Estimation of Milk Solids in Bread CHARLES HOFFMAN, T. ROBERT SCHWEITZER, AND GASTON DALBY Research Laboratory, Ward Baking Company, New York, N. Y.
digestion, and add 10 grams of Filter-Cel. Filter through a Biichner funnel containing a filter paper upon which is a thin pad of Filter-Cel. Apply suction until t.he mass is fairly dried. Transfer the residue to a beaker, stir with ether, and filter again through Filter-Cel into a dry flask. Evaporate the ether, and if the oil is clear it is ready for the Reichert-Meissl number determination. About 5 grams of fat are used for this determination, as is usual in the standard Reichert-Meissl method.
T
HE increased commercial use, in bread, of high percent-
ages of milk solids, both whole and skimmed, has stimulated interest in the quantitative determination of milk in bread. This work was undertaken several years ago t o develop a reasonably rapid and practical method for this determination. Until recently little has been published on this subject. Munsey (3) has described the estimation of milk solids by a determination of the fat number, but this method does not give accurate results when skimmed milk only or partially skimmed milk is present, The Hartmann and Hillig (2) citric acid method has also been reported. As citric acid is present in small quantities in milk, the analytical error doubtless is magnified considerably when milk solids are calculated from the citric acid present. The method to be described is based on the determination of lactose and the estimation of butterfat using the Reichert-Meissl number, and applies to skim-milk solids as well as whole-milk solids. It has been in practical use for several years and has given results which are accurate for all practical purposes.
The average oil content of flour on the dry basis is 0.7 per cent. This oil has a Reichert-Meissl number of 1, for which allowance must be made in estimating the amount of butterfat in the bread. If other shortening is present, an allowance must also be made for the Reichert-Meissl number of this fat. The normal variation to be expected in the Reichert,-Meisal number of butterfat must be considered also. OF FAT-FREEMILK SOLIDSIN TABLE I. DETERMINATION
BREADS
(Moisture-Free basis) Fat-Free Milk Solids Fat-Free Milk Solids Calculated Found by Calculated Found by from formula analysis from formula analysis
Procedure Remove the crust of the bread, air-dry the crumb, then grind sufficiently to pass a 20-mesh sieve. Digest 50 grams of the prepared material in 400 cc. of distilled water at about 40" C. for 3 hours, and transfer the mixture to a large centrifuge tube. Centrifuge and decant the liquid portion into a 1-liter volumetric flask. Wash the residue four times, using 75 cc. of distilled water each time, and separate solids by centrifuging. Decant after each washing and add the liquid portion to the first extract. Add 35 grams of Baker's compressed yeast (suspended in a small amount of water), 0.5 gram of ammonium sulfate, and 0.2 gram of sodium bisulfite, and let stand overnight at room temperature stoppered, but with a vent for the escape of carbon dioxide. The ammonium sulfate is used as a yeast stimulant, and the sodium bisulfite retards bacterial action. After standing overnight add 20 cc. of copper sulfate solution (regular Fehling's A) and sufficient sodium hydroxide solution to give a definite blue color and clarify the solution. Make up to volume in the liter flask, shake, and filter through a good quality filter paper. Take 50 cc. of the filtrate and determine lactose, using the standard Munson and Walker gravimetric method.
%
%
%
%
0.50 2.40 2.86 3.62
0.52 2.58 3.06 3.56
3.88 4.40 6.00
4.04 4.56 5.95
The amount of butterfat that would be present if the bread contained whole-milk solids is calculated from the percentage of fat-free milk solids found. The ReichertMeissl number, after correction for fats other than butterfat present, determines whether the amount of butterfat calculated is actually present. If the Reichert-Meissl number does not indicate any butterfat, skim-milk solids were used in the manufacture of the bread. If the Reichert-Meissl number indicated only part of the butterfat necessary to balance the skim-milk solids in the ratio of skim-milk solids to butterfat in whole-milk solids, then partially skimmed milk was used. The factor 0.4115 multiplied by the percentage of skim-milk or fat-free solids gives the amount of butterfat necessary to balance the skim-milk solids. The ReichertMeissl number alone without a determination of lactose makes an estimation of the milk solids present quite uncertain.
Fifty cubic centimeters of the filtrate are equivalent to 2.590 grams of bread after the correction for the yeast is made. The fat-free milk solids are calculated from the percentage of lactose found, and average 50 per cent lactose with only slight variations. Therefore twice the percentage of lactose found (after calculation to the dry basis) is equal to the percentage of fat-free solids on the dry basis of the bread. The accuracy of the method as determined against known formulas indicates that the amount of lactose attacked by the yeast is negligible, and that interfering sugars are completely removed by the yeast. I n order to test the accuracy of the method, breads mere baked with varying quantities of fat-free milk and analyses obtained thereon as given in Table I. The total fat present in the bread is determined by the standard method of the Association of Official Agricultural Chemists (I).
WHOLE-MILKBREADS" TABLE 11. ANALYSESOF COMMERCIAL (Moisture-free basis) No. 1 No. 2 No. 3 5.76 6.22 6.86 3.98 6.82 6.44
No, 4 No. 5 Fat-free milk solids, yo 7.56 5.56 Total fat % 8.56 4.84 Eatimateh butterfat (fatfree milk solids X 0.4115) % 2.37 2.56 2.82 2.70 2.29 Reichert-Meissl number 13.0 11.5 14,6 10,2 14.5 Butterfat estimated from Reichert-Meissl nurnber % 1.80 2.60 3.20 2.90 2.40 Whol&rnilk solids, % (fat-free milk solids plus butterfat estimated from fat-free milksolids) 8.13 8.78 9.68 10.26 7.85 a For these oalculations the Reiohert-Xeissl number of butterfat was taken a6 28.
Literature Cited (1) Assoc. Official Agr. Cham., Official and Tentative Methods of Analysis, 3rd ed., p. 178 (1930). (2) Hartmann and Hillig, J. Assoc. Oficial Agr. Chem., 16, 431-5 (1933). (3) Muneey, V. E.,Ibid., 18, 573-7 (1935).
Extract the fat necessary for the Reichert-Meissl number determination by placing 200 to 300 grams of finely ground airdried bread, depending upon the fat content, in a 2-liter flask containing 1000 cc. of distilled water and 30 cc. of hydrochloric acid. Digest the mass by boiling for 1 hour or until it shows good
RECEIVED February 21, 1936.
298
Liquid Butane as Motor Fuel Corrosion Test Methods M. M.HOLM, Standard Oil Company of California, Richmond, Calif.
holder is connected to the vaporizer and the orifice meter. A weighed 75-liter (20-gallon) cylinder of the test fuel is inverted to permit withdrawal of liquid and connection is made to the vaporizer. Steam is turned on and superheated fuel containing the suspected contaminant is passed over the test mirrors. Rate of fuel charge varies from about 5 to 25 k . (10 to 50 pounds) per hour. Total quantity charge may be asqow as 0.5 or 1 kg (1 or 2 pounds), but with most fuels it is desirable to charge 10 kg. (20 pounds) or more. Exact rate and total quantity are governed by the appearance of the mirrors, care being taken to limit any darkening or other evidence of corrosion to metal in the first 7.5- t o 10-cm. (3- or 4-inch) section of the gage glass, For making these adjustments, a control valve is provided in the line between the gage glass and orifice meter. Temperature in the line immediately following the gage glass is maintained at 120" C. (250" F.), control being the steam pressure applied to the vaporizer. After a suitable quantity of fuel has been charged, the feed valve is closed and the cylinder is disconnected and again weighed. The gage glass is then removed from its holder for close inspection of the test mirrors.
SE of liquid butane as motor fuel involves certain problems in refinement and handling not encountered with heavier fuels. Origin of the particular problems pertinent to this discussion centers in the specialized equipment required for proper vaporization and carburetion of the liquefied gas. Conventional equipment for this service comprises a pressure-regulating valve, a heater, and a butane-metering valve. Presence of minute traces of contaminants in the fuel eventually results in improper functioning of this equipment. I n many cases the concentration of interfering material may be so low as to defy detection by ordinary methods of analysis. Contaminants may be grouped conveniently as insoluble scale and dirt : butane-soluble, noncorrosive, nonvolatile material; and material which is corrosive to metal equipment under service conditions. Insoluble scale and dirt present no great problem since they are normally removed by a metal screen placed in the liquid fuel line ahead of the pressureregulating valve. On the other hand dissolved nonvolatile material, such as pipe-threading compounds and valve lubricants, even though not corrosive, has a tendency to collect a t points of low gas velocity in the metering valve, eventually contributing to improper seating. Particularly objectionable is the corrosive type of contaminant, since it not only destroys the equipment but interferes with satisfactory operation before complete failure occurs. Any test procedure for determining quality of a given fuel should be rapid and simple, and give results which can be interpreted in terms of actual service. It is believed that such a procedure has been devised for the specific problem outlined.
Discussion Many fuels are perfectly clean; so when the test is completed the mirrors are bright, showing no evidence of oil, scum, or color change. The nonvolatile, noncorrosive, butanesoluble type of contaminant is readily detected by the appearance of a n oil or scum on the mirror surfaces. When the corrosive type of contaminant is present a rapid change in color is noted-for example, darkening is noted in a few minutes with fuel containing 0.000001 per cent of elementary sulfur. mIfIcF METER
Method I n principle the method involves inspection of minute quantities of metals which have been exposed to large quantities of the test fuel under conditions representative of, or more severe than, normal service. To facilitate rough visual comparisons and to provide a large contact surface, the metals are prepared in the form of thin copper or silver mirrors on glass, TJse of both types of mirror is usually desirable, the former being representative of the metal in the conventional butane heater and the latter having the advantage of pronounced change in appearance in presence of even the slightest trace of corrosive sulfur. Copper mirrors are prepared by reduction of cupric ammonium hydroxide solution with phenylhydrazine (2). Silver mirrors are prepared by the conventional Brashear formula ( I ) , using sugar as the reducing agent. A sketch of apparatus suitable for contacting the mirrors with the fuel in question is shown in Figure 1. Essential units comprise a steam-heated vaporizer, a 25-cm. (10-inch) section of 1.9-cm. (0.75-inch) gage glass encased in a slotted metal holder, and an orifice gas meter. All parts coming into contact with either liquid or vaporized fuel must be corrosionproof. Chrome-nickel steel is suitable for metal parts. Any gasket material used in making up tight connections should be of such composition that contamination of the fuel is impossible. Asbestos is a satisfactory packing for sealing the gage glass in its metal holder.
FIGURE1
Fuel may usually be rated as satisfactory or unsatisfactory on the basis of mere visual inspection of the test mirrors. I n cases where qualitative identification of the contaminant is required, the microanalytical procedure to be followed will naturally depend upon the appearance of the mirrors and any clues provided by previous history of the sample. For example, presence of valve lubricant in some fuel samples has been proved by determining saponification number and wax content of the oily scum. Likewise, with another fuel suspected of sulfur contamination, the suspicion was proved correct by decomposition of the darkened copper mirror with zinc and hydrochloric acid and detection of hydrogen sulfide in the gas evolved. With certain fuels it may be desirable to supplement qualitative identification of the contaminant with critical determination of the quantity present. Such determination is feasible by conventional methods only when the proportion is relatively large-for example, 0.0001 per cent by weight or greater. However, a semi-quantitative index of the concen-
In operation the metal test mirrors, supported, for example, on
glass pearls, are packed into the gage glass, and the gage-glass
299
