three fractions exceeded 95% in all cases except for Zn, which exceeded 91%. Ca in the fat fraction of infant formulae ranged from 18 to 30%, whereas only 1.4–1.7% of the total Ca was recovered in the fat fraction of the raw milk and the pasteurized milk samples. P, Zn, Mg and Fe followed patterns similar to Ca. In contrast, 80–90% of the K and Na were found in the serum fraction of the infant formulae and milk samples. Electrophoretograms of the formulae showed that the proteins in the fat fraction were mainly caseins and β-lactoglobulin. The major proteins in the serum were β-lactoglobulin and α-lactalbumin with small casein bands. All the main proteins were found in the pellet. Electron micrographs of the formulae showed extensive attachment of denatured whey proteins and casein micelles to fat globule surfaces. Whey protein-casein micelle complexes were formed due to protein-protein interactions induced during processing. Electron-dense granules were also present on the lipid droplet surfaces and dispersed in the denatured whey proteins clusters and casein micelles of the infant formulae samples. Energy dispersive spectroscopy X-ray microanalysis of these electron-dense granules revealed the presence of K, P, Fe and Zn. These granules were not present in milk samples.

Characterization of Calcium Lactate Crystals on Cheddar Cheese by Image Analysis

Previous research demonstrated that crystal coverage on the surface of Cheddar cheese can be quantitatively and nondestructively measured using image analysis of digital photographs of the cheese surface. The objective of the present study was to extend image analysis methodology to quantify and characterize additional features of visible crystals on cheese surfaces as they grow over time. A random weight (approximately 300 g) retail sample of naturally smoked Cheddar cheese exhibiting white surface crystals was obtained from a commercial source. The total area occupied by crystals and total number of discrete crystal regions on one of the surfaces (approximately 55 x 120 mm) was measured at 3-wk intervals for 30 wk using image analysis. In addition, 5 small (approximately 0.3 mm radius) individual crystals on that surface were chosen for observation over the 30-wk period. The crystals were evaluated for area, radius, and shape factor (circularity) every third week using image analysis. The total area occupied by crystals increased in a linear manner (R(2) = 0.95) from about 0.44 to 7.42% of the total cheese surface area over the 30-wk period. The total number of discrete crystal regions also increased but in a nonlinear manner that was best described by a quadratic relationship. Measurement of discrete crystal regions underestimated the true number of crystals present at the cheese surface due to merging of adjacent crystals as they grew and merged into a single crystal region over time. Throughout this period, the shapes of the 5 individual crystals closely approximated perfect circles, except when adjacent crystals merged to form a single irregular crystal region, and the area occupied by each of the 5 crystals increased in a near-linear manner (R(2) = 0.95). Image analysis approaches may be used to evaluate crystal formation and growth rates and morphology on cheese.

Effect of storage temperature on crystal formation rate and growth rate of calcium lactate crystals on smoked Cheddar cheeses.

Previous studies have shown that storage temperature influences the formation of calcium lactate crystals on vacuum-packaged Cheddar cheese surfaces. However, the mechanisms by which crystallization is modulated by storage temperature are not completely understood. The objectives of this study were to evaluate the effect of storage temperature on smoked Cheddar cheese surfaces for (1) the number of discrete visible crystals formed per unit of cheese surface area; (2) growth rate and shape of discrete crystals (as measured by area and circularity); (3) percentage of total cheese surface area occupied by crystals. Three vacuum-packaged, random weight (∼300 g) retail samples of naturally smoked Cheddar cheese, produced from the same vat of cheese, were obtained from a retail source. The samples were cut parallel to the longitudinal axis at a depth of 10mm from the 2 surfaces to give six 10-mm-thick slabs, 4 of which were randomly assigned to 4 different storage temperature treatments: 1, 5, 10°C, and weekly cycling between 1 and 10°C. Samples were stored for 30 wk. Following the onset of visible surface crystals, digital photographs of surfaces were taken every other week and evaluated by image analysis for number of discrete crystal regions and total surface area occupied by crystals. Specific discrete crystals were chosen and evaluated biweekly for radius, area, and circularity. The entire experiment was conducted in triplicate. The effects of cheese surface, storage temperature, and storage time on crystal number and total crystal area were evaluated by ANOVA, according to a repeated-measures design. The number of discrete crystal regions increased significantly during storage but at different rates for different temperature treatments. Total crystal area also increased significantly during storage, at rates that varied with temperature treatment. Storage temperature did not appear to have a major effect on the growth rates and shapes of the individual crystals that were chosen for analysis. The data indicated that the effect of storage temperature was complex, likely involving solubility changes, the formation of d(-) and l(+) lactic acid, and the occurrence of syneresis, which in turn affected the number of crystal formation sites and total crystal area on the cheese surface.

Chemical changes that predispose smoked Cheddar cheese to calcium lactate crystallization

We have observed a high incidence of calcium lactate surface crystals on naturally smoked Cheddar cheese in the retail marketplace. The objective of this study was to identify chemical changes that may occur during natural smoking that render Cheddar cheese more susceptible to calcium lactate crystal formation. Nine random-weight (approximately 300 g) retail-packaged samples of smoked Cheddar cheese were obtained from a commercial manufacturer immediately after the samples were smoked for about 6 h at 20 degrees C in a commercial smokehouse. Three similarly sized samples that originated from the same 19.1-kg block of cheese and that were not smoked were also obtained. Within 2 d after smoking, 3 smoked and 3 control (not smoked) samples were sectioned into 5 subsamples at different depths representing 0 to 2, 2 to 4, 4 to 6, 6 to 8, and 8 to 10 mm from the cheese surface. Six additional smoked cheese samples were similarly sectioned at 4 wk and again at 10 wk of storage at 5 degrees C. Sample sections were analyzed for moisture, L(+) and D(-) lactate, pH, and water-soluble calcium. The effects of treatment (smoked, control), depth from cheese surface, and their interactions were analyzed by ANOVA according to a repeated measures design with 2 within-subject variables. Smoked samples contained significantly lower moisture and lower pH, and higher total lactate-in-moisture (TLIM) and water-soluble calcium-in-moisture (WSCIM) than control cheeses. Smoked samples also contained significant gradients of moisture, pH, TLIM, and WSCIM, with lower moisture and pH, and higher TLIM and WSCIM, occurring at the cheese surface. Gradients of moisture were still present in smoked samples at 4 and 10 wk of storage. In contrast, the pH, TLIM, and WSCIM equilibrated and showed no gradients at 4 and 10 wk. The results indicate that calcium and lactate in the serum phase of the cheese were elevated because of smoking, especially at the cheese surface immediately after smoking treatment, which presumably predisposes the smoked cheeses to increased susceptibility to calcium lactate surface crystallization.