Effect of pressure and fat content on particle sizes in microfluidized milk.

Average diameters and particle size distributions in fluid milks with different fat contents and subjected to various homogenization pressures with a "microfluidizer" were evaluated. Skim, 2%, and whole milks were microfluidized at 50, 100, 150, and 200 MPa. Cream containing 41% milk fat was microfluidized at 50, 100, and 150 MPa. Particle sizes were determined by laser light scattering. As microfluidization pressure was increased from 50 to 100 MPa, particle sizes in skim, 2%, and whole milks decreased. Microfluidization at pressures greater than 100 MPa had little additional effect on reducing the particle sizes in skim and 2% milks compared with microfluidization at 100 MPa, but the particle sizes in whole milk increased as the microfluidization pressure was increased from 100 to 200 MPa due to formation of homogenization clusters. The particle sizes in cream increased as the microfluidization pressure was increased from 50 to 150 MPa. When the microfluidization pressure was held constant, the particle sizes increased as the milk fat concentration was increased. The coefficients of variations of the volume-weighted particle size distributions for cream were higher than for skim, 2%, and whole milks. Larger "big" particles and smaller "small" particles were formed in whole milk after microfluidization at 200 MPa than at 100 MPa. Although microfluidization can be used to produce small particles in skim, 2%, and whole milks, a higher than optimum pressure (above 100 MPa) applied to whole milk will not lead to the minimum d(43) (volume-weighted average diameter) due to formation of clusters.

Size distribution of fat globules in goat milk.

Milk from French-Alpine goats and Holstein cows was obtained from a bulk tank immediately prior to analyses. Fat globule size was determined by laser particle size analysis. Individual globules of fat in goat milk ranged from 0.73 to 8.58 microm in diameter. The average diameter of particles based on volume to surface area ratio (dvs) was 2.76 microm and was less than the mean (dvs) of 3.51 microm for bovine milk, in which fat globules ranged from 0.92 to 15.75 microm in diameter. The specific surface area of particles in caprine milk was 21,778 cm2/ml, whereas the specific surface area of particles in bovine milk was 17,117 cm2/ml. Ninety percent of the total particles found in goat milk were less than 5.21 microm in diameter, whereas 90% of the total particles in bovine milk were less than 6.42 microm based on the volume frequency distribution. Dissociation of casein micelles by urea in goat whole and skim milk caused larger dvs values due to the effect of fat particles and reduced the specific surface area in both milks because the total number of detectable particles in both whole and skim milk was reduced.

Antimicrobial properties of pepsin-digested lactoferrin added to carrot juice and filtrates of carrot juice.

The objective of this study was to determine the antimicrobial activity of pepsin-digested lactoferrin added to carrot juice and filtrates prepared from carrot juice. Lactoferrin isolated from raw skim milk was digested by pepsin for 4 h at pH 3. The digest of lactoferrin was lyophilized, and the antimicrobial activity of the digests was determined in peptone-yeast-glucose broth, carrot juice, permeate from carrot juice, and the dialysate of carrot juice permeate using Escherichia coli (American Type Culture Collection strain 35343) as the test organism. Growth of E. coli and the inhibitory effect of the peptide were greater in peptone-yeast-glucose broth at pH 7 than at pH 4. The peptic digest of lactoferrin did not have antimicrobial properties in carrot juice at concentrations of less than 10 mg/ml of juice. Carrot juice was filtered through a membrane with a molecular weight rejection of 10,000 or 500 Da, and the permeate was dialyzed against distilled water. Growth of E. coli was delayed in the filtrate by 5 mg but not by 1 mg of the peptic digest of lactoferrin per ml of filtrate. Bacterial counts of the control and experimental samples were not significantly different after 24 h of incubation. The peptic digest of lactoferrin at a concentration of 5 mg of digest per ml of dialysate was bacteriostatic toward E. coli after 24 h of incubation at 23 degrees C. Dialysis of permeate caused a percentage reduction in cation concentration in the permeate ranging from 69.23% (Co) to 99.32% (Na). The antimicrobial activity of lactoferrin added to carrot juice was probably inhibited by cations.

Changes in physicochemical properties of retort-sterilized dairy beverages during storage.

The effects of composition, storage time, and storage temperature on the physicochemical properties of a retort-sterilized dairy beverage were investigated. Drinks with eight formulations were stored at 4, 25, and 37 degrees C for 6 mo and were analyzed monthly for pH, net color difference, apparent viscosity, sedimentation index, homogenization index, particle size index, and soluble calcium. The changes in the physicochemical properties of the beverages increased as storage time and temperature increased. The degree of change was affected by the composition of the product. Sodium tripolyphosphate was implicated in promoting age gelation of samples with 11% nonfat milk solids, but sedimentation was observed in the absence of sodium tripolyphosphate and carrageenan. The apparent viscosity of samples affected the rate of age gelation and sedimentation, both of which increased as viscosity decreased. Interactions between milk fat, carrageenan, and nonfat milk solids were important in determining the apparent viscosity of the beverages and the rate of change observed during storage.

Low molecular weight branched-chain and n-chain fatty acids in caprine and bovine colostrum.

Colostrum from French-Alpine and Anglo-Nubian goats and Holstein cows was collected and analyzed for both total and FFA of 12 and fewer carbon atoms. Short-chain VFA were separated from long-chain fatty acids using simultaneous distillation extraction. The n-butyl esters of fatty acids were quantified by gas chromatography, and their identity was confirmed by gas chromatography-mass spectrometry. The concentration of decanoic acid was 33 and 83% less in Holstein colostrum than in colostrum from Alpine and Nubian goats, respectively. Colostrum from Nubian goats had twice as much decanoic acid as colostrum from Alpine goats. The FFA in colostrum that differed between species but not between goat breeds were octanoic and decanoic acids. These respective fatty acids were approximately two and three times greater in colostrum from goats than in colostrum from Holsteins. The quantity of decanoic acid was different between goat breeds and between animal species. The ratio of total fatty acid concentration to free-state concentration for hexanoic acid appeared to be useful for differentiating between Nubian and Alpine goat colostrum as well as between Nubian and Holstein colostrums.

Heat Inactivation of the Alkaline Phosphatase in Human Milk and Colostrum 1.

Time-temperature relationships were developed for heat inactivation of alkaline phosphatase in pooled human milk and colostrum. Heat inactivation of the enzyme in human milk proceeds at the same rate as in cows' milk. The heat sensitivity of the enzyme is slightly greater in human colostrum than in human milk.

An unusual manifestation of Paget's disease of bone: spinal epidural hematoma presenting as acute cauda equina syndrome.

Neurologic sequelae of Paget's disease of bone include involvement of the spinal cord or cauda equina due to mechanical compression by enlarged vertebrae, ischemia caused by a spinal artery, steal syndrome or neoplasm. We describe a patient with Paget's disease of bone who presented with acute cauda equina syndrome due to a spinal epidural hematoma. Clinicians need to recognize this entity since surgical intervention may result in a favorable outcome.

Heat Stability of the Bile Salt-Stimulated Lipase in Human Milk Fortified with Sodium Taurocholate 1.

Time-temperature relationships for heat-inactivation of the bile salt-stimulated lipase activity were compared in whole human milk and in the same product fortified to 9 mM/ml with sodium taurocholate. Heat treatments were varied from 45 to 70°C for times ranging from 15s to 40 min. Enzyme activity was more heat stable in human milk fortified with taurocholate than in control samples. The temperature required for the onset of heat inactivation at 30-min holding time was increased from 45°C for control samples to 60°C following addition of taurocholate. A temperature differential of approximately 12°C was required in the fortified milks to produce inactivation equivalent to that observed in the control milks over the heating range studied.

Lipolytic Activity During Storage of Human Milk: Accumulation of Free Fatty Acids 1.

Lipolysis was quantitated during storage of fluid and freezedried human whole and skim milks. Fatty acid accumulation was faster in whole fluid milk stored for 1 week at 4°C than in frozen (-20°C) samples stored for 180 d. The rapid accumulation of fatty acids during 24 h of storage at 4°C was enhanced in previously frozen milk samples. While freeze-dried whole milk showed no lipolysis when stored at -20°C, accumulation of free fatty acids was rapid in samples stored at room temperature. Fluid and freeze-dried skim milk samples exhibited no appreciable lipolysis.

Heat Inactivation of Bile Salt-Stimulated Lipase Activity in Human Milk and Colostrum 1.

Time-temperature relationships for heat-inactivation of bile salt-stimulated lipase activity in human milk and colostrum were systematically measured using a pH-stat assay procedure with triolein as substrate. The enzyme was not affected in either menstruum at 45°C for 40 min. The enzyme was destroyed almost instantaneously at 60°C, and was slightly more heat-sensitive in colostrum than in milk. The bile salt-stimulated lipase(s) in human milk was more heat sensitive than lipase in bovine milk.

Lipolytic Activity During Storage of Human Milk: Stability of the Bile Salt-Stimulated Lipase 1.

Bile salt-stimulated lipase activity was monitored in fresh human milk and skim milk during refrigerated (4°C) and frozen (-20°C) storage, and in the lyophilized milks stored at -20°C and at room temperature. Following a sharp initial drop to approximately 77% of the original lipase activity, lipase was relatively stable in frozen or freeze-dried milks during 180 d of storage at -20°C. Activity losses were greatest (P < .05) in freeze-dried whole milks and skim milks stored at room temperature, approximating a 30% loss during 30 d of storage. Lipase activity was stable during refrigerated (4°C) storage of whole milk for 1 week.

Survival of Campylobacter fetus subsp. jejuni in Cheddar and Cottage Cheese.

Campylobacter fetus subsp. jejuni inoculated into Cheddar cheese milk at concentrations ranging from 102-106 cells per ml was not detectable in the curd after 30-60 d of curing. When milk for cottage cheese manufacture was inoculated with 105-106 cells of C. fetus subsp. jejuni , the organism was not detectable in the whey or curd after cooking for 30 min at 55°C.

Ascorbic Acid Stimulation of Diacetyl Production in Mixed-Strain Lactic Acid Cultures.

The effect of three levels of ascorbic acid on diacetyl and acid production by two mixed-strain cultures was investigated. Each culture was grown in nonfat dry milk reconstituted to 11% total solids with 0.1% added sodium citrate. Ascorbic acid concentrations in the milk were 0, 0.10, and 0.25%. Stimulation of diacetyl production was observed at both concentrations of ascorbic acid. The stimulatory effect of ascorbic acid at both concentrations was approximately the same for each culture. Diacetyl production was initiated earlier in samples containing ascorbic acid. Ascorbic acid did not stimulate acid production.

Fat Test Depression During Chilled Storage of Milk Samples in Plastic Containers for Analysis by the Milko-Tester 1.

Ambiguous depressions in fat tests were observed when milk samples were stored before testing by the Milko-Tester procedure. Fat-test depression was augmented by shipping and by chilling samples at the time of collection in an ice-water mixture. The effect was greatest in samples stored in 1-oz. plastic containers and in partially filled plastic bags. The fat-test depression was not significant in samples stored in glass bottles or in plastic containers receiving no refrigeration during the storage period.

Proteolytic Activity in Ultra-Pasteurized, Aseptically Packaged Whipping Cream 1.

The proteolytic activity in three commercial ultra-pasteurized, aseptically packaged samples of cream that developed bitter flavor was studied. Samples were analyzed for microorganisms and rate of proteolysis as affected by reaction temperature and pH. The temperature effect was determined at 20, 30, 37, 45, and 50 C. Samples A and B had an optimum temperature of 37 C for proteolytic activity while Sample C had its optimum between 30 and 37 C. Sample B had increased activity at pH 7.0, 8.0 and 9.0. Sample A had increased activity between pH 7.0 and 7.5 while Sample C exhibited greatest activity at pH 8.0. The rate of proteolysis increased with incubation time.