The Maillard Reaction in Foods and Nutrition - American Chemical

15 Maillard Reaction Products as Indicator Compounds for Optimizing Drying and Storage Conditions K. EICHNER Institut für Lebensmittelchemie der Universität Münster, Piusallee 7, D-4400 Munster, Federal Republic of Germany

Downloaded by STANFORD UNIV on June 12, 2013 | http://pubs.acs.org Publication Date: April 29, 1983 | doi: 10.1021/bk-1983-0215.ch015

W. WOLF Bundesforschungsanstalt für Ernährung, Engesser Strasse 20, D-7500 Karlsruhe 1, Federal Republic of Germany

Chemical analysis of Maillard reaction intermediates (Amadori compounds) renders possible an early detection of this reaction. On this basis an analytical control of drying processes can be exerted, thus avoiding temperature and moisture ranges which are critical in respect of product quality. With different varieties of carrots it was shown that quality retention can be improved by lowering air temperature during an initial high-temperature drying step and final drying at lower temperatures to a water content providing optimum storage stability. P h y s i c a l p r e s e r v a t i o n methods f o r foods, such as s t e r i l i z a t i o n and d r y i n g , are a s s o c i a t e d w i t h the a p p l i c a t i o n of h e a t . I n these c a s e s , because o f i t s h i g h temperature c o e f f i c i e n t , the M a i l l a r d r e a c t i o n becomes the dominant d e t e r i o r a t i v e r e a c t i o n (1_>2.>3θ· I t i s w e l l known t h a t the M a i l l a r d r e a c t i o n i n f o o d s i s i n i t i a t e d by the f o r m a t i o n o f c o l o r l e s s and t a s t e l e s s i n t e r m e d i a t e s , which p r e f e r e n t i a l l y are formed i n lowm o i s t u r e systems (Jt>5) ^ t h i s way by r e a c t i o n of g l u cose w i t h amino a c i d s f r u c t o s e - a m i n o a c i d s are formed v i a Amadori rearrangement of the p r i m a r y g l u c o s y l - a m i no a c i d s (1.). F r u c t o s e - a m i n o a c i d s e.g. have been i s o l a t e d from f r e e z e - d r i e d a p r i c o t s and peaches (É>,_7,8_). Amadori compounds a r i s i n g from a l d o s e s and amino a c i d s are formed d u r i n g d r y i n g of f o o d s of p l a n t o r i g i n and can be e a s i l y d e t e c t e d by amino a c i d a n a l y s i s (5.). During f u r t h e r p r o g r e s s o f the M a i l l a r d r e a c t i o n brown d i s c o l o r a t i o n o c c u r s and a g r e a t v a r i e t y o f d i f f e r e n t compounds are formed which p a r t l y cause u n d e s i 9

n

0097-6156/83/0215-0317$06.00/0 © 1983 American Chemical Society In The Maillard Reaction in Foods and Nutrition; Waller, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


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r a b l e sensory changes (9.). S e v e r a l a u t h o r s (10-13) t r i e d t o c o r r e l a t e a n a l y t i c a l w i t h sensory data by u s i n g some t y p i c a l M a i l l a r d p r o d u c t s such as S t r e c k e r d e g r a d a t i o n p r o d u c t s as c h e m i c a l i n d i c a t o r s u b s t a n c e s . The M a i l l a r d r e a c t i o n r a t e i s g r e a t l y i n f l u e n c e d by temperature and water c o n t e n t ; i n a c e r t a i n l o w m o i s t u r e range i t r e a c h e s a maximum. Hendel and cowork e r s (IjJ.) e s t a b l i s h e d a t e m p e r a t u r e - m o i s t u r e profile f o r browning o f w h i t e p o t a t o d u r i n g d r y i n g , from which they were a b l e to c a l c u l a t e t h e e x t e n t o f browning a t d i f f e r e n t drying p e r i o d s . I t turned out t h a t the l a s t d r y i n g p e r i o d maximized browning, whereas the i n t e r v a l of the browning maximum made o n l y minor c o n t r i b u t i o n to o v e r a l l browning response because o f the s m a l l i n h e r e n t time i n t e r v a l s . They concluded t h a t the temperat u r e s h o u l d be l o w e r e d d u r i n g the l a s t d r y i n g p e r i o d , p a r t i c u l a r l y because the a c t i v a t i o n energy o f t h e M a i l l a r d r e a c t i o n i s i n c r e a s e d by d e c r e a s i n g t h e water content. U s i n g a g l u c o s e - g l y c i n e browning model, Kluge and H e i s s (15) e v a l u a t e d t h e p e r m i s s i b l e r e a c t i o n time f o r a g i v e n p e r m i s s i b l e e x t e n t o f browning f o r each temper a t u r e - w a t e r c o n t e n t c o m b i n a t i o n t h a t c o u l d o c c u r dur i n g d r y i n g . Knowing t h e temperature-water c o n t e n t p r o f i l e s d u r i n g d r y i n g , they added t h e r e c i p r o c a l s o f the p e r m i s s i b l e browning times f o r each time i n t e r v a l , i n t h i s way g e t t i n g p o r t i o n s o f t h e p e r m i s s i b l e browning e x t e n t f o r any d r y i n g t i m e . From these experiments g e n e r a l c o n c l u s i o n s can be drawn w i t h r e s p e c t t o an improvement o f t h e q u a l i t y o f d r i e d p r o d u c t s . However, these i n v e s t i g a t i o n s a r e based on the measurement o f browning b e i n g t h e l a s t s t e p o f a m u l t i s t a g e d e t e r i o r a t i v e r e a c t i o n which n o r m a l l y i s a l r e a d y accompanied by t h e f o r m a t i o n o f o f f - f l a v o r s . I t becomes c l e a r t h a t a n a l y t i c a l methods based on the e v a l u a t i o n o f t h e end p r o d u c t s o f d e t e r i o r a t i v e r e a c t i o n s w i l l n o t be s a t i s f a c t o r y . T h e r e f o r e i n our own experiments amino a c i d a n a l y s i s o f Amadori compounds and gas chromatography o f v o l a t i l e S t r e c k e r aldehydes were a p p l i e d t o d e t e c t t h e onset o f t h e M a i l l a r d r e a c t i o n w e l l b e f o r e d e t r i m e n t a l sensory changes o c c u r r e d . D r y i n g o f foods must be l o o k e d a t i n c o n n e c t i o n w i t h s t o r a g e c o n d i t i o n s , because -- e s p e c i a l l y a t h i g h e r w a t e r c o n t e n t s -- t h e M a i l l a r d r e a c t i o n may cont i n u e . I t may occur d u r i n g s t o r a g e a t a g r e a t e r r a t e , p a r t i c u l a r l y i f i t has been i n i t i a t e d d u r i n g d r y i n g by f o r m a t i o n o f Amadori compounds (_5). I f s h e l f l i f e i s l i m i t e d by t h e M a i l l a r d r e a c t i o n , such l i f e may be i n c r e a s e d on t h e o t h e r hand by l o w e r i n g t h e water content of the product (16).

In The Maillard Reaction in Foods and Nutrition; Waller, G., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

15.

EiCHNER A N D W O L F

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In f o r m e r e x p e r i m e n t s (5) we have shown t h a t c h e m i c a l a n a l y s i s f o r Amadori compounds ( m a i n l y con s i s t i n g o f f r u c t o s e - g l u t a m i c a c i d ) and i s o v a l e r a l d e hyde, formed by S t r e c k e r d e g r a d a t i o n o f the amino a c i d s l e u c i n e and i s o l e u c i n e , can be used f o r an e a r l y d e t e c t i o n o f u n d e s i r a b l e q u a l i t y changes caused by t h e M a i l l a r d r e a c t i o n . In o r d e r to demonstrate the u s e f u l ness o f t h e s e compounds as i n d i c a t o r s u b s t a n c e s f o r q u a l i t y improvement o f d r i e d p r o d u c t s , we performed d r y i n g e x p e r i m e n t s w i t h c a r r o t s as an example o f p l a n t products.


Pro cedure P r e p a r a t i o n of t h e m a t e r i a l and d r y i n g Fresh c a r r o t s were c u t i n t o cubes (edge l e n g t h : 1 c m ) , b l a n c h e d w i t h b o i l i n g water f o r about 2 min, p l a c e d on w i r e s c r e e n s ( s i n g l e p r o d u c t l a y e r ) and d r i e d w i t h upstream c i r c u l a t i n g h o t a i r (about 3 m/s). A f t e r v a r i o u s time i n t e r v a l s , t h e s c r e e n s were removed from the d r y e r and t h e l o s s of water was d e t e r m i n e d by w e i g h i n g . I n samples a s s i g n e d f o r c h e m i c a l a n a l y s i s the water c o n t e n t was d e t e r m i n e d by vacuum d r y i n g a t 70 °C f o r k h. Samples h a v i n g h i g h e r water c o n t e n t s were s t a b i l i z e d by f r e e z e - d r y i n g p r i o r t o a n a l y s i s . For t h e c o n s t a n t - t e m p e r a t u r e h e a t i n g e x p e r i m e n t s d i f f e r e n t p r o d u c t water c o n t e n t s were o b t a i n e d by s t o r a g e o f f r e e z e - d r i e d c a r r o t s over s a t u r a t e d s a l t solutions (17). D e t e r m i n a t i o n o f Amadori compounds and browning D r i e d c a r r o t s (1.5 g) were homogenized i n a mixer w i t h 25 ml d e i o n i z e d water (7x10^ rpm) and c e n t r i f u g e d f o r 30 min a t 5 °C ( 2 0 x 1 0 rpm). F o r e v a l u a t i o n o f t h e e x t e n t o f browning t h e e x t i n c t i o n v a l u e s o f t h e ex t r a c t s were measured a f t e r d i l u t i n g them w i t h water (1:10). The Amadori compounds were d e t e r m i n e d u s i n g an amino a c i d a n a l y z e r ( B i o t r o n i c LC-2000). To 2 ml o f the c a r r o t e x t r a c t 2 ml 0.1 Ν HC1 and 1 ml o f b u f f e r c o n c e n t r a t e A were added; t h e m i x t u r e was d i l u t e d w i t h water t o a t o t a l volume o f 10 ml and 0.1 ml o f t h e r e s u l t i n g s o l u t i o n was i n j e c t e d onto the amino a c i d ana lyzer. Analytical conditions. The a n a l y t i c a l column c o n t a i n e d a s t r o n g l y a c i d c a t i o n exchange r e s i n , Dionex DC-6A; column h e i g h t : 20 cm; column d i a m e t e r : 0.6 cm; column t e m p e r a t u r e : 36 °C. The washing column c o n t a i n e d Dionex D C - 3 L i ; column h e i g h t : 1| cm. B u f f e r c o n c e n t r a t e A: L i c i t r a t e , 1.8 M L i ; pH 2.38. B u f f e r A: L i c i t r a t e , 0.18 M L i , pH 2.38. B u f f e r B: 3

+

+


320

M A I L L A R D REACTIONS

+

L i c i t r a t e , 0.23 M L i , pH 3.10. B u f f e r program (min): A: 0-17; B: 17-60; LiOH (0.4 M) : 60-85; A: 85-UO. B u f f e r f l o w : 30 ml/h; n i n h y d r i n f l o w : 20 ml/h. For c a l c u l a t i o n of the molar r a t i o of Amadori compounds of peak C i n the amino a c i d chromatogram ( F i g u r e 1 ) the f o l l o w i n g f o r m u l a was used: r

(

m

n

l

a \

=

1 , 7 x [ c l x 100

1 , 7x [CJ + [Thré] + [Ser] + £Asp-NH^]+ [GluJ + [Glu-NH j The c o n c e n t r a t i o n s are e x p r e s s e d as i n t e g r a t i o n u n i t s of the peak a r e a s ( c o u n t s ) , the f a c t o r 1.7 being the ninhydrin color-correction factor. Downloaded by STANFORD UNIV on June 12, 2013 | http://pubs.acs.org Publication Date: April 29, 1983 | doi: 10.1021/bk-1983-0215.ch015

u

^

m o ± / o J

2

Head-space gas c h r o m a t o g r a p h i c d e t e r m i n a t i o n of i s o v a l e r a l d e h y d e D r i e d c a r r o t s a m p l e s ( 0 . 5 g) were p l a c e d i n septum v e s s e l s (24- ml) and 5 ml of water cont a i n i n g i s o b u t y l a l c o h o l as an i n t e r n a l s t a n d a r d (1 : 20.000 v/v) were added. A f t e r s e a l i n g w i t h a septum the head-space v e s s e l s were k e p t i n a t h e r m o s t a t a t 85 °C. A f t e r 30 min 1 ml of the head-space gas was withdrawn w i t h a s y r i n g e h e a t e d a t 85 °C and i n j e c t e d i n t o a gas chromatograph. The area of the i s o v a l e r a l d e hyde peak (j5) was d e t e r m i n e d by u s i n g an i n t e g r a t o r . For d e t e r m i n a t i o n of the a b s o l u t e i s o v a l e r a l d e h y d e conc e n t r a t i o n s known amounts of s o l u t i o n s c o n t a i n i n g known c o n c e n t r a t i o n s of i s o v a l e r a l d e h y d e were added to the samples and the r e s u l t i n g peak a r e a s i n the gas chromatogram were measured. In t h i s way the i s o v a l e r a l d e h y d e peak a r e a s c o u l d be c o r r e l a t e d w i t h the i s o v a l e r a l d e hyde c o n c e n t r a t i o n s p r e s e n t i n the s t a n d a r d s o l u t i o n s and the sample. A n a l y t i c a l c o n d i t i o n s : 2-m g l a s s column ( 0.2 mm), f i l l e d w i t h Chromosorb 101. Column t e m p e r a t u r e s : 6 min 120 °C, h e a t e d to 14-0 °C (temperature g r a d i e n t : k °C/min). C a r r i e r gas f l o w : 25 ml ^ / m i n ; d e t e c t o r : FID. R e t e n t i o n t i m e s f o r i s o b u t y l a l c o h o l ( s t a n d a r d ) : 667 s and f o r i s o v a l e r a l d e h y d e : 869 s. Results O p t i m i z a t i o n of d r y i n g by the use of Amadori compounds F i g u r e 1 shows an amino a c i d chromatogram of d r i e d c a r r o t s . Peak C i n the chromatogram r e p r e s e n t s the Amadori compounds f r u c t o s e - t h r e o n i n e , - s e r i n e , - a s p a r a g i n e , - g l u t a m i c a c i d and - g l u t a m i n e formed by r e a c t i o n of g l u c o s e w i t h the r e s p e c t i v e amino a c i d s . These compounds are formed w i t h o u t i n d u c t i o n p e r i o d a t a l l e x p e r i m e n t a l c o n d i t i o n s (5.)· The molar r a t i o of peak C (mol %) can be used as a measure f o r the l a t e n t heat impact d u r i n g d r y i n g , which i s c a u s i n g a r e d u c t i o n



15.

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WOLF

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of s h e l f l i f e . In o r d e r to f i n d o u t , w h i c h p e r i o d o f time produces Amadori compounds, we p e r f o r m e d d r y i n g e x p e r i m e n t s on c a r r o t s . F i g u r e 2 r e p r e s e n t s an a i r d r y i n g experiment w i t h c a r r o t cubes a p p l y i n g an a i r temper a t u r e of 110 °C. As the p r o d u c t t e m p e r a t u r e r i s e s , the f o r m a t i o n o f Amadori compounds s t a r t s and p a r a l l e l s temperature i n c r e a s e u n t i l a maximum i s r e a c h e d , beyond which d e c o m p o s i t i o n of these browning i n t e r m e d i a t e s p r e d o m i n a t e s , whereas browning does n o t become s i g n i f i cant t i l l t h i s p o i n t . F u r t h e r i n v e s t i g a t i o n s aimed a t e l u c i d a t i o n o f temperature and m o i s t u r e ranges c r i t i c a l i n r e s p e c t o f f o o d q u a l i t y impairment were done. F i g u r e 3 shows the d r y i n g course of the c a r r o t v a r i e t y "Bauer's K i e l e r Rot e " a t an a i r temperature of 110 °C, p r o j e c t i n g the dec r e a s e i n m o i s t u r e c o n t e n t (weight % r e l a t e d to wet m a t t e r ) , the r i s e of p r o d u c t t e m p e r a t u r e , and the i n c r e a s e i n c o n c e n t r a t i o n of Amadori compounds (C, mol % ). F i g u r e s 4- and 5 g i v e r e s u l t s of the c o r r e s p o n d i n g d r y i n g e x p e r i m e n t s a t a i r t e m p e r a t u r e s of 90 and 60 C, r e s p e c t i v e l y . From t h e s e e x p e r i m e n t s the s t r o n g i n f l u ence of temperature on f o r m a t i o n of Amadori compounds becomes e v i d e n t , r e l a t e d to the f a c t t h a t the M a i l l a r d r e a c t i o n has a much h i g h e r t e m p e r a t u r e c o e f f i c i e n t than the water v a p o r i z a t i o n r a t e . F i g u r e 6 summarizes the d e s c r i b e d r e s u l t s by p l o t t i n g the c o n c e n t r a t i o n s o f Amadori compounds (C, mol %) v e r s u s water c o n t e n t ( r e l a t e d to wet m a t t e r ) . The s t r o n g i n c r e a s e i n f o r m a t i o n of t h e s e r e a c t i o n i n t e r m e d i a t e s a t l o w e r m o i s t u r e cont e n t s may be a t t r i b u t e d on the one hand to the l o n g e r r e t e n t i o n t i m e s i n t h i s m o i s t u r e i n t e r v a l , on the o t h e r to an i n c r e a s e i n the r a t e of f o r m a t i o n of Amadori compounds below a water c o n t e n t of about 20 %, a p p r o a c h i n g a maximum, as w i l l be shown l a t e r . The dashed l i n e s i n F i g u r e 6 mark the l i m i t of p e r c e p t i b i l i t y of u n d e s i r a b l e s e n s o r y changes ( l i n e 1) and the t o l e r a b l e upper l i m i t of q u a l i t y d e c r e a s e ( l i n e 2) caused by the M a i l l a r d r e a c t i o n . D u r i n g d r y i n g to a f i n a l water c o n t e n t of 7 %, t h i s upper l i m i t i s exceeded a t an a i r temperat u r e of 110 °C, whereas a t an a i r temperature of 90 C o n l y the l i m i t of s e n s o r y p e r c e p t i b i l i t y i s c r o s s e d ; an a i r temperature of 60 °C does not l e a d to any change i n sensory q u a l i t y owing to M a i l l a r d r e a c t i o n p r o d u c t s . F i g u r e 7 i n the same way p r e s e n t s the f o r m a t i o n o f brown p r o d u c t s d u r i n g a i r d r y i n g of the c a r r o t v a r i e t y mentioned. Browning was determined by measuring the ext i n c t i o n v a l u e s of water e x t r a c t s of c a r r o t samples a t 4-20 nm. By comparing F i g u r e 7 w i t h F i g u r e 6, i t a g a i n becomes c l e a r t h a t v i s i b l e browning s t a r t s much l a t e r than the f o r m a t i o n of M a i l l a r d r e a c t i o n i n t e r m e d i a t e s .


322

MAILLARD

Glu-NH

REACTIONS

2

II

Asp


Glu

0

10

20 retention

30 time

40

50

60

( min )

Figure 1. Shortened chromatogram of amino acids in air-dried carrots. Peak C represents Amadori compounds formed by reaction between glucose and the amino acids threonine, serine, asparagine, glutamic acid, and glutamine.

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The Maillard Reaction in Foods and Nutrition - American Chemical

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