Chemical Markers for Processed and Stored Foods - American

Chapter 2

Advanced Maillard Products of Disaccharides: Analysis and Relation to Reaction Conditions

Downloaded by UNIV OF PITTSBURGH on March 15, 2016 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1996-0631.ch002

Monika Pischetsrieder and Theodor Severin Institut für Pharmazie und Lebensmittelchemie der Universität München, Sophienstrasse 10, 80333 München, Germany

The degradation of 1,4-glycosidic linked disaccharides, such as maltose and lactose under the condition of the Maillard reaction has been investigated. Two aminoreductones could be isolated which are derived from the 4-deoxyglucosone. Breakdown via the 1-deoxyglucosone pathway leads to 11 typical disaccharide-products. These compounds are not found in glucose reaction mixtures. All these substances can be analyzed using an HPLC system. The correlation between product composition and reaction temperature, time and pH-value has been investigated.

During the Maillard reaction, reducing sugars react with amino groups of proteins or amino acids which results in the formation of a wide range of products. These compounds are of significant importance for nutrition and food processing (7). The nutritional value of food can be reduced by the loss of essential amino acids, decrease of digestibility and formation of toxic and carcinogenic compounds. On the other hand, the so called nonenzymatic browning of food also leads toflavoring,colored and antioxidative products which improve the quality of food and reduce oxidative spoilage. Several efforts have been made to estimate these quality features or determine heat treatment of food by analyzing Maillard products. Especially Amadori compounds or their analogues fiirosine and pyridosine (2,3), as well as advanced products, such as pyrraline, have been suggested for this use (4). In this paper we concentrated on Maillard products derived from 1,4glycosidic linked disaccharides, such as maltose or lactose. Carbohydrates with a 1,4glycosidic link are of considerable relevance for food chemistry. For example, starch is one of the main components of many food stuffs. Maltose is an important degradation product of starch and occurs as such particularly in malted food, whereas the milk sugar lactose is found in dairy products.

0097-6156/96/0631-0014$15.00/0 © 1996 American Chemical Society Lee and Kim; Chemical Markers for Processed and Stored Foods ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

2. PISCHETSRIEDER & SEVERIN Advanced Maillard Products of Disaccharides 15 Degradation Pathway of Disaccharides


When reducing sugars react with primary or secondary amines, the initial products are N-substituted-l-amino-l-deoxyketoses (Figure 1). These so called Amadori products can be isolated and detected from a large variety of different sugars and amino acids (7). However, they are not stable during prolonged storage or heating and undergo degradation to give several different dicarbonyl compounds. The most common are 1-deoxyghxcosone (1-DG), 3-deoxyghicosone (3-DG) and l-amino-1,4dideoxyglucosone (4-DG). The ratio of the deoxyglucosones are particularly dependent on pH-value. The degradation of these intermediates follows three different pathways. 3- Deoxyglucosone pathway. The formation of 3-DG is favored under slightly acidic conditions, whereas it's of less importance at neutral or alkaline pH-range (5). Further degradation of 3-DG leads to two known advanced products: HMF and pyrraline (6) (Figure 2). HMF is mainly formed after treatment of reaction mixtures with strong acids and it is of minor interest as a naturally occurring Maillard product, whereas pyrraline could be detected in heated food, where it can be formed from mono- and disaccharides (3). This means that neither the extent of formation nor the further composition of 3-DG is influenced by the presence of a glycosidic linked sugar in the molecule, but it can be equally formedfromglucose or maltose/lactose. 4- DeoxygIucosone pathway. 4-DG appears to be produced at slightly higher pHvalues and as a degradation product of 1,4-glycosidic linked disaccharides, such as maltose or lactose. Thus far, only little is known about advanced products which are derived from 4-DG. Recently we were able to isolate and identify two aminoreductones which are obviously formed from this intermediate (6): The 4deoxyaminoreductone (4-DA) is a tautomer form of 4-DG (Figure 3). 4-Deoxyosone has not been isolated in its free form, so that 4-DA must be considered as its more stable tautomer. The other new compound, 5,6-dihydro-3-hydroxypyridone (DHHP), is an isomer with pyridone structure. The formation of both products are favored at relatively low temperatures (e.g. room temperature) and short reaction times (30 min), whereas during prolonged heating they degrade to unidentified products. 4DA and DHHP were isolated from several maltose mixtures, but could not be detected when the reaction starts from glucose. It can be assumed that 4-DA and DHHP are derived only from 1,4-glycosidic linked disaccharides, since the formation of the intermediate 4-DG is favoredfromthis type of sugar (7). Both products can be easily oxidized and may contribute to the antioxidative effect of Maillard compounds in food. 1-Deoxyglucosone pathway. Degradation of Amadori products under neutral conditions leads to the formation of 1-DG. The next steps of the breakdown are cyclization and enolization of 1-DG, resulting in a 5- or 6-membered ring. Starting from these intermediates, the degradation of maltose and lactose differ from that of glucose. For the case of glucose, the pyranoid product eliminates water to give a ypyranone, which is a typical advanced product of monosaccharides. On the other

Lee and Kim; Chemical Markers for Processed and Stored Foods ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

16

CHEMICAL MARKERS FOR PROCESSED AND STORED FOODS CH3

c=o 1 c=o HC-O-R HC-OH HjCOH


1 -deoxyglucosone = 1-DG HC*° HC-OH HO-CH HC-O-R HC-OH H COH

2

R'NH 1 » 2

2

glucose: R = H maltose: R = glu lactose: R = gal

HC'-°

H C-NHR' C=0 HO-CH HC-O-R HC-OH H COH

I

c=o HX HC O - R 1 HC OH HjCOH 3-deoxyglucosone = 3-DG

2

Amadori product H C-NHR' C=0 1 C=0 I H,C HC- OH HjCOH 2

4-deoxyglucosone = 4-DG Figure 1. Initial steps of the Maillard reaction of mono- and disaccharides

HC'° I H

c=o

C

' HC-0 1 HC-OH

R = H,glu,gal

H O ^ J l

0

X ^ O

N

A ^ O

I

R'

1

^COH

H O ^

HMF

pyrraline 6

3-DG Figure 2. 3-Deoxyglucosone pathway Lee and Kim; Chemical Markers for Processed and Stored Foods ACS Symposium Series; American Chemical Society: Washington, DC, 1996.


2. PISCHETSRIEDER & SEVERIN Advanced Maillard Products of Disaccharides 17 hand, this reaction is not facilitated if a sugar is bound to position 4, so that a (3pyranone (1) is formedfrommaltose or lactose (8) (Figure 4). A similar rationale can be made for the 5-membered intermediate. The glucose derivative dehydrates to a 4-furanone. 4-Furanone is a relatively labile substance which can be found only in monosaccharide reaction mixtures. In the furanoid structure which is derivedfromdisaccharides, the bound sugar prevents this reaction and the molecule stabilizes itself by forming a 3-furanone (Figure 4). Recently we were able to isolate 3-furanone (7) and establish its structure by spectroscopic data (9). So it can be concluded that in the case of 1-DG, the glycosidic linked sugar in maltose or lactose causes a degradation pathway which is significantly different from glucose and which givesriseto typical disaccharide products. Further Degradation of Disaccharides (3-Pyranone is not a stable end product of the maltose degradation, but reacts in the presence or absence of amines to give a wide range of advanced products (8). In aqueous solution P-pyranone isomerizes to a certain extent to cyclopentenone (2) (Figure 5). The reversible transformation represents an intramolecular aldol type reaction. During prolonged heating P-pyranone and cyclopentenone eliminate water and are irreversibly converted into the more stable glycosylisomaltol (3). 1, 2 and 3 are stable enough to be isolated or detected, however in the presence of amines they easily condense to nitrogen containing products. p-Pyranone and cyclopentenone react mainly with amines to give acetylpyrrol (5) (Figure 6). Similar to isomaltol, acetylpyrrol can be considered as a late and fairly stable Maillard product of maltose or lactose. Furthermore, isomaltol is able to add an amine, resulting in a mixture of pyridinium betaine (4) and furanoneamine (8). Pyridinium betaine may also be formed by the incorporation of amine into an earlier intermediate. Further decomposition results in the stabilization of the fairly labile pyridinium betaine (Figure 7). Elimination of the sugar residue leads to the formation of a pyridone derivative, a stable compound which can be considered as one of the end products of the Maillard reaction of maltose. Under slightly alkaline conditions an intramolecular rearrangement of the sugar residue can also take place forming a pyridone glycoside. Furthermore, the sugar can be substituted by a second molecule of amine to give pyridone imine. Assuming that the reaction involves two lysine side chains, pyridone imine represents a possible crosslink product of proteins. Analysis of Reaction Products In preliminary experiments, model reaction mixtures were investigated. Maltose was reacted with amines such as propylamine or ct-N-acetyllysine. To detect all the previously mentioned maltose products at the same time, an HPLC system can be used with a water-acetonitrile gradient (8). To avoid chromatographic problems with metal complexing substances like pyridone or pyridone imine, common RP-18 columns are to be replaced by Uhracarb material. Applying diode-array-detection, peaks can be identified by their characteristic UV-spectra which allows an unequivocal analysis of the substances.


18

CHEMICAL MARKERS FOR PROCESSED AND STORED FOODS

H,C-NHR' •i C=0 HO CH HC- O - R HC- OH i H C-OH

H C-NHR' 7

2

1

O

C=0 R *H

c=o HC HC-OH H C-OH

HO

2

e.g. maltose, lactose

HC-NHR' n C-OH OH C=0 i HC HC-OH H C-OH 2

I

R'

2

2

2


Amadori product

DHHP

4-DG

4-Deoxyaminoreductone = 4-DA

Figure 3. 4-Deoxyglucosone pathway

CH, i C=0 C=0 HC-O-R HC-OH H C-OH 3

glucose : R = H maltose : R = glu lactose : R = gal

2

1-DG HO

R-0

OH OH CH

OH OH

N

CH3

3

R=H

/ v

R = glu gal

O HO^l^OH ^O^CH, y-pyranone

.0 OH 0

R=H

R = glu

/

OH

H o J t ^ C CH3

R-0 HO

0^CH3

CH3

P-pyranone 1

4-furanone

3-furanone 7

Figure 4. Glucose- and maltose products of the 1-Deoxypathway


2. PISCHETSRIEDER & SEVERIN Advanced Maillard Products of Disaccharides 19

o

f

T CFL OH cyclopentenone 2 3


P-pyranone 1

O isomaltol 3 glycoside Figure 5. Nitrogenfree products derivingfromP-pyranone

P-pyranone 1

acetylpyrrole 5 OR

isomaltol 3 glycoside

pyridinium 4 betaine

furanoneamine 8

Figure 6. Reaction of P-pyranone and glycosyl isomaltol with amines



OR

0


_ N ^CH R' pyridinium betaine

0

fa™, N CH R' pyridone

3

N '

fa* N CH R' pyridone glycoside

3

+

R

fa» N CH3 R' pyridone inline

3

Figure 7. Degradation of pyridinium betaine

Relation to reaction time

1

2

3

4

5

6

7

8

compounds

Figure 8. Correlation between product composition and reaction time


2. PISCHETSRIEDER & SEVERIN Advanced Maillard Products of Disaccharides 21 A number of experiments has shown so far that lysine side chains of proteins react in a similar way as propylamine or free lysine. So it can be assumed that results which were obtainedfrommodel mixtures can be transferred to reactions of proteins or even to the conditions in food.


Correlation between Product Composition and Reaction Time After short time heating of maltose in the presence of amines (30 min. at 100°C) the early maltose products predominate (Figure 8). 1-DG decomposes mainly to the 3furanone, P-pyranone and its isomerization product cyclopentenone. Further degradation products such as glucosyl isomaltol or nitrogen containing compounds like pyridinium betaine and acetylpyrrol are detected in smaller amounts. The latter request incorporation of amines into early intermediates like 1, 2 or 3. Prolonged heating (e.g. 2 h at 100°C) decreases the amount of early products due to the more stable compounds 3, 4 and 5. This tendency becomes even more obvious when the reaction is continued for longer (4h). Correlation between Product Composition and pH Considering the relevance for food processing, a relatively narrow pH range was investigated (Figure 9): pH 7 for neutral, pH 5 for slightly acidic and pH 9 for slightly alkaline conditions. At lower pH value the 3-deoxypathway is favored over the 1-deoxypathway. Pyrraline is by far the main product under these conditions, whereas of the 1-DGderived compounds only glucosyl isomaltol and acetylpyrrol can be detected in significant amounts. In a neutral mixture pyrraline is found as a minor compound and at pH 9 it couldn't be detected. These experiments confirm a correlation which was previously described using other methods: the 1-deoxypathway is the most important mechanism regarding neutral pH range. Decreasing the pH value favors the 3-deoxypathway. The 4-deoxypathway becomes significant for disaccharides under more alkaline conditions (data not shown). Furthermore, at pH 9 the equilibrium between p-pyranone and cyclo pentenone is significantly shifted in favor to the latter. This fact can be explained, because the isomerization proceeds via an intramolecular aldol reaction which is generally favored at higher pH values (Figure 10). Moreover furanoneamine (8), a condensation product of amine and glucosyl isomaltol, can be detected in considerable amounts under these conditions. Correlation between Product Composition and Reaction Temperature Low temperatures (70°C) favor the formation of early products (1 and 7) and slow down their degradation to more stable compounds (Figure 11). On the other hand higher temperatures lead to more rapid production of early Maillard reaction products. At 130°C for example, P-pyranone, cyclopentenone and 3-furanone are barely detectable, whereas late products such as glucosyl isomaltol, acetylpyrrol and pyrraline become predominant.



Relation to pH value


100

.E 2

1 pH5 • • pH7 17771 pH9 I

80

.S>

Chemical Markers for Processed and Stored Foods - American

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