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Diacetyl and Other Alpha- Dicarbonyl Compounds with Special December, 1939 Research Bulletin 268 Diacetyl and Other Alpha­ Dicarbonyl Compounds With Special Reference to the Fla vor of Butter By E. A. PRILL, N. E. FABRICIUS AND B. W. HAMMER AGRICULTURAL EXPERIMENT STATION IOWA STATE COLLEGE OF AGRICULTURE AND MECHANIC ARTS DAIRY INDUSTRY SECTION AMES, IOWA CONTENTS Sun1n1ary ............................................ 375 Introduction ......................................... 377 Part I. Certain properties of di~cetyl and other a-dicarbonyl compounds ... .. ... .. ... ... .. .... ... ....... 378 A. Literature review .................. .. ..... .... 378 B. Preparation and odors of a-dicarbonyl compounds .. 384 C. Analytical methods for a-dicarbonyl compounds ... , 385 Part II. Effect of diacetyl, acetylpropionyl and dipropionyl on flavor of salted butter ......................... 388 /\. Methods..................................... 388 Preparation of butter . .. 388 Examination of butter ....................... 389 B. Results ...................................... 389 Flavor of butter ....... .................... 389 Retention of diketones in butter . .. 390 C. Discussion ... .......... ............. ......... 390 Part III. Examination of butter cultures for traces of homologs accompanying diacetyl and acetylmethylcarbinol, by a specially developed method ...... ............... 392 A. Method for detection of traces of other a-dicarbonyl compounds in the presence of diacetyl by means of nickel salts of their dioximes ..... .... ....... 392 General considerations .... ............. ... 392 The method ............................... 393 Evidence for mixed nickel derivatives of dioximes 396 B. Examination of butter culture . .. 397 Examination for homologs of diacetyl . .. 397 Examination for homologs of acetylmethylcarbinol 397 Preliminary examination of milk cultures of S. paracitrovorus ............................. 398 C. Disctlssion ................................... 3% Literature cited ....................................... 400 375 SUMMARY PART I. The pertinent literature on various types of a-dicarbonyl com­ pounds was reviewed, and representative compounds were prepared and examined. Certain higher homologs of diacetyl resembled it in odor and other properties, but methylglyoxal and other a-ketoalde­ hydes and the alicyclic and aromatic diketones differed distinctly from it in odor and often in other respects also. These observa­ tions are in general agreement with the chemical literature. The various compounds showed similar behaviors in many of the re­ actions used for the determination of diacetyl. However, methyl­ glyoxal and glyoxal could be distinguished from a-diketones by means of the a-methylindole test. Certain hon1Dlogs of diacetyl, as well as diacetyl, could be determined colorimetrically as diammino­ ferrous derivatives of their dioximes. PART II. When acetylpropionyl or dipropionyl was worked into salted butter, the effect on the flavor definitely suggested the effect of diacetyl but was less than with an equivalent amount of diacetyl and was less with dipropionyl than with acetylpropionyl. In butter, acetylpropionyl or dipropionyl contents coplparable to the diacetyl contents developed through the use of butter cultures were well­ retained over a considerable period at various temperatures. PART III. A method, based on the relative solubilities in benzene and the relative stabilities toward dimethylglyoxime of the various sub­ stituted nickel glyoximates, was developed for detecting homologs of diacetyl (and such a-ketols as yield homologs of diacetyl on oxi­ dation with ferric chloride) in the presence of diacetyl (and acetyl­ methylcarbinol). By means of it, 0.3 mg. (and with certain addi­ tional operations, even a smaller amount) of a higher homolog could be detected in the presence of 100 mg. of diacetyl. Exact quantitative determination of the accompanying homolog was not possible because of complicating factors, such as the formation of mixed nickel derivatives, evidence for which is presented. Distillates from ordinary butter cultures gave no evidence of the presence of higher homologs of diacetyl; also, the specific test with a-methylindole showed no methylglyoxal. Distillates from butter culture plus ferric chloride appeared to contain a very 376 small amount of some accompanying a-dicarbonyl compound, but the evidence strongly suggests that this was an artifact. Higher homologs of acetylmethylcarbinol definitely were absent. Methylglyoxal was not found in ordinary butter cultures, but the data suggest the possibility of its occurrence in other types of cultures. Although probably of little significance from the stand­ point of flavor of butter, its presence would make the apparent analytical values for diacetyl higher than the true values. The failure to find homologs of diacetyl in butter cultures em­ phasizes the importance of the fermentation of citric acid, the mother substance of diacetyl, in the development of flavor in butter cultures and in butter made with cultures. Diacetyl and Other Alpha.-Dicarbonyl Compounds With Special Reference to the Flavor of Butter! By E. A. PRILL2, N. E. FADRIClUS AND B. W. HAMMER Diacetyl is an important flavor contributor of butter and various other foods. Similarity in chemical structure suggests that a number of other a-diketones would be similar in certain properties, including odor, to diacetyl, the simplest member of the seri es. Diacetyl and various homologs were synthesized long ago their reactions studied and certain similar chemical behaviors noted. However, the descriptions of the odors originally given would hardly suggest that diacetyl is involved in the flavor of certain foods. The work of van Niel, Kluyver and Derx (81) showed the importance of diacetyl as a flavor contributor of butter. Epstein and Harris (22-25) patented the use of certain a-diketones as flavoring materials for various foods. Taufel and Thaler (74) incidentally mentioned that in practice acetylpropionyl was some­ times used as a substitute for diacetyl. The data reported herein dealvvith diacetyl and other a-dicar­ bonyl compounds with special reference to the flavor of butter. The material is divided into three parts as follows: Part I. Certain properties of diacetyl and other a-dicarbonyl compounds. Part II. Effect of diacetyl, acetylpropionyl and dipropionyl on flavor of salted butter. Part III. Examination of butter cultures for traces of homologs accompanying diacetyl and acetylmethylcarbinol, by a specially developed method. 1 Project No. 127 of the Iowa Agricultural Experiment Station. :? The studies were fin anced in part through a grant from Chas. Pfizer and Co., I. l1e. , which provided particularly for the services of Dr. Prill. 378 Part 1. Certain Properties of Diacetyl and Other a~Dicarbonyl Compounds By E. A. PRILL AND B. W. HAMMER A. LITERATURE REVIEW The general chemical structure of a-diketones is shown by formula I in which there are two adjacent carbonyl groups and in which Rand R' may represent the same or different univalent radicals, such as -CH3, -C2H5. In the formula for diacetyl (II) both Rand R' are methyl groups. This compound can also be called dimethylglyoxal and, similarly, other a-diketones can be designated both as combinations of two acyl groups or as disubsti­ tuted glyoxals. In the formula for cyclic a-diketones (formula VI), a single divalent group may be considered as replacing l~ and R'. Glyoxal (formula III) and methylglyoxal (formula IV) , al­ though lower homologs of diacetyl, are not true diketones but a dialdehyde and an a-ketoaldehyde, respectively; however, such com­ pounds are also pertinent to this discussion. o 0 o 0 o 0 II II I II II II II I2-C-C-12 CH3'C-C- CH3 H-C-C-H DIACETYL GLYOXAL II ill o 0 o OH II II II I CHS-C-C-H CH-C-C-H 3 I OH METHYLGLYOXAL METHYLGtLYOXAL HYD2.ATE TIl :sz: Hz H /C ........ /C",:::- HeC C=O HeC C-OH I I I I HeC--C=O HeC--C=O CYCLOPENTANE- CYCLOPENTENE -Z­ 1,2-DIONE ONE-\-OL-2, :ill: :sz:rr 379 TABLE 1. PROPERTIES OF SOME a-DICARBONYL COMPOUNDSl. Formula Closs R-CO-CO-R' Boiling!! Melting of Name point point t:o mpounds R R' ·C. ·C. Diacetyl (13iacetyl) CH3 CH. 88· -2.4·. Aliphatic Acetylpropionyl CH. C,H. 108· a-di­ Acetyl,"-butyryl CH. ,,·C.H7 128· ketones Acetyl-isobutyryl CH. isoC.H7 116· Dipropionyl C,H. CoHo 130· ·10· (Diacetyl Acetyl·isovaleryl CH. isoC.Ho 138· and its Propionyl-II-butyryl C,H. 1l-CaH7 146· higher _ Acetyl-II-caproyl CH. 1l-C5Hn 163· homologs) Di·II-butyryl ,,·CaH7 Jl-CaH7 168· Di-isobutyryl isoC.H7 isoC.H7 145· Glyoxal H M3 51· MIS· Methylglyoxal CH. H M 72· Aliphatic (Pyruvaldehyde) 103-110·' a-keto­ Ethylglyoxal C,I-Ir. H aldehydes isoPropylglyoxal iSOC3H7 H 96· isoButylglyoxal isoC.Ho H 46· / 12 mm sec.·Butylglyoxal sec.-C4H9 H Aromatic Benzil I C.Ho C.Ho 348· 95· {J·di­ Acetylbenzoyl I CH3 C.H5 I 218· I ketones Methy Ibenzy 19lyoxal CH. CoHoCI-I2 K5 104· / lOmm K 17· E 0134· / lOmm I E 70· I I Cyc!opentane-l, -(CH')3- 105· /20 mm. 2-dione f 3·Methyicyc!open­ -CH-(CH2),- 210· 106· tane-l.2·dione I Alicyclic CH. a·di­ Cyclohexane-l, ·(CH,).- 193.195. 38·40° ketones 2-dione [ Diosphenol ·CH-(CH2kCH- 109· / 10 mm. 83· (Buchu·camphor) I I 37° CH. isoC.H7 Camphor-quinone (50.600 SUbl.! 198° 1 The data are uSl1al1y from the origin al papers to which reference is made in th~ discussion; otherwise. they are from Beilsteill's Handbuch cler Organischen Chemie, 4th edition with 1st Erganzungswerk. which cover the literature up to 1919 . Unless otherwise indicated, the boiling points are for atmospheric pressure. M-monomeric form. , Also
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