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. Robert J. McGolrin Thomas R. Wahl t W l l h R. cloasmcn Krafl, Inc., Technologv center 801 WaUcegan Rd. Glemlew. 111. 60025
The use of plastic films for food packaging on rare oeeasion causes off-flavor problems, which are a result of residual additives and solvents in improperly made fhs. If present, these residual volatiles can migrate into the food product and contribute sensory defecta because of their low flavor thresholds. Recently, a supplier's plastic packaging f h was rejected by our plant personnel because of a musty off-odor defect. The odor intensity of the film was such that a distinguishable off-tlavor would have been imparted to the fiished food product. Because the supplier was unaware of the source of the odor defect and the reasons for ita occurrence, a sample was submitted to the Basic Flavor group for analysis and identification of the off-odor.
ple using capillary gas chromatography (GC) and to locate the specific component(s) responsible for the musty odor defect. A sample of the f h was heated at 100 "C in a clcaed jar equipped with a septum for gas sampling. T w o mL of the headspace were injected onto a 50 m X 0.32 nun OV-101fused silica capillary column. Figure 1 shows the flame ionization profile from a musty f h headspace. Using simultaneous odor appraisal, only one GC peak, eluting at 19.77 min (Kovata Index 850). had a musty odor. The largest packaging volatile, eluting at 23.66 min, had
no detectable odor. Neitber peak was found in the headspace of a control fh.The large odorless peak subsequently was identified as 2-methyl-2.4pentanediol by capillary GCmS and GC/IR. Because the musty component was present in the headspace sample at relatively high concentration, GC/MS with headspace sampling was used to obtain mass spectra of the unknown. The electron impact mass spectrum yielded limited structural information. Ions at m h 31,45, and 59 suggested an oxygenated species, but no molecular
~ ~ I Y S I S~l the film sample
The odor was evidently quite volatile; ita intensity greatly diminished after the f h was unrolled and left standing on the bench for an hour at room temperature. Hence the first step in the analyticalapproachwas to obtain a volatile headspace profile of the film sam0003-2700/87/A359-1109/501.50/0 @ 1987 American Uwmical Sociely
Figure 1. Capillary GC profile of musty film headspam. ANALYTICAL CHEMISTRY. VOL. 59, NO. 18. SEPTEMBER 15, 1987
1109A
Nonderivatized Sample Chiral Separation HPLC
L Flguro 2. MeUmne chemical ionization mass specbw~of the musty component.
ion could be detected. A methane chemical ionization (CI) m888 spectrUm (Figure2) provided further S t N C turd clues. The M 1 ion at 131 indicated a molecular weight of 130 and suggested that a nitrcgen compound was unlikely. The ion at 113 corresponds to a loss of water, suggesting a secondary alcohol or cyclic ether s h c ture. Finally, an ion at 101 implied a loss of formaldehyde from the molecular ion. To further narrow the structural possibilities, we turned to GC/MS/MS. In this tandem mass spectrometry technique, ions exiting the first maan analyzer collide with an inert gas and undergo further fragmentation. The
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fragment ions are analyzed in the wond maw spectrometer. By setting the first mass analyzer to pass a single maas,and by scanning the seeond analyzer, we obtain a daughter ion spectrum displaying all the ions resulting from the fragmentationof a partieular parent m w . Conversely, by Beanning the fd analyzer while passing a fued mass through the second, we obtain a parent ion spectrum displaying all the ions that can produce a particular daughter ion upon fragmentation. Diagnatic ions from .GC/MS/MS experiments are 8 d as follows. Using electron impact ionization, daughter ions of 100 appear at 67 and 56. These are consistent with loss of a
FlRKLE-TYPE COULYNS C O W of DNBFG and DNBLeu. Pro
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111OA * ANALYTKXL CHEMISTRY. VOL. 59. NO. 18, SEplEMREFl 15. 1987
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prepared the addition product of methyl ethyl ketone and 1,2-propanediol. The corresponding cyclic ketal also failed to match the unknown. At this point we realized what should have been obvious much earlier. The largest volatile in the packaging headspace, 2methyl-2,4-pentanediol, was a potential cyclic ether precursor. Reaction of this diol with paraformaldehyde yielded 4,4,6-trimethyl-1,3-dioxane.This compound eluted at Kovats Index 850 on an OV-101 capillary column. Its electron impact mass spectrum, CI mass spectrum, and IR spectrum matched those of the unknown. Finally, the synthetic product had a distinct, musty odor that matched that of the unknown (Table I). Thus the musty component was conclusively identified as 4,4,6-trimethyl-1,3-dioxane. second oxygen. ( R e d that the 100 ion arises from a loss of CHzO from the molecular ion as indicated by the CI maea spectrum.) With methane chemical ionization, the 75 ion was highly diagnostic. The only significant parent of 75 occurs at 131, indicating that the 75 ion originate by a direct loss of a C& hydrocarbon fragment from the protonated molecular ion. Daughter ions of 75 at 45 and 31 suggested l m e s of formaldehyde and acetaldehyde, respectively. The 75 fragment has a molecular formula of C3H,02. This suggests that the unknown has two oxygen atoms in clase proximity. In summary, S M data require a mocombined M lecular formula of C,HI~OZ,which in turn requires a double bond or cyclic To obtain information on the chemical functionality of the compound, we turned to capillary GC/IR, again using headspace sampling. The vapor-phase IR spectrum of the musty component is shown in Figure 3. Aheence of a band in the 168&1800-cm-' region conclusively excluded a carbonyl functionality. Presence of a strong band in the 1 0 W 1150-cm-' region was consistent with one or more C--O bonds. A h n c e of an 0-H vibration at 35IWl600 cm-1 implied an alcohol was unlikely. Finally, absence of a distinct C=C stretch at 1630-1680 cm-I or an olefinic C-H stretch at SOOO-3100 em-' suggested that an olefm was unlikely and that a cyclic structure was necessary to satisfy the empirical formula. Together, the MS and IR data indicated a cyclic diether of molecular formula C1Hl4O2.
synthesisdmgty~~ At this point we had dramaticallynarrowed the field of possible structures, but we lacked an analytical method to make a final structure determination. We therefore turned to chemical synthesis to prepare candidate compounds for GC, MS,IR, and organoleptic eval1112A
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uation. Table I outlines four synthetic targets envisioned as likely pasihilities for the musty compound, along with the synthetic route used to prepare them, their Kovats Index, and odor. Each has the molecular weight, molecular formula, and functionality suggested by the analytical results. From a chemical point of view, it appeared likely that the musty component arose by the addition of a diol to a carbonyl compound to form either a cyclic ketal or acetal. One possible carbonyl source was acetone, which is often present as a residual solvent in packaging materials. Reaction of acetone with either lb-butanediol or 2,3butanediol produced compounds whose odora, GC retention indexes,and mass spectra failed to match the unknown (Table I). Another possible residual solvent is methyl ethyl ketone, which must be reacted with a propane diol to yield a compound with the correct molecular weinht. Accordinelv, we
M W componenlorlgh How did this material get into the f h ? The 2-methyl-2,4-pentanediolis used as a solvent coating to help ink adhere to the film when the film is printed. During the production of this lot of film, residual coating material remained behind. Apparently, during storage of the film, formaldehydefrom an unknown source reacted with the diol to produce the musty component. To prevent recurrence of this problem, the identity of the musty component and its precursors were communicated to the packaging suppliera to m i s t them in quality control. We have briefly indicated how a combination of chromatographic, spectroscopic, synthetic, and organoleptic methods were collectively used to identify the voltatile component responsible for the musty odor. This analytical approach illustrates how an arsenal of sophisticated methods may be used to solve a real-world analytical problem.
The authors, who are members of the Kraft Basic Flavor Chemistry group, are (left to right):, Thomas R. Pofahl (mass spectrometry), Robert J. McGorrin (group leader), and William R. Croasmun (amlytical spectroscopy).
ANALYTICAL CHEMISTRY, VOL. 59, NO. 18, SEPTEMBER 15. 1987
