Rapid Fat Determination in Plant Control of Cacao Products Centrifuge Method FRANCIS X. KOBE, Rockwood & Co., 88 Washington Ave., Brooklyn 5 , .V. Y .
A method for the centrifugal fat extraction of cacao products is described. Data indicate the relative rate of extraction and comparison is made with the official method of the .&ssociation of Official .4gricultural Chemists.
F
( 8 ) , Hasse and Bake (IS),Leithe (25'), Leithe and IIeinz ( 2 3 ) . Bielefeldt ( 4 ) , Stanley ( 3 2 ) , and Bruchner (6). The centrifugal method of fat extraction as outlined by Hughes (18) consisted of successively extracting the fat-bearing sui)stance with ether and centrifuging the ether layer after each extraction. In the corresponding centrifugal extractive procedure which this paper describes, petroleum ether (benzine) is used, principally herause i t is inexpensive and requires no special preparation other than distillation below 60" C. It will not dissolve theobromine, the cacao alkaloid, to the same extmt. as does ethyl ether, nor is it affected b y trares of moisture which would dissolve sugar aiid other nonfatty material that may be present. The progressive extraction principles upon which this determination is based may be demonstrated in a simple manner.
ATS and oils of vegetable origin usually occur naturally in a partially free state. They may lie at or near the surface of
the plant product, in capillary spaces formed by the ru;)ture of cellular structure, or encased in unrupt,ured cells. Their removal may be effected quantitatively by solution in various solvents. Studies of analytical procedures based on the extraction technique are complicated, however, by several factors. These include the fineness or degree of grind, the quantity and composition of the extractable material, choice of solvent, teniperature, and moisture content. Perhaps the most commonly employed method for total fat determination b y the extraction process is that described by Lewwhich consists essent,ially of extracting a prepared kowitsch (M), sample with a suitable solvent in a Soxhlet apparatus for several hours. Through the years, many modifications of this method have been introduced, some for the purpose of increasing its accuracy, others with a view toward increasing its practicality. Hanus (11),Kreutz (21), and Heller (14) were among the first to suggest improvements. Devices such as Johnson (%), Undcrwriter's ( d o ) , and Butt ( 8 1 ) extractors have found wide application. Lepper and Raterman ( 2 4 ) devised the present official method of the Association of Official Agricultural Chemists, involving a series of extractions in a Knorr tube. The dairy industry has for many years used the Roese-Crottlieb method, performing the estraction in a Rohrig tube or llojonnier flask ( 2 ) . Hillig ( 1 7 ) suggested the use of acid hydrolysis in the manner of Hertwig (15)and Fellenberg (9). Offut ( 2 8 )and Jansen (19) also adopted this technique. Other variations include the methods of Bailey and Walker (S), Macara and Hinton ( Z 6 ) , Francis (IO), Sabine (SO), Stone (SS), and hlicaelli and Desnudle (27). Herty (16) and Harris (12) deviated from the usual procedures by basing their analyses on the specific gravity of the fat-solvent extracts. Richter (29) developed a method based on the refractive index of the fat estract. This avenue of approach has been followed by DemikovskiX(7), Ermakov Wesson ( S i ) , Coleman and Fellows (6),
If we assume that a 2-gram sainple of chocolate containing 50% cocoa butter is progressively washed with 25-gram portions of petroleum ether, we have approximated the conditions for a fat determination. The solid matter (cocoa solids-not-fat, carbohydrates, etc.) is wet by the same solution of fat and approximatel>2 grams or less of such solution are always left in contact with the solids remaining in the centrifuge tube. These 2 grams of solution carry a certain amount of the original fat which will be removed by subsequent extractions. The effect of three such extractions is shown in Table I. The accurate estimation of fat in any shredded or ground food product depends on the distance through which the solvent must pass t o reach the fat and the distance through which it must return. Diffusion or dialysis and ease of solubility are of the utmost importance. Time is also a critical factor. One very important assumption is that a complete state of equilibrium exists between all of the solvent and all of the fat present in the system at the time of centrifugal separation. This is usually the case with most cocoas and chocolates when 3 t o 5 minutes are allowed t o elapse between the time the dry matter is wetted by the solvent and thc time the solids are separated in the centrifuge. The time for equilibrium is only a matter of seconds in extremely finely divided matter. Thus it is an advantage t o work with the most finelyground material possible. CESTRIFUGE METHOD FOR RAPlD FAT DETERMIN 4TION
Progressive Centrifugal Extraction of Cacao"
Tahle I.
Original sample 2 grams
1 .0 gram of cocoa matter 1 .0 grain of cocoa butter
Separation
Residiie, Grams Residual Cocoa petroleum butter ether
Cocoa matter
Cumulative
Extract, Grams
- Gram Fat Extracted % Fat Extracted
0.9240 24.00 1,9240 1,0000 0,0760 0,0700 1,9940 25.00 1,0000 0,0060 0,0050 1,9990 23.00 3 1,0000 0.0010 (Fat in solvent-free residue, 0.10%) 25.00 grams of petroleum ether used in each separation.
1
2
6%
46.20 3.50
16.20
0 25
49.93
19.70
700
Apparatus. Heavy-\\ alled borosilicatc glass centrifuge tubes, ungraduated, with lip, roundbottomed, annealed. Length, 120 * 2 mm., outside diameter, 28 * 1 mm. Capacity, 50 ml. Petroleum ether, distilled tielow 60" C. Aluminum beaker, 250 ml. International centrifuge, size 2, 0.75 lip., 110 volts, 0 amperes. Preparation of Sample. In determining fat by this method, the need for a well-prepared, representative sample cannot be overemphasized, particularly in the analysis of cacao beans, cacao
V O L U M E 2 2 , N O . 5, M A Y 1 9 5 0 Table 11.
H o i r t i i i e Plant Control of Cacao Products
\\-eight of Arerase Sainple, Satiiide yo Fat Grains I-passage t,hrough a Wiley mill or a niilm>r)ulverizcr. Press r&e samples arr obtained by scraping ttic. ritkra :ind sieving thc scr:ipings t.hrough a scrren of approsimntely 60mesh. Procedure. Place a thoroughly clean 250-mt. aluniinuni beaker in a drying oven at 100" C. for approximately 5 minutes, transfer t o a desiccator, cool, and weigh. Weigh out approximately 2 grams of the material t o he anaIyzcd into a previously weighed 50-nil. lipped centrifuge tube, add 30 ml. of petroleum ether t o the material in the tube, and stir with a n aluminum rod. If the sample is sucet chocolate or c-hocolate liquor (baking chocolate), it should be ir. a fluid condition and free from lumps. After stirring, raise the rod slowly and rinse off with :t sni:tll quantity of petroleum ether from :t \r.:tsh bottle. Provide the tuhr wit.h a cork stopper and balanre in :I centrifuge cup. Crntrifuge until the supernatant liquid is c.lrar. Ilernove the tuhc from the rentrifuge and pour the estract carefully into ttie weighrd aluiniiiuni hraker. IV'ash the lip of the tube arid thc stopper n i t h :iddition:iI prtroleum ether, adding the \v:tshings to the estract. \\-liile the solvent containing the est r w t e d fat is beinK cv:ipor:itcd o w r :I hot plate, add 30 nil. or niore of fresh petroleuni c>ttirrto the crt r:tction tube and stir carefully i n order to disperse the c~wtr,ifugtd solids. Complete the esti~actionusing the sanie pree:tutions its in the first estraction. Three estractions are usually sufficient, but for samples such as chocolate liquors, ice crc::m roatirigs, and ice creani flakes, cont:tining co~isidernblef:it, four rrtrnctions are reconiniended. Allo~vthe solvent i n the t m k e r t o rvaporate almost to dryness :ind then p:w a cwrciit of air over i t , using n rubber bulb aspirator. After tlic odor of solvciit h:is c~oinplctrlydisappeared, cool tlrr h i k e r i n a desirc:itor and w i g h . Kcport the gain in weight :LS totnl f a t ; it inclutlcs n o t nnly ttie snporiifi:tble glyceryl esters t)ut :iIso a11 other crtrac.t:it)lc ni:itter.
R . P. Jl ." . F'iitnl &I? 11in. J.ight 2 .\rrr.t 27.42 n , i i
.\v.
2 8 . 1.5 28 I 4 28.15 98 23
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