Nonfat Milk Solids Research Articles

Relationship of cellular fatty acid composition to survival of Lactobacillus bulgaricus in liquid nitrogen.

Concentrated cultures of Lactobacillus bulgaricus were prepared by resuspending cells grown in semisynthetic media in sterile 10% non-fat milk solids. The concentrated cultures were frozen in liquid nitrogen for 24 h. The cell suspensions exhibited decreased viability after storage, and the amount of death varied among the different strains tested. Storage stability of all strains examined was improved by supplementing the growth medium with sodium oleate. Radioisotopes were used to study the fate of sodium oleate with L. bulgaricus NCS1. [1-(14)C]sodium oleate was incorporated solely into the lipid portion of the cells, including both neutral and polar lipids. The fatty acid composition of L. bulgaricus NCS1, NCS2, NCS3, and NCS4 grown with and without sodium oleate was studied. The major fatty acids of strains NCS1, NCS2, and NCS3 grown without sodium oleate were dodecanoic, tetradecanoic, hexadecanoic, hexadecenoic, and octadecenoic acids. In addition to these, strain NCS4 contained C(19) cyclopropane fatty acid. The major fatty acids of all strains grown with sodium oleate were tetradecanoic, hexadecanoic, hexadecenoic, octadecenoic, and C(19) cyclopropane fatty acids. All strains grown in broth containing sodium oleate contained larger amounts of octadecenoic and C(19) cyclopropane fatty acid, and less saturated fatty acids than when grown without sodium oleate. Statistical analyses indicated that C(19) cyclopropane fatty acid was most closely related to stability of the lactobacilli in liquid nitrogen. A negative regression line that was significant at P < 0.001 was obtained when the cellular content of this fatty acid was plotted against death.

Relationship of Cellular Fatty Acid Composition to Survival of Lactobacillus bulgaricus in Liquid Nitrogen1

Concentrated cultures of Lactobacillus bulgaricus were prepared by resuspending cells grown in semisynthetic media in sterile 10% non-fat milk solids. The concentrated cultures were frozen in liquid nitrogen for 24 h. The cell suspensions exhibited decreased viability after storage, and the amount of death varied among the different strains tested. Storage stability of all strains examined was improved by supplementing the growth medium with sodium oleate. Radioisotopes were used to study the fate of sodium oleate with L. bulgaricus NCS1. [1-(14)C]sodium oleate was incorporated solely into the lipid portion of the cells, including both neutral and polar lipids. The fatty acid composition of L. bulgaricus NCS1, NCS2, NCS3, and NCS4 grown with and without sodium oleate was studied. The major fatty acids of strains NCS1, NCS2, and NCS3 grown without sodium oleate were dodecanoic, tetradecanoic, hexadecanoic, hexadecenoic, and octadecenoic acids. In addition to these, strain NCS4 contained C(19) cyclopropane fatty acid. The major fatty acids of all strains grown with sodium oleate were tetradecanoic, hexadecanoic, hexadecenoic, octadecenoic, and C(19) cyclopropane fatty acids. All strains grown in broth containing sodium oleate contained larger amounts of octadecenoic and C(19) cyclopropane fatty acid, and less saturated fatty acids than when grown without sodium oleate. Statistical analyses indicated that C(19) cyclopropane fatty acid was most closely related to stability of the lactobacilli in liquid nitrogen. A negative regression line that was significant at P < 0.001 was obtained when the cellular content of this fatty acid was plotted against death.

Research into foods from animal sources. II. Recent developments in beef and dairy products

Research on increasing the polyunsaturated fatty acid content of the fat of beef and of milk, and of lamb and other ruminant animals has been stimulated by the discovery that polyunsaturated vegetable oils can be encapsulated or “protected” by a coating of casein treated with formaldehyde. The “protected” oil passes through the rumen of the animal, is digested in the stomachs, and is adsorbed without the hydrogenation that occurs normally in the rumen. Human feeding tests have shown that a diet containing beef, cheese, butter, and milk produced in this way ( P S ratio = 0.89 ) has a marked effect in reducing serum cholesterol and blood plasma lipids and increasing fecal cholesterol. The magnitude of the changes in blood constituents is produced by a controlled diet of P S ratio = 1 obtained by feeding vegetable oils. A court ruling has declared the Filled Milk Act of 1923 unconstitutional, thus opening up the market for filled milk products (containing nonfat milk solids and vegetable oils) in interstate commerce. Thus, the technological basis for increasing the P S ratio of animal products is relatively well established, for high P S ratios in hog and chicken fat had already been attained. Economic, and marketing problems remain. Also, state and local regulations are changing rapidly. The “nutrition community” must be aware of these changes and be in a position to give sound nutritional advice on the laws and regulations which will control the production and distribution of animal products desirable in the prudent diet.

Repair of injury in Salmonella anatum cells after freezing and thawing in milk

Fast freezing and slow thawing of Salmonella anatum cells in nonfat milk solids resulted in about 20% death and 50% injury of the cells surviving the treatment. Death was defined as the inability to form colonies on a nonselective plating medium [xylose-lysine-peptone agar (XLP)] after freezing and thawing. Injury was defined as the inability to form colonies on a selective plating medium (XLP with 0.2% sodium desoxycholate added). The injured cells repaired rapidly and within 2 hr at 25 °C, in the presence of 0.1% milk solids; all the injured cells regained the ability to form colonies on the selective medium. The treated cells showed a 1-hr extended lag phase of growth as compared to the unfrozen cells. Milk solids concentration in the freezing and repair menstrua influenced injury, repair of injury, and death. The repair process was affected by the pH and temperature of environment in which the injured cells were incubated. Maximum repair occurred at pH values between 6.0 and 7.4 and temperatures from 25 to 42 °C. The data suggested repair did not require the synthesis of protein, ribonucleic acid, or cell-wall mucopeptide but did require energy synthesis.

Discrepancies in the enumeration of Escherichia coli.

Stationary-phase cells of Escherichia coli were enumerated by the pour plate method on Trypticase soy agar containing 0.3% yeast extract (TSYA), violet red-bile agar, and desoxycholate-lactose agar, and by the most-probable-number method in Brilliant Green-bile broth and lauryl sulfate broth. Maximum counts were assumed to be those on TSYA. In general, numbers detected were lower with the selective solid media and higher with the selective liquid media. Inhibitory effects, especially on selective solid media varied with the strains of E. coli. The lower detection on selective solid media was partly due to the stress induced in some cells by the temperature of the melted media used in the pour plate method. These cells apparently failed to repair and form colonies in the selective media. Improved detection on the selective solid media was achieved by using 1% nonfat milk solids, 1% peptone, or 1% MgSO(4).7H(2)O in the dilution blanks. Higher detection on selective agar media was effected by surface plating or by surface-overlay plating of the cells. The surface-overlay method appeared to be superior for the direct enumeration of E. coli in foods.

Discrepancies in the Enumeration of Escherichia coli1

Stationary-phase cells of Escherichia coli were enumerated by the pour plate method on Trypticase soy agar containing 0.3% yeast extract (TSYA), violet red-bile agar, and desoxycholate-lactose agar, and by the most-probable-number method in Brilliant Green-bile broth and lauryl sulfate broth. Maximum counts were assumed to be those on TSYA. In general, numbers detected were lower with the selective solid media and higher with the selective liquid media. Inhibitory effects, especially on selective solid media varied with the strains of E. coli. The lower detection on selective solid media was partly due to the stress induced in some cells by the temperature of the melted media used in the pour plate method. These cells apparently failed to repair and form colonies in the selective media. Improved detection on the selective solid media was achieved by using 1% nonfat milk solids, 1% peptone, or 1% MgSO(4).7H(2)O in the dilution blanks. Higher detection on selective agar media was effected by surface plating or by surface-overlay plating of the cells. The surface-overlay method appeared to be superior for the direct enumeration of E. coli in foods.

The determination of non-fat milk solids in milk bread from the orotic acid content.

A method is described for the determination of the content of non-fat milk solids in milk bread. Orotic acid (2,6-dihydroxypyrimidine-4-carboxylic acid) present in the milk solids is extracted from the bread with water and determined by a colorimetric procedure, and the content of non-fat milk solids is calculated from the orotic acid content of the milk bread. The mean orotic acid content of the non-fat milk solids examined was 62·5 mg per 100 g (range 48·0 to 74·5 mg per 100 g).

THE VALUE OF ADDING IRON AND NONFAT DRY MILK SOLIDS TO A MILK DIET IN THE RECOVERY OF ANEMIC RATS

Weanling rats were fed only homogenized vitamin D milk for 3 weeks at which time the body weights were about 105 g and the hematocrit values were 20.4 for males and 22.8 for females. They were then fed milk plus 10 ppm elemental iron in the form of ferric pyrophosphate, milk plus 10% added nonfat dry milk solids, or milk plus 10 ppm iron plus 10% nonfat dry milk solids. After 3 weeks on the milk-plus-iron diets, the hematocrit values for males and females were about 30 and 40, respectively. Weekly body weights and hematocrit values showed the two iron-supplemented diets to be nutritionally similar (P>.05) when rats were fed ad libitum. Rats fed milk plus added nonfat dry milk solids were significantly lower (P<.05) in body weight after 10 weeks of age and significantly lower (P<.05) in hematocrit value after 8 weeks as compared to rats fed either of the iron-supplemented diets.

FILLED MILKS, IMITATION MILKS, AND COFFEE WHITENERS

Certain fluid milk-like products packaged in the same type of container as fresh fluid milk are marketed in grocery stores in many states. These products may be mistaken for fresh fluid milk and skim milk; therefore, the Committee on Nutrition is concerned about the nutritive value of such products if they are used in the diets of infants and children. These milk-like products are classsified as filled milks and imitation milk. According to the provisions of the Filled Milk Act, Public Law No. 513, a filled milk is defined as any milk, cream, or skim milk to which any fat or oil other than milk fat has been added so the resulting product is in semblance to or imitation of a milk product. More simply stated, any mixture of milk solids with fats other than milk fat is called a "filled" product. However, imitation milk resembles milk but contains no skim milk or nonfat milk solids. Filled milks are and have been marketed in many states, whereas imitation milks have only recently been offered to the public in several areas, notably New York, Arizona, and California. Most imitation milks on the market are totally unsuitable for infant feeding and constitute a public health risk, even though these products are presently marketed in just a few areas. However, it appears advisable to inform physicians about the nutritional values of milk-like products because they could become more widely available. This statement does not deal with proprietary infant formulas, which are specifically exempted under the provisions of the Filled Milk Act1 and which are covered by Food and Drug Administration regulations on Special Dietary Foods.

The assay of non-fat milk solids by the determination of orotic acid in milk chocolate and in the milk.

When the orotic acid content of the milk that is used in the manufacture of chocolate is known, non-fat milk solids can be determined with satisfactory accuracy by the described method. The method is equally valid for chocolate products that contain milk protein that has been subjected to high-temperature heat treatment and consequently cannot be analysed satisfactorily by the method of the Association of Official Analytical Chemists.Natural variations in the orotic acid content of milk of various origins are too great to permit the determination of milk solids, for arbitration purposes, in milk chocolate.

Effect of Dietary Oleates on Lymph Lipids in the Young Bovine

The effect of feeding mono-, di-, and triolein and oleic acid with skimmilk on thoracic duct lymph flow and lipid composition was studied in dairy calves. Administration of either reconstituted skimmilk only (aqueous dispersion containing 20% nonfat milk solids) or reconstituted skimmilk plus any of the lipids increased the flow rate of lymph in the thoracic duct. The concentration of lipid in the lymph and the amount of lipid transported per hour increased significantly by 2 to 5 hours after the lipids were fed; feeding only reconstituted skimmilk did not alter the lipid concentration in the lymph. Feeding of each test lipid also caused about a 2-fold increase of the proportion of oleic acid in the triglycerides of the lymph lipids. This elevation of oleic acid and the concomitant decrease of the other fatty acids occurred less rapidly after the monoolein feeding than when other lipids were fed. Free fatty acids and cholesterol esters in the lymph were altered only slightly, suggesting that most of the oleic acid in the dietary lipids was incorporated into triglycerides.

Repair of injury in freeze-dried Salmonella anatum.

Repair of injury induced by freeze-drying Salmonella anatum in nonfat milk solids occurred rapidly after rehydration. Injury in surviving cells was defined as the inability to form colonies on a plating medium containing deoxycholate. Death was defined as inability to form colonies in the same medium without this selective agent. The rate of repair of injury was reduced by lowering the temperature from 35 C to 10 C and was extremely low at 1 C. Repair was independent of influence of pH between 6.0 and 7.0. Repair did not require synthesis of protein, ribonucleic acid, or cell wall mucopeptide, but did require energy in the form of adenosine triphosphate (ATP) synthesized through oxidative phosphorylation. The requirement for ATP was based on dinitrophenol or cyanide interference with repair. Dinitrophenol activity was pH-dependent; no repair occurred at pH 6.0 and some repair was observed at pH 6.5 and above. Injured cells were extremely sensitive to low concentrations of ethylenedinitrilotetraacetate. This indicated that freeze-drying injury of S. anatum may involve the lipopolysaccharide portion of the cell wall and that repair of this damage requires ATP synthesis.

Effect of rehydration on recovery, repair, and growth of injured freeze-dried Salmonella anatum.

From 70 to 90% of the Salmonella anatum cells that survived freeze-drying in nonfat milk solids were injured. After rehydration, these injured survivors failed to grow on a selective plating medium containing deoxycholate but could form colonies on a nonselective medium. In a suitable environment after rehydration, injury disappeared in most of these cells. The rate of this repair at 25 C was very rapid initially and, in a medium containing milk solids, was completed within 1 hr after rehydration. The repaired cells initiated growth about 1 hr later than normal cells and grew at a slower rate. In a medium containing milk solids, initial recovery, extent of repair of injury, initiation of growth, and rate of growth were not influenced by supplementation with extra nutrients in other rehydration media. Rehydration controlled by modifying the concentrations of lactose, sucrose, or milk solids in the rehydration medium influenced the recovery of cells and the time that growth was initiated. Glycerol failed to increase recovery. Higher numbers of cells were recovered by rehydrating at 15 to 25 C, but an earlier initiation of growth and more rapid growth were observed at 35 C.

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.

Effect of Rehydration on Recovery, Repair, and Growth of Injured Freeze-Dried Salmonella anatum1

From 70 to 90% of the Salmonella anatum cells that survived freeze-drying in nonfat milk solids were injured. After rehydration, these injured survivors failed to grow on a selective plating medium containing deoxycholate but could form colonies on a nonselective medium. In a suitable environment after rehydration, injury disappeared in most of these cells. The rate of this repair at 25 C was very rapid initially and, in a medium containing milk solids, was completed within 1 hr after rehydration. The repaired cells initiated growth about 1 hr later than normal cells and grew at a slower rate. In a medium containing milk solids, initial recovery, extent of repair of injury, initiation of growth, and rate of growth were not influenced by supplementation with extra nutrients in other rehydration media. Rehydration controlled by modifying the concentrations of lactose, sucrose, or milk solids in the rehydration medium influenced the recovery of cells and the time that growth was initiated. Glycerol failed to increase recovery. Higher numbers of cells were recovered by rehydrating at 15 to 25 C, but an earlier initiation of growth and more rapid growth were observed at 35 C.

Repair of Injury in Freeze-Dried Salmonella anatum1

Repair of injury induced by freeze-drying Salmonella anatum in nonfat milk solids occurred rapidly after rehydration. Injury in surviving cells was defined as the inability to form colonies on a plating medium containing deoxycholate. Death was defined as inability to form colonies in the same medium without this selective agent. The rate of repair of injury was reduced by lowering the temperature from 35 C to 10 C and was extremely low at 1 C. Repair was independent of influence of pH between 6.0 and 7.0. Repair did not require synthesis of protein, ribonucleic acid, or cell wall mucopeptide, but did require energy in the form of adenosine triphosphate (ATP) synthesized through oxidative phosphorylation. The requirement for ATP was based on dinitrophenol or cyanide interference with repair. Dinitrophenol activity was pH-dependent; no repair occurred at pH 6.0 and some repair was observed at pH 6.5 and above. Injured cells were extremely sensitive to low concentrations of ethylenedinitrilotetraacetate. This indicated that freeze-drying injury of S. anatum may involve the lipopolysaccharide portion of the cell wall and that repair of this damage requires ATP synthesis.

Concentrated cultures of Leuconostoc citrovorum.

Two single-strain cultures of Leuconostoc citrovorum were grown in a broth medium with automatic pH control. Culture concentrates were prepared by centrifugally harvesting the cells and resuspending them in 1/50th the original volume in 10% nonfat milk solids. The concentrates were stored in liquid nitrogen until analyzed. The maximum population attainable was approximately equal when cultures were grown at pH 6.0, 6.5, or 7.0 with sodium hydroxide or ammonium hydroxide as the neutralizer. Citrate was required in the growth medium for the cultures to be able to produce diacetyl subsequently in milk. At pH 6.0, the cells reached maximum population and ability to produce diacetyl. Organoleptic analysis by an experienced flavor panel showed a preference for cottage cheese creamed with a creaming mixture prepared with a culture concentrate rather than a normal culture. The culture concentrates maintained their viability and ability to produce diacetyl for at least 30 days when stored in liquid nitrogen.

Concentrated Cultures of Leuconostoc citrovorum1

Two single-strain cultures of Leuconostoc citrovorum were grown in a broth medium with automatic pH control. Culture concentrates were prepared by centrifugally harvesting the cells and resuspending them in 1/50th the original volume in 10% nonfat milk solids. The concentrates were stored in liquid nitrogen until analyzed. The maximum population attainable was approximately equal when cultures were grown at pH 6.0, 6.5, or 7.0 with sodium hydroxide or ammonium hydroxide as the neutralizer. Citrate was required in the growth medium for the cultures to be able to produce diacetyl subsequently in milk. At pH 6.0, the cells reached maximum population and ability to produce diacetyl. Organoleptic analysis by an experienced flavor panel showed a preference for cottage cheese creamed with a creaming mixture prepared with a culture concentrate rather than a normal culture. The culture concentrates maintained their viability and ability to produce diacetyl for at least 30 days when stored in liquid nitrogen.

Effect of Age and Diet on Fasting Blood and Plasma Glucose Levels, Plasma Nonesterified Fatty Acid Levels, and Glucose Tolerance in Dairy Calves

Fifteen male dairy calves were used to investigate the effects of age and diet on blood and plasma glucose and plasma nonesterified fatty acid levels, and glucose tolerance. Nine Holsteins and six Jerseys, one day old, were placed on one of three diets for a 100-day experimental period. The diets were: (I) milk, fortified with nonfat milk solids, (II) milk plus high-starch concentrate, and (III) milk plus high-fiber concentrate. Once each week a 16-hr fasting blood sample was obtained and 500mg glucose/kg body weight were administered to each calf for a glucose tolerance test. Blood and plasma glucose levels increased with advancing age in calves fed Diet I. There were decreases in blood and plasma glucose levels with advancing age in calves fed Diet II. Blood glucose declined, whereas plasma glucose levels increased, with advancing age in calves receiving Diet III. No change was detected in plasma nonesterified fatty acid levels with advancing age. Correlations between glucose and nonesterified fatty acid levels were negative and significant. The inverse relationship observed between these metabolites supports the view that nonesterified fatty acids are mobilized to maintain caloric homeostasis during periods of fast. Glucose tolerance decreased with advancing age in calves fed each of the diets, but rates of decrease were not significantly different among diets.

Consumer Preference for “Imitation” Milk Beverages

TMITATION milk is not new. Production records of 1916 show 6,400 metric tons of milk processed in that year alone [13, p. 38]. However, during the past few years sales of non-dairy and partially non-dairy products have increased rapidly. There are two broad categories of imitation milk: (1) a beverage containing non-fat milk solids with the milk fat replaced by vegetable fat (henceforth referred to as filled milk); and (2) a beverage containing no milk products (henceforth referred to as synthetic milk) [9, p. 17]. Either of the above types of milk would have adverse effects on the dairy industry should it capture a substantial part of the fluid milk market. Available data indicates that filled milk products enjoy a constant and rapid increase in sales. In the federal market order areas of the United States, filled milk sales increased from 2.4 million pounds in November of 1967 [16, p. 23] to 4.9 million pounds in April of 1969 [17, p. 24]. No comparable data is available for synthetic milk.1 The major problem faced by the dairy industry is the price advantage enjoyed by the products. A recent USDA publication compared the price per one-half gallon for raw materials used in whole milk, filled milk, and synthetic milk. As shown in Table 1, the cost difference per one-half gallon between whole milk and filled milk (using Class I fluid skim milk base), was 6.5 cents per one-half gallon. The difference in cost between whole milk and synthetic was 14.2 cents, while the difference between filled milk and synthetic milk was 7.7 cents. The best case history of filled milk sales is found in the Central Arizona marketing area. Go, marketed by Sarival Guernsey Farms [14, p. 36], has grown from 1.3 percent of regulated pool plant (Class I) sales in October, 1966, to 11.5 percent of sales as of August, 1968 [9, p. 21].