Casein Matrix Research Articles

Effect of commercial fat replacers on the microstructure of low‐fat Cheddar cheese

SummaryThis objective of this study was to determine the effect of protein‐ and carbohydrate‐based fat replacers on the microstructure of low‐fat Cheddar cheese. Microstructure was studied by transmission and scanning electron microscopy. Protein‐based fat replacers were Dairy Lo™ (DL) and Simplesse™ (SIMP), while the carbohydrate‐based fat replacers were Novagel™ (NOV) and Stellar™ (STEL). Low‐fat Cheddar cheese was manufactured using these commercial fat replacers and aged for 6 months at 5 °C. Low‐fat control (LFC) and low‐fat Cheddar cheese made with SIMP and DL showed a rippled surface microstructure while incorporation of NOV and STEL resulted in cheese with an undulated and rough surface microstructure. Cheese made with SIMP showed void areas around the SIMP particles. Fat replacers SIMP and NOV softened low‐fat Cheddar cheese by imparting discontinuity to the casein matrix. A method in which fat replacers DL and STEL appeared to soften low‐fat Cheddar cheese was by having the fewest layers (that conceivably resist crushing) at the fat–protein interface. Microstructure of low‐fat Cheddar cheese was effected by fat replacers.

Effect of High Pressure Microfluidization on Microstructure of Mozzarella Cheese

Microstructure was compared in low-fat and full-fat mozzarella cheeses prepared from milk homogenized by microfluidization at various temperatures and pressures. Milk heated to 10, 43, or 54°C and containing 1.0 or 3.2 g fat/100 g fluid milk was homogenized at 34, 103, or 172 MPa prior to cheesemaking. Scanning electron microscopy was performed after 1 d and 6 wk of storage at 4°C. The micrographs showed that relatively large fat globules were dispersed throughout the casein matrix in each of the cheeses made from milk homogenized at 10°C, and in each of the nonhomogenized controls. As expected, fat globules were much smaller in the cheeses made from milk homogenized at the higher pressures. Increasing the milk temperature also caused the globule size to decrease since the fat became liquid and more easily fragmented. The results indicate that both homogenization temperature and pressure affect development of microstructure in mozzarella cheese.

Rheology of Dairy Foods that Gel, Stretch, and Fracture

Casein gels are found in hard and soft dairy foods such as cheese and yogurt, and their rheological properties can be analyzed with various instrumental techniques. Empirical tests of cheese have been used since cheese making began, and imitative tests have been conducted in laboratories since the 1930s. Texture profile analysis is now the most frequently used imitative test. Fundamental tests provide a better representation of cheese and yogurt rheology because of the systematic mathematical treatment involved. Uniaxial compression and stress and strain relaxation tests are among the fundamental tests performed on cheese, and viscosity data are often used to investigate the physical characteristics of yogurt. Small amplitude oscillatory shear measurements are applicable to both products. Food scientists can acquire a clearer picture of the structure of dairy foods by performing appropriate rheological studies of the casein matrix.

Whiteness Change During Heating and Cooling of Mozzarella Cheese

Whiteness (L-value) changes in low-fat and low-moisture, part-skim Mozzarella cheeses during heating (7 to 60°C) and cooling (60 to 7°C) were evaluated. In low-fat Mozzarella, a large increase in whiteness was observed during heating, and a decrease in whiteness was observed during cooling. In low-moisture, part-skim Mozzarella, the whiteness changes during heating and cooling were smaller. Serum phase was removed from low-fat and low-moisture, part-skim Mozzarella cheeses. White protein gels were formed when the isolated serum phase from either low-fat or low-moisture, part-skim Mozzarella was heated. The white gel that formed was composed predominantly of casein and casein proteolysis products. The gel might have been produced by heat-induced, hydrophobic protein-protein interactions, and it tended to dissociate when cooled. Formation of a gel during heating increased light scattering, which increased the L-value. The gel dissociated during cooling and no longer scattered light, which decreased the L-value. We hypothesized that a gel, which was reversible, formed in the serum phase of cheese during heating and might have been responsible for the observed changes in the L-value of low-fat Mozzarella cheese during heating and cooling. The additional fat in low-moisture, part-skim Mozzarella compared with low-fat Mozzarella masked some of the color changes in the serum phase of low-moisture, part-skim Mozzarella. A model was developed to describe the contributions of the casein matrix plus serum phase of Mozzarella cheese and the contribution of fat to the changes in whiteness of Mozzarella cheese during heating and cooling.

Lignocellulosic Fibre Reinforced Caseinate Plastics

Caseinate plastics were reinforced with two lignocellulosic fibres, i.e. wood pulp fibre and flax bast fibre by means of kneading and subsequent injection moulding. The tensile modulus increased from 200 MPa for the unfilled plastic to 1200 MPa at 20 wt% fibre addition. Simultaneously, the tensile strength increased from 6 to 30 MPa going from 0 to 20 wt% fibre incorporation. These results indicate a good interaction between the fibres and the mainly hydrophilic caseinate matrix.

Adrenomedullin binding protein in the plasma of multiple species: characterization by radioligand blotting.

Frequently, peptide hormones circulate in plasma associated with specific binding proteins that modify the clearance and biochemical activities of the peptide. Our experimental approach was to use 125I-ligand blotting procedures to probe for the presence of specific adrenomedullin (AM) binding proteins (AMBPs). Plasma proteins from chick, calf, dog, goat, guinea pig, human, mouse, pig, rabbit and sheep blood were separated electrophoretically in 10% nonreducing SDS-polyacrylamide gels and transferred to nitrocellulose. Nonspecific binding of tracer was blocked on the nitrocellulose with a hydrolyzed casein matrix. Blots were probed with synthetic human 125I-AM. Autoradiogram scanning of blots revealed a mixture of 140- and/or 120- kD protein complexes that bound 125I-AM in all species tested. Binding of the ligand was specific as judged by a linear competitive displacement of the tracer binding from human, bovine and pig plasma AMBP bands with increasing concentrations of nonlabelled AM in the binding buffer. A series of peptide fragments of AM representing amino- and carboxyterminal regions of the hormone, or amylin, calcitonin gene-related peptide (CGRP), or insulin failed to displace intact 125I-AM from ligand blot bands. Bovine plasma proteins from healthy and parasitized calves with an infection-related stunting syndrome were separated electrophoretically, transferred to nitrocellulose and probed with 125I-AM; phosphoimage densitometry analysis revealed a 67% decrease in AMBP band intensity in the 120 and 140 kD proteins from infected calves. We conclude that a specific binding protein(s) for AM exists in mammalian and avian blood that might impact on the bioactivity and function of AM in health and disease.

The Effect of Milk Fat, the Ratio of Casein to Water, and Temperature on the Viscoelastic Properties of Rennet Casein Gels

The objective of this study was to evaluate the effects of milk fat, the ratio of casein to water, and temperature on the viscoelastic properties of a model system for cheese based on dried rennet casein power. Casein gels were formed by mixing rennet casein, butter (as a source of milk fat), water, and some minor ingredients at 0.89, 0.58, and 0.38 ratios of casein to water; milk fat was added at 0, 12, and 24% at each ratio. Strain sweep, frequency sweep, melting behavior, and stress relaxation were used to characterize the viscoelastic properties of casein gels. The addition of milk fat reduced the linear viscoelastic region of casein gels. The complex modulus increased as milk fat content increased at temperatures ≤20°C, decreased at temperatures ≥30°C, and increased at all temperatures as the ratio of casein to water increased. Any particular value for the complex modulus could be obtained by a number of different combinations of the milk fat content, the ratio of casein to water, and temperature. The casein gels showed three distinctive zones of viscoelastic behavior over a temperature range of 5 to 70°C: rubbery solid, transition, and melt. The melting temperature and relaxation time of the casein gels increased as the ratio of casein to water increased; milk fat content had less effect on these gel properties. The casein matrix alone (0% added milk fat) showed a gradual softening with temperature starting at about 10°C. Thus, these composite gels represent a rather unique system by which the dispersed filler phase (milk fat) melts over the same temperature range as the underlying polymer matrix dissociates.

Characterization of liposomes and their effect on the properties of Cheddar cheese during ripening

This study was undertaken to observe the location and structure of liposomes in the cheese matrix and to identify their effect on the characteristics of Cheddar cheese during ripening. Com- position, proteolysis, microstructure and texture of Cheddar cheeses treated with either empty lipo- somes or liposomes containing cell-free extracts of Lactobacillus casei ssp. pseudoplantarum were ana- Iysed during two months of ripening. Results were compared with control Cheddar cheeses. Observations on cheese microstructure showed that sorne liposomes were included in the casein matrix, but most vesicles were located in areas close to fat globules and appeared destabilized as early as the first day after manufacture, inducing sorne changes in the cheese microstructure. The pre- sence of liposomes greatly increased the moisture of cheeses, modified the microstructure and the rheo- logical characteristics of ripened cheese. Cheeses containing liposomes were softer, less cohesive and elastic and more brittle than control cheeses. After two weeks of ripening and until the end of the study, proteolysis, particularly peptidolysis, was higher in cheeses treated with liposomes containing cell- free extracts. HPLC-analysis confirmed intensive peptidolysis between one and two months of ripe- ning. © InralElsevier, Paris liposome / cheese / microstructure / ripening

Texture and microstructure of chhana and rasogolla made from cows' milk

SummaryThe relationships between the composition, texture and microstructure of chhana (an Indian-style soft cottage cheese analogue) and rasogolla (a sweetened dairy product made from chhana) were analysed. Chhana contained a significantly higher proportion of fat, protein, lactose and minerals than did rasogolla. Cooking of chhana in 60% sucrose solution introduced sucrose and changed the texture and structure to that typical of rasogolla. As chhana was transformed to rasogolla, the Instron textural properties, hardness, gumminess and chewiness, fell significantly, whereas springiness increased dramatically. Market rasogolla had a slightly different composition from the laboratory-made samples, but both had similar Instron textural and sensory textural attributes. Scanning electron microscopy showed that chhana had a structure like cottage cheese or cream cheese, a compact, coalesced casein matrix with fat globules embedded in it. Rasogolla had a conglomerated, ragged and porous casein matrix with uneven surface and numerous large void spaces. The collapsed and ruptured fat globules were found embedded in the agglomerated protein particles of rasogolla. The textural attributes of both chhana and rasogolla could be explained by the microstructure.