Flavor is one of the most important factors in attracting consumers and maximizing food quality, and the Maillard reaction (MR) is highly-involved in flavor formation. However, Maillard reaction products have a big drawback in their relatively low stability in thermal treatment and storage. Amadori rearrangement products (ARPs), MR intermediates, can alternatively act as potential flavor additives for their better stability and fresh flavor formation ability.
1. Introduction
The Maillard reaction has been one of the most important reactions in flavor generation since its first discovery by French chemist Louis-Camille Maillard in 1912
[1]. The sophisticated reaction cascades start with the formation of a Schiff base (glycosylamine) from the condensation reaction between the carbonyl groups of reducing sugars and amino groups of amino acids, peptides or proteins. The Schiff base then goes through Amadori rearrangement with a nucleophilic catalyst and forms a more stable 1-amino-1-deoxy-2-ketose, called Amadori rearrangement products (ARPs)
[2]. While ARPs are specific for a Schiff base derived from aldose sugar, Heyns rearrangement products (HRPs, 2-amino-2-deoxyaldose) are derived from ketose sugar
[3]. The successive breakdown of ARPs or HRPs generates abundant volatile carbocyclic and heterocyclic compounds, oligomers and polymers, thus bring various flavor and yellowish to brown colors to food products
[4].
The Maillard reaction is commonly seen in thermally processed food with attractive and complex flavors, such as bread, cereal, coffee, roasted meat. These flavors mainly come from the formation of pyrazines, pyrroles, alkylpyridines, acylpyridines, furanones, furans, oxazoles, and thiophenes
[5]. Each gives a unique flavor of cooked food. However, these Maillard reaction-derived flavors are of unsatisfactory stability. Food products likely go through high temperature processing like boiling, baking, frying or pasteurization and then a specific shelf life range from a few days to years before consumption. The loss of attractive flavor compounds such as acetaldehyde, furfural and butanal, has been a major concern regarding flavor quality and consumer acceptance
[6]. Enormous efforts have been reported to stabilize flavor compounds, and among which nanoencapsulation is considered an efficient method
[7]. Not until recently, have people started to pay attention to flavorless intermediates, ARPs. A big advantage of ARPs is better stability during storage and synchronous production of fresh and desirable flavors during thermal treatment, which makes them potential flavor enhancers and food additives. However, to our best knowledge, there is no comprehensive review on ARPs as potential food additives. Therefore, this review aims to, for the first time, elucidate aspects related to ARPs and discuss the possibility of being food additives.
For convenience, the ARP of amino acid/peptide and reducing sugar starting now is referred to as amino acid/peptide-reducing sugar-ARP. The ARP would share a similar chemical structure, named as N-(1-deoxy-d-fructos-1-yl)-amino acid/peptide (amino acid-glucose system) after the Amadori rearrangement. Some papers adopt abbreviations like fru-val for N-(1-deoxy-d-fructos-1-yl)-valine (herein after referred to as valine-glucose-ARP).
2. Occurrence in Foods
Starting from the 1950 s, ARPs have drawn attention, and an array of studies have focused on analyzing ARPs in foods since then. ARPs were first found in browned freeze-dried apricots using ion-exchange chromatography in 1958
[8]. Though the resulting spectrum is highly complicated, it proved the existence of ARPs. After that, purified glycine-, alanine- and valine-glucose-ARPs were present in beer malt and were also found in soy sauce together with isoleucine- and leucine-glucose-ARPs
[9]. As shown in
Table 1, seven amino acid-glucose ARPs were detected in cocoa, coffee, barley malt, wheat malt, wheat beer, bell pepper and tomato, of which tyrosine and histidine ARPs were found present for the first time in foods
[10]. The drying of food accelerated ARP formation, and formed ARPs also degraded during roasting in coffee and cocoa. The highest ARP concentration is valine-glucose in unroasted cocoa and dried bell pepper at 342 and 3460 mg/kg, respectively. The results have been correlated with other studies and shown in
Table 1 [11]. Eight ARPs existed in dried fruit and vegetables, milk powder, tomato juice and paste, and red peppers, and the total ranges from 1.36 to 3415 mg/100 g. The drying of tomato juice facilitated ARP formation, which was further increased under vacuum. Though amino acid-APRs are identified from foods, peptides like oligopeptides should also be a focus for their abundance in foods. Unfortunately, only a few studies paid attention and succeeded in detecting peptide-ARPs, such as carnosine-glucose-ARP from meat broth. Therefore, more attention should be paid to oligopeptide-ARP analysis in future studies to fill the gap.
Table 1. Concentration (mg/kg) of ARPs in different foods.
Fru-Ile |
Fru-Tyr |
Fru-Phe |
Fru-His |
Fru-Met |
Fru-Leu |
Fru-Val |
|
Cocoa (unroasted) |
104.00 ± 10.40 |
73.00 ± 2.92 |
104.00 ± 8.32 |
27.20 ± 1.36 |
2.33 ± 0.33 |
152.00 ± 12.16 |
342.00 ± 10.26 |
|
Cocoa (roasted) |
5.38 ± 0.32 |
3.04 ± 0.09 |
3.99 ± 0.28 |
0.62 ± 0.06 |
1.34 ± 0.12 |
6.47 ± 0.39 |
19.00 ± 0.95 |
|
Coffee (green) |
2.51 ± 0.13 |
0.18 ± 0.03 |
2.80 ± 0.81 |
0.36 ± 0.08 |
0.59 ± 0.08 |
4.65 ± 0.65 |
0.60 ± 0.03 |
|
Coffee (roasted) |
0.87 ± 0.14 |
ND |
0.09 ± 0.02 |
15.33 ± 2.30 |
ND |
0.81 ± 0.11 |
ND |
|
Barley malt |
29.20 ± 2.04 |
11.00 ± 1.65 |
25.40 ± 3.05 |
13.10 ± 1.97 |
5.91 ± 0.95 |
33.80 ± 2.70 |
39.40 ± 4.73 |
|
Wheat malt |
27.80 ± 3.89 |
6.70 ± 0.34 |
21.10 ± 2.53 |
10.60 ± 1.06 |
4.31 ± 0.26 |
35.40 ± 5.00 |
148.00 ± 8.88 |
|
Wheat beer |
6.05 ± 0.12 |
2.91 ± 0.12 |
5.28 ± 0.05 |
2.77 ± 0.28 |
ND |
11.50 ± 0.92 |
34.60 ± 0.00 |
|
Bell pepper |
0.10 ± 0.00 |
ND |
0.08 ± 0.00 |
0.97 ± 0.20 |
0.10 ± 0.00 |
0.07 ± 0.01 |
0.58 ± 0.12 |
|
Bell pepper (DW) |
1.00 |
ND |
0.80 |
9.70 |
1.00 |
0.70 |
ND |
|
Bell pepper powder |
509.00 ± 15.27 |
210.00 ± 42.00 |
329.00 ± 26.32 |
405.00 ± 52.65 |
81.90 ± 4.10 |
592.00 ± 11.84 |
3460.00 ± 103.8 |
|
Tomato |
0.12 ± 0.01 |
ND |
0.19 ± 0.03 |
0.57 ± 0.02 |
ND |
0.16 ± 0.05 |
ND |
|
Tomato (DW) |
2.40 |
ND |
3.80 |
11.40 |
ND |
3.20 |
ND |
|
Tomato powder |
9.30 ± 1.67 |
7.96 ± 1.59 |
22.60 ± 3.39 |
45.00 ± 4.95 |
ND |
9.60 ± 0.38 |
10.60 ± 1.70 |
|
|
Fru-Arg |
Fru-Ala |
Fru-Phe |
Fru-His |
Fru-Met |
Fru-Leu |
Fru-Val |
Fru-Glu |
Dried strawberries (DW) |
8.4 ± 1.7 f |
30.5 ± 9.7 f |
9.0 ± 1.7 e |
12.5 ± 3.6 fg |
4.5 ± 2.2 e |
8.1 ± 1.6 e |
16.2 ± 4.5 d |
4.8 ± 2.0 d |
Dried bananas (DW) |
2.3 ± 0.1 f |
1.6 ± 0.1 f |
0.2 ± 0.1 f |
8.2 ± 5.6 gh |
0.3 ± 0.2 e |
0.1 ± 0.1 e |
0.9 ± 0.3 d |
ND |
Dried taro (DW) |
2.3 ± 0.1 f |
74.5 ± 16.5 f |
11.4 ± 1.2 e |
16.6 ± 1.5 ef |
32.6 ± 8.1 c |
20.6 ± 8.9 e |
ND |
ND |
Milk powder (DW) |
5.4 ± 0.3 f |
ND |
0.2 ± 0.1 f |
0.2 ± 0.1 h |
0.7 ± 0.1 e |
0.2 ± 0.1 e |
ND |
ND |
Pulled figs (DW) |
78.6 ± 3.7 e |
431.0 ± 43.8 d |
32.9 ± 2.7 d |
24.6 ± 1.4 e |
9.1 ± 0.7 de |
101.7 ± 24.1 d |
93.9 ± 20.3 c |
ND |
Tomato juice (DW) |
90.0 ± 0.8 e |
ND |
10.0 ± 2.0 e |
10.0 ± 2.0 f |
16.0 ± 4.0 d |
10.0 ± 2.0 e |
ND |
154.0 ± 1.5 b |
Tomato paste (DW) |
156.0 ± 13.7 d |
295.2 ± 3.7 e |
428.7 ± 62.1 c |
186.0 ± 3.7 d |
46.3 ± 3.7 c |
262.5 ± 3.7 c |
103.3 ± 3.7 c |
1517.7 ± 3.7 a |
Red pepper I (DW) |
2171.1 ± 103.5 b |
1291.5 ± 100.7 c |
974.3 ± 73.7 b |
454.4 ± 41.2 b |
300.0 ± 23.1 b |
1299.9 ± 90.8 b |
1341.5 ± 101.1 b |
ND |
Red pepper II (DW) |
1092.9 ± 101.1 c |
1952.2 ± 113.3 a |
836.1 ± 62.4 b |
264.5 ± 34.5 c |
240.2 ± 21.2 b |
1260.7 ± 123.1 b |
1453.9 ± 112.1 b |
ND |
Red pepper III (DW) |
24477.8 ± 212.6 a |
1479.7 ± 100.5 b |
2120.6 ± 183.7 a |
560.3 ± 49.2 a |
660.5 ± 65.2 a |
2613.6 ± 155.2 a |
2181.3 ± 143.5 a |
65.4 ± 8.7 c |
This entry is adapted from the peer-reviewed paper 10.3390/molecules26144314