Food and Packaging Interactions - American Chemical Society

Chapter 5

Flavor—Polymer Interactions

Downloaded by UNIV OF MISSOURI COLUMBIA on October 29, 2017 | http://pubs.acs.org Publication Date: March 9, 1988 | doi: 10.1021/bk-1988-0365.ch005

Coffee Aroma Alteration Ann L. Hriciga and Donald J. Stadelman Polymer Products Department, Ε. I. du Pont de Nemours and Company, Experimental Station, Wilmington, DE 19898 Because organoleptic testing is time-consuming and expensive, we have developed a gas chromatographic test to screen polymer films for their ability to change the aroma profile of coffee. The retention or alteration of flavor components of foods packaged in contact with polymer films is of concern both to suppliers of those polymers and to food manu facturers. Ground coffee is a product which is beginning to move away from the traditional metal can and into new, polymeric types of packaging. Incubation of ground coffee with films in sealed vials for up to three days preceded gas chromato graphic analysis of volatile compounds in the headspace. After statistically analyzing the data, we ranked the films for alterations to the coffee aroma profile. Our ranking matched that of a professional olfactory panel working with ground coffee stored for six months in bags made from the same polymers. Our method results in a substantial savings in time and cost with no change in qualitative result. The r e c e n t t r e n d on the p a r t o f the food i n d u s t r y t o r e p l a c e t r a d i t i o n a l g l a s s and metal c o n t a i n e r s w i t h p l a s t i c ones has f o c u s s e d a t t e n t i o n on t h e i n t e r a c t i o n s between aromas o r f l a v o r s and t h e polymers used i n these new s t r u c t u r e s . I n o r d e r f o r these p l a s t i c packages t o g a i n widespread a c c e p t a n c e by t h e consumer, foods packaged i n p l a s t i c s must c o n t i n u e t o s m e l l and t a s t e as they d i d i n t h e i r former p a c k a g i n g . Polymers may i n t e r f e r e w i t h those aromas i n s e v e r a l ways. A d s o r p t i o n o r a b s o r p t i o n by the p l a s t i c may s i m p l y reduce t h e t o t a l v o l a t i l e c o n t e n t o f the packaged m a t e r i a l , r e s u l t i n g i n a l o s s o f odor. A l t e r n a t i v e l y , t h e polymer may a l t e r t h e c h a r a c t e r i s t i c aroma o f a food by s e l e c t i v e l y a b s o r b i n g one o r more key compounds which make up the c h a r a c t e r i s t i c aroma o f a f o o d . O f f - s m e l l s may be produced i f t h e polymer a c t s t o c h e m i c a l l y change a component o f

0097-6156/88/0365-0059$06.00/0 © 1988 American Chemical Society

Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.


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FOOD AND PACKAGING INTERACTIONS the f o o d : enhanced d e g r a d a t i o n i s an example of t h i s . Polymeric m a t e r i a l s themselves can c o n t r i b u t e aromas from such t h i n g s as r e s i d u a l monomers, s o l v e n t s o r p r o c e s s i n g a d d i t i v e s . The most r e l i a b l e method of e v a l u a t i n g a polymer's impact on a packaged food i s s e n s o r y e v a l u a t i o n o f the food by a human p a n e l . A c o n t a i n e r must be f a b r i c a t e d , the food s e a l e d i n s i d e and the e n t i r e package i n c u b a t e d to s i m u l a t e s h e l f s t o r a g e b e f o r e p a n e l t e s t i n g can be done. T h i s p r o c e s s may c o s t thousands of d o l l a r s f o r each polymer and food t e s t e d . In a d d i t i o n , the i n c u b a t i o n p e r i o d b u i l d s an i n h e r e n t d e l a y i n t o the e v a l u a t i o n p r o c e s s . The number of samples t h a t can be e v a l u a t e d f o r aroma by a s i n g l e p a n e l limits throughput. The development of a c c e p t a b l e p l a s t i c s f o r food c o n t a i n e r s c o u l d be q u i c k e n e d i f an a l t e r n a t e s e n s o r y e v a l u a t i o n t e s t c o u l d be d e s i g n e d . Many more m a t e r i a l s can be t e s t e d w i t h a r e l a t i v e l y s h o r t , i n e x p e n s i v e , a n a l y t i c a l method. Such a t e s t does not r e p l a c e o r e l i m i n a t e s e n s o r y e v a l u a t i o n , but r a t h e r a c t s as a p r e s c r e e n i n g so t h a t o n l y the most p r o m i s i n g p l a s t i c s are used i n c a n d i d a t e packages. These packages would then undergo the same r i g o r o u s a r o m a / f l a v o r e v a l u a t i o n t h a t i s now b e i n g used p r i o r to consumer m a r k e t i n g . The g o a l o f our work was to e s t a b l i s h such a t e s t . We had to choose a s o u r c e of f l a v o r s ( r e a l food v e r s u s odorous compounds), some type of p a c k a g i n g m a t e r i a l and c o n s t r u c t i o n , and an a n a l y t i c a l technique. Any method d e v e l o p e d had to be v a l i d a t e d by comparing i t s r e s u l t s to those from a s e n s o r y e v a l u a t i o n o f the same f l a v o r package c o m b i n a t i o n . To s i m p l i f y our t e s t , we d e c i d e d to s t a r t by l o o k i n g at a l t e r a t i o n s i n aroma, l e a v i n g t a s t e f o r f u t u r e s t u d y . Our c h o i c e o f t e c h n i q u e then became r a t h e r s t r a i g h t f o r w a r d - a n y t h i n g which i s v o l a t i l e enough to be s m e l l e d i s v o l a t i l e enough to be a n a l y z e d by gas chromatography (GC). We r e c o g n i z e the i n h e r e n t l i m i t a t i o n s of t h i s t e c h n i q u e , though. A gas chromatograph cannot d e t e c t a l l aroma components w i t h the same s e n s i t i v i t y as the human nose. C o n s e q u e n t l y , our t e c h n i q u e may not see a l t e r a t i o n s i n c o n c e n t r a t i o n s o f a component which i s key to the aroma, but p r e s e n t o n l y at an e x t r e m e l y low l e v e l . A n o t h e r b e n e f i t o f GC i s t h a t a d d i t i o n of components from the polymer, such as r e s i d u a l s o l v e n t s , can a l s o be d e t e c t e d a l t h o u g h , a g a i n , e x t r e m e l y low l e v e l s may e i t h e r be below the d e t e c t i o n l i m i t of the GC or be o b s c u r e d by components of the aroma. In o r d e r to make our system as r e a l i s t i c as p o s s i b l e , we d e c i d e d not to use model compounds f o r development of t h i s method, but r a t h e r a r e a l f o o d . A c t u a l food aromas a r e o f t e n v e r y complex m i x t u r e s and i t i s not n e c e s s a r i l y p o s s i b l e to p r e d i c t which components o f the m i x t u r e w i l l be most a f f e c t e d by the p o l y m e r i c p a c k a g i n g m a t e r i a l . However, a s t r o n g food aroma o f t e n has a h i g h c o n c e n t r a t i o n o f v o l a t i l e components which can then be a n a l y z e d by GC. Thus, we w i l l be more apt to d e t e c t changes i n t h i s w e l l d e f i n e d aroma p r o f i l e . The i d e a l m a t e r i a l i s a food whose s t r o n g aroma i s p o s i t i v e l y p e r c e i v e d by the consumer. T h i s thought p r o c e s s made the c h o i c e of food r e l a t i v e l y straightforward. One food whose aroma i s v e r y important to i t s consumer a p p e a l i s ground c o f f e e . To most c o f f e e d r i n k e r s , the s m e l l o f a newly opened c o n t a i n e r of c o f f e e i s pure perfume. If c o f f e e i s packaged i n a way t h a t a l t e r s t h a t aroma s i g n i f i c a n t l y ,



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the consumer w i l l not buy i t more than once. In the past f i v e y e a r s , we have seen the i n t r o d u c t i o n o f new types of c o f f e e packages on supermarket s h e l v e s , so we know the c o f f e e i n d u s t r y i s e v a l u a t i n g new p a c k a g i n g m a t e r i a l s . C o n s e q u e n t l y , ground c o f f e e seemed a v e r y good c h o i c e as the food to be e v a l u a t e d . As an added b e n e f i t , i t i s a s o l i d m a t e r i a l and i s e a s i l y h a n d l e d . With the c h o i c e of c o f f e e as food and the knowledge that the new c o f f e e packages a r e f l e x i b l e , i t was n a t u r a l to choose polymer f i l m s as the m a t e r i a l s to e v a l u a t e . Two DuPont f i l m s ( F i l m A and F i l m B) had a l r e a d y been e v a l u a t e d by a s e n s o r y p a n e l f o r t h e i r impact on c o f f e e aroma; they became the f i r s t m a t e r i a l s we examined. Indeed, the r e s u l t s of that p a n e l p r o v i d e d us w i t h the means of comparing our l a b o r a t o r y method w i t h a r e a l s e n s o r y evaluation. Methodology The p a n e l t e s t e d ground c o f f e e which had been s t o r e d f o r s i x months i n pouches made from polymer film/aluminum f o i l l a m i n a t e s . The aluminum f o i l o u t e r l a y e r a c t e d as a m o i s t u r e , oxygen and l i g h t b a r r i e r so that o n l y the i n t e r a c t i o n between the c o f f e e and the p o l y m e r i c i n n e r l a y e r was b e i n g examined by the p a n e l . The c o n t r o l was s i m p l y ground c o f f e e packed i n a metal can. In t h i s t e s t , c o f f e e packed i n the m e t a l can had the best aroma of the three c a s e s w h i l e c o f f e e packed w i t h F i l m A had an a c c e p t a b l e aroma. The aroma of the c o f f e e packed w i t h F i l m Β was u n a c c e p t a b l e . Simply put, our t e s t i n v o l v e s e v a l u a t i n g the c h r o m a t o g r a p h i c p r o f i l e of c o f f e e aroma i n the p r e s e n c e and absence of polymer films. T h i s i s a c o m p a r a t i v e t e c h n i q u e which e s t a b l i s h e s a r a n k i n g of the f i l m s t e s t e d , from most s i m i l a r to most d i s s i m i l a r to a s e n s o r i a l l y acceptable container. Because we d i d n ' t know ahead of time what the magnitude of the a l t e r a t i o n s i n the aroma would be, we used a v e r y h i g h r a t i o of polymer f i l m to ground c o f f e e to i n c r e a s e our chances of s e e i n g changes i n the aroma p r o f i l e . A l t h o u g h t h i s i s not the s i t u a t i o n i n a r e a l f l e x i b l e c o f f e e package, the h i g h r a t i o maximizes the i n t e r a c t i o n between the polymer and the c o f f e e and s h o u l d make any d i f f e r e n c e s i n the aroma more pronounced. We i n c u b a t e d r o u g h l y f i v e grams of ground c o f f e e (from f r e s h l y opened cans of ground c o f f e e ) e i t h e r a l o n e or i n the p r e s e n c e of a f i l m candidate. F i l m s of the same t h i c k n e s s (-1.8 m i l ) and a r e a (4" χ 5") were used so that both the volume and the s u r f a c e a r e a a r e the same from sample to sample. The c o f f e e , w i t h or w i t h o u t f i l m , was p l a c e d i n t o a g l a s s c o n t a i n e r ( a p p r o x i m a t e l y 40 mL volume) which was then s e a l e d w i t h a Teflon®-faced septum and cap. T h i s s e a l i n g system a l l o w e d us to p e r i o d i c a l l y sample the headspace of the v i a l w i t h a g a s - t i g h t s y r i n g e . I n c u b a t i o n was at 500°C f o r a p e r i o d o f up to t h r e e days. The h i g h temperature was chosen to speed up the a g i n g p r o c e s s and as such i t d i d not r e p l i c a t e s t o r a g e at room temperature. (However, i t i s a temperature which packaged c o f f e e might see i n s i d e u n r e f r i g e r a t e d v e h i c l e s w h i l e b e i n g t r a n s p o r t e d i n the s o u t h e r n p o r t i o n s of the U. S. d u r i n g the summer.) A n a l y s i s of the headspace, which i s s i m p l y the aroma of the c o f f e e or the c o f f e e p l u s polymer system, was done by gas chroma tography. P r e v i o u s work on the a n a l y s i s of c o f f e e aroma by s e v e r a l workers (1,2) used narrow bore g l a s s c a p i l l a r y columns w i t h p o l a r



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FOOD AND PACKAGING INTERACTIONS stationary phases. Most of the v o l a t i l e s eluted above 400°C in these studies. Consequently, we chose a 25 meter, 0.53 mm I. D. fused s i l i c a c a p i l l a r y column coated with three microns of Carbowax 20M (Quadrex Corp.). With this column, there was no need to s p l i t or concentrate the aliquot of the headspace which we wished to chromatograph and we avoided problems with possible discrimination or loss of v o l a t i l e compounds. The c a r r i e r gas was helium at 8 mL/min. The injection port was maintained at 200°C and the flame ionization detector was kept at 250°C. The oven temperature started at 500°C and was programmed to 250°C at 800/min and then held. An a i r t i g h t syringe was used to inject 0.5 mL of the headspace onto the column. In order to maintain a constant pressure i n the sample v i a l , 0.5 mL of laboratory a i r was injected into the v i a l using the same syringe prior to each sampling. For the development of this method, a l l the samples (Films A and B) and the control (coffee alone) were prepared i n t r i p l i c a t e . Each v i a l was sampled once a day for three days. Results As can be seen from the chromatogram ( F i g . 1), the aroma p r o f i l e i s quite complicated. In fact, well over 150 different compounds have been i d e n t i f i e d in the l i t e r a t u r e (2,3) as v o l a t i l e components of coffee. To start characterizing the aroma p r o f i l e , we chose the 49 largest components in the chromatograms of the control headspace (coffee alone) and followed their behavior as a function of time in a l l nine v i a l s . The peak area of each of these components was divided by the t o t a l area of these components, and this r a t i o was plotted as a function of incubation time. The behavior of each component was characterized by f i t t i n g the peak area ratios to a curve of either zero, f i r s t or second order i n time and generating values which represented the expected upper and lower l i m i t s (at the 95% confidence l e v e l ) of each curve. Each component, therefore, had three curves associated with i t s behavior - one i n glass alone, one in the presence of Film A and one i n the presence of Film B. The curves for a given component in these three systems were compared to one another and declared to be s t a t i s t i c a l l y different from one another i f there was no overlap between the curves. Typical results are discussed below. In one common result, the component behaved quantitatively the same i n the three systems. The presence of the films made no difference i n the behavior of that p a r t i c u l a r component, so any change i n the aroma when the films were present was not due to absorption of this component. A second case i s one i n which the component behaved the same in the presence of either Film A or Film B, but d i f f e r e n t l y when i n glass alone. Although components which f e l l into this category might contribute to the o v e r a l l aroma of ground coffee, they were not changed to an unacceptable l e v e l (which was the same in the presence of either film) because coffee packaged with Film A passed sensory evaluation. These components cannot be used to rank the films because they react the same to either film. The category of result where a given component behaved s t a t i s t i c a l l y d i f f e r e n t l y in the presence of Film A than i t did with Film Β comprised 23 components of the 49 which we examined. This category could be further divided into three subclasses:


Flavor-Polymer


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0

5

10

15

20 TIME (min)

25

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30

35

40

F i g u r e 1: T h i s i s a t y p i c a l chromatogram of the aroma of f r e s h l y ground c o f f e e . The r i s e i n the b a s e l i n e a f t e r 24 minutes i s due to the temperature programming of the column i t s e l f and i s not due to components i n the aroma.



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ο The component behaved the same i n g l a s s a l o n e and w i t h F i l m A, but d i f f e r e n t l y w i t h F i l m Β (13 components). See F i g . 2. ο The component behaved the same i n g l a s s a l o n e and w i t h F i l m B, but d i f f e r e n t l y w i t h F i l m A (no component i n the headspace f e l l into this subclass). ο The component behaved d i f f e r e n t l y i n each o f the t h r e e systems o f i n c u b a t i o n (10 components). T h i s l a s t s u b c l a s s can be f u r t h e r d i v i d e d by r a n k i n g the com ponent's b e h a v i o r i n the t h r e e systems by r e l a t i v e c o n c e n t r a t i o n . F o r seven components, the component c o n c e n t r a t i o n was h i g h e s t i n g l a s s a l o n e , next h i g h e s t w i t h F i l m A, and lowest w i t h F i l m Β ( F i g . 3 ) . Only two components had the h i g h e s t c o n c e n t r a t i o n i n g l a s s a l o n e , next h i g h e s t w i t h F i l m B, and lowest i n F i l m A. The r e m a i n i n g component i n t h i s s u b c l a s s had a c o n c e n t r a t i o n i n g l a s s a l o n e t h a t was i n t e r m e d i a t e between the v a l u e s w i t h F i l m A and F i l m B. A review o f these r e s u l t s y i e l d s the f o l l o w i n g i n f o r m a t i o n . In 20 out of 23 components (SIX) where b e h a v i o r i n the p r e s e n c e of F i l m A was d i f f e r e n t from t h a t w i t h F i l m B, F i l m A a l t e r e d the component's b e h a v i o r l e s s than d i d F i l m B. In o n l y t h r e e cases was the s i t u a t i o n d i f f e r e n t . We had been h o p i n g to f i n d s e v e r a l com ponents which would show b e h a v i o r f o r F i l m A that was i n t e r m e d i a t e between no f i l m and F i l m B; what we found was that i n 87% of the c a s e s where t h e r e was a d i f f e r e n c e , the d i f f e r e n c e was i n e x a c t l y that d i r e c t i o n . We knew from the s e n s o r y p a n e l t e s t i n g that c o f f e e packaged w i t h F i l m A had an a c c e p t a b l e aroma, a l t h o u g h not as good as t h a t o f c o f f e e packaged i n a t r a d i t i o n a l metal can. Coffee packaged w i t h F i l m B, however, had an u n a c c e p t a b l e aroma. So here we have a f i r s t r a n k i n g of p a c k a g i n g m a t e r i a l s : F i l m Β i s u n a c c e p t a b l e , F i l m A i s a c c e p t a b l e , but the metal can i s best of all. C l e a r l y our GC r e s u l t s echo the same p a t t e r n . F u t u r e Work How can t h i s method be used and improved? F i r s t , we have found 20 peaks which seem to c o r r e l a t e w i t h the s e n s o r y a n a l y s i s . We can reduce the number o f components we t r a c k ; t h i s w i l l reduce the time spent on s t a t i s t i c a l a n a l y s i s . Secondly, we can t r y to i d e n t i f y these 20 peaks. We might be a b l e to assemble a s y n t h e t i c m i x t u r e o f aroma components to be used i n t h i s t e s t , r e d u c i n g the c o m p l e x i t y o f the chromatograms and p r o v i d i n g us w i t h a s t a n d a r d m i x t u r e which we can c o n t r o l . Such a m i x t u r e would e l i m i n a t e the l o t - t o - l o t v a r i a t i o n which may be p r e s e n t i n the aromas of c o m m e r c i a l l y o b t a i n e d packaged c o f f e e , and we c o u l d d i r e c t l y compare e x p e r i m e n t s done w i t h d i f f e r e n t f i l m s a t d i f f e r e n t t i m e s . C u r r e n t l y , we can o n l y rank f i l m s which were t e s t e d w i t h the same l o t and age o f c o f f e e . I d e n t i f i c a t i o n o f these peaks, which we a r e w o r k i n g on by GC/MS, a l o n g w i t h some knowledge o f the c h e m i c a l n a t u r e of these polymer f i l m s , s h o u l d g i v e us a b e t t e r u n d e r s t a n d i n g o f how the aroma i s i n t e r a c t i n g w i t h the f i l m s . We would have more i n f o r m a t i o n on how to d e s i g n o r choose c a n d i d a t e p a c k a g i n g material.



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F i g u r e 2: The b e h a v i o r of Component 46 i s p l o t t e d as a f u n c t i o n o f time f o r each of the t h r e e systems. Three l i n e s a r e a s s o c i a t e d w i t h each system: the middle l i n e o f a s e t i s the best f i t to the d a t a and the upper and lower l i n e s a r e the 95% c o n f i d e n c e l e v e l l i m i t s a s s o c i a t e d with that f i t . Symbols used a r e as f o l l o w s : x, C o f f e e a l o n e ; Δ, Coffee w i t h F i l m A; •, C o f f e e with F i l m B. Component 46 e x h i b i t s the same b e h a v i o r i n the presence of the g l a s s v i a l a l o n e as i t does i n the presence o f F i l m A. F i l m B, however, reduces the r e l a t i v e c o n c e n t r a t i o n o f t h i s component i n the headspace by a t l e a s t a f a c t o r o f f o u r .



FOOD AND PACKAGING INTERACTIONS

•. 5-1 1G

1 25

! 40 HOURS AT

1 55

1 70

50* C

F i g u r e 3: The b e h a v i o r of Component 26 i s p l o t t e d as a f u n c t i o n of time f o r each of the three systems. Three l i n e s a r e a s s o c i a t e d w i t h each system: the middle l i n e of a set i s the best f i t to the d a t a and the upper and lower l i n e s are the 95% c o n f i d e n c e l e v e l l i m i t s a s s o c i a t e d with that f i t . Symbols used a r e as f o l l o w s : x, C o f f e e a l o n e ; Δ, Coffee w i t h F i l m A; •, C o f f e e with F i l m B. Component 26 behaves d i f f e r e n t l y i n each of the three cases, w i t h i t s h i g h e s t r e l a t i v e c o n c e n t r a t i o n i n the g l a s s v i a l a l o n e . F i l m A reduces t h i s component's l e v e l to 75% of the r e l a t i v e c o n c e n t r a t i o n i n the g l a s s v i a l a l o n e , but F i l m Β has an even g r e a t e r e f f e c t , d i m i n i s h i n g Component 26 to 40% of i t s r e l a t i v e c o n c e n t r a t i o n i n the g l a s s v i a l a l o n e .


5. HRICIGA & STADELMAN

Flavor-Polymer

Interactions

67

Acknowledgment The help of s t a t i s t i c i a n Mary Dunleavy i s g r a t e f u l l y

acknowledged.


References 1.

Vitzthum, O. G.; Werkhoff, P. In Analysis of Food and Beverages; Charalambous, G., Ed.; Academic:New York, 1978; pp 115-133.

2.

T r e s s l , R.; Silwar, R. 1078-1082.

3.

Stoffelsma, J . ; Sipma, G.; Kettenes, D. K.; Pypker, J . J . Agric. Food Chem. 1968, 1000-1004.

Agric. Food Chem. 1981, 29,

R E C E I V E D September 24, 1987


Food and Packaging Interactions - American Chemical Society

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