Sept., 1917
T H E J O G R N A L O F I , V D U S T R I A L .4ND ENGIiVEERILVG C H E M I S T R Y
THE DETERMINATION OF FAT IN CERTAIN MILK PRODUCTS' BY C K FRUCIS A K D D G. ~ I O R G A S Received M a y 19, 1917
ifany lnethods based on t h e ~ a b c o c ktest have ponrders, been proposed for use on ice cream, etc., b u t have not received t h e endorsement of t h e &sociation of Official .Igricultural Chemists, Iyhich is in charge of t h e methods recognized by t h e various courts. The official hlethod of t h e Association of Official Agricultural Chemists for t h e determination of fat in t h e products mentioned, is known as t h a t of ~ ~ ~ ~ ~ and - ~ is ~based ~ tonl t hie use ~ bof , ether or some other substance having t h e poI\Ter t o dissolve fats, objections are made t o t h e method because a special a n d someTThat expensive apparatus is necessary, and it appears t h a t lower results are obtained when working on powders and semi-liquid preparations.
number of t h e more recent methods for t h e determination of f a t IIrere tested b y applying t h e m t o malted milk and powdered milk, b u t t h e most encouraging \\'ere those in which sulfuric acid mas used. I t appears t h a t large quantities of acid were necessary to t h e carbohydrates, considerable sugar was found in some samples, and when this a n d other organic matter was carbonized t h e separation of t h e f a t from t h e black mass was poor, and in many experiments no fat ~ T a sobtained. t o the extreme affinity of the sulfuric acid f o r water and carbohydrates, t h e action of this acid on powders a n d semiliquid preparations m'as severe, a n d often excessive carbonization resulted. After this had once occurred t h e addition of more sulfuric acid appeared t o have no effect. an effort t o separate the f a t , other substances were added t o t h e milk-acid mixture. T h e presence of small quantities of nitric acid appeared to influence the reaction, and as the preliminary tests seemed to meet \\,ith success, t h e method as herein described was developed. PREPARATION OF SAMPLES
ICE CREAN-Some special precautions are necessary in order t o obtain a representative sample of ice cream. Usually a good sample may be collected in t h e factory directly from t h e freezer b y withdrawing small portions on a large spoon from different parts of t h e container a n d from t h e blades of t h e stirrer. When t h e ice cream is firmly frozen in a packer or can, a butter trier or thief should be used; t h e trier should be thrust into t h e cream f r o m t o p t o bottom at least three times a n d t h e separate portions combined into one sample. If t h e cream has become soft in t h e container i t will be necessary t o stir i t well with a spoon or paddle before sampling. If t h e ice cream is not t o be analyzed a t once, or is t o be fmwarded t o a laboratory a t a distance, i t should be a h w e d t o melt a t room temperature a n d a small quantity of bichloride of mercury added as a Preservative. If a tablet is used i t should be finely Pulverized and thoroughly mixed with t h e sample, 1
From Bull. 114, Oklahoma Agricultural Experiment Station
86 I
using one-fourth of a tablet for every quart of ice cream. The representative sample, if in good condition, should be allowed t o melt at room temperature, but if t h e f a t has separated, i t is neressary t o heat t o about 50' c. If t h e Sample is sour or contains much
curd, a f e w cc. Of ammonia ma). be added. The melted sample should be thoroughly mixed by pouring from one ~ s s e lt o another and approximately Io cc. of t h e uniform sample remored a t once with a large bore Pipette a n d 9 g. quickly weighed into a 3' per cent cream test 1. E V A P O R A T E D mLK--Mix as under ice cream and weigh 4.5 g. of t h e sample into a 3 0 per cent cream test bottle. If t h e sample is in a diluted form, use a 9 g. In the Of sweetened condensed milk. warm slightly b y immersing in warm water before mixing. M A L T E D MILK A N D DRIED NILK-WIix t h e entire thoroughly a n d quickly weigh 4.5 g. into a small beaker. Transfer t o a 3 0 per cent cream test bottle with t h e aid O f t h e least possible amount Of hot xater. If the has a loTT f a t content, Of dried skimmed a I o per cent as i n the milk test bottle, or a skimmed milk test bottle, should be used. DETERMINATION O F FAT
mLEc-Prepare a mixture of equal parts of glacial acetic and sulfuric acids, 4 t o 5 cc. Of the mixture at a and add to the time, mixing thoroughly after each addition, until a , d a r k . brown "lor Add concentrated nitric acid, I t o 2 drops at a time, and shake thoroughly after each addition until t h e action of t h e acid has subsided, O r excessive foaming may After of drops may two Or three such additions, the be increased t o j or 6 if t h e precautions t o prevent excessive foaming are obserl'ed. When a light Yellow color results, immerse t h e bottle in boiling water for 3 t o 4 minutes, or until t h e dark brown color returns. Then centrifuge for 5 minutes a t 1 2 0 0 r. p. m., fill nearly t o t h e neck with hot water, a n d centrifuge a n additional z minutes. Bring t h e fat column into t h e scale portion of t h e neck with more hot water and centrifuge for another minute, reduce t h e meniscus with glymol, a n d multiply t h e reading by z for g g. samples a n d by 4 for 4.5 g. samples. LIALTED NILK-prepare a mixture of sulfuric and nitric acids ( 2 0 cc. of &SO1 t o I CC. "03) and add t o t h e sample I t o 1.5 cc. a t a time, shaking thoroughly after each addition until a llght yellow color results (this ordinarily requires about ~j t o 20 CC. of t h e mixture). Immerse in boiling water until a dark brown. almost black, color develops. Now add a mixture of sulfuric a n d nitric acids ( I O CC. of H2SO4t o 2.j cc. of "OB), I cc. a t a time, shaking thoroughly after each addition, until a light red color has developed a n d started t o darken. Immerse again in boiling water until t h e dark brown color returns. Centrifuge for j minutes. fill nearly t o t h e base of t h e neck with hot water a n d centrifuge 2 minutes. Raise t h e fat ICE C R E A M A K D E V A P O R A T E D
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
862
column into t h e scale portion of the neck with more Reduce t h e mehot water a n d centrifuge I minute. niscus with glymol and multiply t h e reading by 4. DRIED mLK-Add concentrated sulfuric acid, j t o 6 cc. a t a time, until a dark brown, almost black, color develops. Prepare a mixture of sulfuric and nitric acids ( I O cc. of H2S04 t o 2.5 CC. of ” 0 3 ) , and add 0 . j cc. a t a time, shaking thoroughly after each addition, until a clear, light red color results (this requires ordinarily j t o 6 cc. of t h e mixture). Immerse in boiling water until t h e dark brown color returns, add more of t h e mixture until t h e light red color is produced, and again immerse in t h e boiling water until t h e dark brown color appears. Centrifuge j minutes a n d proceed as for malted milk. DISCUSSIOK O F RESCLTS
The results obtained b y this method on different products have been compared with those obtained b y t h e Roese-Gottlieb method, as indicated in t h e accompanying table. COMPARATIVE TESTS-PERCENTAGES OF FAT ROESB-GOTTLIEB AUTHORS’ METHOD METHOD
SAMPLE
Ice C r e a m . . ..................... Ice Cream. . . . . . . . . . . . . . . . . . . . . . . Unsweetened Evaporated M i l k . , . , , Sweetened Condensed Milk., . , , , , , Malted Milk . . . . . . . . . . . . . . . . . . . . . Dried Skim M i l k . , . . , . , . , , , , , , , , ,
7.7
7.58 7 .93 9.35 7.26 1.36
...
7.68 7 .90 9.35 7.14 1.29
...
7.7 8.0 10.0 7.4 1.2
..
7.7 8.0 10.0 7.4 1.2
I t appears t h a t our method gives uniformly higher results t h a n t h e Roese-Gottlieb method. I n every case a good separation of fat was obtained free from particles of carbon and bubbles. I t is important t h a t t h e nitric acid be added with care and a n excess avoided; too much nitric acid may cause t h e formation of a large quantity of gas, t h e gas bubbles continuing t o rise for some time and producing a froth which interferes with t h e reading of t h e fat column. The action of t h e acid is more rapid when added t o t h e warm mixture, a n d i t is suggested t h a t t h e bottle be immersed in warm water while t h e acid is being added. S L-M LIAR Y
A method for determining f a t , including treatment of t h e samples, in such dairy products as ice cream, evaporated milk, malted, dried skim milk and similar milk products, is described. The procedure is similar t o t h a t followed when using t h e well known Babcock test, b u t in place of sulfuric acid, mixtures of glacial acetic, sulfuric and nitric acids are prescribed. The fat is separated and read in a Babcock bottle. CHEMICALDEPARTMENT OKLAHOMA AGRICULTURAL EXPERIMENT STATION STILLWATER, OKLAHOMA
APPLICATION OF THE CRYOSCOPIC METHOD FOR DETERMINING ADDED WATER IN MILK’ B y J. T. KEISTER Received M a y 3 1 , 19 17
Later J. Winter’ reported results of similar work and found t h e freezing point t o vary from -0.j4 t o -0. j7 ’. The freezing points determined by Bordas a n d Genin2 showed for normal milk as great variation as -0.44 t o -0.56’ C. Hamburger3 found t h a t t h e freezing point of “fore” milk a n d “strippings” differed. Pins4 states t h a t evening’s milk showed a slightly higher freezing point t h a n morning’s milk, although his findings were not confirmed by Abati and Sohn5 who found no difference. \‘an Eck6 showed t h a t too low temperature of t h e freezing b a t h a n d excessive supercooling of t h e milk raised t h e freezing point. Stroecklin’ found t h a t t h e acid content and the-freezing point of t h e sour milk could not serve as a means of accurately calculating t h e freezing point of t h e fresh milk. Koeppe,s Van R a ~ u l t Reicher,Io ,~ Henderson a n d hlestonll and others have published results of freezing-point determinations of milk where results are reported quite similar t o those recorded in t h e work mentioned here. Monier-Williamsl* showed t h a t t h e presence of fat is without influence in t h e determination of t h e freezing point. He concludes further t h a t neither t h e proportion of total milk solids nor t h e non-fatty solids exerts any influence. The most striking fact found by a n examination of t h e results of t h e freezing-point determinations of milk in t h e literature is t h e slight variation in readings made by t h e different investigators. S o determination of any constituent of milk has given such closely agreeing values as t h e freezing points recorded in t h e literature by t h e different experimenters. The range in temperature is from-0. j4 t o - 0 . jj ’ C., in general. Hence, t h e value of this determination for detecting added water in milk is evident. One of t h e chief difficulties encountered in t h e -interpretation of t h e results of milk analysis is t o distinguish between rich milk containing a small amount of added water a n d naturally thin milk. The freezing-point determinations appear to serve as a n index for making this distinction in almost every case. The freezing point of milk is evidently controlled by substances in solution. Substances like fat exert no influence on t h e freezing point a n d as fat is t h e most variable constituent of milk t h e most widely varying factor is removed. On this point the majority of observers have agreed, though there are some conflicting s t a t e m e n u . I t has been shown t h a t t h e freezing point is independent of breed, age of cow, period of lactation or quantity of milk. I t is also claimed t h a t substances which are in colloidal condition, such as albuminoids, affect t h e freezing point either not a t all or t o a very slight extent. I n a n y 1 Compt. rend., 121 (1895), 696; 123 (1896). 1298; 124 (1897), 777. ZIhid., 123 (1896), 425. 3 .Won. sci., 666 (18971, 462.
Dissertation, Leipzig. 1910. Milchzeitung, 28 (1899), 177. 6 Chem. Weekblad., 12 (1914). 108. 7 Ann. fais., 4 (1911), 232. 8 Jahr. Kinderheilk., 47 (18981, 398. 9 Chem. Weekblad., 11 (1914), 206. 10 Ihid., 11 (1914), 323. 1 1 Proc. Roy, SOL.Queensland, 24 (19131, 168. 12 Report Local Govt. Board Pub. Health (Great Britain), Food Reporf 22 (1914). 4
6
Beckmann a n d Jordis2 determined t h e freezing point of different samples of normal milk a n d found t h a t t h e freezing points varied from -0.j; to- 0.56’ C. 1 Published b y permission of t h e Secretary of Agriculture; read a t t h e meeting of t h e American Chemical Society, New York City, September 25 t o 30, 1916. Forschungsherichl uher Lehensmittel, 2 (1895). 367.
Vol. 9, No. 9
