Thermal Generation of Aromas - American Chemical Society

Chapter 11

Processing Parameters and Volatile Compounds from Milk Fat 1

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0409.ch011

Y. J . Yoo, R. C. Whiteman, J . K. Dore, M . A. Amer , and Wassef W. Nawar Department of Food Science and Nutrition, University of Massachusetts, Amherst, MA 01003 Butteroil is known to generate unique flavors when exposed to heat. Not only the quantitative nature of the volatiles produced, but also the relative concentrations of these volatiles are important to flavor. The purpose of this study was to investigate the effect of certain factors on the quantitative pattern of volatiles produced from butteroil by heating. Although the compounds formed reflect thermal oxidation of the major fatty acids present in the butteroil, the relative amounts of these volatiles may vary significantly depending on the concentration of each substrate fatty acid, the surface-tovolume ratio during heating, the heating time and losses by volatilization. M i l k f a t i s known t o g e n e r a t e unique flavor-compounds when exposed to heat ( 1 - 5 ) . I n a p r e v i o u s r e p o r t ( 6 ) , we p r o v i d e d a d e t a i l e d q u a l i t a t i v e and q u a n t i t a t i v e a n a l y s i s o f the v o l a t i l e components generated from b u t t e r o i l by h e a t i n g f o r 1 h r a t 185 C. More t h a n 200 compounds were d e t e c t e d and, o f t h e s e , 152 were i d e n t i f i e d and measured. The major v o l a t i l e compounds c o n s i s t e d o f a l k a n a l s , a l k e n a l s , m e t h y l and e t h y l k e t o n e s , a l k a d i e n a l s , a l k a n e s and V~and ^ " - l a c t o n e s . A d e f i n i t e c o r r e l a t i o n was e v i d e n t between f a t t y a c i d c o m p o s i t i o n o f the m i l k f a t and the v o l a t i l e s expected from s i m p l e c l e a v a g e o f the monohydroperoxides formed by o x i d a t i o n o f the major f a t t y a c i d s . Thus, 2-decenal and 2-undecenal were the most abundant o f the a l k e n a l s e r i e s , w h i l e n o n a n a l and o c t a n a l were the most abundant o f the n - a l k a n a l s e r i e s . The 2-ketone found i n the g r e a t e s t amount was the C15 homolog f o l l o w e d by the C13. A l l members o f t h e Y - l a c t o n e s e r i e s were produced by h e a t i n g but o n l y the ^ " - l a c t o n e s o f even c a r b o n numbers were formed i n s i g n i f i c a n t q u a n t i t i e s . I t i s o b v i o u s t h a t many o f t h e s e v o l a t i l e s c o n t r i b u t e t o t h e aroma g e n e r a t e d from m i l k f a t by h e a t i n g . I n 1967, K i n s e l l a e t a l . emphasized the f l a v o r c a p a b i l i t i e s o f m i l k f a t and o u t l i n e d a scheme f o r t h e i r u t i l i z a t i o n ( 7 ) . The l a c t o n e s and m e t h y l ketones a r e Current address: The Montreal General Hospital Institute, McGill University, Montreal H3G 1A4, Canada 0097-6156/89/0409-0114$06.00/0 © 1989 American Chemical Society Parliment et al.; Thermal Generation of Aromas ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


11. YOOETAL.

Processing Parameters andVolatile CompoundsfromMilk Fat 115

h i g h l y f l a v o r f u l compounds which c o n t r i b u t e s i g n i f i c a n t l y t o t h e p l e a s a n t f l a v o r a t t r i b u t e s o f many d a i r y p r o d u c t s . I f generated i n e x c e s s i v e amounts, however, they c a n impart o f f - f l a v o r s . The f l a v o r potency o f t h e m e t h y l ketones v a r y w i t h c a r b o n - c h a i n l e n g t h , w i t h heptanone h a v i n g t h e l o w e s t f l a v o r t h r e s h o l d , i . e . 0.7 ppm i n m i l k ( 8 ) . Both V- and ^ " - l a c t o n e s impart t y p i c a l f l a v o r s d e s c r i b e d as b u t t e r y , coconut and p e a c h - l i k e . T h e i r f l a v o r t h r e s h o l d v a l u e i s a p p r o x i m a t e l y 5 ppm i n b u t t e r f a t . The a l k a n a l s , a l k e n a l s and a l k a d i e n a l s have been i m p l i c a t e d i n a wide range o f f l a v o r s , b o t h p l e a s a n t and u n p l e a s a n t . " F r u i t y " , "creamy", "cucumber", "beany", " g r a s s y " , " f i s h y " , " p a i n t y " , " t a l l o w y , " c a r d b o a r d " and " o x i d i z e d " , a r e some o f t h e many terms w h i c h have been used t o d e s c r i b e t h e s e f l a v o r s . Some u n s a t u r a t e d aldehydes e x i b i t e x t r e m e l y l o w t h r e s h o l d v a l u e s , e.g. 1.5 ppb f o r 4 - h e p t e n a l i n b u t t e r f a t ( 9 ) . C l e a r l y , t h e f l a v o r impact o f any g i v e n compound a t any g i v e n time depends n o t o n l y on i t s c h e m i c a l n a t u r e , b u t a l s o on i t s quan t i t a t i v e l e v e l , i t s t h r e s h o l d v a l u e and i t s i n t e r a c t i o n w i t h t h e o t h e r components p r e s e n t . The purpose o f t h e p r e s e n t work was t o s t u d y t h e v a r i o u s parameters which i n f l u e n c e t h e q u a n t i t a t i v e p a t t e r n o f v o l a t i l e s produced from b u t t e r o i l by h e a t i n g . Experimental M a t e r i a l s : Reagents and a u t h e n t i c compounds f o r use as s t a n d a r d s were purchased i n t h e h i g h e s t a v a i l a b l e p u r i t y . B u t t e r o i l was p r e p a r e d from u n s a l t e d b u t t e r by c e n t r i f u g a t i o n a t 60 C. Four b u t t e r o i l f r a c t i o n s of d i f f e r e n t f a t t y a c i d composition, obtained by c r y s t a l l i z a t i o n a t 19 C and 29 C (10) , were p r o v i d e d by t h e D a i r y Bureau o f Canada. Heat Treatment: H e a t i n g o f b o t h 5 g- and 350 g-samples were s t u d i e d . In t h e case o f t h e 5 g-samples, t h e o i l was p l a c e d i n 225 mL round bottomed f l a s k s which were e i t h e r s e c u r e l y capped o r l e f t open. S u r f a c e - t o - v o l u m e r a t i o f o r these samples was 22.6/cm. I n case o f the 350 g-samples, t h e o i l was p l a c e d i n 1 L s t a i n l e s s - s t e e l beakers w i t h i n t e r n a l d i a m e t e r s o f 10.0 cm, p r o v i d i n g a s u r f a c e - t o - v o l u m e r a t i o o f 0.9/cm. H e a t i n g was conducted i n a s i l i c o n e o i l b a t h , m a i n t a i n e d a t 185± 2 C. A n a l y s i s : The v o l a t i l e s were c o l l e c t e d by high-vacuum c o l d - f i n g e r d i s t i l l a t i o n as d e s c r i b e d p r e v i o u s l y ( 1 1 ) , and f r a c t i o n a t e d on s i l i c a i n t o p o l a r and n o n p o l a r f r a c t i o n s t o reduce component o v e r l a p p i n g d u r i n g gas chromatographic a n a l y s i s ( 6 ) . S e p a r a t i o n was conducted on a 30 m χ 0.32 mm i . d . Supelcowax 10 c a p i l l a r y column i n a H e w l e t t P a c k a r d Model 5890 chromatograph equipped w i t h a flame i o n i z a t i o n d e t e c t o r ( F I D ) . Q u a n t i t a t i o n was done w i t h the a i d o f two i n t e r n a l s t a n d a r d s , one p o l a r and one n o n p o l a r , which were added t o t h e o i l sample b e f o r e v o l a t i l e c o l l e c t i o n . A H e w l e t t - P a c k a r d model 5985B chromatography-mass s p e c t r o m e t r y (GC/MS) system was used f o r i d e n t i f i c a t i o n o f t h e v o l a t i l e s . R e s u l t s and D i s c u s s i o n To examine t h e e f f e c t o f f a t t y a c i d c o n c e n t r a t i o n on t h e major v o l a t i l e s produced, f i v e 5 g-samples o f d i f f e r e n t f a t t y a c i d

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


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THERMAL GENERATION OF AROMAS

c o m p o s i t i o n ( i . e . whole b u t t e r o i l p l u s the f o u r b u t t e r o i l f r a c t i o n s o b t a i n e d by c r y s t a l l i z a t i o n ) were heated i n a c l o s e d f l a s k a t 185 C f o r 1 h r , and t h e v o l a t i l e s a n a l y s e d . A l i n e a r r e l a t i o n s h i p was e v i d e n t when the c o n c e n t r a t i o n s o f s u b s t r a t e f a t t y a c i d s were p l o t t e d a g a i n s t c o n c e n t r a t i o n s of t h e i r o x i d a t i o n p r o d u c t s , as f o r example between o l e i c a c i d and d e c e n a l , u n d e c e n a l , n o n a n a l , o c t a n a l and n o n e n a l ( F i g u r e l a ) ; p a l m i t i c a c i d and 2-pentadecanone ( F i g u r e l b ) ; and l i n o l e i c a c i d and 2 , 4 - d e c a d i e n a l (Figure l c ) . I n another e x p e r i m e n t , t h e e f f e c t s o f h e a t i n g time and s u r f a c e to-volume r a t i o o f t h e h e a t i n g o i l were s t u d i e d . Four d i f f e r e n t h e a t i n g c o n d i t i o n s were compared: 5 g o i l , r e p r e s e n t i n g a r e l a t i v e l y l a r g e s u r f a c e - t o - v o l u m e r a t i o , heated f o r 1 h r i n b o t h c l o s e d and open systems; 350 g o i l , r e p r e s e n t i n g s m a l l e r s u r f a c e - t o - v o l u m e r a t i o , heated f o r 1 h r ; 350 g o i l heated f o r 37 h r . The q u a n t i t a t i v e r e s u l t s a r e g i v e n i n T a b l e I , where the compounds l i s t e d c o r r e s p o n d t o numbered peaks i n F i g u r e 2. I t i s c l e a r t h a t t h e s u r f a c e - t o volume r a t i o of t h e o i l d u r i n g h e a t i n g i s an e x t r e m e l y important f a c t o r . I n g e n e r a l , the amounts o f t h e a l d e h y d e s , k e t o n e s , and l a c t o n e s produced were much h i g h e r when t h a t r a t i o was h i g h , t h a t i s , when a l a r g e s u r f a c e a r e a e x i s t s . The d i f f e r e n c e i n v o l a t i l e amounts between t h e c l o s e d and open 5 g - h e a t i n g s i s not s u r p r i s i n g . The s h o r t e r c h a i n compounds (Peaks 13 - 37) were found i n lower q u a n t i t i e s i n t h e open system, p r o b a b l y due t o l o s s e s v i a v o l a t i l i z a t i o n . The a l d e h y d e s e l u t i n g a f t e r peak 37 were found a t h i g h e r l e v e l s i n the open system, perhaps due t o t h e r e s u l t of t h e g r e a t e r a v a i l a b i l i t y o f oxygen. T h i s was not always the case f o r the k e t o n e s w h i c h can be produced by n o n - o x i d a t i v e mechanisms, and a r e a l s o more v o l a t i l e than t h e i r corresponding aldehydes. Comparison between 1 h r and 37 h r - h e a t i n g s does not p r o v i d e a c o n s i s t e n t t r e n d ; some v o l a t i l e s r e m a i n i n g a t t h e same l e v e l , w h i l e o t h e r s i n c r e a s i n g a t d i f f e r e n t r a t e s . To c l a r i f y t h e e f f e c t of h e a t i n g t i m e , a new experiment was conducted w i t h more f r e q u e n t measurements over a p e r i o d o f 5 days. S e v e r a l samples o f b u t t e r o i l , 10 g e a c h , were p l a c e d i n s p e c i a l g l a s s tubes t o m a i n t a i n a s u r f a c e to-volume r a t i o s i m i l a r t o t h a t o f t h e 350 g b a t c h e s o f the p r e v i o u s e x p e r i m e n t . A l l samples were h e a t e d i n t h e same 185 C o i l b a t h , and tubes t a k e n out f o r v o l a t i l e a n a l y s i s a t s p e c i f i e d i n t e r v a l s . F i g u r e 3a shows t h e q u a n t i t a t i v e b e h a v i o r of 2 - a l k e n a l s . The amount o f each compound reached a maximum a f t e r 4 h r of h e a t i n g , t h e n d e c r e a s e d t o a p l a t e a u . F o r a l l f o u r compounds a s h o u l d e r was o b s e r v e d between a p p r o x i m a t e l y 12 h r and 40 h r . The same t r e n d s were observed f o r t h e a l k a n a l s ( F i g u r e 3 b ) , t h e m e t h y l k e t o n e s ( F i g u r e 3 c ) , t h e a l k a n e s ( F i g u r e 3 d ) , and the a l k a d i e n a l s ( F i g u r e 3 e ) . The b e h a v i o r o f t h e l a c t o n e s was not c l e a r ( F i g u r e 3 f ) . The ' s h o u l d e r phenomenon, w h i c h was observed f o r most of t h e compounds t e s t e d , can n o t be e x p l a i n e d a t t h i s t i m e . I t i s c l e a r from t h e above t h a t w h i l e t h e q u a n t i t a t i v e n a t u r e of t h e v o l a t i l e s g e n e r a t e d from b u t t e r o i l by h e a t i n g i s p r e d i c t a b l e , the r e l a t i v e q u a n t i t i e s of such v o l a t i l e s may v a r y s i g n i f i c a n t l y depending on t h e c o n c e n t r a t i o n s o f t h e d i f f e r e n t f a t t y a c i d s i n t h e b u t t e r o i l , surface-to-volume r a t i o during h e a t i n g , heating time, and any f a c t o r w h i c h may i n f l u e n c e l o s s e s by v o l a t i l i z a t i o n o f t h e d i f f e r e n t components o f the v o l a t i l e m i x t u r e , e.g. vapor p r e s s u r e , 1


11. YOO ET AL.

Processing Parameters and Volatile Compounds from Milk Fat 117

T a b l e I . Q u a n t i t a t i v e A n a l y s i s o f t h e P o l a r Components (ug v o l a t i l e s / g o i l ) Produced from B u t t e r o i l by H e a t i n g


Pk no. Fig.2

13 14 15 17 18 19 21 22 23 24 27 28 29 30 34 35 37 44 45 46 47 51 52 53 54 57 58 59 60 64 65 66 70 72 75 76 80 83 85 88 89 94 95 96

5 g,Heated 185 C, 1 h r Compound

2-heptanone heptanal t,2-hexenal 2-octanone octanal t,2-heptenal 2-nonanone nonanal t,2-octenal t,c-2,4-heptadienal t,t-2,4-heptadienal 2-decanone decanal t,2-nonenal 2-undecanone undecanal t,2-decenal 2-dodecanone dodecanal t,2-undecenal t,c-2,4-decadienal t,t-2,4-decadienal 2-tridecanone tridecanal t,2-dodecenal y-octalactone 2-tetradecanone tetradecanal t,2-tridecenal ï-nonalactone 2-pentadecanone pentadecanal ^-decalactone $"-decalactone Y-undecalactone 2-heptadecanone V-dodecalactone t>-dodecalactone >£-tridecalactone -tetradecalactone S-tetradecalactone Y-hexadecalactone S-hexadecalactone hexadecanoic a c i d

Unheated Control 0.7 0.1 tr tr tr tr 0.3 0.2 tr 0 0.3 0.2 0.4 0 0.3 0 0.8 0 0 0 0 0 0.5 tr 0 0 0.1 0.5 0 0.3 0.8 0.3 tr 4.8 0 0 1.6 8.2 0 tr 5.8 tr 7.0 tr

c

l

o

s

e

d

12.1 40.5 9.9 4.1 41.0 32.0 8.1 66.8 24.4 6.8 17.8 2.9 13.0 26.8 9.9 10.1 77.8 2.1 10.0 77.8 9.0 28.7 14.0 9.4 3.4 6.8 2.9 8.2 2.8 5.0 35.4 8.1 6.2 9.2 2.7 10.2 5.5 17.4 2.4 7.1 17.6 19.6 11.9 (4.2)

Q

p

e

n

1,.1 10,.8 2,.5 0,.9 13,.3 9,.2 1,.1 30,.9 9,.6 3,.0 7,.3 3,.7 2,.1 13,.3 4,.8 5,.9 62 .3 5 .1 5.7 80 .6 13.2 50 .5 7 .3 13 .9 7 .8 4.6 tr 8.2 3 .6 4.9 39 .1 16.9 6.6 8.8 5 .7 4.0 9.8 41 .6 tr 16.5 57.8 18 .0 25 .2 (40.4)

350 g, Heated, 185 C, open χ h

r

5.6 1.4 0.4 tr 1.1 1.7 3.6 3.2 1.1 0.4 1.9 tr 0.7 2.1 5.8 0.3 4.9 tr 0.5 4.9 0.8' 3.5 11.6 0.6 tr tr 1.4 1.2 tr 0.3 32.5 1.4 0.9 8.6 tr 3.0 2.5 22.5 tr 0.7 22.3 3.1 7.1 (9.8)

3

y

h

r

0.3 2.2 0.6 0.2 2.7 2.0 0.3 5.3 2.1 0.4 1.2 0.4 1.2 2.7 0.4 0.8 10.5 0.3 1.3 12.7 1.2 4.9 0.9 1.2 0.8 0.5 0.5 1.9 0.8 0.7 5.4 3.2 1.9 0.6 0.9 5.6 1.5 1.4 1.0 4.9 9.9 11.9 13.6 (10.9)



(%)

F i g u r e 2. Gas c h r o m a t o g r a p h i c a n a l y s i s o f the p o l a r v o l a t i l e components from b u t t e r o i l h e a t e d f o r 1 h r a t 185 C. Only t h e r e l e v a n t peak i d e n t i f i c a t i o n s a r e g i v e n i n T a b l e 1.

F i g u r e 1. R e l a t i o n s h i p between c o n c e n t r a t i o n o f s u b s t r a t e f a t t y a c i d and v o l a t i l e s produced: a) p a l m i t i c , b) o l e i c , c) l i n o l e i c .

Substrate Fatty Acid


Q g S

00

YOOETAL.

Processing Parameters and

Volatile Compounds from Milk Fat


11.

Heating T i m e

(day)

F i g u r e 3. E f f e c t of h e a t i n g time on the amount of v o l a t i l e produced: a) a l k e n a l s , b) a l k a n a l s , c) m e t h y l k e t o n e s , d) d i e n a l s , e) a l k a n e s , and f ) l a c t o n e s .


119

THERMAL GENERATION OF AROMAS

120

s o l u b i l i t y i n t h e o i l , temperature o f h e a t i n g , e t c . Such v a r i a t i o n s , i n t u r n , would c e r t a i n l y have a d e f i n i t e impact on the f i n a l aroma. I t i s v e r y d i f f i c u l t however t o determine t h e f l a v o r impact s i g n i f i c a n c e o f i n d i v i d u a l components, due t o the l a r g e number o f compounds p r e s e n t and t h e g r e a t d i f f e r e n c e s i n t h e i r r e l a t i v e c o n c e n t r a t i o n s and f l a v o r t h r e s h o l d v a l u e s . I n our o p i n i o n , an approach s i m i l a r t o t h a t proposed by U l l r i c h and Grosch (12) i s needed t o more e f f e c t i v e l y e v a l u a t e the s i g n i f i c a n c e of t h e v o l a t i l e s g e n e r a t e d from m i l k f a t i n s p e c i f i c f l a v o r s . These a u t h o r s d e s c r i b e an e l e g a n t p r o c e d u r e t o d e t e r m i n e " f l a v o r d i l u t i o n f a c t o r s " by gas c h r o m a t o g r a p h i c a n a l y s i s and e f f l u e n t s n i f f i n g of a d i l u t i o n s e r i e s of the o r i g i n a l aroma e x t r a c t s .


Acknowledgments T h i s work was s u p p o r t e d i n p a r t by U n i v e r s i t y of M a s s a c h u s e t t s A g r i c u l t u r a l Experiment S t a t i o n P r o j e c t No. 586 and a g r a n t from the D a i r y Bureau of Canada. Literature Cited 1. Wong, Ν. P.; Patton, S.; Forss, D. A. J. Dairy Sci. 1958, 41, 1960. 2. Nawar, W. W.; Cancel, L. E.; Fagerson, I. S. J. Dairy Sci. 1962, 45, 1172. 3. Langler, J. E.; Day, E. A. J. Dairy Sci. 1964, 47, 1291. 4. Parliment, T. Η.; Nawar, W. W.; Fagerson, I. S. J. Dairy Sci. 1965, 48, 615. 5. Forss, D. A. J. Agric. Food Chem. 1969, 17, 681. 6. Nawar, W. W.; Yoo, Y. J.; Bradley, M.S.; Morin, O.; Potter, T.; Whiteman, R. C. Rev. Franc. des Corps Gras 1988, 35, 117. 7. Kinsella, J. E.; Patton, S.; Dimmick, P. S. J. Am. Oil Chem. Soc. 1967, 44, 449. 8. Langler, J. E.; Day, E. A. J. Dairy Sci. 1964, 47, 1291. 9. Dejong, K.; Vander Wei, H. Nature 1964, 202, 553. 10. Amer, Μ. Α.; Kupranycz, D. B.; Baker, Β. Ε. J. Am. Oil Chem. Soc. 1985, 62, 1551. 11. Nawar, W. W.; Champagne, J. R.; Dubravcic, M. F.; Letellier, P. R. J. Agric. Food Chem. 1969, 17, 645. 12. Ullrich, F.; Grosch, W. Z. Lebensm. Unters. Forsch. 1987, 184, 227. RECEIVED June 8, 1989


Thermal Generation of Aromas - American Chemical Society

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