Physical properties of cream reformulated with fractionated milk fat and milk-derived components

Emulsifying properties of milk-derived components influence the physical characteristics of reformulated creams. Fractionated butter oils with different melting ranges (low-melt: 10 to 25 degrees C; medium-melt: 25 to 35 degrees C) were recombined into fluid dairy systems using skim milk, or sweet buttermilk and butter-derived aqueous phase to manufacture 20% milk fat creams. Separation temperature (49 degrees C or 55 degrees C) in obtaining emulsifying components was examined for its effect on physical properties of pasteurized reformulated creams. Rate of creaming, viscosity, feathering, and sensory characteristics of reformulated and natural creams stored at 3.3 degrees C were evaluated over a 13-d period. Creaming rate of reformulated and natural creams was unaffected by formulation and was most influenced by duration of storage. Melting characteristics of butter oils influenced viscosity at some shear rates. With the exception of natural cream, all formulations were consistent in apparent viscosity during the 2-wk storage period. All creams feathered in a pH range of 4.70 to 5.20 and were classified as moderately stable to slightly unstable. All reformulated and natural creams met sensory quality specifications with the exception of creams formulated with skim milk and lower melting range butteroil. Creams formulated with buttermilk, butter-derived aqueous phase, and lower-melting range butter oil most closely mimicked natural creams with regard to sensory quality and viscosity.     

Physical Properties of 20% Milk Fat Reformulated Creams Manufactured from Cholesterol-reduced Butteroil

A cholesterol-reduced butteroil was emulsified with various milk-derived components into three different cream formulations having 20% milk fat. Viscosity, creaming stability, and feathering stability of the cream formulations and a control homogenized at two pressures (10.2/3.4 MPa; 13.6/3.4 MPa) were measured over 2 wk. All creams demonstrated non-Newtonian fluid behavior at 7 °C. Apparent viscosity varied with formulation (p ≦ 0.05). Creaming stability was affected by formulation, homogenization pressure, and storage time (p ≦ 0.05). Feathering was unaffected by any treatments. The formulation using buttermilk and butter-derived aqueous phase best simulated viscosity and creaming stability of the control cream.     

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.     

Effect of processing on the composition and microstructure of buttermilk and its milk fat globule membranes

The effect of cream pasteurization on the composition and microstructure of buttermilk after pasteurization, evaporation and spray-drying was studied. The composition of milk fat globule membrane (MFGM) isolated from buttermilk samples was also characterized. Pasteurization of cream resulted in higher lipid recovery in the buttermilk. Spray-drying of buttermilk had a significant effect on phospholipid content and composition. After spray-drying, the phospholipid content decreased by 38.2% and 40.6%, respectively in buttermilk from raw or pasteurized cream when compared with initial buttermilks. Pasteurization of cream resulted in the highest increase in whey protein recovery in MFGM isolates compared with all other processing steps applied on buttermilk. A reduction in phospholipid content was also observed in MFGM isolates following spray-drying. Transmission electron microscopy of the microstructure of buttermilks revealed extremely heterogeneous microstructures but failed to reveal any effect of the treatments.     

Polybrominated biphenyls in raw milk and processed dairy products.

Milk from four dairy herds identified by the Michigan Department of Agriculture as containing less than .3 ppm (fat basis) physiologically incorporated polybrominated biphenyls was processed individually into cream, skim milk, butter, and stirred curd cheese. Pasteurized and freeze-dried whole milk, skim milk, and cream, spray-dried whole milk and skim milk, and condensed whole milk were made also. Polybrominated biphenyls were concentrated in the high-fat products. Pasteurized skim milk, buttermilk, and whey had slightly more polybrominated biphenyls than pasteurized whole milk on a fat basis. Spray-drying reduced the polybrominated biphenyls in whole milk and skim milk while pasteurization, freeze-drying, aging of cheese, and condensation were not effective.     

Reexamination of Fat Globule Clustering and Creaming in Cow Milk

Fat globule clustering, as characterized by cream volume and cluster time, was studied in raw milk, heated milk, homogenized milk, and in model systems. Immunoglobulin M was confirmed as the heat-labile component in fat globule clustering and was shown to function as a cryoagglutinin rather than as a cryoglobulin as previously indicated. Hapten inhibition studies demonstrated that the antigen is carbohydrate. Skim milk membrane was identified as the homogenization-labile component. Although immunoglobulin M can agglutinate milk fat globules to a limited extent, normal creaming requires both immunoglobulin M and skim milk membrane. Approximately 7% of the immunoglobulin M in normal milk participates in a single creaming. The lower portion of creamed milk (gravity separated skim milk) failed to support creaming on addition of washed fat globules but did so on addition of skim milk membrane. A theory of fat globule clustering consistent with observed experimental results depicts immuno-globulin M interacting in an antigen-antibody mode simultaneously with skim milk membrane and milk fat globules through specific carbohydrate moieties.     

Effects of buttermilk powders on emulsification properties and acid tolerance of cream

Emulsifying properties and acid tolerance are 2 of the most important characteristics of cream. The effects of the buttermilk component, especially its phospholipids, on the emulsifying properties and acid tolerance of cream were investigated in this study. Two buttermilks with differing phospholipid contents and skimmed milk were used to evaluate the effects of phospholipids on the aforementioned parameters. The mean diameter of fat globules and the cream viscosity were used as indicators of emulsifying properties. Acid tolerance was evaluated by studying the effect of citric acid on the maximum viscosity of cream. This was tested by adding 400 μL of 10% (w/w) citric acid solution to cream every minute and simultaneously measuring pH and viscosity. In 45% and 40% fat cream systems, buttermilk, and especially that with higher phospholipid content, improved the emulsifying properties and acid tolerance of the cream. The components of buttermilk could alter the properties of the surface of fat globules, thereby altering the emulsification properties of the cream. However, neither of the tested buttermilks affected the emulsifying properties and acid tolerance of lower-fat (35% and 30%) cream systems. Emulsifying components exist in proportionately larger amounts in lower-fat creams, which could render the emulsifying properties resistant to change. The number of fat globules may also influence acid-induced changes in viscosity. The addition of phospholipids or lysophospholipids did not improve the acid tolerance of creams, a finding that may be attributable to the formation of complexes of phospholipids and protein. PRACTICAL APPLICATION: The findings presented herein demonstrate the ability to improve the acid tolerance of cream using materials derived from milk. Implementing these findings appropriately may result in a high-quality cooking cream.     

Microfiltration of buttermilk and washed cream buttermilk for concentration of milk fat globule membrane components

Buttermilk, the by-product from butter manufacture, has gained much attention lately because of the application potential of its milk fat globule membrane (MFGM) components as health ingredients. Microfiltration (MF) has been studied for buttermilk fractionation because of its ability to separate particles from dissolved solutes. However, the presence in this by-product of skim milk solids, especially casein micelles, restricts concentration of MFGM. The use of cream washed with skim milk ultrafiltrate to produce buttermilk with lower casein content was studied as well as fractionation of this buttermilk by MF. Results have shown that washing the cream prior to churning yields buttermilk with 74% less protein than normal cream buttermilk. Analysis of the protein profile of washed cream buttermilk revealed that caseins and whey proteins were the main classes of proteins removed. The MF of washed cream buttermilk resulted in permeation fluxes 2-fold higher than with normal cream buttermilk. The second separation of the cream induced high losses of phospholipids in the skim phase. However, retention of remaining phospholipids in washed cream buttermilk by the MF membrane was higher resulting in a phospholipids concentration factor 66% higher than that of normal cream buttermilk. The results presented in this study highlight the impact of casein micelles on the separation of MFGM components as well as their effect on permeation flux during MF.     

Compositional and functional properties of buttermilk: a comparison between sweet, sour, and whey buttermilk

Buttermilk is a dairy ingredient widely used in the food industry because of its emulsifying capacity and its positive impact on flavor. Commercial buttermilk is sweet buttermilk, a by-product from churning sweet cream into butter. However, other sources of buttermilk exist, including cultured and whey buttermilk obtained from churning of cultured cream and whey cream, respectively. The compositional and functional properties (protein solubility, viscosity, emulsifying and foaming properties) of sweet, sour, and whey buttermilk were determined at different pH levels and compared with those of skim milk and whey. Composition of sweet and cultured buttermilk was similar to skim milk, and composition of whey buttermilk was similar to whey, with the exception of fat content, which was higher in buttermilk than in skim milk or whey (6 to 20% vs. 0.3 to 0.4%). Functional properties of whey buttermilk were independent of pH, whereas sweet and cultured buttermilk exhibited lower protein solubility and emulsifying properties as well as a higher viscosity at low pH (pH ≤ 5). Sweet, sour, and whey buttermilks showed higher emulsifying properties and lower foaming capacity than milk and whey because of the presence of milk fat globule membrane components. Furthermore, among the various buttermilks, whey buttermilk was the one showing the highest emulsifying properties and the lowest foaming capacity. This could be due to a higher ratio of phospholipids to protein in whey buttermilk compared with cultured or sweet buttermilk. Whey buttermilk appears to be a promising and unique ingredient in the formulation of low pH foods.     

Shelf life of pasteurized microfiltered milk containing 2% fat

The goal of this research was to produce homogenized milk containing 2% fat with a refrigerated shelf life of 60 to 90 d using minimum high temperature, short time (HTST) pasteurization in combination with other nonthermal processes. Raw skim milk was microfiltered (MF) using a Tetra Alcross MFS-7 pilot plant (Tetra Pak International SA, Pully, Switzerland) equipped with Membralox ceramic membranes (1.4 μm and surface area of 2.31 m²; Pall Corp., East Hills, NY). The unpasteurized MF skim permeate and each of 3 different cream sources were blended together to achieve three 2% fat milks. Each milk was homogenized (first stage: 17 MPa, second stage: 3 MPa) and HTST pasteurized (73.8°C for 15 s). The pasteurized MF skim permeate and the 3 pasteurized homogenized 2% fat milks (made from different fat sources) were stored at 1.7 and 5.7°C and the standard plate count for each milk was determined weekly over 90 d. When the standard plate count was >20,000 cfu/mL, it was considered the end of shelf life for the purpose of this study. Across 4 replicates, a 4.13 log reduction in bacteria was achieved by MF, and a further 0.53 log reduction was achieved by the combination of MF with HTST pasteurization (73.8°C for 15 s), resulting in a 4.66 log reduction in bacteria for the combined process. No containers of MF skim milk that was pasteurized after MF exceeded 20,000 cfu/mL bacteria count during 90 d of storage at 5.7°C. The 3 different approaches used to reduce the initial bacteria and spore count of each cream source used to make the 2% fat milks did not produce any shelf-life advantage over using cold separated raw cream when starting with excellent quality raw whole milk (i.e., low bacteria count). The combination of MF with HTST pasteurization (73.8°C for 15 s), combined with filling and packaging that was protected from microbial contamination, achieved a refrigerated shelf life of 60 to 90 d at both 1.7 and 5.7°C for 2% fat milks.     

Improvement of storage stability and foaming properties of cream by addition of carrageenan and milk constituents

The increasing automation in the dairy industry and the longer guaranteed shelf life of the packed products of cream lead to a loss in the quality of liquid and whipped cream associated with the formation of irreversible plugs, too long whipping times and high degrees of liquid separation of the whipped product. In test series 0.015% carrageenan, 0.25% protein—fat as the dry matter (whey proteins with high-melting milk fat fractions) or a combination of both were added to homogenized and unhomogenized, pasteurized or ultra-high temperature treated (UHT) cream from the winter and summer feeding period (fat content: 30%). The creaming behaviour after storage at 7 or 20°C was characterized by determining the fat content in different layers of a cream package. In cream samples without additives ünstirrable layers had been formed after 2–7 weeks, in particular during the long storage times of UHT cream without cooling. A desired (i.e. low) degree of creaming of the liquid cream as well as little separation in the whipped product could be achieved for all samples only by means of a combination of carrageenan and protein—fat powder. Of the rather varying carrageenan fractions examined, a combination of similar proportions of kappa- and iota-carrageenan has proved to be particularly effective without excessively increasing viscosity.     

Composition and Microscopy of Reformulated Creams from Reduced-Cholesterol Butteroil

A reduced-cholesterol butteroil was emulsified with different milk-derived components into three 20% milk fat cream formulations. Electron microscopy showed an oil-in-water emulsion typical of milk lipid globules in natural cream. Heat treatment and homogenization had no effect on cream composition (p > 0.05). Homogenization pressure had no effect on amount of protein associated with lipid globules but more phospholipid was associated with the lipid globules at 13.6/3.4 MPa (p ≦ 0.05). Formulation had significant effects on cream composition and amount of protein and phospholipid associated with lipid globules. Cholesterol was reduced 65 to 76% lower than that of natural cream.     

Free and membrane-bound xanthine oxidase in bovine milk during cooling and heating

The effect of cold storage (5 C, 24 h) and heat treatment (60 C, 5 min) of milk on activities of free and membrane-bound xanthine oxidase has been studied. Both treatments enhanced total xanthine oxidase activity in milk. Activity of membrane-bound xanthine oxidase increased and free xanthine oxidase decreased in buttermilk while it increased in skim milk on cold storage. Heat of milk increased free and membrane-bound xanthine oxidase activities in both buttermilk and skim milk. The state of xanthine oxidase activity in skim milk from reconstituted milk, which was prepared by mixing xanthine oxidase inactivated skim milk and fresh cream, showed that only the free enzyme migrated from the cream phase to skim milk on cold storage. Very little xanthine oxidase activity was detectable in skim milk on heat treatment of the reconstituted milk sample. The overall increased activity of xanthine oxidase in milk during cold storage or heat treatment may not be due to the release of fat globule membrane enzyme to skim milk.     

Effect of proteose-peptone addition on some physico-chemical characteristics of recombined dairy creams

The effect of the addition of the total proteose-peptone (TPP) fraction on some physico-chemical properties of recombined cream was studied. Oil-in-water emulsions, 30% or 20% (w/w) fat, were prepared using only the dairy components buttermilk, milkfat and TPP. The effect of different concentrations of TPP on droplet size, creaming stability, flow behaviour, viscosity and whippability of recombined creams was tested. Of the different creams, those containing 2% (w/w) or more TPP were more viscous, showed different flow behaviour, and had improved stability and whippability compared with the other creams. The modifications in physico-chemical properties appeared to be driven by changes in particle size distribution caused by droplet aggregation. The percentage of fat also influenced the properties of the final product. It may therefore be possible to obtain desirable modifications in recombined cream using only dairy ingredients.     

Observations on the Whipping Characteristics of Cream

With the application of UHT technology to the processing of whipping creams, consumers 5 purchase creams with whipping characteristics different from creams processed by conventional pasteurization. This study observed differences in whipping properties among raw, pasteurized, and UHT whipping creams. Whipping time to reach maximum volume, number of days before and after retail sell-by date, and overrun were recorded. Mean whipping time and maximum overrun varied significantly by processor, product composition, and retail cream age. Mean whipping time ranged from 1.6 min for raw unpasteurized creams to 3.4 min for UHT heavy cream without whipping aids. Mean maximum overrun ranged from 141% for UHT heavy creams without whipping aids to 216% for UHT whipping creams with aids. There was considerable variation in mean whipping time and mean maximum overrun among processors for creams of the same composition. Regression analysis between whipping time and retail cream age revealed a positive relationship for some product types and a negative relationship for others. Whipping time and maximum overrun of retail whipping creams vary substantially by product type, processing treatment, and processor.     

Factors affecting the inactivation of the natural microbiota of milk processed by pulsed electric fields and cross-flow microfiltration

Prior to processing milk and cream were standardised and homogenised. Skim milk was cross-flow microfiltered (CFMF) prior to treatment with pulsed electric fields (PEF) or high temperature short time (HTST) pasteurization. The effect of temperature of the skim milk and product composition on the efficacy of PEF treatment was determined. The electrical conductivity of the product was related to fat and solids content and increased 5% for every g/kg increase of solids and decreased by nearly 0·7% for every g/kg increase of fat. From the three microbial groups analyzed (mesophilic, coliform, and psychrotroph) in milks differences (P<0·05) in the inactivation of mesophilic microorganisms were observed between the counts following PEF treatment, while HTST pasteurization resulted in higher reductions in all different counts than those obtained after PEF. Increasing the skim milk temperature prior to PEF treatment to about 34°C showed equivalent reductions in microbial counts to skim milk treated at 6°C in half the time. The reductions achieved by a combination of CFMF and PEF treatments were comparable to those achieved when CFMF was combined with HTST pasteurization. A higher reduction in coliform counts was observed in homogenised products subjected to PEF than in products that were only standardised for fat content.     

Heat inactivation of hepatitis A virus in dairy foods

Experiments were performed to determine the thermal resistance of hepatitis A virus (HAV) in three types of dairy products containing increased amounts of fat content (skim milk, homogenized milk; 3.5% MFG, and table cream; 18% MFG). HAV-inoculated dairy products were introduced into custom-made U-shaped microcapillary tubes that in turn were simultaneously immersed in a waterbath, using custom-made floating boats and a carrying platform. Following exposure to the desired time and temperature combinations, the contents of each of the tubes was retrieved and was tested by plaque assay to determine the reduction in virus titer. Our data indicated that < 0.5 min at 85 degrees C was sufficient to cause a 5-log reduction in HAV titer in all three dairy products, whereas at 80 degrees C, < or = 0.68 min (for skim and homogenized milk), and 1.24 min (for cream) were needed to cause a similar log reduction. Using a nonlinear two-phase negative exponential model (two-compartment model) to analyze the data, it was found that at temperatures of 65, 67, 69, 71, and 75 degrees C, significantly (P < 0.05) higher exposure times were needed to achieve a 1-log reduction in virus titer in cream, as compared to skim and homogenized milk. For example, at 71 degrees C, a significantly (P < 0.05) higher exposure time of 0.52 min (for cream) was needed as compared to < or = 0.18 min (for skim and homogenized milk) to achieve a 1-log reduction in virus titer. A similar trend of inactivation was observed at 73 and 75 degrees C where significantly (P < 0.05) higher exposure times of 0.29 to 0.36 min for cream were needed to cause a 1-log reduction in HAV in cream, as compared to < or = 0.17 min for skim and homogenized milk. This study has provided information on the heat resistance of HAV in skim milk, homogenized milk, and table cream and demonstrated that an increase in fat content appears to play a protective role and contributes to the heat stability of HAV.     

Native milk fat globule size and its influence on whipping properties

The objective of this study was to investigate the influence of native milk fat globule size on the aeration of high fat dairy products with regard to maximum firmness time, gas inclusion and foam stability. The results showed that whipping time to maximum firmness was inversely proportional to mean fat globule size for both unhomogenised and slightly homogenised (2 MPa) creams. Additionally, increasing native mean fat globule size of the creams resulted in increased overrun. No significant differences in serum drainage were found between creams with different native milk fat globule size. Furthermore, when creams with native large mean fat globules were homogenised, the results showed that the maximum firmness time was in accordance with the mean fat globule size of non-aggregated creams. In the present study, cream fractionation was achieved by creaming or in a cost effective and fast manner using a modified centrifugal separator.     

Effect of green tea catechins on physical stability and sensory quality of lactose-reduced UHT milk during storage for one year

Ultra-high temperature (UHT) processed lactose-reduced milk containing added green tea extract (GTE) at two concentrations (0.1% and 0.25%) was stored at 22 ± 2 °C for one year. The effect of GTE addition on physical stability, protein binding, and sensory quality was evaluated. Sedimentation in skim milk and creaming of full fat milk were inhibited by addition of GTE. The formation of Maillard-related flavour compounds was inhibited during storage as determined by dynamic headspace GC–MS. Using Western blot analysis, milk proteins were found to be highly conjugated to polyphenols. Addition of GTE before UHT treatment resulted in increased bitterness and astringency in UHT milk and this remained during storage. Even though GTE addition improved the physical stability and inhibited Maillard reactions in the milk, the taste and flavour contribution from GTE was dominating throughout storage, and alternative sources of polyphenols should be explored for increasing shelf-life stability of long-life milk.