Sorption of Flavor Compounds by Polypropylene - ACS Publications

Chapter 17 Sorption of Flavor Compounds by Polypropylene 1

D. K. Arora , A. P. Hansen, and M. S. Armagost Department of Food Science, North Carolina State University,

Downloaded by UNIV LAVAL on July 14, 2016 | http://pubs.acs.org Publication Date: September 13, 1991 | doi: 10.1021/bk-1991-0473.ch017

Raleigh, NC 27695-7624

The sorption of aldehydes (C -C ), methyl ketones (C -C ), methyl esters (C -C ), sulfur compounds and alkylpyrazines by polypropylene (PP) was investigated. PP discs (163.9 cm ) were immersed in a buffer solution containing a flavor compound (200 ppm) for 24 hr at room temperature. The flavor compound remaining in the buffer and sorbed by the PP was quantitated using GC. The percent of flavor compounds sorbed by PP was: aldehydes from 17.2% to 63.8%, methyl ketones from 4.2% to 73.7%, methyl esters from 13.0% to 79.4%, and sulfur compounds from 38.7% to 48.6%. Alkylpyrazines were sorbed to an insignificant level (1.0-2.2%). For each group of flavor compounds, the sorption increased as the carbon number increased. 7

7

10

9

7

9

2

The u s e o f p l a s t i c s i n t h e p a c k a g i n g o f f o o d p r o d u c t s and p h a r m a c e u t i c a l s has i n c r e a s e d c o n s i d e r a b l y o v e r t h e l a s t s e v e r a l y e a r s . I n terms o f d o l l a r v a l u e , an i n c r e a s e o f 56% i s e s t i m a t e d f o r p l a s t i c s f r o m 1984 t o 1990 ( 1 ) . Bob S c h w i e r o f S c h o t l a n d B u s i n e s s R e s e a r c h p r e d i c t e d t h a t the use of coextruded p l a s t i c b a r r i e r m a t e r i a l s i n f o o d p r o c e s s i n g w o r l d w i d e w o u l d e x c e e d $4 b i l l i o n by 1990 ( 2 ) . Many r e c e n t d e v e l o p m e n t s i n f o o d packaging a r e r e l a t e d to using the b a r r i e r p r o p e r t i e s of p l a s t i c s to extend s h e l f l i f e . R e c e n t l y , t h e r e has been a s u r g e i n a s e p t i c p r o c e s s i n g and p a c k a g i n g o f f o o d and p h a r m a c e u t i c a l p r o d u c t s f o r q u a l i t y , c o n v e n i e n c e and l o n g e r s h e l f l i f e . F r u i t j u i c e s and d r i n k s had t h e most i m p r e s s i v e g r o w t h 1

Current address: Engineering Resources, Inc., Fayetteville, AR 72702

0097-6156/91/O473-0203$06.00/0 © 1991 American Chemical Society

Risch and Hotchkiss; Food and Packaging Interactions II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


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FOOD AND PACKAGING INTERACTIONS

in aseptic packaging. Other aseptic products include tomato sauce, apple sauce, gravies, cheese dips, soups, flavored milks, puddings and yogurt products. Currently, high acid liquid foods account for 90% of the aseptic market (3). When s t e r i l i z a t i o n techniques for particulates in low acid foods are commercially feasible, a large increase in aseptic packaging is anticipated. It is estimated that in the year 2000 the U.S. market may have a volume of over 15 b i l l i o n aseptic packages (4). Aseptic foods are packaged in a variety of polymeric materials. The aseptic packages are formed from thermoplastics or made by combining thermoplastics with paperboard and metal f o i l . Plastics used in aseptic packages may be single polymers or coextruded polymers designed to improve barrier properties. Most aseptic food containers have an inner plastic liner for heat sealing. Plastics are not as inert as glass and metals, and can interact with foods and pharmaceuticals packaged in the container. Various interactions between plastics and food products, such as permeability, migration and sorption, have been described ( 1 ) . The sorption of flavor compounds by polymeric materials refers to the scalping of flavor and aroma components of foods by p l a s t i c s . Scalping of flavor compounds has been shown to influence the sensory quality and acceptability of food products

(5,6).

The shelf s t a b i l i t y of f r u i t juices and f r u i t drinks in aseptic packages has been documented ( 5 - 1 1 ) . The PE liner in brick type aseptic containers scalps d-limonene, neral, geranial, octanal and decanal from juice products (Adams, J . P . , International Paper C o . , personal communication, 1 9 8 8 . ) . As a result, the packaged f r u i t juice lacks flavor notes characteristic of fresh juice. Using headspace chromatography, Abbe et a l . (12) attempted to "fingerprint" key flavor compounds sorbed by the aseptic package containing a juice product. The package that contained juice showed extra peaks in the chromatogram as compared to the control container, which did not contain juice. The extra peaks represented the uptake of flavor compounds by the package. Salame (Salame, Μ., Paper presented at Bev-Pak '88, unpublished data, 1988.) reported an average of 62% and 37% sorption of non-polar and polar organics, respectively, by PP. Polypropylene was ranked second after PE in the quantity of flavor compounds sorbed (Salame, Μ., Paper presented at Bev-Pak '88, unpublished data, 1 9 8 8 . ) . Juice packaged in coextruded polypropylene containers, consisting of PP outer and inner layers surrounding an internal ethylene vinyl alcohol layer, showed a marked decrease in d-limonene content as compared to juice packaged in f o i l containers due to sorption ( 1 3 ) . A layer of Saran has been suggested with


17. ARORA ET A L

Sorption of Flavor Compounds by Polypropylene

PP and HDPE t o r e d u c e t h e s o r p t i o n o f d - l i m o n e n e ( 1 4 ) . The p o l a r i t y and s i z e o f t h e p e r m e a n t , t h e a r e a o f polymer, the t h i c k n e s s of f i l m , the s t o r a g e temperature and t h e r e l a t i v e h u m i d i t y a f f e c t t h e s o r p t i o n o f f l a v o r compounds by p o l y m e r s ( 1 5 ) . The s o r p t i o n o f f i v e c l a s s e s o f f l a v o r compounds (aldehydes, methyl ketones, methyl e s t e r s , a l k y l p y r a z i n e s and s u l f u r compounds) r e p r e s e n t i n g a wide v a r i e t y o f f o o d p r o d u c t s , s u c h as d a i r y , f r u i t , v e g e t a b l e and meat p r o d u c t s by PP a t room t e m p e r a t u r e was investigated.


Materials

and

Methods

Materials. The f o l l o w i n g f l a v o r compounds were u s e d : a l d e h y d e s ( h e p t a n a l , o c t a n a l and n o n a n a l ) , m e t h y l k e t o n e s ( 2 - h e p t a n o n e , 2 - o c t a n o n e , 2-nonanone and 2-decanone), methyl e s t e r s (methyl hexanoate, methyl h e p t a n o a t e and m e t h y l o c t a n o a t e ) , alkylpyrazines ( m e t h y l - and e t h y l p y r a z i n e ) and s u l f u r compounds ( 2 - m e t h y l t h i o p h e n e and b e n z y l m e t h y l s u l f i d e ) . These c h e m i c a l s were o b t a i n e d from A l d r i c h C h e m i c a l Company, M i l w a u k e e , WI. The p o l y p r o p y l e n e (PP) s h e e t (0.3 mm t h i c k ) was o b t a i n e d from K r a f t G e n e r a l F o o d s , I n c . , Glenview, IL. S o r p t i o n A p p a r a t u s and M e t h o d . The PP was cu£ i n t o d i s c s o f 2.7 cm d i a m e t e r . F o u r t e e n d i s c s (163.9 cm , s u r f a c e a r e a ) were mounted o n t o a s i l a n i z e d s t a i n l e s s s t e e l w i r e a l t e r n a t i n g w i t h s i l a n i z e d g l a s s beads (4 mm, #4000) ( F i g u r e 1 ) . The s t a i n l e s s s t e e l w i r e w i t h PP d i s c s and g l a s s beads was i n s e r t e d i n t o a s i l a n i z e d s c r e w t i g h t g l a s s b o t t l e . The s c r e w cap was l i n e d w i t h t i n f o i l (Fisher S c i e n t i f i c , Raleigh, NO to p r e v e n t s c a l p i n g of t h e f l a v o r compound by t h e c a p . E a c h o f t h e g l a s s b o t t l e s c o n t a i n e d a 2% a l c o h o l i c b u f f e r (100 mL) of s i m u l a t e d m i l k u l t r a f i l t r a t e (SMUF) (16) and a f l a v o r compound (200 ppm). The b o t t l e s were p l a c e d on a s h a k e r f o r u n i f o r m d i s p e r s a l o f t h e f l a v o r compound f o r 24 h o u r s a t room t e m p e r a t u r e ( 2 4 ° C ) . Two s e t s o f c o n t r o l s ( b u f f e r s o l u t i o n c o n t a i n i n g o n l y t h e f l a v o r compound and b u f f e r s o l u t i o n c o n t a i n i n g t h e f l a v o r compound, wire and g l a s s b e a d s ) were p l a c e d on t h e s h a k e r a l o n g w i t h t h e b o t t l e s c o n t a i n i n g t h e PP s a m p l e s . F l a v o r Compound E x t r a c t i o n . The f o l l o w i n g e x t r a c t i o n method was a d o p t e d f o r q u a n t i t a t i n g f l a v o r compound sorption. A f t e r 24 h o u r s , t h e PP sample was removed f r o m t h e b o t t l e . Sodium c h l o r i d e (10 g) was added t o t h e b u f f e r s o l u t i o n t o b r e a k t h e e m u l s i o n . The f l a v o r compound i n t h e b u f f e r s o l u t i o n was e x t r a c t e d w i t h m e t h y l e n e c h l o r i d e (5 mL χ 4 ) . The m e t h y l e n e c h l o r i d e f r o m e a c h e x t r a c t was p o o l e d and t r e a t e d w i t h a n h y d r o u s


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N a S 0 - t o remove a l l t r a c e s o f w a t e r b e f o r e a n a l y s i s by GCT W i t h t h e PP d i s c s s t i l l mounted on t h e w i r e , t h e sample was r i n s e d w i t h d i s t i l l e d w a t e r (100 mL) to remove t h e l o o s e l y a d h e r e d f l a v o r compound f r o m t h e s u r f a c e o f t h e d i s c s , w i r e and g l a s s b e a d s . The r i n s e w a t e r was a n a l y z e d i n t h e same manner as t h e b u f f e r . A f t e r r i n s i n g , t h e d i s c s were e x t r a c t e d w i t h m e t h y l e n e c h l o r i d e (5 mL χ 3 ) . The m e t h y l e n e c h l o r i d e f r o m t h e t h r e e e x t r a c t i o n s was p o o l e d and t r e a t e d w i t h a n h y d r o u s N a S 0 . t o remove a l l t r a c e s o f w a t e r b e f o r e a n a l y s i s by GCT The b u f f e r s o l u t i o n i n the c o n t r o l s was extracted i n t h e same manner as t h e b u f f e r s o l u t i o n c o n t a i n i n g t h e PP d i s c s . F o r c o n t r o l s c o n t a i n i n g t h e w i r e and g l a s s b e a d s , t h e w i r e and beads were e x t r a c t e d f o r a d h e r e d compounds i n t h e same manner as t h e d i s c s . The q u a n t i t a t i o n o f f l a v o r compounds e x t r a c t e d f r o m t h e PP and f r o m t h e b u f f e r were p e r f o r m e d i n t r i p l i c a t e . The q u a n t i t y o f f l a v o r compound e x t r a c t e d was d e t e r m i n e d u s i n g peak a r e a s . C a l i b r a t i o n c u r v e s were g e n e r a t e d u s i n g peak a r e a s f r o m known c o n c e n t r a t i o n s o f f l a v o r compounds. R e c o v e r y s t u d i e s were p e r f o r m e d t o d e t e r m i n e t h e e f f i c i e n c y o f t h e e x t r a c t i o n method. The statistical a n a l y s e s were p e r f o r m e d u s i n g G e n e r a l L i n e a r M o d e l s P r o c e d u r e by W a l l e r - D u n c a n ( 1 7 ) . 9

4

9


q

Gas Chromatography.

Gas c h r o m a t o g r a p h i c a n a l y s i s was p e r f o r m e d u s i n g a V a r i a n model 3700 gas c h r o m a t o g r a p h w i t h a FID d e t e c t o r c o n n e c t e d t o a H e w l e t t P a c k a r d model 3390A i n t e g r a t o r . The column o v e n t e m p e r a t u r e was programmed as f o l l o w s : 120°C f o r 1 min i n i t i a l h o l d , 1 2 0 ° C - 2 4 0 ° C a t 5 ° C / m i n , and 240°C f o r 10 min f i n a l h o l d . I n j e c t o r and d e t e c t o r t e m p e r a t u r e s were 240°C and 2 5 0 ° C , respectively. A S u p e l c o w a x " 10, ( S u p e l c o , Inc., B e l l e f o n t e , PA) f u s e d s i l i c a c a p i l l a r y column (30 m χ 0.53 mm and 1.0 μπ\ f i l m t h i c k n e s s ) was u s e d . Results

and

Discussion

The p e r c e n t o f f l a v o r compounds s o r b e d by t h e PP s a m p l e s and t h e q u a n t i t y o f f l a v o r compounds e x t r a c t e d and q u a n t i t a t e d f r o m t h e PP, b u f f e r and r i n s e w a t e r a r e presented i n Table I.

Recovery Study.

The p e r c e n t r e c o v e r y f o r e a c h f l a v o r compound was c a l c u l a t e d by c o m p a r i n g t h e q u a n t i t y r e c o v e r e d f r o m t h e two s e t s o f c o n t r o l s w i t h t h e q u a n t i t y i n i t i a l l y p l a c e d i n the b u f f e r . T h e r e was no s i g n i f i c a n t d i f f e r e n c e (P

Sorption of Flavor Compounds by Polypropylene - ACS Publications

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