Microstructure and fracture properties of semi-hard cheese: Differentiating the effects of primary proteolysis and calcium solubilization

The impact of seasonal calving systems with varying pasture allowance on Cheddar cheese composition, nutritional quality and ripening characteristics

The objective of this study was to examine the impact of stage of lactation (early, mid and late) and proportion of pasture in the cows diet (high: GRS, medium: PMR and no: TMR) on the composition and quality of Cheddar cheese. Triplicate trials were carried out in each stage of lactation, and milk protein and fat contents were standardized for Cheddar cheese manufacture at pilot scale. As cheese milks were standardized for milk fat and protein contents, gross composition did not differ as a result of diet. Fatty acid profiles of GRS cheese were significantly different from TMR, while PMR profiles were less distinct and more similar to both GRS and TMR profiles, as illustrated by partial least squares discriminatory analysis. Fatty acids including CLA C18:2 cis-9, trans-11, C22:1 n-9 and C18:3 n-3 were most influential in this separation of profiles. Fatty acid profiling revealed that GRS derived cheese contained higher proportions of nutrients considered beneficial for human health including higher proportions of unsaturated fatty acids and omega-3 fatty acids. A biomarker model utilizing the proportions of 5 fatty acids was constructed and was effective at distinguishing between cheese of GRS, TMR and PMR feeding systems. Proportions of ρ-κ-casein, αs2-casein and αs1-casein in cheese also differed between diets while proportions of ρ-κ-casein, αs1-casein and β-casein were lowest in late lactation cheese. The impact of diet was less influential compared with that of stage of lactation on the ripening characteristics of cheese. An index of primary proteolysis was highest in late lactation cheese. The peptides derived from the proteolysis of κ-casein and β-casein and levels of secondary proteolysis, in particular, the proportions of 12 free amino acids were most influenced by stage of lactation. Overall this study demonstrated the effects of increasing pasture allowance and stage of lactation on the nutritional quality and ripening properties of Cheddar cheese.

Ice crystallization and structural changes in cheese during freezing and frozen storage: implications for functional properties

Temperature-mediated preservation techniques offer a simple, scalable, effective, and fairly efficient method of long-term storage of food products. In order to ensure the uninterrupted availability of cheese across the globe, a critical understanding of its techno-functional properties as affected by freezing and frozen storage is essential. Detailed studies of temperature-mediated molecular dynamics are available for relatively simpler and homogeneous systems like pure water, proteins, and carbohydrates. However, for heterogeneous systems like cheese, inter-component interactions at sub-zero temperatures have not been extensively covered. Ice crystallization during freezing causes dehydration of caseins and the formation of concentration gradients within the cheese matrix, causing undesirable changes in texture-functional attributes, but findings vary due to experimental conditions. A suitable combination of sample size, freezing rate, aging, and tempering can extend the shelf life of high- and low-moisture Mozzarella cheese. However, limited studies on other cheeses suggest that effects and suitability differ by cheese type, in most cases adversely affecting texture and functional attributes. This review presents an overview of the understanding of the effects of refrigeration, freezing techniques, and frozen storage on structural components of cheese, most prominently Mozzarella cheese, and the corresponding impact on microstructure and functionality. Also included are the mechanism of ice formation and relevant mathematical models for estimation of the thermophysical properties of cheese to assist in designing optimized schemes for their frozen storage. The review also highlights the lack of unanimity in critical understanding concerning the effect of freezing on the long-term storage of Mozzarella cheese with respect to its functionality.

Effect of plasmin on casein hydrolysis and textural properties of rennet-induced model cheeses

Plasmin plays an important role in casein hydrolysis during cheese ripening, which may influence the properties of the casein network and the texture of the final product. In view of this, the relation between plasmin-induced casein hydrolysis and textural changes of cheese during ripening was investigated in this study. Four batches of model cheese with different concentrations of added plasmin (0, 0.4, 0.6 and 1.0 μL/g milk) were prepared, and were stored for 12 weeks at 16 °C. During this period, plasmin activity, casein hydrolysis, textural properties and other compositional characteristics (pH, dry matter) were determined. Our results show that the addition of plasmin had significant effect on both the degree and the pattern of proteolysis. As a result, cheeses with different plasmin content showed different textural properties. With increased plasmin concentration, Young's modulus, hardness, resilience and cohesion decreased, while brittleness increased. All textural properties showed linear relations with the degree of casein hydrolysis, and logarithmic relations with the percentage of intact casein fractions. At the beginning of ripening, only slight changes in textural properties were found, although a substantial part (40-60 %) of the casein fractions was already been broken down. When ripening progressed, ongoing proteolysis significantly weakened the protein network and consequently led to noticeable textural changes. Model cheeses became softer, more brittle and less elastic. The knowledge gained from this study provide new insights in the changes of different textural parameters of model cheese. This will help to optimize the existing products and create new ones.

Biochemical and technological properties of moose (<i>Alces alces</i>) recombinant chymosin

Recombinant chymosins (rСhns) of the cow and the camel are currently considered as standard milk coagulants for cheese-making. The search for a new type of milk-clotting enzymes that may exist in nature and can surpass the existing “cheese-making” standards is an urgent biotechnological task. Within this study, we for the first time constructed an expression vector allowing production of a recombinant analog of moose chymosin in the expression system of Escherichia coli (strain SHuffle express). We built a model of the spatial structure of moose chymosin and compared the topography of positive and negative surface charges with the correspondent structures of cow and camel chymosins. We found that the distribution of charges on the surface of moose chymosin has common features with that of cow and camel chymosins. However, the moose enzyme carries a unique positively charged patch, which is likely to affect its interaction with the substrate. Biochemical and technological properties of the moose rChn were studied. Commercial rСhns of cow and camel were used as comparison enzymes. In some technological parameters, the moose rChn proved to be superior to the reference enzymes. Сompared with the cow and camel rСhns, the moose chymosin specific activity is less dependent on the changes in CaCl2 concentration in the range of 1–5 mM and pH in the range of 6–7, which is an attractive technological property. The total proteolytic activity of the moose rСhn occupies an intermediate position between the rСhns of cow and camel. The combination of biochemical and technological properties of the moose rСhn argues for further study of this enzyme.

Effect of inulin/kefiran mixture on the rheological and structural properties of mozzarella cheese

The relationships between chemical, textural, rheological and microstructural properties of low fat mozzarella cheese incorporated with different ratios of inulin/kefiran mixture were studied. By increasing inulin content, the protein and moisture content was increased and as a result, the meltability was reduced. Although, textural properties of low-fat mozzarella was completely influenced by inulin incorporation and hardness was increased, but the lower springiness and higher cohesiveness of cheese was achieved at high level of inulin which may be related to the increase in moisture and protein. Rheological properties of low-fat mozzarella cheese confirmed its shear-thinning behavior in which the G' value was more than G″. Mechanical properties of cheese showed that inulin incorporation into cheese did not significantly change the rheological properties of the cheese matrix. Consequently, the formation of a more rigid and cross-linked protein structure which is less plasticized achieved at high inulin incorporation through keeping more water and protein and less fat content. SEM results indicated the sponge honeycomb structure of mozzarella cheese which clearly confirmed the textural and rheological properties and there was an interrelationship among chemical, textural, rheological and microstructural properties of low-fat mozzarella cheese incorporated at different ratios of inulin.

Kinetics of proteolysis in stored Mongolian cheese at ice-temperatures and split-split-plot analysis of storage factors affecting cheese quality

Mongolian cheese is non-fermented cheese, which easily deteriorates during storage because of hydrolysis. The freezing points of sucrose and sucrose-free cheese were measured -5.16 °C and -4.29 °C, respectively. Ice-storage temperatures of -2 °C and -4 °C were used and 0 °C was used as reference temperature. In this study, the changes of proteolytic indexes (PI) and total viable counts (TVC) of cheese at different ice-temperatures during storage were studied. The PIs of all treatments increased over storage time, which conformed to the Arrhenius first-order kinetic model. The shelf lives of sucrose and sucrose-free cheese were predicted. In addition, -4 °C effectively suppressed the increases in TVC and PIs. The split-split-plot design was applied in comparing the effects of cheese type, the storage time and storage temperature on PI. Storage time was the most important factor followed by cheese type and storage temperature.

Solubility of carbon dioxide in renneted casein matrices: Effect of pH, salt, temperature, partial pressure, and moisture to protein ratio

The solubility of carbon dioxide (CO₂) in the moisture and protein components of cheese matrices and the influence of changing pH, salt and temperature levels remains unclear. In this study, model casein matrices were prepared, by renneting of micellar casein concentrate (MCC), with modulation of salt and pH levels by adding salt and glucono delta-lactone, respectively, to the MCC solutions prior to renneting. Different moisture-to-protein levels were achieved by freeze-drying, incubation of samples at different relative humidities, or by applying varying pressures during gel manufacture. The CO₂ solubility of samples decreased linearly with both increasing temperature and salt-in-moisture content, whereas solubility of CO₂ increased with increasing pH. A non-linear relationship was observed between CO₂ solubility and the moisture-to-protein ratio of experimental samples. Overall, such knowledge may be applied to improve the quality and consistency of eye-type cheese, and in particular to avoid development of undesirable slits and cracks.

Effect of frozen and refrigerated storage on proteolysis and physicochemical properties of high-moisture citric mozzarella cheese

High-moisture mozzarella is one of the most-exported Italian cheeses worldwide, but its quality is affected by storage. Freezing is regarded as a solution to decrease product waste, extend market reach, and increase convenience, but its effect on quality has to be estimated. In this study, the details related to proteolysis, physicochemical properties, and sensory quality parameters of high-moisture mozzarella as a function of frozen storage (1, 3, and 4 mo) and subsequent refrigerated storage after thawing (1, 3, and 8 d) were evaluated. Frozen cheeses stored at -18°C showed a higher extent of proteolysis, as well as different colorimetric and sensory properties, compared with the fresh, nonfrozen control. Sensory evaluation showed the emergence of oxidized and bitter taste after 1 mo of frozen storage, which supports the proteolysis data. The extent of proteolysis of frozen-stored cheese after thawing was greater than that measured in fresh cheese during refrigerated storage. These results help better understand the changes occurring during frozen storage of high-moisture mozzarella cheese and evaluate possible means to decrease the effect of freezing on the cheese matrix.

Effect of Pseudomonas fluorescens proteases on the quality of Cheddar cheese

The objective of this study was to investigate the effect of adding different levels of a thermoresistant protease produced by a Pseudomonas fluorescens strain to milk on the manufacture and quality of Cheddar cheese. Fresh raw milk was collected, standardized, and pasteurized at 72°C for 15 s, and the enzyme was added to give a protease activity of 0.15 or 0.60 U/L (treatments P1 and P4, respectively), while one sample had no enzyme added (control). Milk was stored at 4°C for 48 h and Cheddar cheese was manufactured after 0 and 48 h of storage. Results indicated that the protease was active in milk during 48 h of storage; however, its effect on milk composition was minimal. The protein that was preferentially hydrolyzed by the protease over storage was β-casein, followed by κ-casein. The mean cheese yield and recovery of fat and protein obtained for all cheeses were not affected by protease activity. The protease showed low activity during cheese manufacture, possibly because of unfavorable conditions, including low pH. One of the factors that might have influenced protease activity was the pH of the curd (approximately 6.55 after acidification and 5.35 at milling), which was lower than that at which the enzyme would have optimum activity (pH 7 to 9). Consequently, the composition, pH, patterns of proteolysis, and hardness of all cheeses produced were similar and in accordance with values expected for that type of cheese, independently of the protease activity level. However, slight increases in proteolysis were observed in P4 cheeses and produced using milk stored for 48 h. Both the P1 and P4 cheeses had higher concentrations of free amino acids (FAA) compared with the control, whereas urea-PAGE electrophoretograms indicated a greater breakdown of caseins in the P4 cheese samples, which may be related to possible increases in numbers of proteolytic bacteria in milk during storage. Therefore, the thermoresistant psychrotrophic bacterial protease(s) tested in this study may affect the manufacture or quality of Cheddar cheese during ripening to a relatively limited extent. However, controlling initial levels of proteolytic bacteria in raw milk remains essential, because proteolysis affects the development of flavor and texture in cheese.