Impact of whey pH at drainage on the physicochemical, sensory, and functional properties of mozzarella cheese made from buffalo milk

In this study, the effects of whey pH at drainage on the physicochemical, sensory, and functional properties of mozzarella cheese made from buffalo milk during storage were investigated. Four cheese samples were manufactured using starter culture at different whey pH values [(A) 6.2, (B) 5.9, (C) 5.6, and (D) 5.3] and analyzed on the 1st, 28th, and 56th day. Ash, calcium, and phosphorus concentrations decreased as the whey pH at drainage was lowered. Cheese yield and calcium recovery were the highest in D cheeses. During storage, expressible serum levels decreased and nonexpressible serum levels increased, indicating an increase in the water holding capacity of the cheeses. Reducing the calcium content of cheeses increased meltability values, but an overly low calcium level (D cheeses) had an adverse effect on the meltability. The melting properties of cheese samples, except D cheeses, were improved with aging. A cheeses were the hardest and D cheeses the softest throughout storage. The 1st day sensory evaluations revealed that C and D cheeses were preferred and that A cheeses were not. All sensory properties of A cheeses were improved with storage. D cheeses were rated inferior to the others at the end of the storage time.     

Transmission electron microscopy of mozzarella cheeses made from microfluidized milk.

The nanostructure of Mozzarella cheeses prepared from microfluidized milk was compared with that of control cheeses made from untreated milk. Milk heated to 10 or 54 degrees C and containing 1.0 or 3.2% fat was homogenized by microfluidization at 34 or 172 MPa prior to cheesemaking. The effects on the casein particles and fat globules in the cheese were determined by transmission electron microscopy after 1 day and 6 weeks of storage at 4 degrees C. The micrographs showed that electron-dense regions theorized to be casein submicelles rearranged from a homogeneous configuration to a pattern of clusters during the storage period. The nanostructure of the cheeses made from milk processed under the mildest conditions resembled the controls, but otherwise the fat droplets decreased in size and increased in number as the pressure and temperature were increased. The results indicate that both homogenization temperature and pressure affect the nanostructure of Mozzarella cheese.     

Starter bacteria are the prime agents of lipolysis in cheddar cheese

To assess the contribution of starter lactic acid bacteria (LAB) to lipolysis in Cheddar cheese, the evolution of free fatty acids (FFAs) was monitored in Cheddar cheeses manufactured from pasteurized milks with or without starter. Starter-free cheeses were acidified by a combination of lactic acid and glucono-delta-lactone. Starter cultures were found to actively produce FFAs in the cheese vat, and mean levels of FFAs were significantly higher in starter cheeses over ripening. The contribution of nonstarter LAB toward lipolysis appears minimal, especially in starter-acidified cheeses. It is postulated that the moderate increases in FFAs in Cheddar cheese are primarily due to lack of access of esterase of LAB to suitable lipid substrate. The results of this study indicate that starter esterases are the primary contributors to lipolysis in Cheddar cheese made from good quality pasteurized milk.     

全脂和低脂模拟干酪的流变及质构特性研究

分别通过TA.XT2i质构分析仪和AR1000流变仪对全脂和低脂模拟干酪进行全质构分析以及稳态及动态流变分析。结果表明，降低脂肪含量，全质构分析数据除了弹性及内聚性以外全部显著下降。稳态流变结果显示，模拟干酪在不同温度下均表现出非牛顿假塑性流体特性。采用power－law模型可以很好地对其数据进行拟合。动态流变分析表明，相对于低脂样品来说，高脂干酪更具有固态特性。黏弹性参数如弹性模量、黏性模量、复合黏度均与振荡频率有关。从流变和质构的角度来看，低脂和高酯干酪有明显区别。因而对干酪样品的流变和质构特性进行分析对于改善其加工工艺及品质保证是非常有意义的。     

Effect of different membrane separation technologies (Ultrafiltration and microfiltration) on the texture and microstructure of semihard low-fat cheeses

Semihard low-fat cheeses made from ultrafiltered (UF) or microfiltered (MF) milk were compared. The use of MF membranes and milder pasteurization of the milk reduced the retention of whey proteins in the retentate to 35%, compared with approximately 100% retained in the UF process. Microbiological development, physicochemical composition, and cheese ripening were not altered by the concentration processes. The lower retention of whey protein in MF cheeses accounted for their higher hardness, which correlated with higher firmness values in the textural analysis. Microstructure showed a protein matrix with open spaces through the protein network, although micrographs of UF cheeses showed the presence of spongy structures linked to the casein, which did not appear in MF cheeses and which correspond to the denatured whey protein bound to the casein. Firmness was scored better in MF cheeses, although when MF membranes were used, the optimum yields achieved using UF membranes were not attained.     

Composition of the water-soluble fraction of different cheeses

Volatile and nonvolatile compounds present in the water-soluble fraction (WSF) and water-soluble fraction with molecular weight lower than 1000 Da (WSF < 1000 Da) of six Spanish cheeses, Cabrales, Idiazábal, Mahón, Manchego, Roncal, and a goat's milk cheese, were analyzed. Different nitrogen fractions (determined by Kjeldahl method), caseins (by capillary electrophoresis), peptides and amino acids (by HPLC), and volatile components (by dynamic headspace coupled to GC-MS) as well as mineral content in the cheese fractions were analyzed and compared. The different nitrogen and volatile compounds identified in the WSF were characteristic of each cheese variety. Cabrales cheese displayed the highest content of free amino acids and the highest quantity and variety of volatile compounds. The WSF < 1000 Da fraction was less representative, especially for volatile compounds, as some of the components were lost in the ultrafiltration. Alcohols were better recovered than ketones and esters.     

Crystallization properties and polymorphism of triacylglycerols in goat's milk fat globules

The sensorial, functional, and nutritional properties of goat dairy products result from the specific fatty acid composition of goat's milk fat. However, information on the physical and thermal properties of goat's milk fat is scarce. In this study, crystallization of triacylglycerols (TG) in goat's milk fat globules was investigated using polarized light microscopy and the coupling of time-resolved synchrotron radiation X-ray diffraction (XRD) and high-sensitivity differential scanning calorimetry (DSC). The molecular organization of the solid fat phase was characterized for cooling rates between 3 and 0.1 degrees C/min. Quenching of goat's milk fat globules from 50 to -8 degrees C and 4 degrees C was also examined to identify the most unstable polymorphic forms of TG. Then, the melting behavior of fat crystals was studied on subsequent heating at 1 degrees C/min. Triple chain length (3L: 68.6-70 A) and double chain length (2L: 37-45.4 A) structures were characterized and 5 polymorphic forms, alpha, sub-alpha, beta' 1, beta' 2, and beta were identified. Polymorphic transitions were observed within goat's milk fat globules as a function of time after quenching and as a function of temperature on heating. From a technological point of view, this work will contribute to a better understanding of the rheological properties as well as on the flavor evolutions of goat's milk-based products.     

Multiscale characterization of the organization of triglycerides and phospholipids in emmental cheese: from the microscopic to the molecular level

The chemical composition and properties of lipids, both triglycerides and phospholipids, play a major role in the functional and nutritional properties of food products. In this study, the suprastructure of fat, solid fat content, and crystallographic properties of triglycerides were investigated in hard-type cheeses from the microscopic scale to the molecular level using the combination of relevant techniques. Two industrial cheeses with different oiling off properties were compared with experimental cheeses manufactured in the laboratory. Microstructural analysis performed using confocal laser scanning microscopy showed that milk processing led to the disruption of fat globules with the formation of nonglobular fat. For a similar fatty acid composition, oiling off was mainly related to the fat in dry matter content and to the suprastructure of fat in cheese. An exogenous fluorescent phospholipid permitted the localization of milk phospholipids in the cheese matrix, which mainly remain around fat inclusions after disruption of the milk fat globule membrane, and to show heterogeneities. We also showed using differential scanning calorimetry that the suprastructure of fat did not affect the solid fat content in cheese at 4 degrees C: 71.6 +/- 4.9%. The organization of triglyceride molecules in fat crystals, elucidated at a molecular level using X-ray diffraction, corresponded to the coexistence of 2 lamellar structures (2L 40.5 angstroms and 3L 54.6 angstroms) with four polymorphic forms: alpha, two beta' and beta. A schematic representation of the multiscale organization of triglycerides and phospholipids in cheese is proposed.     

Enrichment of cheeses manufactured from cow's and sheep's milk blends with sheep-like species-related alkylphenols

Enhancement of concentrations of species-related sheep-like alkylphenols, p- and m-cresols and 3- and 4-ethylphenols, in experimental Manchego-type cheeses manufactured from cow's and sheep's milk blends (80:20) by using arylsulfatases was investigated. A food-grade arylsulfatase from Aspergillus oryzae (ATCC 20719) was produced using a stimulatory medium, and crude dried cells were used as the enzyme source. Exogenous arylsulfatases from Helix pomatia and A. oryzae were added to cheese curd, and the amounts of species-related alkylphenols were measured. Arylsulfatase from H. pomatia released limited amounts of alkylphenols in the cheese only when used at a high level. Arylsulfatase from A. oryzae released substantial amounts of alkylphenols during 2 months of ripening. The concentrations of alkylphenols in A. oryzae arylsulfatase-treated cheese were comparable to the previously reported levels present in aged Manchego-type cheeses manufactured from pure sheep's milk.     

Evaluation of APHA and AOAC methods for phosphatase in cheese

Varieties of market cheese were analyzed for alkaline phosphatase by the modified rapid colorimetric method of the American Public Health Association (APHA) and the official AOAC method, 16.304-16.306. In the APHA method, 5 g cheese (pH less than 7.0) is macerated with 2 mL 1:1 carbonate buffer, or 2 mL water (for cheese with pH greater than 7.0). Addition of 0.1 mL magnesium acetate (1 mg magnesium) to test portions of cheese extracts yielded reproducible and quantitative recovery of added phosphatase. In the AOAC method, macerating 0.5 g cheese with 1 mL borate buffer before adding milk phosphatase improved recovery among cheeses. Addition of magnesium ion increased phosphatase activity in some cheeses. Phosphatases in blue mold-ripened and Swiss cheeses were inactivated by heat faster than was milk phosphatase, yet milk phosphatase added to various soft cheeses was completely inactivated at 60 degrees C for 10 min. The lability of phosphatase was due to the heat-denaturing effect of NaCl present in finished cheeses. Some Mexican style soft cheeses contained both heat-labile and heat-stable phosphatases. These data suggest that the phosphatase test to differentiate milk and microbial phosphatases on the basis of repasteurization and analysis of cheese is no longer valid.     

The viscoelastic properties of processed cheeses depend on their thermal history and fat polymorphism

Both the composition and the thermal kinetics that are applied to processed cheeses can affect their texture. This study investigated the effect of the storage conditions and thermal history on the viscoelastic properties of processed cheese and the physical properties of the fat phase. The microstructure of processed cheese has been characterized. Using a combination of physical techniques such as rheometry, differential scanning calorimetry, and X-ray diffraction, the partial crystallization of fat and the polymorphism of triacylglycerols (TG; main constituents of milk fat) were related to changes in the elastic modulus and tan δ as a function of temperature. In the small emulsion droplets (<1 μm) dispersed in processed cheeses, the solid fat phase was studied at a molecular level and showed differences as a function of the thermal history. Storage of processed cheese at 4 °C and its equilibration at 25 °C lead to partial crystallization of the fat phase, with the formation of a β' 2 L (40.9 ?) structure; on cooling at 2 °C min(-1), the formation of an α 3 L (65.8 ?) structure was characterized. The cooling of processed cheese from 60 to -10 °C leads to the formation of a single type of crystal: α 3 L (72 ?). Structural reorganizations of the solid fat phase characterized on heating allowed the interpretation of the elastic modulus evolution of processed cheese. This study evidenced polymorphism of TG in a complex food product such as processed cheese and allowed a better understanding of the viscoelastic properties as a function of the thermal history.     

Plasmin system and microbial proteases in milk: characteristics,roles, and relationship

Proteolysis of milk proteins can be attributed to both native proteases and the proteases produced by psychrotrophic bacteria during storage of fresh raw milk. These proteases cause beneficial or detrimental changes, depending on the specific milk product. Plasmin, the major native protease in milk, is important for cheese ripening. Milk storage and cheese-making conditions can affect the level of plasmin in the casein and whey fractions of milk. A microbial protease from a psychrotrophic microorganism can indirectly increase plasmin levels in the casein curd. This relationship between the plasmin system and microbial proteases in milk provides a means to control levels of plasmin to benefit the quality of dairy products. This paper is a short review of both the plasmin system and microbial proteases, focusing on their characteristics and relationship and how the quality of dairy products is affected by their proteolysis of milk proteins.     

Effect of processing and storage on the stability of flaxseed lignan added to dairy products

This study investigated the effects of processing and storage on the stability of purified, flaxseed-derived secoisolariciresinol diglucoside (SDG) added to milk prior to the manufacture of different dairy products. We analyzed the effect of high-temperature pasteurization, fermentation, and milk renneting as well as storage on the stability of SDG added to milk, yogurt, and cheese. Also, the stability of SDG in whey-based drinks was studied. Added SDG was found to withstand the studied processes well. In edam cheese manufacture, most of the added SDG was retained in the whey fraction and 6% was found in the cheese curd. SDG was also relatively stable in edam cheese during ripening of 6 weeks at 9 degrees C and in yogurt during storage of 21 days at 4 degrees C. Up to 25% of added SDG was lost in whey-based drinks during storage of 6 months at 8 degrees C. We conclude that SDG can be successfully supplemented in dairy-based products.     

Rheological properties of concentrated skim milk: influence of heat treatment and genetic variants on the changes in viscosity during storage

Heat treatment during manufacturing of milk powder is one of the most important tools for manipulation of its functional properties, and it is the basis of the classification of these proteins into low-, medium-, and high-heat types. Slight differences in the sequences of the major proteins in milk (genetic variants) seem to have also a significant effect in milk powder processing (U.S. patent). Therefore, the effects of high-temperature storage and heat treatment on skim milk of defined genetic variants of beta-lactoglobulin (beta-LG) were measured. The samples had 45% total solids, the temperature of aging was 50 degrees C, and the heat treatment was 90 degrees C for 10 min prior to evaporation. Measurements on shear rate and on apparent viscosity were determined for each sample. During storage of the concentrated milk, the apparent viscosity and yield values increased markedly, and the age-dependent increase in viscosity in heat-treated concentrated skim milks was much more pronounced than in those prepared from unheated skim milks. The increase in apparent viscosity and yield value with storage time was notably different for milks containing different genetic variants. Unheated concentrated milks containing the B variant of beta-LG showed the most rapid increase in apparent viscosity with storage time, whereas the viscosity increase was slowest in the concentrate containing the A variant. In contrast, heat-treated concentrated milks containing the A variant of beta-LG showed the most rapid increase in viscosity with storage time, whereas the viscosity increase was slowest in the concentrate containing the AB variant. The changes in apparent viscosity of concentrated milk were largely reversible under high shear during the early stages of storage, but samples stored for a long time showed irreversible changes in apparent viscosity. Particle size analysis confirmed irreversible aggregation and fusion of casein particles during storage.     

The addition of Propionibacterium freudenreichii to Raclette cheese induces biochemical changes and enhances flavor development

Two mixtures of Propionibacterium freudenreichii commercial strains were tested as adjunct cultures in pasteurized milk Raclette cheese to investigate the ability of propionibacteria (PAB) to enhance flavor development. Cheese flavor was assessed by a trained sensory panel, and levels of free amino acids, free fatty acids, and volatile compounds were determined. The PAB level showed a 1.4 log increase within the ripening period (12 weeks at 11 degrees C). Eye formation, which was not desired, was not observed in PAB cheeses. PAB fermented lactate to acetate and propionate and produced fatty acids by lipolysis, branched chain volatile compounds derived from isoleucine and leucine catabolism and some esters. One of the experimental cheeses received the highest scores for odor and flavor intensity and was characterized by higher frequencies of detection for some minor notes ("propionic"and "whey" odor, "sweet" taste). PAB can therefore be considered as potential adjunct cultures to enhance or modify cheese flavor development.     

Antioxidants, free radicals, storage proteins, puroindolines, and proteolytic activities in bread wheat (Triticum aestivum) seeds during accelerated aging

Seeds of bread wheat were incubated at 40 degrees C and 100% relative humidity for 0, 3, 4, 6, and 10 days. The effects of accelerated aging on seed germinability and some biochemical properties of flour (carotenoid, free radical, and protein contents and proteolytic activity) and gluten (free radical content and flexibility) were investigated. Seed germinability decreased during aging, resulting in seed death after 10 days. A progressive decrease of carotenoid content, in particular, lutein, was observed, prolonging the incubation, whereas the free radical content increased in both flour and gluten. A degradation of soluble and storage proteins was found, associated with a marked increase of proteolytic activity and a loss of viscoelastic properties of gluten. On the contrary, puroindolines were quite resistant to the treatment. The results are discussed in comparison with those previously obtained during accelerated aging of durum wheat seeds.     

Identification and enumeration of beta-hemolytic Listeria monocytogenes in naturally contaminated dairy products

A DNA probe was used to identify hemolytic Listeria monocytogenes in naturally contaminated dairy products: unpasteurized milk, ricotta cheese, and imported semisoft cheeses. Of 34 milk samples, 12 were suspected to contain hemolytic L. monocytogenes; 1 contained greater than 6000 viable organisms/g. The ricotta cheese, although temperature-abused, had a titer of 3.6 x 10(6) beta-hemolytic L. monocytogenes cells/g, whereas the semisoft cheeses reached a maximum of 5.6 x 10(6) cells/g. Pure cultures of L. monocytogenes isolated from both types of cheese were found positive by the CAMP test and the DNA probe.     

Ethyl ester formation is enhanced by ethanol addition in mini Swiss cheese with and without added propionibacteria

Esters are important contributors to cheese flavor, but their mechanisms of synthesis in cheese are largely unknown. This study aimed to determine whether ethanol concentration limits the formation of ethyl esters in cheese. Mini Swiss cheeses were manufactured with (E) or without (C) the addition of ethanol to cheese milk. Ethanol concentrations (enzymatic analysis) were 64 +/- 17 and 330 +/- 82 microg g(-1), respectively, in C and E cheeses. E cheeses also contained 5.4 +/- 2.3 times more of the five ethyl esters quantified than C cheeses, regardless of the concentrations of esters in C cheeses (range 1-128 ng g(-1)). Furthermore, the presence of propionibacteria added as acid-producing secondary starters was associated with greater concentrations of esters, due to the increase in acid concentrations that propionibacteria induced and/or to an involvement of propionibacteria enzymes in ester synthesis. This study demonstrates that ethanol is the limiting factor of ethyl ester synthesis in Swiss cheese.     

Formation of early and advanced Maillard reaction products correlates to the ripening of cheese

The present study deals with the characterization of the ripening of cheese. A traditional German acid curd cheese was ripened under defined conditions at elevated temperature, and protein and amino acid modifications were investigated. Degree of proteolysis and analysis of early [Amadori compound furosine (6)] and advanced [N(ε)-carboxymethyllysine (4), N(ε)-carboxyethyllysine (5)] Maillard reaction products confirmed the maturation to proceed from the rind to the core of the cheese. Whereas 6 was decreased, 4 and 5 increased over time. Deeper insight into the Maillard reaction during the ripening of cheese was achieved by the determination of selected α-dicarbonyl compounds. Especially methylglyoxal (2) showed a characteristic behavior during storage of the acid curd cheese. Decrease of this reactive structure was directly correlated to the formation of 5. To extend the results of experimental ripening to commercial cheeses, different aged Gouda types were investigated. Maturation times of the samples ranged from 6 to 8 weeks (young) to more than 1 year (aged). Again, increase of 5 and decrease of 2 were able to describe the ripening of this rennet coagulated cheese. Therefore, both chemical parameters are potent markers to characterize the degree of maturation, independent of coagulation.