J.R. Marier

M. Boulet

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TECHNICAL NOTES 1885  pletely under the same test conditions. These trials were both repeated using two pipes show- ing discoloration. Results similar to the above were obtained. The sodium hypochlorite con- centration is the same in both detergent formu- lations. Since the quantity of detergent "B" used was about one-half that of "A," it follows that the actual level of chlorine varied in the detergent solutions. I t  is also important to note that efficient film removal was observed at the lower concentration of chlorine. I t  has been suggested that the low metasilicate con- tent in detergent "B" might permit greater detergent action, owing to a more favorable pH for chlorine activity (1). A cleaning procedure is described whereby an iridescent fihn was built up in a stainless steel pipeline by using a selected commercially available nonionic detergent at 120 ° F. Increas- ing the temperature of the nonionic and anionic cleaner to 160 ° F. did not remove the film after it had formed. A highly alkaline bottle-washing compound and an organic acid cleaner failed to remove the fihn. Chlorinated alkali detergents varied considerably in their ability to remove the iridescent fihn. O. W. K~UF~rANN Department of Microbiology and Public Health Michigan State University, East Lansing AND P. H. TIcAc¥ Department of Food Technology University of Illinois, Urbana REFERENCES (1) BARRETT, R. B. Personal communication. I~lenzade Products, Inc., Beloit, Wisconsin. (2) •AUFMANN, O. W., ANDREWS, ~:~. ~I., AND TRACY, P. ]:t. Further Studies on In-Place Cleaning. J. Dairy Sci., 38: 371. 1955. ADDENDU~J[ Since the completion of this study, a strong iridescent discoloration was observed on the glass- ware used in our laboratories. Replacing the commercial detergent routinely used with chlo- rinated alkali " B "  removed the rainbow film on all test tubes and Petri plates. P R E P A R A T I O N  O F  A S T A N D A R D  F O R  C I T R I C  A C I D  A N A L Y S I S  Considerable difficulty has been experienced with crystalline citric acid as a basis for preparation of a standard solution. Both the anhydrous and monohydrate forms of the acid are unstable at room temperature and hu- midity, with the result that the water content can vary between 0 and 2.5 M/M. Although the anhydrous acid is stable in a desiccator, it is difficult to obtain it by drying the mono- hydrate, because crystals of citric acid tend to melt at temperatures above 75 ° C. (4). Consequently, we have studied trisodium cit- rate as a standard material. The composition of trisodium citrate all- hydrate was verified by analyzing two lots (reagent grade) obtained from different manu- facturers. The salt was of high puri ty  and was probably obtMned by reerystallization under controlled conditions of temperature and pressure (2). Sample A was taken from a freshly opened bottle, whereas the bottle containing Sample B had been opened for at least 1 yr. No preliminary drying was given either sample before analysis. Carbon was determined by dry combustion (1), water was estimated by heating to 150 ° C. overnight (4), and sodium was measured by flame photom- etry (5). The following results were obtained: Found, % by wt.: CARBON (Theor. : 24.50) A B 24.28 24.36 All of these results fell within the experi- mental error of the various techniques. Although this study indicated that tri- sodium citrate dihydrate was stable at room temperature and humidity, its stability was further studied by storing for three-day intervals under various extreme conditions. Exposure to dry 80 ° C. air caused a small loss in weight (0.041%). At room temperature, storage in the desiccator resulted in a negli- gible loss of weight (0.003%), whereas hold- ing at 100% relative humidity caused a gain in weight of 3.65%. I t  is, therefore, apparent that trisodium citrate dihydrate is quite stable under normal laboratory conditions. In  a previous publication (3), a stock solu- tion containing 50 mg. of anhydrous citric acid per milliliter was recommended, from which suitable standards could be prepared. On the basis of the above study of sodium citrate, the following preparation is now recommended: 76.4712 g. of trisodium citrate dihydrate (reagent grade) is made up to one liter with water. This solution is 0.260 M and, therefore, compares with one containing 50 mg. of anhydrous citric acid per milliliter. The solution is stored at 0 ° C. Fresh dilutions WATER SODIUM (Theor.: 12.25) (Theor.: 23.46) A B A B 12.36 12.19 22.70 22.95 ]886 JOURNAL OF DAIRY SCIENCE of this stock solution are prepared each month and are also stored at 0 ° C. J. R. MARIER M. B OULF~ Division of Applied Biology, National Research Council, Ottawa, Canada REFERENCES (1) CHRISTI~IAN, D. R., DAY, N. E., HANSELL, P. R., AND ANDERSON, R. C. Improvements in Isotopic Carbon Assay and Chemical An- alysis of Organic Compounds by Dry Com- bustion. Anat. Chem., 27:1935. 1955. (2) HOLT(~N, H. H. Sodium Citrate Dihydrate. Chem. Abstrs., 33:6881. 1939. (3) MA~mR, J. R., AND BOULET, M. Direct Deter- mination of Citric Acid in Milk, with an Im- proved Pyridine---Aeetic Anhydride Method. J. Dairy Sei., 41: 1683. 1958. (4) Merct~ Index. 6th ed. pp. 252 and 877. Merck and Co., Rahway, New Jersey. 1952. (5) P u m ~ s ,  M., AND NESSI~, N. E. Comparison Between Flame Photometric and Chemical Methods for Sodium and Potassium in Soils, Plants, Serum, and Water. Analyst, 82: 467. 1957. T H E  M E T A B O L I S M  O F  S E R I N E - 3 - C  ~4 B Y  T H E  L A C T A T I N G  S H E E ' P  M A M M A R Y  G L A N D  1.2 The contribution of serine to the metabolism of the mammary gland in capacities other than protein synthesis is unknown. Recent reports of Wood et al. (6, 7) qualitatively show that serine can be formed in the mammary gland from glucose and glycerol. The conversion most likely occurs by way of phosphoglycerate and phosphohydroxypyruvate (3). A reversal of this reaction sequence could lead to the for- mation of phosphoglyceraldehyde from serine. Since triose phosphate isomerase is active in the gland (7), it would be possible for serine to contribute to the formation of glycerol. To study the metabolism of serine by the mammary gland, 90 t~c. of serine-3-C 1. was placed, immediately after milking, into the gland cisterns of the udder of each of two lactating ewes. After  8 hr., the ewes were milked, sacrificed, and the glands removed for analysis. Various substances (Table 1) were isolated from the milk and lnanmmry gland tissue by conventional means and assayed for radioactivity in a thin-window gas-flow G.M. counter. Both milk and mammary tissue were analyzed to eliminate the effect of differences in secretion rates of the various nfilk components on the distribution of C ~. During the 8-hr. period between the addi- tion of the labeled compound to the udder and the sacrifice of the animal, 94 and 87% of the labeled serine were utilized from the gland cisterns in Experiments A and B, respectively. Of the serine taken up, 16% was recovered from milk and glandular tissue in Experiment A, whereas 36% was recovered from these sources in Experiment B. Of this recovered C ~', 98% (Experiment A) and 99% (Experi- ment B) were located in the proteins of the milk and mammary gland. Table 2 shows the Authorized for publication on J'une 5, 1959, as Paper No. 2368 in the Journal Series of the Pennsylvania Agricultural Experiment Station. 2 Supported by the U. S. Public Health Service (H3632). TABLE 1 Distribution of recovered C ~* from serine-3-C 1. metabolized following administration to the lactating sheep udder" Per cent of metabolized, Metabolites isolated recovered C 1~ Milk Exp. A Exp. B Triglyceride glycerol Trace Trace Triglyceride fatty acids 0.0 0.0 Phospholipids 0.2 0.1 Proteins 33.6 82.9 Lactose 0.0 0.2 Mammary gland Triglycerlde glycerol 0.4 Trace Triglyceride fatty acids 0.0 0.0 Phospholipids 0.9 0.1 Proteins 64.7 16.7 Glycogen Trace Trace In Experiment A, 94% of the administered seriae was metabolized, of which 16% was re- covered in the substances isolated. In Experiment B, 87% of the serine was metabolized, of which 36(/c was recovered. TABLE 2 Specific activity of the classical fractions of milk proteins following the arministratlon of serine-3-C ~4 to the lactating sheep udder (Experiment A) Protein fraction a Specific activity (c.p.m/mg) Casein 147 Lactoglobulin 49 Lactalbumin 103 Nomenclature as suggested by Reference 4. specific activity of the classical protein frac- tions in the milk from Experiment A. The specific activity of casein and lactalbu- rain, in relation to the per cent serine in each (casein 6.3, lactalbumin 4.8), suggests that 

Preparation of a Standard for Citric Acid Analysis

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