Raw Cream Research Articles

Surface Characterization of Bovine Milk Phospholipid Monolayers by Langmuir Isotherms and Microscopic Techniques

Monolayers were prepared from phospholipids extracted from bovine milk and used as a model system to mimic the native milk fat globule membrane (MFGM) surface structure in various microscopic experiments. The natural complex mixtures of phospholipids were isolated from bovine raw milk, raw cream, processed whole milk, and buttermilk powder by total lipid extraction and solid-phase extraction. A Langmuir film balance mounted on an epifluorescence microscope was used to analyze the physical behavior of the monolayer films and the phase coexistence resulting from the formation of phospholipid microdomains within these films. Atomic force microscopy was used for nanometer-scale topographic resolution of the microdomains. This study allowed comparison of the behavior of phospholipid monolayers from dairy products at different stages of processing, analysis of the formation of microdomains, and the study of the effect of milk processing on lipid-lipid interactions and phase coexistence. It was observed that milk processing changes the physical behavior of phospholipid monolayers by altering the phospholipid profile and the fatty acid distribution.

Composition and Fatty Acid Distribution of Bovine Milk Phospholipids from Processed Milk Products

The aim of this work was to assess the accuracy of different extraction methods of phospholipids and to measure the effect that processing has on phospholipid composition. Four methods of extracting phospholipids from buttermilk powder were compared to optimize recovery of sphingomyelin. Using the optimal method, the phospholipid profile of four dairy products (raw milk, raw cream, homogenized and pasteurized milk, and buttermilk powder) was determined. A total lipid extraction by the Folch method followed by a solid-phase extraction using the Bitman method was the most efficient technique to recover milk sphingomyelin. Milk processing (churning, centrifuging, homogenization, spray-drying) affected the profile of milk phospholipids, leading to a loss of sphingomyelin and phosphatidylcholine after centrifugation for cream separation. A corresponding decrease in the saturation content of the raw cream phospholipids and a loss of phosphatidylethanolamine after spray-drying to produce buttermilk powder were also observed.

Using Confocal Laser Scanning Microscopy To Probe the Milk Fat Globule Membrane and Associated Proteins

The bovine milk fat globule membrane (MFGM) is an important, biologically relevant membrane due to its functional and health properties. Its composition has been thoroughly studied, but its structure, especially the lateral organization of its components, still remains unclear. We have used confocal laser scanning microscopy (CLSM) to investigate the surface structure of the MFGM in globules with different degrees of processing using two types of fluorescently labeled phospholipid probes and a protein dye. Using this technique, we have observed heterogeneities in the distribution of MFGM lipids and proteins relating to the processing and size of the globules. The effect of pretreating the milk (centrifugation, pasteurization-homogenization and churning) was studied by double-staining the surface of the milk fat globules, followed by observation using CLSM, and by determining the phospholipid profile of raw milk, raw cream, processed milk and buttermilk powder. Our findings agree with other techniques by showing that the composition of the MFGM changes with processing through the loss of phospholipids and the adsorption of caseins and whey proteins onto the surface.

Effect of Buttermilk Made from Creams with Different Heat Treatment Histories on Properties of Rennet Gels and Model Cheeses

Although many studies have reported negative effects on cheese properties resulting from the use of buttermilk in cheese milk, the cause of these effects has not been determined. In this study, buttermilk was manufactured from raw cream and pasteurized cream, as well as from a cream derived from pasteurized whole milk. Skim milks with the same heat treatments were also manufactured to be used as controls. Compositional analysis of the buttermilks revealed a pH 4.6-insoluble protein content approximately 10% lower than that of the skim milk counterparts. Milk fat globule membrane (MFGM) proteins remained soluble at pH 4.6 in raw cream buttermilk; however, when heat was applied to cream or whole milk before butter making, MFGM proteins precipitated with the caseins. Rennet gel characterization showed that MFGM material in the buttermilks decreased the firmness and increased the set-to-cut time of rennet gels, but this effect was amplified when pasteurized cream buttermilk was added to cheese milk. The microstructure of gels was studied, and it was observed that gel appearance was very different when pasteurized cream buttermilk was used, as opposed to raw cream buttermilk. Model cheeses manufactured with buttermilks tended to have a higher moisture content than cheeses made with skim milks, explaining the higher yields obtained with buttermilk. Superior retention of MFGM particles was observed in model cheeses made from pasteurized cream buttermilk compared with raw cream buttermilk. The results from this study show that pasteurization of cream and of whole milk modifies the surface of MFGM particles, and this may explain why buttermilk has poor coagulation properties and therefore yields rennet gels with texture defects.

The Effect of Phospholipids on Milkfat Crystallization Behavior

AbstractDepending on the production method, the fat component in butter can either be in a continuous phase or entrapped by milk fat globule membranes (MFGM). Phospholipids like those present in the MFGM are known to affect milk fat crystallization behavior. This study examines the effect of MFGM phospholipid concentration on butter crystal structure. Regular raw cream was first concentrated to 85% fat via centrifugation to produce a “plastic” cream, and was then blended with anhydrous milk fat (AMF) and skim milk in order to maintain the total fat‐to‐water ratio while altering the total amount of MFGM in the butter product. Whereas mixtures of AMF and skim milk contained large spherulites that had finer structures as the degree of supercooling was increased, the addition of globular fat (GF) broke up these structures, eventually producing smaller individual needle‐like crystals. However, high levels of GF also lead to the coalescence of the aqueous phase, creating large water pockets that adversely affect sensory properties. Thus, the phospholipid concentration in the final butter product must be controlled in order to obtain optimal crystal structure and product quality.

Detection of biologically active isomers of conjugated linoleic acid in kaymak

Numerous physiological effects are attributed to conjugated linoleic acids (CLA). Biologically active isomers of CLA ( cis -9, trans -11 (C18:2) and trans - 10, cis - 12 (C18:2)) have been reported to have anticarcinogenic, antioxidative and antiatherosclerotic properties. Relatively rich sources of CLA include milk fat-containing foods such as kaymak. Kaymak is a kind of concentrated cream which is traditionally manufactured from buffalo or cow's milk mainly in Turkey . The objective of this study was to determine CLA concentrations during kaymak production. Kaymak was manufactured from cow's milk which was enriched with unfermented cream. Biologically active isomers of CLA in raw milk, cream and kaymak were analyzed using gas chromatography. The method was quick, repeatable and sensitive for the CLA determination of samples. Significant differences were found among the concentrations of both isomer and total CLA during the production process (p<0.01). The total CLA contents of raw milk, cream and kaymak were determined as 0.08 ± 0.02, 0.234 ± 0.04 and 0.091 ± 0.08 g/ 100 g lipid, respectively.

A survey on the presence of listeria species in raw milk, ice cream and human stools with characterization of some isolates by sds-page

A survey on the presence of listeria species in raw milk, ice cream and human stools with characterization of some isolates by sds-page

Genotyping of Cryptosporidium spp. isolated from human stool samples in Switzerland.

In a study to estimate the frequency of Cryptosporidium infections in Switzerland, stool samples from patients found to be positive for Cryptosporidium spp. by modified Ziehl-Neelson staining and fluorescence microscopy were used for genotyping experiments. With 9 of 12 samples, DNA extraction and subsequent genotyping was successful. All Cryptosporidium-isolates belonged to the bovine genotype. In one stool sample, two strains of Cryptosporidium were demonstrated, suggesting a mixed infection. In comparison with reference strains from calves, one of the isolates showed a full sequence identity and the other a similarity of 97.5%. The fact that only bovine genotypes were detected suggests, that cryptosporidiosis must primarily be considered as a zoonotic disease in Switzerland. This is in contrast to other countries, where the human genotype of C. parvum was shown to dominate the epidemiological situation. The results of our study are supported by the previous finding, that two of the analysed strains originated from patients who used to consume raw milk or raw cream, a known risk factor for cryptosporidiosis.

Modification of Enrichment Protocols for TECRA Listeria Visual Immunoassay Method 995.22: Collaborative Study

A collaborative study was conducted to validate new enrichment methods for the TECRA Listeria Visual Immunoassay (TLVIA). These new methods incorporate a newly formulated medium, TECRA Listeria Enrichrment Broth, which does not contain the highly toxic antifungal agent, cycloheximide. The new procedures will provide an alternative to the enrichment procedures described in AOAC Method 995.22. Three food types (raw ground beef, lettuce, and ice cream) were analyzed in the United States, and 2 food types (cooked turkey and cooked fish fillets) were analyzed in Australasia. Thirty collaborators participated in the study, 16 in Australasia and 14 in the United States. With the exception of one batch of ground beef, comparison of the proportion of positive test portions (p > or = 0.05) showed no significant difference between the TLVIA and the reference method for the 5 foods at 3 inoculation levels. For the one batch of naturally contaminated raw ground beef, the TLVIA gave significantly more confirmed positive results than the reference method.

Influence from Raw Milk Flora on Cheese Ripening Studied by Different Treatments of Milk to Model Cheese

To study the influence from the raw milk microbial flora on the biochemistry of cheese during ripening, cheese was made in an unreplicated 23full factorial design in two blocks of four cheese vats. Semi-hard round-eyed model cheese with 45% fat in dry matter and a moisture content of 55% was made from raw, pasteurized and microfiltered skim milk in combinations with raw or pasteurized cream. Indices of proteolysis, amino acid composition, carboxylic acids, and volatile flavour compounds in cheese were analysed on four occasions during 120 days of ripening. Breakdown of casein progressed similarly in all cheeses and the influence of milk treatments was first seen in the varying composition of the amino acids. Principal component analysis (PCA) of the amino acid composition data showed a clear separation of the cheeses during ripening. The PCA separated the cheeses firstly by age and then by milk treatment. The cheeses made from unpasteurised and non-microfiltered milk (raw skim milk) separated out in one direction, and to some extent in the same direction those with only the cream untreated. In cheeses produced from raw skim milk, no citrulline was present and arginine increased slightly during ripening contrary to cheeses produced from treated skim milk. Typically for the raw milk cheeses, the results indicated; production of γ -amino butyric acid (GABA) from glutamic acid, histamine from histidine, tyramine from tyrosine and utilization of serine. An increase in the pyruvate content could be seen in all cheeses at the end of the ripening period. Formic acid and 2-butanol were only found in cheeses made with raw skim milk or raw cream, while ethanol was produced in all cheeses, but to a greater extent in the cheese from raw milk. Non-starter lactic acid bacteria (NSLAB) were found at higher numbers in cheese from raw milk or cream.

Heat Stability of Buttermilk

Buttermilk prepared on a laboratory scale from raw cream, or on a commercial scale from flash-pasteurized cream (90°C for 1 to 2s), exhibited a type B heat coagulation time-pH profile (i.e., stability increased as a function of pH). The high heat stability of buttermilk in the pH range of the minimum of a type A milk (pH ∼6.8 to 7.0) appears to be related to differences in the serum phase constituents (i.e., a low calcium and β-Lg concentration and a high nonmicellar κ-CN content).

Effect of hydrogen peroxide treatment on the quality of raw cream

The effect of hydrogen peroxide on the attributes of raw cream was studied. The samples with 500 mg/kg and 1500 mg/kg hydrogen peroxide (H2O2) were compared with an untreated control sample. The results indicated that the addition of hydrogen peroxide prevented, to a great extent, the development of lipolysis, proteolysis and acidity, as well as the growth of psychrotrophic microorganisms. However, the treatment had a negative effect on the oxidative stability of the cream.

Characterization of the interface of an oil-in-water emulsion stabilized by milk fat globule membrane material

A fraction derived from the membrane of milk fat globules (MFGM) was isolated from fresh raw cream. The adsorption of MFGM at the interface of oil-in-water emulsions was studied as well as the stability of the emulsions under different conditions (pH, temperature treatment) and the surface potential. The emulsions prepared with MFGM isolates were stable at neutral pH and were destabilized at low pH. By analysis of the protein adsorbed at the interface by polyacrylamide gel electrophoresis, we also determined that the MFGM that covered the surface of the oil-in-water emulsion could not be displaced by surfactants such as Tweens and Triton X-100 and was not affected by the presence of other proteins such as caseins and β-lactoglobulin added to the emulsion. A strong molecular interaction between the adsorbed MFGM, composed of phospholipid and protein, may exist at the interface, rendering the newly formed membrane very little affected by the presence of other surfactants. This MFGM-stabilized emulsion was characterized by a behaviour very different from that of emulsions stabilized by other milk proteins.

Surface properties of the fat globule in treated creams

Surface properties and susceptibility to lipolysis by a generic lipase were studied on raw cream, pasteurized cream and UHT-treated, homogenized cream. Heat treatments did not modify extensively the structure of the fat globule membrane, either in terms of its surface properties or of the nature of the associated proteins. Homogenization of cream resulted in markedly increased susceptibility to the lipolytic action of added enzymes, and was accompanied by extensive modifications of the surface properties. The protein composition of the milk fat globule membrane in treated cream was different from that reported when cream was isolated from treated milk. Attempts at discriminating commercial creams on the basis of lipolysis and surface hydrophobicity indicated that measuring the susceptibility to lipolytic action could discriminate pasteurized, non-homogenized cream from UHT-treated, homogenized cream, while estimating surface properties did not allow such differentiation.

Performance of Homogenizers in Infrared Milk Analyzers: A Survey

Abstract The objective of this survey was to determine if infrared milk analyzers can achieve a &amp;lt;0.05% difference in fat test between unhomogenized and homogenized portions of the same milk, as stated in official methods. Two batches of pasteurized, unhomogenized milk (3 and 6% fat) were prepared from a single source of raw cream and skim. Homogenized milks were produced at 3 pressures: 0, 10342, and 17238 kPa. Pairs of unhomogenized and homogenized portions of the same milk were tested on 22 infrared analyzers. More instruments exceeded the 0.05% difference between homogenized and unhomogenized milk than expected; differences between homogenized and unhomogenized milk increased with increasing homogenization pressure and fat concentration. At 3% fat, differences between homogenized and unhomogenized milks at both 10342 and 17238 kPa were &amp;lt;0.05% for 21 of 22 instruments for fat A; only 17 and 13 of 22 instruments for fat B achieved a difference of &amp;lt;0.05% at 10342 and 17238 kPa, respectively. At 6% fat, differences between homogenized and unhomogenized milks for fat A were &amp;lt;0.05% for 15 and 14 of 22 instruments at the 2 pressures, respectively. For fat B, 8 and 5 of 22 instruments achieved a difference of &amp;lt;0.05% at 10432 and 17238 kPa. Instruments were also evaluated for homogenization efficiency by a revised criterion that is dependent on the fat content of the samples used for the evaluation.

The Effect of Various UHT Processing Parameters and Storage Conditions on the Saturated Aldehydes In Half-and-Half Cream

Raw cream was standardized to 10% fat and processed by ultra-high-temperature (UHT) steam injection at 149°C for 20 s, 149°C for 3.4 s, 138°C for 20 s, and 143°C for 7 s, then aseptically packaged by a Tetra Pak AB3-250 filler. Packages were stored for 12 months at 24°C and analyzed at 0, 1, 3, 6, and 12 months. Fat-soluble carbonyls were extracted from the UHT cream with carbonyl-free hexanes and converted to their 2,4-dinitrophenyl-hydrazone derivatives. Alkanal hydrazones were separated by column chromatography into pure fractions. Spectrophotometry and gas chromatography were used to identify the alkanals. Butanal, hexanal, heptanal, nonanal, and decanal were identified and found to decrease in concentration during storage.

Factors Affecting Lipase Flavor in Butter

In studies to determine the effect of cream quality, pasteurization temperature, and storage temperature on the development of lipase flavor in butter, raw cream, fresh and aged 24h, was divided into three fractions and heated at 72C, 85C, and 93C, respectively, for 18s. Each fraction of cream was churned into butter, which was divided and stored at −28.9C and 4.4C. Lipase flavor development was measured organoleptically, by acid degree value, and by free fatty acid concentration. Age of the cream significantly affected free fatty acid and acid degree values whereas heat treatment of the cream affected free fatty acids, acid degree values and flavor, and the temperature of storage affected free fatty acids and flavor. Correlation between free fatty acids and acid degree values was .86. There was no correlation between flavor and either free fatty acids or acid degree values.

BACTERIOPHAGE TYPING OF STAPHYLOCOCCI ISOLATED FROM FOODSTUFFS AND FOOD HANDLERS IN TEHRAN

Studies were done to assess contamination of 3247 samples of foods and food handlers with coagulase-positive staphylococci. Food specimens were collected from retail shops and a Tehran milk pasteurizing plant; in addition 510 food handlers of different professional groups were examined. Three swabs for bacteriological examination were randomly collected from nose, hands, and throat. Of samples tested for coagulase-positive staphylococci, 28.02% were positive and almost half of them were obtained from foodstuffs. Of 546 isolates that were phage typed, we found that group III predominated in the nose and cream cake, while group II was more prevalent in raw cream, throat, and hands. Although group IV was not prominent, nose and hands yielded 3 and 1 positives, respectively. Untypable isolates comprised about 47.2% with most from hands and nose, 61.7 and 60.5%, respectively, and the least from raw cream, 33.3%.

Studies on Alkaline Milk Phosphatase III: A Theory for the Mechanism of Reactivation of Alkaline Milk Phosphatase in a Model System

AbstractA hypothesis on the mechanism of the reactivation of alkaline phosphatase from cream and milk is formulated. By adding pasteurized cream to raw cream the isozyme pattern of the alkaline phosphatases was found to be characteristically changed, leading to the formation of a strong zone of β‐isozyme. This so called „β‐effect”︁ principally resembles the reactivation process and may be considered as a simple model system for this process. During pasteurization of cream a part of the outer surface layer of the fat globule membrane particularly rich in the β‐isozyme of alkaline phosphatase is dispersed into the aqueous phase. By this mechanism denatured β‐isozyme migrates into the aqueous phase of cream or milk after pasteurization. When the pasteurized extract containing the denatured β‐AP is admixed to raw cream, a renaturation of the denatured dß‐AP to renatured rß‐AP is effected under influence of the conformation of the native β‐AP and associated lipoproteins present in the membrane.

Volatile Components of Milk Fat Steam Distillates Identified by Gas Chromatography and Mass Spectrometry1,2

Vacuum steam distillates of butteroil, fresh raw cream, fresh pasteurized cream, and pasteurized stored cream were analyzed by packed column and open-tubular column gas chromatography in conjunction with mass spectrometry. High-temperature (210 C) distillations of different butteroils yielded over 120volatile compounds. Identification (or tentative identification) of more than 100 of these compounds was made from mass spectral-gas chromatographic data. Over 30volatiles not previously reported in milk products were encountered. Many of the volatile compounds were obviously heat-produced, as the number of them was small in fresh, raw cream compared to heated cream and butteroil. However, aromatic compounds and some aliphatic hydrocarbons, not previously reported were found in fresh, raw cream. Control experiments were conducted to determine laboratory contaminants and distillation artifacts.