The Chemistrv of Menhaden Oil J
Component Fatty Acids W.H. BALDWIN AND W.B. L.4NH.431, JR. Division of Fishery Industries, United States Department of t h e Interior, College Park, Ald.
0
Saponification equivalents were determined by the method of Chargoff ( 3 ) . The Hanus method was used for the determination of iodine numbers. Seutral equivalents were determined in warm alcohol by direct titration with alkali to a phenolphthalein end point.
ILS of domestic origin are becoming more important by
reason of the increasing inability to import foreign oils. Marine oils in particular are available in large quantities and should be given serious consideration as replacements for foreign materials. Because much is still unknown of the chemistry of marine oils, the present investigation has been undertaken. hIenhaden oil was chosen for the start of this research, since it is the most abundant marine oil produced on the Atlantic coast. Table I records some of the published results.
Experimental Procedure Six hundred grams of commercial oil produced by centrifugation were saponified with alcoholic potassium hydroxide and the unsaponifiable matter was removed with ether. The residual soaps were acidified. The fatty acids were taken up in ether, mashed xith distilled water, and dried with anhydrous sodium sulfate, and the ether was removed. The recovered acids weighed 552 grams, a yield of 92 per cent of the original oil. Double precipitation of the lead soaps in alcohol and liberation by the usual methods yielded 27.9 per cent saturated and 72.1 per cent unsaturated acids. The methyl esters of the saturated acids were prepared by dissolving in dry methanol and saturating with dry hydrogen chloride gas. After standing at room temperature for 12 hours they were treated in the usual manner. The methyl esters so obtained had a saponification equivalent of 267.4 and an iodine number of 4.0. The esters were fractionated and the data are tabulated in Table 11.
Twitchell (8)in 1917 investigated the composition of menhaden oil by the lowering of the melting point of the mixtures of fatty acids which he isolated. Saturated and unsaturated acids were studied separately, the latter after hydrogenation. His results revealed no unsaturated acids with fewer than 18 carbon atoms. Brown and Beal ( 2 ) fractionated the methyl esters, finding acids of 14, 16, 18, 20, and 22 carbon atoms. Armstrong and Allan ( 1 ) reported, in addition to those previously found, small amounts of saturated acids with 20 and 22 carbon atoms. Richardson, Knuth and Milli an ( 5 ) have published ester distillation data and more recently btingley ( 7 ) has reported the component fatty acids of menhaden oil (Table I). TABLE I. Carbon Atoms
COJlPONEST FATTY
ACIDS O F
Fraction 1 was saponified with alcoholic potassium hydroxide and acidified and the precipitate was crystallized from 95 per cent alcohol. The observed melting point was 63" C., while Francis and Piper (4) reported 54.4" C. for synthetic myristic acid. From fraction 3 a n acid was separated and crystallized from acetone. The observed melting point was 63" C.; reported for palmitic acid, 62.9" C. (4). The acid isolated from fraction 6 was crystallized from acetone and recrystallized from methanol and had a melting point' of 57.5-58.5' C. The observed neutral equivalent was 264.8; that calculated for palmitic acid is 256.3 and for stearic acid is 284.3. The freezing point of this mixture as calculated from cooling curves was found to be 55.8" C. Shriner, Fulton, and Burks (6) have studied the cooling curves of many mixtures of palmitic and st'earic acids and of the two mixtures reported freezing a t 55.8" C.; that consisting of 0.85 mole of palmitic acid and 0.15 mole of stearic acid has a calculated neutral equivalent of 260.5 which comes closer to the observed.
~ ~ E S H A D EON IL
Twitchell ( 8 )
Armstrong and Allan (I)
Stingley (7)
This Research
%
%
%
%
7 0 16 0 1 0
8.3 14.9 4.7
Saturated Acids 14 16 18 20 22
9.2 22.7 1.8
.. ..
5.9 16.3 0.6 0 6 0.8
.. ..
.. ..
Unsaturated Acids
Commercial menhaden oil from the Atlantic coast was examined by the ester fractionation procedure. Among the saturated acids (Table I) v-ere found myristic, 8.3 per cent; palmitic, 14.9 per cent; and stearic, 4.7 per cent. Myristic and palmitic acids were isolated from the corresponding esters. Attempts to isolate an acid of higher molecular weight than palmitic have ended with mixtures. Fraction 6 yielded a mixture n-ith a melting point of 57.5-58.5" C. and a neutral equivalent of 264.8 which lies between that calculated for palmitic and stearic acids. The neutral equivalent and the freezing point of 65.8' C., according to the data of Shriner, Fulton, and Burks (e),indicate a mixture of 0.86 mole of palmitic acid and 0.15 mole of stearic acid. This mixture has a neutral equivalent calculated to be 260.4. The fractional distillation of the methyl esters of the unsaturated acids and the saponification equivalents of the fractions were used to calculate the composition. As a check upon this method, the acid from fraction 4 was hydrogenated catalytically to palmitic acid.
TABLE 11. FRACTIOXATIOX O F METHYL ESTERS OF FATTY ACIDS Fraction 1 2 3
.1 6 Residue6
\!-eight Gram 11.1 9.9 7.3 18.7 12.5 4.4 5.4
Boiling Range ( 5 Mm.)
SATURATED
Saponification Equivalent
c. 147-154 154-160 160-165 165-169 161-163" 170-178
...
244.1 254.5 258.2 279.2 277.1 284.9
...
Difficulty was experienced in maintaining pressure a t 5 mm. pump and other improvements helped in later experiments. b D a r k brown i n color. a
A new
The methyl esters of the unsaturated acids prepared by the methanolic hydrochloric acid method had a saponification equivalent of 293.7 and a n iodine number of 187.4. The data for the fractions obtained from the electrically heated packed column are summarized in Table 111.
Analytical Methods The methyl esters were fractionated through an electrically heated column packed with small helices. On top of the column was fitted a head designed for total reflux with partial take-off. 615
616
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 13, No. 9
TABLE 111. FRACITONATION OF METHYL ESTERS OF UNSATURATED was removed. Hydrogenation in acetic acid with palladiumFATTY ACIDS barium sulfate catalyst produced an acid with a melting point Boiling Range Saponification Iodine of 61” C.; that recorded for palmitic acid is 62.9” C. (4). Fraction Weight (5 Mm.) Equivalent NO. The neutral equivalent found was 258.3, while that calcuGrams c. 1 lated for palmitic acid is 256.3. 2.2 120-123 248.5 24.8 2
1.8 3.6 10.7 5 3.2 6 6.9 7 6.6 8 7.2 9 4.5 10 6.2 11 3.7 12 5.5 13 4.4 Residue” 9.3 Dark brown in color.
3 4
123-135 135-140 140-147 147-155 155-160 160-165 165-170 170-175 175-180 180-185 185-190 190-195
260.0 254.7 272.0 280.0 291.0 292.0 298.0 308.0 310.0 325.0 311.5 352.0
.....
...
83.6 103.7 123.1 125.4 127.3 153.1 166.5 183.2 212.2 226.2 208.1 232.7
...
To confirm the composition as calculated from the sauonification equivalents, the Saponification product from fraction 4 was acidified, extracted with ether, and dried, and the ether
Literature Cited (1) Armstrong, E. F., and Allan, J., J . SOC.Chem. I d . , 43, 207T (1924). (2) Brown, J. B., and Bed, G. D., J . Am. Chem. SOC., 45, 1289 (1923). (3) Chargoff, E., 2. physiot. Chem., 199,221 (1931). (4) Francis, F., and Piper, S. H., J . Am. Chem. SOC.,61,577 (1939). IF\ Richardson, A. S., Knuth, C. A., and Milligan, C. H., IND. ENG. CHEM.,17,80 (1925). Shriner, R. L., Fulton, J. M., and Burks, D. J., J . Am. Chem. SOC., 55,1494 (1933). IND.ENG.CHEM.,32, 1217 (1940). (7) Stingley, D. 18) . , Twitchell, E., Ibid., 9,581 (1917).
v.,
PRESENTED before t h e Division of Agricultural and Food Chemistry a t t h e i o i s t Meeting of t h e American Chemical Society,
st. Louis,
MO.
Reducing Power of Starches and Dextrins F. F. FARLEY
AND
R. &I. HIXON, Iowa Agricultural Experiment Station, Ames, Iowa
A rapid ferricyanide method for determining the reducing power of starches and dextrins is presented in which the reduced iron is measured directly by a ceric sulfate titration. For starches hydrolyzed by hot or cold acid or oxidized by alkaline hypochlorite, and for raw starches and dextrins, the reducing power values by this method parallel those determined by the longer procedure of Richardson, Higginbotham, and Farrow. Many other modified starches such as the “chlorinated” and “thin-boiling” types have been measured.
T
H E copper number has been used extensively for reporting the reducing power of cellulosic materials and recently by Richardson, Higginbotham, and Farrow (7) for starch This paper describes a much simpler method for determining the reducing power or copper number of starches and dextrins, which shortens the time required to less than 25 minutes. While measuring the reducing power of a series of starches by the Gore and Steele (2) modification of the Hagedorn and Jensen (3) method, the authors noticed that the apparent maltose equivalent of the more soluble products when converted to milligrams of copper gave values equal to the copper numbers determined by the Richardson, Higginbotham, and Farrow method. For raw starch and very slightly solubilized starch, high values were obtained by the Gore and Steele method. These high values were attributed to the visible entrapment in the starch of iodine which was very difficultly released for measurement in the thiosulfate titration. I n the determination of the maltose equivalent of starchmaltose mixtures Martin and Newton (6) avoided the diffi-
culty due to iodine entrapment by using Hassid’s (4) ceric sulfate titration. It seemed probable that the same ceric sulfate titration could be used to advantage here to measure the reducing power: not of a starch-maltose mixture, but of starch or dextrin alone. This proved to be true. Consideration of the above statements reveals that any reducing value obtained for maltose in the presence of dextrins and modified starches is only an apparent maltose value. TABLE I. REDUCISC POWER OF STARCHES ASD DEXTRIXS R c u , JIg./Gram
Sample Pearl starch (control) Other commercial cornstarches Waxy maize starch Thin-boiling starch, 40-fluidity Thin-boiling starch, 90-fluidity Chlorinated starch, 2.5% chlorine Chlorinated starch, 5 % chlorine Electrolytically oxidized starch Alkali dextrin, A Alkali dextrin, B Alkali dextrin, C Acid dextrin, A Acid dextrin, B Acid dextrin, C Gore ( 1 ) starch 5-hour conversion Gore (1) starch: 42-hour conversion Gore (1) starch, 96-hour conversion LMaltose Glucose
6 I
8-7.9 . 7 , 9 . 4 , 10.1, 11.2. 11.6
12.0 25.5 39.0 19.6 61.6 120.0 1900 2800
The potentiometric measurement used by Martin and Newton was eliminated because the color change of the solution from green to yellow just before the large voltage change was a satisfactory indication of the end point. However, starch products with very little reducing power produced only a slight green color and made accurate determination of the end point difficult. The addition of a measured amount of glucose solution to each starch sample obviated this dificulty. A correction for the reducing power of this added glucose was made by a blank determination. When, in the hydrolysis of starch by acid, the RcU values (milligrams of copper per gram of starch) were plotted against the time, there resulted a straight line for RcU values up to
