Thermally Generated Volatile Compounds in Packaging Materials

Chapter 37

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Thermally Generated Volatile Compounds in Packaging Materials H. Kim and S. G. Gilbert Department of Food Science, New Jersey Agricultural Experiment Station, Cook College, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903

The increasing application of complex natural and/or synthetic polymers to food packaging has required definitive information on the characteristics of the finished products. High temperature encountered during the manufacturing process may induce thermal decomposition products which can migrate into the packaged product and cause undesirable flavor. A general methodology for testing polymer odor and odor contributors is discussed in this paper with examples representing the odor of PVC film, ionomer laminate and gelatin. The precursors and the mechanisms of the major volatile components of each packaging material are presented, including the effects of processing conditions on the odor quality of polymers.

Food p a c k a g i n g h a s been d o m i n a t e d i n t h e l a s t f e w d e c a d e s b y i n n o v a t i o n s i np l a s t i c packages. These i n c l u d e t h e developments o f d i f f e r e n t types o f polymers, copolymers, t h e laminates and, e s p e c i a l l y , packaging m a t e r i a l s s u i t a b l e f o r microwave h e a t i n g . C o n s i d e r a b l e improvement i n d e s i g n e f f e c t i v e n e s s h a s been produced w i t h t h e i n t r o d u c t i o n o f new m a t e r i a l s a n d p r o c e s s e s , m a k i n g t h i s a r e a o n e o f t h e most a c t i v e i n f o o d p r o d u c t d e v e l o p m e n t . T h i s growth h a s been p a r a l l e l e d by an i n c r e a s i n g a t t e n t i o n t o t h e i n t e r a c t i o n between p l a s t i c packaging m a t e r i a l s and f o o d s . One o f t h e p r a c t i c a l c o n c e r n s i n polymeric package i s t h e p r e s e n c e o f compounds i n t o x i c o l o g i c a l l y i n s i g n i f i c a n t a m o u n t s , b u t a t l e v e l s a f f e c t i n g aroma a n d / o r t a s t e o f t h e p a c k a g e d f o o d (1-2). There h a s been an e x t e n s i v e h i s t o r y o f odor and t a s t e p r o b l e m s e x p e r i e n c e d i n t h e d e v e l o p m e n t o f new p a c k a g e s ( 3 ^ 7 ) . A package can d i r e c t l y d i s r u p t t h e f l a v o r balance o f a food i n three ways; ( a ) s u b t r a c t i o n , (b) r e a c t i o n , and ( c ) a d d i t i o n . S u b t r a c t i o n o c c u r s when c o m p o n e n t s c o n t r i b u t i n g t o t h e d e s i r e d f l a v o r o f t h e p r o d u c t a r e a b s o r b e d b y t h e p a c k a g e . R e a c t i o n t a k e s p l a c e when package components c h e m i c a l l y i n t e r a c t with t h e food product t o 0097-6156/89/0409-0396S06.00/0 ο 1989 American Chemical Society Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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produce f l a v o r a r t i f a c t s . A d d i t i o n occurs when the package r e l e a s e s compounds which a l t e r the f l a v o r balance o f the food. A d d i t i o n i s by f a r the most common ( 3 ) . The manufacture o f packaging m a t e r i a l s i s o f t e n conducted under c o n d i t i o n s o f high temperatures. A burnt p o l y e t h y l e n e odor has been experienced i n the p a p e r / f o i l / p o l y e t h y l e n e laminate f i e l d . These c o n d i t i o n s can e a s i l y induce thermal degradation with the formation o f v o l a t i l e compounds i n packaging m a t e r i a l s (8-13). T h i s a r t i c l e summarizes v o l a t i l e compounds d e r i v e d d u r i n g manufacturing packaging m a t e r i a l s as well as the p r e c u r s o r s o f the major v o l a t i l e components. Methodology Sensory E v a l u a t i o n . The odor q u a l i t y o f t e s t p l a s t i c m a t e r i a l s such as r e s i n s , f i l m s or laminates can be d i r e c t l y estimated by p a n e l i s t s using r a t i n g s c a l e e v a l u a t i o n o f i n t e n s i t y or f o r c e d c h o i c e methods such as t r i a n g l e t e s t as the t e s t forms(14-15). The extent o f m i g r a t i o n o f r e s i d u a l v o l a t i l e compounds i n packaging m a t e r i a l s to the c o n t a c t i n g phase can be evaluated a f t e r exposing water or actual food to packaging m a t e r i a l s at a c c e l e r a t e d c o n d i t i o n s or at ambient temperature (3,8). Food can be exposed to packaging m a t e r i a l s by d i r e c t c o n t a c t or by vapor phase t r a n s f e r to determine i f the adverse o d o r / f l a v o r problem i s caused by any o f the more v o l a t i l e package c o n s t i t u e n t s or caused by c o n s t i t u e n t s t h a t can only be t r a n s f e r e d by d i r e c t c o n t a c t s o l v a t i o n . Glass c o n t a i n e r s are g e n e r a l l y used as c o n t r o l packages. Sensory e v a l u a t i o n can be p a r a l l e l e d with o b j e c t i v e instrumental analyses and the c o r r e l a t i o n between the sensory and instrumental r e s u l t s can be obtained (16). Instrumental A n a l v s i s . D i r e c t headspace a n a l y s i s has been g e n e r a l l y used to analyze the r e s i d u a l s o l v e n t s i n packaging m a t e r i a l s (1,4,5,7,17-19). Vapor samples can be prepared by drawing the headspace o f s e a l e d packages through tubes c o n t a i n i n g sorbents such as Tenax GC. Both f i l l e d and empty packages can be used i n these analyses. A g e n t l e vacuum was a p p l i e d to one end o f the t r a p using an a s p i r a t o r with a needle attached at the other end o f the t r a p to puncture the bag (20χ. The c o n c e n t r a t i o n o f v o l a t i l e s i n the headspace i s necessary to o b t a i n a more complete p i c t u r e o f the v o l a t i l e composition as well as to o b t a i n a p o s i t i v e i d e n t i f i c a t i o n o f v o l a t i l e compounds. Dynamic headspace/gas chromatography (DH/GC) has gained p o p u l a r i t y as an e f f e c t i v e and s e n s i t i v e technique f o r the a n a l y s i s of v o l a t i l e compounds (21). Residual v o l a t i l e compounds i n the p l a s t i c materials were i n v e s t i g a t e d u s i n g similar procedures (8,11,12,14,22). K i n e t i c s t u d i e s on the e f f e c t o f oxygen c o n c e n t r a t i o n , temperature and a d d i t i v e s , such as a n t i o x i d a n t s , on the g e n e r a t i o n o f v o l a t i l e s under simulated p r o c e s s i n g c o n d i t i o n s were conducted with r e s i n s (Paik, S. W. and G i l b e r t , S. G., Rutgers U n i v e r s i t y , unpublished d a t a ) . A t o t a l o f 15 mg o f r e s i n s were ground to about 40 mesh by a F r e e z e r / m i l l (Spex I n d u s t r i e s

Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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I n c . , M e t u c h e n , NJ) a t l i q u i d n i t r o g e n t e m p e r a t u r e , m i x e d w i t h 3 g o f DMCS t r e a t e d 6 0 / 8 0 mesh g l a s s b e a d s ( A l l t e c h A s s o c . , D e e r f i e l d , I L ) a n d p a c k e d i n s i d e a 1/4''ID χ 6 " L s t a i n l e s s s t e e l t u b e . T h e s a m p l e - c o n t a i n i n g t u b e w a s p l a c e d i n s i d e a n o v e n and c o n n e c t e d t o h e a t e d o x y g e n and n i t r o g e n and t h e r e a c t i o n p r o c e e d e d u n d e r a g a s f l o w r a t e o f 15 mL/min a t a n i n c r e a s e d t e m p e r a t u r e f o r one h o u r . Oxygen c o n c e n t r a t i o n i n t h e c a r r i e r gas was v a r i e d b y d i l u t i n g t h e o x y g e n w i t h n i t r o g e n g a s and m o n i t o r e d b y i n j e c t i n g 0.5 mL i n t o a gas chromatograph equipped w i t h a CTRI-8700 column (Alltech A s s o c . , D e e r f i e l d , I L ) and a t h e r m a l c o n d u c t i v i t y d e t e c t o r ( T C D ) . D e g r a d a t i o n p r o d u c t s were c o l l e c t e d d u r i n g the r e a c t i o n a t from 160 t o 2 2 0 ° C d i r e c t l y i n t h e a n a l y t i c a l c o l u m n k e p t a t a subambient t e m p e r a t u r e u s i n g d r y i c e . T h e r e a c t i o n was t e r m i n a t e d by s w i t c h i n g t o h e l i u m g a s a t room t e m p e r a t u r e and t u r n i n g o f f t h e r e a c t i o n oven. A f t e r removing t h e d r y i c e from the a n a l y t i c a l o v e n , t h e c o l l e c t e d compounds w e r e a n a l y z e d f o r t o t a l p e a k a r e a for kinetic studies. The r a t e o f r e a c t i o n (dA/dT : area/min) a t d i f f e r e n t oxygen c o n c e n t r a t i o n s (%) i n t h e c a r r i e r g a s p r o v i d e s t h e e f f e c t o f oxygen c o n c e n t r a t i o n on t h e g e n e r a t i o n o f v o l a t i l e compounds. L i k e w i s e , t h e e f f e c t o f t e m p e r a t u r e was o b t a i n e d f r o m t h e r a t e o f reaction against the r e a c t i o n temperature. V o l a t i l e Compounds I d e n t i f i e d i n S p e c i f i c P a c k a g i n g M a t e r i a l s Polyethylene Terephthalate (PET). The m a j o r s i g n i f i c a n t v o l a t i l e compound i n t h e p o l y e t h y l e n e t e r e p h t h a l a t e ( P E T ) w a s c h a r a c t e r i z e d as a c e t a l d e h y d e , a l s o known t o b e a m a j o r c a u s e f o r t h e c o l o r change o f PET d u r i n g aging and o f concern i n odor q u a l i t y . T h e mechanism f o r the thermal d e g r a d a t i o n o f PET i s c o n s i d e r e d t o be s i m i l a r to that f o r simple e s t e r p y r o l y s i s proceeding v i a a c y c l i c s i x - m e m b e r t r a n s i t i o n s t a t e ( 2 3 - 2 4 ) . PET d e c o m p o s e s b y a m o l e c u l a r mechanism w i t h random c h a i n s c i s s i o n a t t h e e s t e r l i n k s ( 2 5 ) . Thermal d e g r a d a t i o n p r o d u c t s d e r i v e d from p o l y e s t e r have been s t u d i e d u s i n g model compounds s u c h a s e t h y l e n e d i b e n z o a t e , 2hydroxyethyl benzoate and d i e t h y l e n e g l y c c o l dibenzoate (26-27). The v i n y l compounds f o r m e d d u r i n g t h e s e r e a c t i o n s c a n u n d e r g o f u r t h e r r e a c t i o n s t o g i v e a c o m p l e x m i x t u r e o f end p r o d u c t s . Rubber A r t i c l e s . Rubber a r t i c l e s have a c h a r a c t e r i s t i c objectionable odor formed by a thermal degradation o f p o l y u n s a t u r a t e d compounds. Thermal o x i d a t i o n p r o d u c t s o f r u b b e r a r t i c l e s have been e x t e n s i v e l y r e v i e w e d (28-29). Major v o l a t i l e compounds g e n e r a t e d from o x i d a t i o n o f s y n t h e t i c c i s - p o l y i s o p r e n e c o n t a i n e d a (CH3CO) t e r m i n a l g r o u p i n c l u d i n g a c e t a l d e h y d e , m e t h y l formate, propionaldehyde, acetone, methyl acetate, methanol, m e t h a c r o l e i n , e t h a n o l , butanone, butenone, pyruvaldehyde, a c e t i c a c i d , f o r m i c a c i d , a n d l e v u l i n a l d e h y d e , most o f them h a v i n g a pungent odor. T h e y i e l d o f v o l a t i l e p r o d u c t s i n c r e a s e d a s t h e t e m p e r a t u r e was r a i s e d , p a r a l l e l i n g i n c r e a s e d s c i s s i o n e f f i c i e n c y . As i n p u r e l y t h e r m a l d e g r a d a t i o n , t h e r m a l o x i d a t i o n o f r u b b e r i s accompanied by formation o f low-molecular-weight products i n y i e l d s t o o h i g h t o be a c c o u n t e d f o r b y random a t t a c k o n t h e


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hydrocarbon. U n l i k e thermal d e g r a d a t i o n , i n which, " u n z i p p i n g " can y i e l d many s m a l l m o l e c u l e s f r o m e a c h p r i m a r y s c i s s i o n , o x i d a t i o n i n v o l v e s f o r m a t i o n o f a s i n g l e l o w - m o l e c u l a r - w e i g h t compound o r s m a l l g r o u p o f compounds a t e a c h s c i s s i o n e v e n t and i s d e t e c t a b l e down t o room t e m p e r a t u r e (30)· O x i d a t i o n w i t h o u t s c i s s i o n h a s n o t been e x p e r i m e n t a l l y observed, a l t h o u g h p o s s i b l y p h o t o o x i d a t i o n at l o w t e m p e r a t u r e may i n v o l v e p e r o x i d a t i o n w i t h o u t s c i s s i o n (11). Polyethylene (PE). In an u n p u b l i s h e d s t u d y , p o u c h e s w e r e made f r o m p a p e r / f o i 1 / P E l a m i n a t e s , and h e a d s p a c e g a s was t a k e n f r o m t h e b a g a f t e r i n c u b a t i o n a t 6 0 ° C f o r 20 m i n u t e s and a n a l y z e d by a g a s chromatograph. Three major components were identified as a c e t a l d e h y d e , a l l y l a l c o h o l and a c r o l e i n . When o d o r o u s b a g s w e r e c o m p a r e d w i t h n o n - o d o r o u s b a g s , t h e r e showed a d i r e c t c o r r e l a t i o n between odor, acetaldehyde and a l l y l alcohol levels. Those c o m p o u n d s w e r e c o n s i d e r e d t o be t h e r m a l o x i d a t i v e d e c o m p o s i t i o n p r o d u c t s o f p o l y e t h y l e n e ( B a x t e r , J . Α . , W. G r a y s o n and A s s o c . , Ltd., unpublished d a t a ) . U s u a l l y LDPE (Low D e n s i t y P o l y e t h y l e n e ) t e n d s t o d e g r a d e to s h o r t e r c h a i n h y d r o c a r b o n s a t t e m p e r a t u r e s g r e a t e r t h a n 3 0 0 ° C and f u r t h e r u n d e r g o e s o x i d a t i o n t o f o r m a l a r g e number o f o x i d a t i o n p r o d u c t s s u c h as a l d e h y d e s and a l c o h o l s ( 9 ) . The p r o d u c t s o f t h e r m o - o x i d a t i v e r e a c t i o n s o f p o l y o l e f i n s can develop adverse f l a v o r s t h a t c a n be e a s i l y d e t e c t e d i n d e g r a d e d s a m p l e s . A f r e e r a d i c a l c h a i n mechanism i s g e n e r a l l y accepted t o e x p l a i n the thermal o x i d a t i o n of polyethylene (9). S t r u c t u r e , morphology, p r e s e n c e o f s t a b i l i z e r s , and t y p e o f e n v i r o n m e n t a r e t h e m o s t r e l e v a n t f a c t o r s i n the degradation o f p o l y e t h y l e n e . I n t e r a c t i o n s of t h e polymer w i t h v e r y s m a l l amounts o f oxygen can cause o x i d a t i v e d e g r a d a t i o n , and e x p o s u r e t o e l e v a t e d t e m p e r a t u r e s i n the absence o f oxygen can a l s o promote d e g r a d a t i o n (10). Ionomers. I o n o m e r s a r e d e f i n e d as l i n e a r o r g a n i c p o l y m e r s w h i c h a r e c o p o l y m e r i z e d w i t h a m i n o r p o r t i o n o f an a c i d f u n c t i o n w h i c h i s n e u t r a l i z e d t o v a r y i n g d e g r e e s by a m e t a l o r q u a r t e r n a r y ammonium i o n ( 3 2 ) and t h e u n i q u e p r o p e r t i e s o f t h i s c l a s s o f compounds a r e u s e f u l i n f l e x i b l e f o o d p a c k a g i n g m a t e r i a l s . E x t r u s i o n l a m i n a t e s are produced from ionomers e l i m i n a t i n g the need f o r a d h e s i v e s w i t h s o l v e n t problems, s i m u l t a n e o u s l y r e d u c i n g c o s t . H o w e v e r , t h e p r o c e s s o f i o n o m e r r e s i n s as c o a t i n g f o r s t r u c t u r e s i n v o l v e s two h i g h t e m p e r a t u r e s t e p s t h a t c a n p r o m o t e some t h e r m o - o x i d a t i v e r e a c t i o n s i n t h e m a t e r i a l . The f i r s t s t e p o c c u r s d u r i n g t h e p e l l e t i z a t i o n o f t h e r e s i n , when t e m p e r a t u r e s o f 2 3 0 ° C a r e u s e d and o x y g e n i s p r e s e n t , t h e s e c o n d d u r i n g t h e e x t r u s i o n c o a t i n g p r o c e s s , when t h e t e m p e r a t u r e s a r e r a i s e d a b o v e 3 0 0 ° C f o r r e l a t i v e l y s h o r t p e r i o d s o f t i m e . D e g r a d a t i o n c a n be i n i t i a t e d d u r i n g t h e f i r s t s t e p and a c c e l e r a t e d d u r i n g t h e s e c o n d s t e p . Fernandes e t a l (8) s t u d i e d t h e f o r m a t i o n o f v o l a t i l e compounds d u r i n g e x t r u s i o n l a m i n a t i o n o f e t h y l e n e ionomer. A l a r g e number o f h y d r o c a r b o n s , a l c o h o l s , a l d e h y d e s , k e t o n e s and e t c . w e r e i d e n t i f i e d f r o m e t h y l e n e i o n o m e r r e s i n s and f o i l / i o n o m e r l a m i n a t e s and many o f t h o s e compounds h a v e b e e n i d e n t i f i e d i n the degradation products o f p o l y e t h y l e n e (9.13.33). T h e r e f o r e , the


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major machanism f o r the formation o f those compounds i s c o n s i d e r e d to be s i m i l a r t o t h a t f o r the d e g r a d a t i o n o f p o l y e t h y l e n e . The t o t a l a r b i t r a r y peak area o f each GC/FID p r o f i l e o b t a i n e d from t h r e e d i f f e r e n t ionomer laminates processed a t d i f f e r e n t p r o c e s s i n g c o n d i t i o n s was c o r r e l a t e d t o the sensory e v a l u a t i o n data as shown i n F i g . 1. Likewise, the t o t a l peak area o f each GC/FID p r o f i l e obtained from t h r e e d i f f e r e n t ionomer laminates which c o n t a i n e d d i f f e r e n t l e v e l s o f an a n t i o x i d a n t was p l o t t e d versus the a n t i o x i d a n t l e v e l and shown i n F i g . 2. The data showed a s i g n i f i c a n t c o n t r i b u t i o n o f an a n t i o x i d a n t to the i n h i b i t i o n o f thermal d e g r a d a t i o n r e a c t i o n (Paik, S. W. and G i l b e r t , S. G., Rutgers U n i v e r s i t y , unpublished d a t a ) . These data demonstrate the dépendance o f d e g r a d a t i o n on the p r o c e s s i n g c o n d i t i o n as well as a high c o r r e l a t i o n o f sensory data with the formation o f v o l a t i l e compounds d u r i n g p r o c e s s i n g . P o l v v i n v l c h l o r i d e (PVC). Kim e t a l . ( H ) analyzed the v o l a t i l e s of p o l y v i n y l c h l o r i d e (PVC), one o f the most v e r s a t i l e packaging m a t e r i a l s . The major p r e c u r s o r s f o r the formation o f the v o l a t i l e compounds were c o n s i d e r e d to be PVC polymer, b i s - ( 2 - e t h y l h e x y l ) a d i p a t e (D0A), b i s - 2 - ( e t h y l h e x y l ) p h t h a l a t e (D0P) and t r i s nonylphenyl phosphite and e p o x i d i z e d soybean o i l . The most predominant v o l a t i l e compound i d e n t i f i e d was d i b u t y l a d i p a t e which i s a decomposition product o f D0A. The second predominant v o l a t i l e compound was 4-nonyl phenol which i s again a decomposition product o f t h e a n t i o x i d a n t t r i s-nonyl phenyl p h o s p h i t e . Most s h o r t - c h a i n p h t h a l a t e s were c o n s i d e r e d t o be e i t h e r decomposition or t r a n s e s t e r i f i c a t i o n products o f D0P, which i n d i c a t e d t h a t the type and the amount o f a d d i t i v e s c o u l d be a major cause o f o f f - o d o r problem. The composition o f thermal d e g r a d a t i o n products was p r e v i o u s l y shown to be g r e a t l y a f f e c t e d by the p r o c e s s i n g temperature (34)· PVC i s i n h e r e n t l y u n s t a b l e because o f the presence o f a l l y l i c c h l o r i n e atoms throughout the polymer. These c h l o r i n e atoms are e a s i l y removed by exposure t o minimal heat and/or l i g h t which r e s u l t s i n the well-known u n z i p p e r i n g r e a c t i o n (35)· Gelatin. G e l a t i n i s used as an e d i b l e packaging m a t e r i a l i n food and p a r t i c u l a r l y i n pharmaceutical a p p l i c a t i o n s (36)· V o l a t i l e compounds were i s o l a t e d and i d e n t i f i e d from commercial g r a n u l a r g e l a t i n and were c o n s i d e r e d t o be formed through the thermal decomposition o f amino a c i d s (12). Phenylethyl amine i d e n t i f i e d i n the study had a c h a r a c t e r i s t i c f i s h y odor and was c o n s i d e r e d a major c o n t r i b u t o r to the o b j e c t i o n a b l e f i s h y odor o f the g r a n u l a r g e l a t i n sample. I t was presumed to be d e r i v e d from p h e n y l a l a n i n e . Paperboard. Vaccaro i d e n t i f i e d s e v e r a l v o l a t i l e s r e l e a s e d from PET coated paperboard d u r i n g h e a t i n g (37). When the paperboard and PET f i l m s were analyzed s e p a r a t e l y to e s t a b l i s h the o r i g i n o f the r e l e a s e d v o l a t i l e s , no v o l a t i l e s were d e t e c t e d from the PET f i l m used f o r the c o a t i n g d u r i n g a n a l y s i s . A l l o f the v o l a t i l e s d e t e c t e d were r e l e a s e d from the paperboard. Seven compounds were i d e n t i f i e d : acetone, 2,3-butanedione, c h l o r o f o r m , f u r a n , f u r f u r a l ,


KIM AND GILBERT

Volatile Compounds in Packaging Materials

2.8

3.2

3.6

4.0

4.4.

401

4.8

Flavor Score

F i g u r e 1. T o t a l peak area v s sensory e v a l u a t i o n d a t a o f ionomer l a m i n a t e s extruded a t d i f f e r e n t temperatures. (A: Ionomer Processed a t 282° C; B: Ionomer Processed a t 304° C; C: Ionomer Processed a t 324° C)

4.5 +

4 0 0

800

1200

1600

2000

Antioxidant Cone, (ppm)

F i g u r e 2. The e f f e c t o f t h e a n t i o x i d a n t l e v e l on t h e g e n e r a t i o n o f v o l a t i l e compounds. ( · ; Ionomer Resin 1, β ; Ionomer Resin 2)


402


and m e t h y l e n e c h l o r i d e , c a r b o n d i s u l f i d e , a n d a c e t a l d e h y d e . T h e c h l o r i n a t e d compounds may b e p r e s e n t a s a r e s u l t o f t h e b o a r d b l e a c h i n g p r o c e s s a n d t h e CS2 a s a r e s u l t o f s u l f a t e p u l p p r o c e s s t o r e m o v e l i g n i n . T h e o t h e r compounds a r e commonly a s s o c i a t e d w i t h t h e d e c o m p o s i t i o n o f wood t h r o u g h b r o w n i n g r e a c t i o n ( 3 8 ) . Among them, f u r f u r a l which i s t h e primary p y r o l y s i s product o f paperboard c a n c o n t r i b u t e an undesirable f l a v o r t o contained foods. The a b s o r p t i o n o f i d e n t i f i e d v o l a t i l e s b y f o o d s i m u l a n t s s u c h a s o i l s a t u r a t e d c o t t o n b a l l s a n d g e l a t i n i z e d c o r n s t a r c h was a l s o s t u d i e d . T h e a c t u a l q u a n t i t i e s o f t h r e e compounds (methylene c h l o r i d e , carbon d i s u l f i d e , a n d chloroform) r e l e a s e d from t h e o v e n a b l e b o a r d d u r i n g h e a t i n g r a n g e d f r o m 0.3 t o 3.3 χ 10"6 g compound/g b o a r d . The t r a n s f e r t o f o o d s i m u l a n t s o f t h e t h r e e t a r g e t compounds r e l e a s e d from paperboard d u r i n g h e a t i n g was e v a l u a t e d b y two methods: p a r t i t i o n s t u d i e s a n d oven t e s t s t u d i e s . In c l o s e d systems, the p a r t i t i o n c o e f f i c i e n t s f o r methylene c h l o r i d e , carbon d i s u l f i d e a n d c h l o r o f o r m between t h e headspace and food s i m u l a n t s ( o i l a n d c o r n s t a r c h g e l ) w e r e d e t e r m i n e d a t 8 0 , 100, a n d 1 2 0 ° C. A l t h o u g h s o r p t i o n o f t h e t h r e e t a r g e t compounds i n t o o i l w a s d e t e c t e d a t 1 2 0 ° C, n o n e o f t h e t h r e e compounds t e s t e d w e r e t r a n s f e r r e d a t t h e ppb l e v e l o f d e t e c t i o n from an u n l i d d e d ovenable t r a y t o t h e food s i m u l a n t s d u r i n g cooking i n an a c t u a l o v e n . T h i s r e s u l t was a t t r i b u t e d t o t h e h i g h t e m p e r a t u r e o f t h e f o o d s d u r i n g c o o k i n g w h i c h may a c t u a l l y f a v o r d e s o r p t i o n . In c o n t r a s t t o t h e c o n v e n t i o n a l o v e n , t h e s u r f a c e t e m p e r a t u r e o f f o o d i n t h e m i c r o w a v e g e n e r a l l y d o e s n o t e x c e e d 1 0 0 ° C. T h e r e f o r e , p a r t i t i o n c o e f f i c i e n t o f t h e v o l a t i l e s would be d i f f e r e n t from t h a t i n t h e c o n v e n t i o n a l oven, which i n d i c a t e s t h e p r o b a b i l i t y t h a t t h e v o l a t i l e s emitted from an ovenable t r a y d u r i n g cooking may b e t r a n s f e r r e d t o t h e f o o d c o n t e n t s . In summary, h e a d s p a c e c o n c e n t r a t i o n m e t h o d i s t h e u s u a l w a y o f a n a l y z i n g t h e odor q u a l i t y o f p a c k a g i n g m a t e r i a l s a n d h a s been shown t o g i v e r e l i a b l e d a t a w h i c h c a n b e c o r r e l a t e d w i t h s e n s o r y e v a l u a t i o n d a t a . O v e n - h e a t e d m i c r o w a v a b l e p a c k a g i n g m a t e r i a l s may pose a s p e c i a l f l a v o r problem i n t h e food consumed. Acknowledgments T h i s w o r k w a s p e r f o r m e d a s a p a r t o f NJAES N o . D - 1 0 5 0 0 - 6 - 8 8 , s u p p o r t e d b y t h e New J e r s e y A g r i c u l t u r a l E x p e r i m e n t a l S t a t i o n .

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Wilks, R. Α., Jr.; Gilbert, S. G. J. Food Sci. 1972, 37, 72. Gilbert, S. G. Food Technol. 1985, 39, 54. Morano, J. M. S. Thesis, Rutgers University, New Brunswick, 1974. Heydanek, M. G.; Woolford, G.; Baugh, L. C. J. Food Sci. 1979, 44, 850. Kumai M.; Koizumi, H.; Saito, K. Indust. Health. 1983, 21, 185.


37. KIM AND GILBERT

6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33.

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Miltz, J. L.; Elisha, L.; Mannheim, C. H. J. Food Processing 1980, 4, 281. Hollifield, H. C.; Snyder, R. C.; Breder, C. V. J. Chrom. Sci. 1981, 19, 514. Fernandes, M. H.; Gilbert, S. G.; Paik, S. W.; Stier, E. F. J. Food Sci. 1986, 51, 722. Hoff, Α.; Jacobsson, S. J. Appl. Polym. Sci. 1981, 26, 3409. Hansen, R. H. In Thermal Stability of Polymers; Conley, R. T., Ed.; Macel Dekker, Inc.: New York, 1970; ρ 153. Kim, H.; Gilbert, S. G.; Hartman, T. G. In Frontiers of Flavor; Charalambous, G., Ed.; Elsivier Science Publishers: Amsterdam, Netherlands, 1988; ρ 249. Kim, H.; Gilbert, S. G. In Frontiers of Flavor; Charalambous, G., Ed.; Elsivier Science Publishers: Amsterdam, Netherlands, 1988; ρ 271. Barabas, K.; Irving, M.; Tudow, F. J. Poly. Sci. 1976, 17, 65. Fales, N. J . ; Stover, L. C. Polym. Plast. Technol. Eng. 1983, 21, 111. ASTM. In Manual on Sensory Testing Methods. Spec. Tech. Pub. # 434., American Society for Testing and Materials, Philadelphia, 1968. Powers J. J. In Food Flavors; Morton, I. D., and Maclead, A. J., Ed.; Elsevier Scientific Publ. Co.: New York, 1982; ρ 121. Gilbert, S. G.; Wilks, R. Α., Jr. Materials Res. and Stands. 1968, 8, 29. Wilks, R. Α., Jr.; Gilbert, S. G. Food Technol. 1969, 23, 47. Pausch, J. B.; Sodsis, I. Rubber Chem. Technol. 1977, 50, 828. Eiceman, G. Α.; and Karasek, F. W. J. Chromat. 1981, 210, 93 Charalambous, G. Analysis of Foods and Beverages - Headspace Techniques; Academic Press: New York, 1978. Singleton, J. Α.; Patee, H. E. J. Amer. Oil Chem. Soc. 1980, 57, 405. Halek, G. W. J. Poly. Sci.: Polymer Symposium 1986, 74, 83. Baxbaum, L. H. Angew. Chem. Internat. Edit. 1968, 7, 182. Pohl, H. A. J. Amer. Chem Soc. 1951, 73, 5660. Goodings, E. P., Soc. Chem. Ind. 1961, 13, 211. Taylor, R.; Smith, G. G.; Wetzel, W. H. J. Amer. Chem. Soc. 1962, 84, 4817. Bevilacqua, Ε. M. In Thermal Stability of Polymers; Conley, R. T., Ed.; Marcel Dekker, Inc: New York, 1970; ρ 189. Bevilacqua, Ε. M.; English, E. S.; Norling, P. M. J. Appl. Polym. Sci. 1964, 8, 1029. Bevilacqua, E. M. J. Amer. Chem. Soc. 1955, 77, 5394. Hart, E. J . ; Matheson, M. S. J. Amer. Chem. Soc. 1948, 70, 784. Longworth, R. Plast. and Rubber: Mater. Appl. 1978, 3, 75. Holmstrom, Α.; Sorvik, E. J. Appl. Polym. Sci. 1974, 18, 779.



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Received January 16, 1989


Thermally Generated Volatile Compounds in Packaging Materials

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