S E P T E M B E R 1947 slightly acidic -acetic acid solution, viithout the presence of tartaric acid, gave escellent results. However, the spectrograph revealcd that manganese \?-as definitely present in the precipitate. Kickel, 0.1486 taken; 0.1486 found. Antimony. Eight gramr of tartaric acid were necessary t o keep tlie ant,imnny (as the chloride! in solution. The gravimetric data rrveal(Jd that the separation \vas good. Spectrographically no an:imony was indicated in the precipitate. Kickel, 0.1486 taken: 0.1187 found. Barium, Calcium, Strontium. \\-eeldenburg (4) reported that nickel rould not lie precipitated from an ammoniacal solution in the prl:senw ?if iiarium, calcium, or strontium, because of their reaction with cnrtion dioxitlc to form insoluble carbonates. fully precipitatrti from an acetic acid solution,
655 free from sulfate and tartrate ions. The precipitate was not contaminated with the alkaline earths. Sickel, 0.1623 taken; 0.1623 found. LITERATURE CITED
(1) Brunck. O . , Z . angew. Chem., 20, 834 (1907). (2) Diehl, H., “Applications of the Dioximes t o Analytical Chem-
istry,” Columbus, Ohio, G. Frederick Smith Chemical Co., 1940. (3) “LI.1.T. 11-ax-eLength Tables,” Yew York, John Wiley 8; Sons, 1939. (4) Weeldenburg, J. G., Chem. Weekhlad, 21, 358 (1924).
A s s T i u c T m from part of a thesis subniitted b y Margaret Griffing i n partia fulfillment for the P h D. degree.
Physical and Chemical Methods for Characterizing Peanut Butter J . F. VINCEST‘ fr\D L. Z. S Z . i B 0 , Southern Reseurch I n s t i t u t e , Birmingham, Ala. Quantitatire procedures for the physical and chemical characterization of peanut butter, with special emphasis on factors which influence spreadability and oil separation, are described. Values obtained on experimental and commercial samples of peanut butter are included.
T
HE marked expansion of the peanut industry in recent years car1 br traced in part to a steadily increasing consumer acceptanrc. oi’ peanut butter as a staple item of diet. T h e national consumptioil I ~ O Kesceeds 2 pounds per capita annually. Meanwhile tliorc has been a gro\ving realization among progressive peanut butter manufacturers that more suitable laboratory re neerled to assist in the maiiitenance of product quality )rmit>-. Although analyses of peanuts and peanut butters have been reported ( 4 , 8,. 9), no directions particularly well suited to peanut butter characterization have been presented. This paper sets forth several methods developed in this that have given usefll results. ccepta?ce of peanut butter is influcnced by the spreadability a i d oil-separation characteristics of the product. For this reason it hsa become necessary to evaluate spreadability and also thCJSe factors influencing spreadability and oil separation. Variouy viscometers, tenderometers, and penetrometers have becri ~ of food mat(%used t o nieasilre t h e tcsture and f l o characteristics rial. However, tlie high viscosity of peanut butter precludes tlic use of thrse iti~truments,except the penetrometer. Penetrometer readings have tieen found to give a valuable indication of sprcadability . The ,ize distrihution of the particlw in peanut butter influencris the sprwding i.!inrscteristics and the tendency to oil separation. Standard method. of &ve analysis, followed by microscopic esaminntioil of t tint portion passing a 3’&niVSh screen, are useful in char:ic.Ierizir,g the grind. Hydr8Jgcnatrcivegetable oil is comnionly added in small quan\>;liter t o prevent oil separation. The proportion iiiu.-t be carefully rcyulatcd if stabilization is to !:#)ut undue hardening and loss of spreadability. In flip coilritl t:f choosing a method for control of this variable, iodine nui!itici., inelring point, and titer determinations m r e made O I Iwnnut oil containing 0 to G 7 , hydrogenated oil. tliods proved sufficiently accurate t o dein thr. Ii?thogi.iintcd oil content, it n-as obistry Department, Georgia S t a t e College f o r
served that the melting points of the mixtures ivere distributed over a n-ide temperature range and depended to some estent on thermal history. h satisfactory procedure has been evolved using standardized heating and cooling techniques and the principle of the falling-hall viscometer to determine the thermal flow point. The proportion of air incorporated into peanut butter during the grinding process may vary widely, even to the estent that it becomes impossible to place the required weight of material in a standard jar. B suitable method for determining air content provides the means for routine checks, as well as for studying the effects of process variables on this property. N o h r and Eysank ( 7 ) determined the air in butter by heating a sample under glycerol in an evaporatng diPh and collecting the escaping air in an inverted funnel. Air content of ice cream is measured by comparing the w i g h t of a gallon of ice cream mix with the m i g h t of a gallon of finished ice cream (3j. Coffey and Spannuth ( 2 ) determined the air content of shortening by finding the concentration of an alcohol solution just sufficient to buoy the sample. Loeffler (6) measured the air content of citrus juice by subjecting it to a vacuum and noting the volude of gas evolved. Since the viscosity of peanut butter is not greatly altered by heat, and peanut particles quickly absorb water or alcohol, the mocit satisfactory approach seemed to be to adapt the vacuum estraction technique to this determination. Standiii,d methods that have been found most useful for the of sugar and salt in peanut butter are described. DESCRIPTION OF METHODS
Spreadability. .I representative sample of peanut butter a t 25’ C. is placed in a cylindrical crystallizing dish 8 cm. in dianietcr and 2 cin. high, taking care to leave no air pockets and to have thc top of the butter smooth and level ivith the edge oi the dish. The filled dish is placed on the stagc of a food-t:,ye precision penrtrometer and thc point of the plunger is Ion-ered until it just malics contact with the surface of the sample. The plunger is then released for exactly one niinute and the depth in niillimeters !):netrated kv the plungrr is read from tlie instrument dial. Each nieasuwnicnt should be repeated several times to ensure consistcnt results.
656
V O L U M E 19. N O . 9
Penetrations of approximately 39.0 rnm. are obtained with very fluid peanut butters; fine grinds of optimum spreading qualities give values in the range of 33.0 and 36.0 mm.; commercial samples commonly fall within the 25.0-30.0-mm. range; and difficultly spreadable butters exhibit penetrations as low as 18.0 t o 22.0 mm.
Particle Size Distribution. Approximately one pound (454 grams) of peanut butter is extracted with two 500-ml. portions of hot benzene followed by two extractions with 300 ml. of warm
I
-
50
I
1
5
6
-
J
I
4s461
FF LL O OW W POINT POINT
/"
40-
petroleum ether. hfter each extraction, the oil-bearing solvent is removed by vacuum filtration. The resulting peanut meal is placed in a large evaporating dish, dried for several hours, and then subjected to a Ro-Tap sieve analysis. This operation is followed by a microscopic particle size distribution count of that portion passing through a 325-mesh sieve. The microscopic count is made by means of a Filar micrometer and a Spencer bright line counting chamber, and recorded as the per cent of particles falling within a given diameter range. The results obtained by means of this examination are subject t o the same limitations as are found in blood cell and dust measurements, but'they are direct and, if sufficient numbers of particles are measured, give useful data. Although the over-all method may not give absolute values for peanut particle size in situ, i t results in measurements of sufficient accuracy to differentiate between medium, medium fine, and fine grind peanut butters.
PERCENT
IO F 10
Table I. Flow Points of Peanut Oil-Hydrogenated Oil
HY DR 0 GE N ATE D HYDROGENATED
Mixtures Run No.
0 a
c.
1
c.
Per Cent Hydrogenated Oil 2 3
c.
c.
4
c.
I
0
5
c.
... 27.0 37.8 44.0 47.5 50.0 ... 25.0 35.0 44.0 47.0 49.0 10 0 ... 36.0 42.0 46.0 48.0 10.0 25.0 33.5 41.0 46.0 49.0 10.5 21.0 32.6 41.0 47.0 49.0 * 10.2 27.2 34.5 40.5 45.0 48.0 Av. 10.2 25.3 34 9 41.8 46.4 48.8 Note. Blank spaces are due t o faot t h a t during some runs glass bead fell a t outset of test. -4 cold bead a n d a n adequately frozen oil mixture will prevent this.
Hydrogenated Oil Content. The peanut oil obtained in the particle size determinations is recovered from the solvent and dried in a 90" C. vacuum oven. A 10 X 650 mm. lipless test tube which has an inner bore of 8 mm. is carefully select,ed, and is marked with try0 lines 1 em. apart and perpendicular to the long axis of the tube. The lower of the two lines is placed slightly above the curved portion of the bottom of the tube. The test tube is filled to the upper mark with the hot oil sample, corked, and frozen in a dry ice-trichloroethylene bath. While the tube is in t,he freezing bath, a cold glass bead exactly 6 mm. in diameter is dropped on the surface of the frozen oil; then the tube should remain in the freezing bath for 20 minutes. Three sets of control tubes containing known mixtures of peanut oil and hydrogenated oil, solvent-extracted from peanut butter containing known amounts of hydrogenpted oil, covering the range of interest, are prepared in the same manner. All the tubes are placed in a conventional melting point apparatus previously cooled t o 2" to 3" C. Khen the temperature of the samples has reached 0" C., the rate of temperature increase is regulated to about 3 minutes per degree. The flow point is judged as the temperat,ure of the oil a t the time the glass ball just reaches the lo\+-ermark under the conditions outlined above.
3
4
Average Flow Points
reweighing the syringe. The cap, D, is then placed on the upright tube. Air is removed from the cap by raising the column of mercury with all stopcocks open until brine enters stopcock B. Stopcocks A and B are then closed and a vacuum is drawn by lowering the mercury approximately two thirds the distance down the cap. Stopcock C is then closed and sufficient heat is applied to the tube adjacent t o the sample to cause boiling. Heating is discontinued after a few minutes and the samA ple allowed to cool to room temperature. The mercury is again raised and the pressure carefully adjusted with stopcock B open. The quantity of air collect,ed is read on the graduated stem. This air is then ejected through stopcock A and the evacuation process is repeated until no more. air is obtained from the sample.
D
Table I indicates the flow points of five peanut oil-hydrogenated oil mixtures and of pure peanut oil observed during six separate runs. riverage flow points are plotted in Figure 1. Air Content. The apparatus developed to determine air content of peanut butter (Figure 2) consists of a vacuum chamber, a calibrated measuring tube, a small capillary msri,-meter, and mercury leveling bottle. A sample of peanut butter is taken by pressing the open end of a 5-ml. hypodermic syringe (having the constricted end of the syringe removed) into the peanut butter sample while holding the plunger stationary. Syringe and contents are then wiped clean of excess butter and weighed. The sample is edtruded into brine floating on a column of mercury in the lon-er portion of the vacuum chamber. Sample weight is obtained by difference after
2
Figure 1.
C r e 2,
IThile checks may occasionally be obtained IT-ith an accuracy of 5%, it is usual for a set of results to vary within 10%. Since the air content of peanut butter may vary 200% or more, this error is not excessive. Commercial peanut butter contains an average of about 0.72 ml. of air per 10 grams. Sucrose. A slight modification of the Lane-Eynon method ( 5 ) has been found well suited to the estimation of sucrose in peanut butter. Although the method is thoroughly described elsewhere (I), the present clarification and inversion techniques ap-
Table 11. Recovery of Added Sucrose from Peanut Butter Sucrose per 5 Grams of B u t t e r Gram R 0.2246 4 49 0.2246 4.49
...
..,
Sucrose hdded Gram 70 0 0500 1 00 0 1000 2 00 0 , 1 5 0 0 3 00
Sucrose Recovered Gram ?& 0.2722 5 . 4 4 0.3207 6 . 4 1 0,3742 7 . 4 8
Error Gram % -0 -0 -0
01124 0 . 8 7 0039 0 . 9 2 004 0 01
657
SEPTEMBER 1947 A 5-gram sample of %he oil-free peanut' meal is placed in a beaker n-ith 200 nil. of 807, alcohol, warmed for 30 minutes, and then filtered. This extraction is then repeated. The residue is washed with 80% alcohol and t,he combined filtrate and washings are evaporated to a few milliliters on a steam bath. The concentrate is quantitatively transferred to a 100-ml. volumetric flask with distilled water, and 5 ml. of saturated normal lead acetate are added, followed in a few minutes by 10 ml. of saturated disodium phosphate solution. The solution is then diluted to volume with distilled water, mixed, and filtered. A 50-ml. aliquot is pipetted into a 100-ml. volumetric flask with 5 ml. of invertase, the pH is adjusted to approximat,ely 4 with concentrated hydrochloric acid, and the flask is placed in a 55" C. water bath for 30 minutes. Flask and contents are cooled and diluted to volume with distilled water. This solution is titrated against 10 nil. of boiling Lane-Eynon copper sulfate-alkaline t'artrate mixture suitably diluted in a 250-ml. Erlenmeyer flask. Four drops of 1% methylene blue are added as a n indicator just before the titration is begun. The factor corresponding to the number of milliliters of sample required to complete the titration is found in a Lane-Eynon table and the results are calcula+ed by the expression : Grams of sucrose per 100 mi.
=
factor X 95 ml. of sample required
Results of duplicate analyses on a sample of peanut butter containing no added sucrose and recoveries of sucrose added to the sample are indicated in Table 11.
Salt. A 10-gram sample of well-mixed unsieved peanut meal is placed in a 100-ml. volumetric flask, which is then filled to the mark n-ith distilled water. The resulting suspension is filtered and a 10-ml. aliquote of the filtrate is pipetted into a flask containing a small amount of distilled rvater and 2 or 3 drops of in-
dicator solution (saturated potassium bichromate). The chloride ion is then titrated with 0.1 N silver nitrate by the standard Mohr procedure. The range of salt concentrations observed in commercial samples of peanut butter has been from 0.45 to 1.58%. ACKNOWLEDGMENT
The authors wish to express their appreciation to Cinderella Foods, D a m o n , Ga., under whose sponsorship this work w a ~ carried out. LITERATURE CITED
(1) Bates, F. J., and associates, "Polarimetry, Saccharimetry, and the Sugars," Natl. Bur. Standards, Circ. C440, 185-9 (1942). (2) Coffey, C. A , and Spannuth, H. T., Oil and Soap, 16, 158 (1939). (3) Eckles, H. C., Combs, W. B., and Macy, H.. "Milk and Milk Products," 3rd ed., p. 343, New York, McGraw-Hill Book Co., 1943. 4) Guthrie, J. D., Hoffpauir, C. L., Steiner, E. T., and Stansburg, 31. F., "Survey of the Chemical Composition of Cotton Fibers, Cottonseed, Peanuts, and Sweet Potatoes," Southern RegionalResearch Laboratory, pp. 39-59,1944. (5) Lane and Eynon, J . SOC.Chem. Znd.,42, 32T (1923). (6) Loeffler, H. F., ISD.ENO.CHEM., ANAL.ED.,12, 533 (1940). ( 7 ) Mohr, W., and Eysank, E., Fette u.Seijen, 50, 143 (1943). (8) Wikoff, H. L., Bussey, M., and Kaplan, A . M.,I n d . Eno. Chem., 26,291 (1934). (9) Winton. A. L., and Winton, K. B., "Structure and Composition of Foods," Vol. I, pp. 497-512, Kew York, John Wile?. & Sons, 1932. PREJEVTED before t h e Division of Agricultural and Food C h e n h t r y a t t h e 110th Xeetinp of the AMERICAX CHEXICAL SOCIETY,Chicago. Ill. Work sponsored by Cinderella Foods, Dawson, G a .
Water Analyses by Selective Specific Conductance J . W. POLSKY, W . H . & L . D . Beta, Philadelphia 24, P a . Individual ions may be quantitatively determined by simply measuring the specific conductance of the sample before and after addition of the proper reagent. No titrations are necessary. A correction i s easily made for the interference due to other ions. The method, which is both rapid and accurate, was developed primarily for water analysis, but should prove useful in other fields as well.
LTFIODS used in making chemical analyses have been, for the most part, adequate to take care of the vast majority of determinations that are necessary or desirable. Gravimetric, volumetric, colorimetric, nephelometric, photoelectric, and spectrophotonietric methods and x-ray djffraction are used in various degrees, each possessing some particular advantage. Most laboratories employ the methods that best) suit their needs with respect to accuracy, convenience, and cost. Kolt,hoff (2) suggested that chemical analysis by conductometric titrations is possible under certain special conditions, but pointed out that the accuracy of a conductometric titration always suffers from the presence of electrolytes that do not take part in the reaction. By employing a different procedure as outlined in this paper, the effects of these electrolytes are easily controlled, arid dcterminations can be made both accurately and n.ith sufficient speed . to be applicable to industrial control xvork, THEORY
The specific conductance of an aqueous solution of an electrolyte n-ill vary with the ionic concentration. If a definite quantity of a reagent is added to a sample containing the ion whose determination is desired, a relationship can be established between the quantity of that ion present and the difference in specific conductance readings before and after addition of the reagent. This relationship will provide an accurate measurement of the
ion? if correction is made for other electrolytes that may be Present in the solution. The first step is to measure the specific conductance of the sample in question, T o the sample is added a definite constant quantitj- of a reagent that will precipitate the ion to be determined, and the specific conductance is again measured. The addition of the reagent d l increase the specific conductarlce of the sample and the reagent must be of such strength as to be present in excess over the ion to be precipitated. At the. same time t h a t this increase in specific conductance is taking place, a decrease in specific conductance will occur due to precipitation. SiIlce the amount of the reagent is constant, the act,ual increase in specific conductance reading after addition of the reagent !vi11 vary inversely as the quantity of material being precipitated. This can be s h o w graphically by plotting the difference in the t x o specific conductance readings against various concentrations of the ion solut,ion. If the reagent is added to solutions having the same specific conductance, the increase in specific conductance due to the agent will be practically constant, regardless of the ions responsible for the original specific conductance of the sample. Plotting the data in Tables 111, IV, and V confirms this statement for such dilute solutions where the activity of each ion is essentially unity. The next step is to determine the effect of the reagent on the
