Portion Of Milk Research Articles

Studies of human milk relevant to milk banking.

Issues regarding the efficacy of feeding human milk to premature infants include the development of optimal protocols for collecting, storing, and processing human milk. Studies of the nutritional and immunologic composition of milk produced by women who delivered term or premature infants and who weaned their infants gradually from human milk have been studied to identify optimal donors. The effects of specific collection, storage, and processing conditions on the composition of mature human milk also have been evaluated. Collection, storage, and processing conditions have distinct effects on specific functional components. The caloric content of milk, the content of nutrients carried in the lipid portion of milk, and selected enzymatic activities depend on the completeness with which the breast is emptied. Storing milk in polyethylene, polypropylene, and pyrex containers influences key immunologic components in human milk as do storage temperatures. None of the nutrient compositions of milks studied matched current estimates of the nutritional needs of premature infants. Importantly, both the concentrations and the pattern of change in nutrient and immunologic contents are distinct in milks of women delivering infants at term or prematurely. Further changes are seen during the process of gradual weaning.

Impedance Measurements to Detect Post-pasteurization Contamination of Pasteurized Milk

Investigated was whether, or to what extent, impedance measurements are suitable to detect post-pasteurization contamination of pasteurized milk by gram-negative bacteria. Results were compared with those obtained with the benzalkon-crystal violet-ATP method (BC-ATP method). When 1-L portions of milk, containing agents selective for gram-negative bacteria (0.06% benzalkon and 0.002% crystal violet), were incubated at 30°C, a detection time of less than 24 h was found for post-pasteurization contaminated milk. When post-pasteurization contaminating gram-negative bacteria were absent in pasteurized milk, the detection time varied between 26 and 52 h. In total, 83 samples were investigated. This study shows that impedance measurements are useful to trace post-pasteurization contamination of pasteurized milk. The detection time obtained as such for 1-L portions does, however, not give sufficiently reliable information on the degree of contamination. Suitable information could be obtained by investigating different milk portions, as in the BC-ATP method.

Pyruvate in Producer and Commingled Manufacturing Grade Milk

The automated test for pyruvate concentration, [P], was evaluated as a substitute for the direct microscopic count (DMC) in determining quality of manufacturing grade milk. Samples of manufacturing grade milk from producers and tank trucks as well as skim milk were collected at a large milk drying plant. Each sample was tested immediately for standard plate count (SPC), psychrotrophic plate count (PPC) and DMC. Portions of milk were heated to 85°C for 10 min to stabilize [P] before being returned to the laboratory for analysis of initial pyruvate concentration, [IP]. Unheated samples stored at 4°C were analyzed for [P] and DMC daily for up to 120 h. [IP] was a good indicator of PPC in milk from individual producers (r=0.81). However, [IP] was not highly correlated (r=0.26) with PPC in skim milk samples which were characteristically high in SPC and homogeneous in PPC. With skim milk, [IP] was more highly and significantly correlated with initial DMC (r=0.61) than with initial SPC (r=0.31) or initial PPC (r=0.26). [IP] was a good indicator of [P] in stored fluid samples until counts exceeded about 107/ml. Initial DMC and initial PPC were about equally correlated with [P] determined at 24-h intervals, and the initial DMC was a reasonably good indicator of DMC determined at 24-h intervals. Using 6.5 mg of pyruvate/L to represent bacterial counts of 3 × 106/ml by the three methods tested, the pyruvate test correctly classified 91% of 57 samples of producer milk based on PPC, 88% based on SPC and 82% based on DMC. Most of the error was of the false-negative type in which samples with high counts had less than 6.5 mg of pyruvate/L. This was probably because some bacteria catabolize pyruvate once their numbers exceed 107/ml.

Vitamin D and Its Metabolites in Human and Bovine Milk

Human and bovine milk were analyzed for vitamin D, 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, 25,26-dihydroxyvitamin D and 1,25-dihydroxyvitamin D using exhaustive chromatographic purification procedures coupled with ligand binding assays. Human milk contained the following amounts of antirachitic sterols (pg/ml, mean ± sd, n = 5): 39 ± 9 vitamin D; 311 ± 31 25-hydroxyvitamin D; 52 ± 8 24,25-dihydroxyvitamin D; 32 ± 9 25,26-dihydroxyvitamin D; 5.1 ± 0.3 1,25-dihydroxyvitamin D. Normal bovine milk contained levels of these sterols comparable to those found in human milk. Increasing the oral dose of vitamin D to the cows was reflected by an increase of the parent vitamin and 25-hydroxyvitamin D in the milk. Vitamin D-binding protein concentration in human milk whey, determined by Ouchterlony immunodiffusion and radioimmunoassay, was 1–2% of the levels observed in the plasma and was dependent on the stage of lactation. Vitamin D and its metabolites were shown initially to be present in the whey portion but with time migrated into the fat portion of milk. The antirachitic sterols detected account for approximately 25 iu/liter and 27 iu/liter of antirachitic activity in human and bovine milk, respectively. In both species 25-hydroxyvitamin D comprised the majority of the antirachitic sterols detected in normal milk.vitamin D metabolites milk high pressure liquid chromatography

Progesterone in bovine milk fat

The progesterone (P 4) concentration (ng/5 μl) in the fat portion of cow's milk was measured on days 0, 12, 20, 24, and 30 after insemination in an effort to assess the ability of this analysis to judge the reproductive status of dairy cows. Pregnancy was determined by rectal palpation at approximately 40 days after insemination. The mean P 4 concentration (ng/5 μl) ± SD in the pregnant cows (n=17) was 0.14±.07, 1.31±.36, 1.41±.52, 1.22±.21, and 1.30±.43 on post-insemination days 0, 12, 20, 24, and 30 respectively. At these same intervals the P 4 concentration in the non-pregnant (NP) cows (n=18) was 0.14±.06, 1.26±.37, 0.56±.52, 0.57±.42, and 1.08±.59. On days 20 and 24 after insemination, mean P 4 levels were significantly (P<.001) elevated in the pregnant cows. It was concluded that an accurate assessment of the reproductive status of a cow, milk samples from days 0, 20, and 24 post-insemination would have to be analyzed for milkfat P 4 concentrations. In order to determine the percentage of cows inseminated out of the periestrual period, milkfat P 4 concentrations were ascertained in milk collected from 165 cows at the time of insemination. Cows that conceived (n=38) had a mean milkfat P 4 concentration at the time of insemination of 0.16±.09. The upper limit for P 4 in the milkfat at the time of insemination in cows that conceived was calculated to be 0.43 ng/5 μl milkfat. Subsequently, it was found that of the 14 cows that had P 4 levels above this upper limit at time of insemination, nine were inseminated at a period other than in the periestrual period and five were inseminated while already pregnant.

Glucocorticoids in Mammary Secretions and Blood Serum during Reproduction and Lactation and Distributions of Glucocorticoids, Progesterone, and Estrogens in Fractions of Milk

Concentrations of glucocorticoids were measured in milk and blood serum during the estrous cycle, prepartum, parturition, postpartum, and early and late lactation. Glucocorticoids in milk did not change during the estrous cycle, averaging .35ng/ml whereas they averaged .50ng/ml prepartum, 3.08 ng/ ml at parturition, and .50ng/ml 1 wk postpartum. Glucocorticoids in milk declined from .59ng/ml to .25ng/ml as lactation advanced from 1 to 10 mo. Concentrations of glucocorticoids in blood serum were approximately 8 to 10ng/ml during all reproductive states. There was no positive relationship between percentage of milk fat and concentrations of glucocorticoids in milk. Cortisol was the predominant glucocorticoid in serum; in milk corticosterone concentrations exceeded those of Cortisol. Glucocorticoids, being more polar, had higher affinity for the nonlipid portion of milk; in contrast, progesterrone, estradiol 17β, and estrone were located predominantly in the lipid fraction of milk.

Effects of Protein and Fat Pricing on Farm Milk Prices for the Five Major U.S. Dairy Breeds

The possibility of applying price differentials to the protein or the solids-not-fat portions of milk has been promoted with varying degrees of support for several years. Multiple component pricing may some day become a reality over a large portion of the United States, but how soon this will happen depends a great deal on the attitude of milk producers toward any particular pricing alternative that may be proposed. Lower levels of butterfat are associated with lower levels of both protein and solids-not-fat, so we might expect owners of Holstein herds to be skeptical of payment plans which would include differentials in addition to fat. Owners of Jersey herds, on the other hand, would be expected to look upon such plans with favor. Since

Sensitive Colorimetric Determination of Cholesterol in Dairy Products

Cholesterol can be determined colorimetrically in dairy products at levels of larger than or equal to 10 mug (coefficient of variation = 5.3%) with an o-phthalaldehyde reagent when non-cholesterol lipids are eliminated prior to color development. Absorbance for 2 mg tripalmitin was found to be equivalent to about 20 mug cholesterol. Saponification followed by hexane extraction removed interfering lipids. Using the described procedure, 238 individual raw milk samples were found to contain 144.4+/-37.9 mug cholesterol/ml, while their skim milk portions had 26.5+/-6.4 mug cholesterol/ml (mean +/- standard deviation). The o-phthalaldehyde cholesterol estimates agreed with those obtained by a gas-liquid chromatographic procedure when cheese and ice cream were analyzed by the colorimetric procedure with and without prior fat extraction.

COMPOSITION OF RAW AND PROCESSED SKIMMILK

Many processors make a more palatable skimmilk by adding nonfat dry milk solids and/or lactose. Compared to the skimmilk portion of raw milk, processed skimmilk contained more solids not fat and its freezing point was lower. The data do not indicate many, if any, processed samples in the study with added lactose, other than that contained in the added nonfat dry milk solids.

Relationship Between Some Chlorinated Hydrocarbon Insecticides and Lactic Culture Organisms in Milk

Portions of sterile milk containing 1ppm of aldrin, DDT, or lindane were inoculated with strains of Streptococcus lactis, Streptococcus cremoris, Streptococcus diacetilactis, and Lactobacillus casei and incubated at 32C for 14 days. When the insecticides were extracted from the milks and the extracts analyzed by gas-liquid chromatography there was no perceptible evidence of degradation or chemical alteration of the insecticides by the lactic culture organisms.L. casei cells grown in trpyticase soy broth containing 0.01 and 0.02ppm of 14C-dieldrin showed 353 and 830%, respectively, higher radioactive counts than corresponding cells grown in the absence of 14C-dieldrin, suggesting that a small amount of dieldrin was either adsorbed or incorporated by the cells.

CHEDDAR CHEESE: COMPARISON OF EFFECTS OF RAW AND HEATED MILK ON QUALITY AND RIPENING

Abstract2Portions of identical milk of manufacturing quality were made into cheese: (a) without heating; (b) after pasteurizing by the holder method; (c) after short-time heating at 71 C; (d) over 71 C (74–87); and (e) less than 71 C (50–69). These variations in heating did not require extensive modifications of cheese-making operations. Measurements were made of moisture, pH, and salt. Cheese was cured at 7 C, scored at 1, 3, 6, and 12 months, and analyzed for total nitrogen, water-soluble nitrogen, and amino nitrogen at 3, 6, and 12 months. Milk pasteurized by the holder method or by heating to 71 C produced better cheese than raw milk or milk heated for a short time at less than 71 C. Raw-milk cheese cured most rapidly, had the most intense flavors, and was least stable in storage. Rate of curing and intensity of flavor decreased and storage stability increased with the severity of heat treatments. Changes in protein were less extensive in heated-milk cheese and were more extensive in cheese of lower grades. Although there are risks involved, markets for cheese with pronounced cheese flavor can be met with the products produced from milk heated for short times at less than 71 C.

Status of Iodine in Milk Preserved with Sodium Metabisulfite and Formaldehyde

Fresh raw whole milk labeled in vitro with iodine-131 was preserved with 0.2 to 1.0g of Na2S2O5 per liter of milk at 23–26C. Analyses of portions of milk by ion exchange resin treatment showed quantitative recoveries of 131I up to three days; mold growth and spoilage were observed on the fourth day. The sample with 1.0g of Na2S2O5 showed mold growth but no spoilage up to seven days. Although Na2S2O5 maintained 131I in the reduced state, it had no bactericidal effect and was considered ineffective for preserving milk.Reconstituted powdered milk labeled in vitro with 131I was preserved with formaldehyde and stored for 18 days at 23–26C. Analyses of portions of milk showed 97–100% recoveries of 131I. No xanthine oxidase activity was found in the freshly reconstituted milk, indicating no protein-binding of 131I.Standardizing radionuclide methods for collaborative testing of reconstituted powdered milk labeled in vitro with radio-nuclides and preserved with formaldehyde are satisfactory.

Chemical and Flavor Changes in Sterile Concentrated Milk During Storage

Three lots of concentrated milk (ultra-high temperature, high-temperature short-time, and conventionally sterilized) were stored at 4, 20, and 37C for eight months, and examined monthly for changes in flavor, volatile compounds as detected by GLC, acid degree values, and severity of browning. One lot of sterile concentrated skimmilk also stored at 4, 20, and 37C was analyzed occasionally during the eight months.Flavor deterioration was rapid at 20 and 37C, with cooked, scorched, and stale flavor defects most apparent. The ultra-high temperature milk had a flavor advantage initially, but after storage flavor scores for all processed milks were at similar levels. Some methyl ketones, furan, and methyl furan increased during storage at 20 and 37C. Milk fat was the precursor of 2-heptanone and 2-pentanone. Increases in acetone, butanone, acetaldehyde, furan, and methyl furan concentration during storage appeared to come from the nonfat portion of milk. Methyl sulfide was derived from the serum phase, but did not increase in concentration during storage. Methyl sulfide was the only volatile compound found at concentrations greater than its threshold value in milk. Acid degree values were high in all freshly sterilized milks and increased slightly at 20C and rapidly at 37C. Browning reaction values increased at 37C storage.

A study of the results obtained from bacteriological and cytological examinations of various portions of cow's milk.

A study of the results obtained from bacteriological and cytological examinations of various portions of cow's milk.

The effect of incomplete milking or of an extended milking interval on the yield and composition of cow's milk

SummaryThe effect of incomplete milking or of an extended milking interval on the yield and composition of cow's milk has been investigated. At the 1st milking after either treatment, the yield of milk was augmented by a carry-over of milk but at the 2nd milking the yield was invariably depressed and then increased until the original yield, or slightly less, was recovered within 5 days. The concentration of lactose and potassium decreased and of sodium, chloride, whey proteins and casein increased during the period of the treatment, and on the resumption of normal milking the original composition was rapidly recovered. The changes in the composition of fat were less clearly defined because of residual milk effects but over the period of the treatment and the succeeding 6 milkings the effect was invariably to increase fat percentage. The differing effects on composition resulted in a more marked effect on the yields of lactose, potassium and casein than on those of sodium, chloride or the whey proteins throughout the treatment and recovery periods. When milk was removed in portions after an extended milking interval there were decreases in the concentrations of lactose and potassium and increases in those of sodium and chloride throughout normal milking. When the residual milk was obtained after an injection of oxytocin the composition of the portions of milk resembled that of the first portions of milk removed from the udder. The possible effects of the treatments on the secretory cells and the permeability of the udder tissue are discussed.

Comparison of the Removal of Radiostrontium from In Vivo- and In Vitro-Labeled Milk by Ion Exchange Resins

Summary Studies were made to determine differences in the amount of radiostrontium removed by ion exchange resins from milk labeled in vivo and in vitro with Sr 85 or Sr 89 , or both. The distribution of Sr 85 and calcium between phases of centrifugally fractionated milk was also studied. The milks were adjusted to pH levels as low as 5.2 with citric acid before passing through ion exchange columns, and before centrifuging. The amount of strontium removed varied from about 95% at pH 5.25 to 45% at pH 6.65 for in vitro-labeled milk. The amounts for in vitro-labeled milk were only slightly higher at low pH, but ranged from 79 to 50% at pH 6.65, for equilibration times of 30min and 120 hr, respectively, before resin contact. Portions of milk labeled in vivo with Sr 85 were centrifuged at 105,000×G for 90min. The amounts of strontium in the serum were 86, 46, and 19%, respectively, for pH levels of 5.2, 5.8, and 6.6. Corresponding calcium levels were 84, 59, and 33%. Practically all of the remainder was in the sediment. Less than 1% was recovered in the fat layer.

Milkstone—It Can Be Controlled

The amount of milkstone formed in a piece of milk-heating equipment, as well ss its composition, bears a direct relationship to temperature. I t has been shown by chemicM mmlysis that the milkstone formed at low temperatures (vat pasteurization) is largely composed of adhesive fat and protein material, ttowever, at higher temperatures (short-time, high-temperature pasteurization, 161 ° F. and higher) large amounts of ash materials, especially calcimn and phosphorus, are precipitated. I t has been further shown that milkstone formation is greatest at the temperatures that are faw)rable to the coagulation of albumin. 'X-ray studies have confirmed the composition of milkstone fihns. There is some confusion about the terms milkstone and burn-on. Burn-on is the material cooked onto the surface of milk-heating tubes, plates, or jackets, and it consists largely of the solids found in milk. Alkaline detergents will easily renmve the burn-on nmterial from these surfaces. ~Iilkstone, however, being largely composed of milk minerals from the ash portion of milk, is not readily removed by alkaline detergents alone but must be subjected to acid treatment for complete removal. Many factors, in addition to temperature, influence milkstone formation. Among these are rate of heating, rate of flow of milk through equipment, type of product processed, amount of product processed, type and construction of equipment, kind of metal involved, and the surface area used for heating. The formation of milkstone is the cause of one of the most important problems with which the nfilk plant operator must cope, namely, the cleaning of heating equipment. The use of HTST pasteurization equipment, as well as high-temperature preheaters and forewarmers, has greatly increased the milkstone problem because in these units large volumes of milk are heated to very high temperatures in relatively confined spaces.

Free Fatty Acid Content of Fresh Milk as Related to Portions of Milk Drawn

Sumamry Various portions of milk as drawn from different cows, representing five breeds and different periods of lactation, were analyzed for free fatty acid content by utilizing an extraction procedure to obtain the fat for titration. Three portions were obtained, with about 85% of the milk drawn being in the second portion. Measurable quantities of free fatty acids were found in all samples analyzed. Generally, the trend was for the first-drawn milk to be the highest and the last-drawn milk to be the lowest in acid degree. However, for individual cows late in lactation there was a tendency for all three portions of milk to exhibit more nearly the same acid degree. When the fat content was nearly that of normal milk no correlation was noted between fat content of the milk and acid degree of the milk fat. The same portions of milk from individual cows, i.e., first, second, or third, were found to vary widely in acid degree values from day to day. Also, milk from different cows varied daily in free fatty acid content.

Rasva- ja valkuaisainepitoisuuden suhteesta suomalaisessa maidossa

The present investigation deals with the determination of the relation between the fat and protein contents of Finnish milk as well as the possibility of estimating the casein content by the formol titration method described by Walker, modified by McDowall and Dolby. The ratio of protein to fat in Finnish milk is lower than in the other Northern Countries. In the past 30 years the ratio of protein to fat in Finnish milk has been slightly reduced, apparently owing both to the feeding and to the influence of breeding, which have tended to increase the fat content. It is well known that in milk samples with a high fat content the protein content is proportionally lower than in milk with a fat content below the average. The correlation between the fat and total protein contents both in bulk milk and in milk samples from various herds is, from a practical point of view, the same as the correlation between their fat and casein contents. The smaller the portion of milk involved, the more difficult it is to estimate its protein content from the fat percentage. The correlation between fat and protein contents in bulk milk is, again, much more stable than in milk from individual cows. The correlation coefficient for the fat and protein contents in bulk milk is + 0.726 ± 0.06, the corresponding coefficient in milk from various herds is + 0.535 ± 0.05 and in milk samples from individual cows, + 0.432 ± 0.07. The respective correlation coefficients for the fat and casein contents are: + 0.735 ± 0.05; + 0.590± 0.03 and + 0.277 ± 0.09. The casein percentages in milk samples from various herds and in those from individual cows have been determined by the formol titration method. For the calculation of the conversion factor between formol valne and true casein content, the latter has also been determined by the A.O.A.C. method, after which the conversion factor has been given as the ratio between the A.O.A.C. value and the formol valne. The accuracy of the various determinations with formol titration is indicated by the standard deviations (table 2). The standard deviations of the conversion factors indicate that the casein content of milk samples from various herds can be estimated with an accuracy of ± 5 %. The accuracy of casein estimations in milk samples from individual cows is on the average ± 13 %, which cannot be considered adequate even for practical purposes. In addition, the conversion factors reveal seasonal fluctuations which are due to the proportional variations between casein and other protein components in various milk samples.

Observations on the Tactual Flavor Qualities of Heated Milk1,2

Summary Five experienced taste observers were used to investigate tactual flavor changes induced in milk by momentary heating to 95° C. Such heat treatment of milk increased materially the number of “rough”-“chalky” type of taste responses elicited by the group and lowered the number of “smooth” responses. Heat coagulable substances from the whey portion of milk were found responsible for the flavor defect. These substances may be removed rather readily from heated whey by supercentrifuging. However, they are not readily recovered from heated skimmilk, apparently because of protective colloid action by casein.