No job name

J. Agric. Food Chem. 2002, 50, 806−812
Generation of Maillard Compounds from Inulin during the
Thermal Processing of Agave tequilana Weber Var. azul
NORMA A. MANCILLA-MARGALLI AND MERCEDES G. LOÄPEZ* Unidad de Biotecnologı´a e Ingenierı´a Gene´tica de Plantas, Centro de Investigacio´n y Estudios Avanzados del IPN, Apartado Postal 629, 36500 Irapuato, Gto., Mexico During the cooking process of Agave tequilana Weber var. azul to produce tequila, besides thehydrolysis of inulin to generate fermentable sugars, many volatiles, mainly Maillard compounds, areproduced, most of which may have a significant impact on the overall flavor of tequila. Exudates(agave juice) from a tequila company were collected periodically, and color, °Brix, fructoseconcentration, and reducing sugars were determined as inulin breakdown took place. Maillardcompounds were obtained by extraction with CH2Cl2, and the extracts were analyzed by GC-MS.
Increments in color, °Brix, and reducing sugars were observed as a function of time, but a decreasein fructose concentration was found. Many Maillard compounds were identified in the exudates,including furans, pyrans, aldehydes, and nitrogen and sulfur compounds. The most abundant Maillardcompounds were methyl-2-furoate, 2,3-dihydroxy-3,5-dihydro-6-methyl-4(H)-pyran-4-one, and 5-(hy-droxymethyl)furfural. In addition, a series of short- and long-chain fatty acids was also found. A largenumber of the volatiles in A. tequilana Weber var. azul were also detected in tequila extracts, andmost of these have been reported as a powerful odorants, responsible for the unique tequila flavor.
KEYWORDS: Agave tequilana; inulin; Maillard compounds; tequila; GC-MS
INTRODUCTION
into free sugars, mainly fructose (6), for their subsequentfermentation. Shu (8) in 1998 showed that inulin heated with The well-known Maillard reaction results from an interaction asparagine, even under mild conditions, produced Maillard between amino compounds, usually amino acids or proteins, molecules in an analogous way to fructose.
and reducing carbohydrates (1). This reaction leads to the The cooking conditions of the agave pines such as high formation of compounds that, because their volatility, influence temperature, low pH (4.5), time, and humidity are highly the overall flavor of a product (2, 3). Since Ruckdeschel in 1914 favorable to the Maillard reaction (9). Therefore, the main reported aroma generation by Maillard pathways, the food objective of this study was to determine the Maillard compounds industry has patented flavor formation processes from the heated generated in the thermal processing of A. tequilana Weber var.
aqueous mixtures of amino acids and reducing sugars. In the same way, thermal treatments of foods as well as their basicityare favorable conditions for the generation of these compounds(4).
MATERIALS AND METHODS
Tequila is one of the most consumed Mexican liquors Materials. The sweet liquid generated during the cooking of A.
worldwide and is made from AgaVe tequilana Weber var. azul, tequilana Weber var. azul pines, known as exudates or cooking honey, a native plant of Mexico (5), the only raw material appropriate was collected from an oven of a tequila company every 4 h during the to produce this beverage (6). During tequila production, stems whole cooking process (32 h). The following determinations were of A. tequilana are submitted to a cooking process for at least 32 h at ∼100 °C. The exudates (agave juice or cooking honey) Color and pH Determination. One hundred microliters of each obtained are then fermented and double-distilled to generate exudate was diluted to a final volume of 1 mL with water. The tequila blanco (white). This product can be matured from 3 to absorbance of each sample was read in a 1 cm quartz cell at 490 nm 12 months in oak casks to produce tequila reposado (rested) or with a visible spectrophotometer (Spectronic 20, Bausch and Lomb).
The pH of all samples was also determined.
from 1 to 5 years to produce tequila an˜ejo (aged) (7).
Sugar Determination. Total and reducing sugars were determined The main reason for the cooking process during tequila by spectrophotometric methods described previously (10, 11). Fructose production is to hydrolyze the inulin, the principal polysaccha- concentration was also measured according to the procedure of Somani ride in the core of the agave pine plants. Inulin is thus converted et al. (12). Ten microliters of each sample was used to measure Brixgrades using a refractometer (Sper Scientific, 0-80%).
Maillard Compounds. Ten milliliters of each exudate was diluted * Corresponding author (telephone 52-462-623-9632, fax 52-462-624- 5996; e-maill mlopez@ira.cinvestav.mx).
with the same volume of water and extracted with 6 mL of dichlo- Maillard Compounds from Inulin of Agave tequilana J. Agric. Food Chem., Vol. 50, No. 4, 2002 Figure 1. Rate of browning and pH value changes in exudates generated from the cooking process of A. tequilana Weber var. azul during tequila
elaboration. Exudates were collected every 4 h for 32 h. Absorbance was read at λ 490 nm.
romethane in a separatory funnel. The phases were separated by more noticeably to browning via caramelization than glucose centrifugation for 10 min at 10000 rpm at 4 °C. This step was repeated (14). The pH decrease might also be due to the formation of three times. The organic phases were combined and passed through an organic acids in the sample or to the inability of amino moieties anhydrous Na2SO4 column and completely evaporated in a Kuderna- to act as bases when the amino compounds have reacted.
Sugar Determination. Inulin is the principal carbohydrate
Gas Chromatography-Mass Spectrometry (GC-MS). The evapo-
present in A. tequilana Weber var. azul. Measurement of °Brix rated samples were diluted with 25 µL of CH2Cl2, and 1 µL was injected shows the efficiency of the hydrolysis of this polysaccharide in a splitless mode on a gas chromatograph (Hewlett-Packard 5890series II) coupled to mass spectrometer (Hewlett-Packard 5972 series) made of fructose, indicated as reducing sugars content. Figure
as a selective detector for the characterization of all compounds present 2 shows the correlation between °Brix and sugar determinations
in the extracts. Compound separations were carried out using an HP- throughout the cooking process. A drastic increment in °Brix FFAP column (25 m × 0.32 mm i.d. × 0.52 µm film). Helium was values was observed during the first 8 h followed by a constant used as carrier gas (2 mL/min) with a starting temperature of 40 °C value to 32 h. A similar pattern was shown during reducing for 5 min followed by a temperature program of 20 °C/min to 100 °C sugar determination. Fructose concentration and total sugar for 1 min, followed by a second rate of 3 °C/min to a final temperature content displayed a similar behavior, with maximum concentra- of 230 °C for 40 min. Injector and detector temperatures were 220 and tions being reached at 16 h and then almost constant concentra- 240 °C, respectively. Because chromatograms were so complex, tions after this time. In addition, the high fructose concentration quantitative data were obtained by injection of methyl undecanoate as observed confirms the presence of inulin as the major carbo- an external standard in an independent run under the same conditionsas the samples. Peaks were identified by comparison with the mass spectra library and commercial standards when possible.
Identification of Maillard Compounds. Chromatograms
obtained from the exudates of agave pines at different times(4, 8, 12, 16, 20, 24, and 28 h) showed very complex profiles RESULTS AND DISCUSSION
(data not shown). Generally, >240 components were identified Color and pH Determination. Agave exudate color became
in each exudate. Acids, alcohols, and furans were the most darker as a function of time. Figure 1 shows the absorbance
abundant compounds, followed by aldehydes, ketones, aromatic increments observed, the lowest set at 0.26 at 4 h and the highest compounds, terpenes, pyrans, and nitrogen and sulfur com- 0.44 at 28 h. Contrary to the absorbance increments, pH values pounds. Thirty-six percent of the volatile compounds found in decreased from 4.95 to 4.56. Although the pH changes were agave exudates have been reported previously as Maillard not very drastic, the tendency was always to be more acidic.
reaction products that might be generated by different pathways.
The absorbance increments concomitant with the pH decrements Hollnagel and Kroh (15) reported that large differences in the are characteristics observed in many Maillard systems (13). On volatile profiles from mono- and oligosaccharides exist. Whereas the basis of these parameters, it can be concluded that the monosaccharides undergo reactions to yield simple heterocyclic Maillard reaction was occurring during the cooking process of compounds, disaccharides and oligo- and polysaccharides gener- agave pines. The browning color is usually directly correlated ate heterocyclic compounds that still possess either glycosidic with the Maillard reaction based on the generation of compounds substituents or anhydrous sugars, respectively. However, we did such as furfural, 5-(hydroxymethyl)furfural, and pre-melanoi- not find any of these compounds, because cooking conditions dins, although carotenoids or other pigments might be contribut- favored the total hydrolysis of inulin toward fructose generation.
ing to the brown color. Besides the Maillard reaction, caramel- Table 1 lists the appearance and disappearance of some
ization of the sugars could take place under these conditions compounds, which must be related to a dynamic transformation and might also lead to browning. Fructose is known to contribute process. For instance, the concentration of some volatiles, such J. Agric. Food Chem., Vol. 50, No. 4, 2002 Figure 2. Correlation between °Brix and sugar content as indicator of inulin breakdown during cooking of agave pines. Determinations were done in
exudates obtained every 4 h during the whole process. Bars represent SE and, where not shown, were smaller than the symbol.
as 3-hydroxy-2-butanone and 1,2-butanediol, decreased with pathway for their formation. Another alcohol present in the time. Therefore, polyols and hydroxylated ketones might be exudates was 1-octen-3-ol. Its presence is characteristic of considered as precursors of compounds such as pyridine, shellfish and tomato, and it has been considered the most furfural, 2-furanmethanol, 5-methylfurfural, methyl-2-furoate, important odorant in mushrooms such as huitlacoche (Ustilago and 5-(hydroxymethyl)furfural, concentrations of which in- maydis) and austern pilzen (Pleutorus sp.) (21).
creased throughout the cooking process. Table 1 also lists the
Only one amino acid derivative was detected and quantified principal compounds found in the agave pine exudates and their in the exudates: N-acetylalanine was observed only in the first abundance with cooking time. The presence of short and long 8 h. The presence of amino heterocyclic compounds such as fatty acids in the extracts, from acetic acid (C2) to octadecanoic pyrazines, pyranones, and pyrroles is evidence of the presence acid (C18), was used to calculate the Kovats indices (KI). The of other amino acids in the agave pines. Most of these presence of heterocyclic compounds is further evidence that a compounds were detected between 20 and 32 h. Phenylacetal- Maillard reaction took place during the cooking of agave pines.
dehyde and phenylacetic acid are known to come from the Furans represented the majority followed by pyrans, sulfur interaction of phenylalanine and sugars by Strecker degradation compounds, and ketones. Other compounds such as benzyl (19). On the other hand, the presence of sulfur compounds alcohol, benzaldehyde, 3-hydroxy-2-butanone, and acetic acid indicated that amino acids such as cysteine and methionine have also been reported as Maillard compounds (2, 13, 16, 17).
were also present in A. tequilana pines; for example, 2,4,5- The exudates also contained compounds considered to be trimethylthiazole has been shown to come from ribose-cysteine relevant to the final tequila flavor profile. Among them, the -damascenone has been reported to result from the The kinetic patterns of the cooking process showed a great thermal degradation of carotenoids (18). Terpenes such as variation, but three principal groups can be differentiated. In linalool, phytol, and (Z)- and (E)-geraniol probably come from the first group, most compounds showed a maximum concentra- the agave plant per se. On the other hand, the series of organic tion during the first 4 h. Hydroxylated ketones, polyols, organic acids found in the exudates might come from cell membranes acids, unsaturated compounds, and terpenes such as hydroxy- that could be degraded during the cooking treatment, although linalool belong to this group. A second group includes sub- acetic acid is also generated by the Strecker degradation of stances such as 3-methyl-2-(5H)-furanone, 2-furancarboxylic alanine (19). Phenolic compounds such as vanillin, syringalde- acid, and 2(5H)-furanone among others, which reached their hyde, phenol, and phenol derivatives may be formed by the maximum at 20 h; after this time, their concentrations decreased.
thermal degradation of lignin. It is important to emphasize that This behavior is related to the disappearance of amino- is believed that both vanillin and syringaldehyde are formed during the resting or aging of alcoholic beverages through Figures 3 and 4 show profile changes of some minor and
contact with the wood casks; however, these compounds were major compounds over time, respectively. 3-Hydroxy-2-bu- found in tequila exudates, and it is known that their concentra- tanone, like 1,2-butanediol, showed a drastic decrease in the tions increase during aging. Alcohols such as 1-hexanol, first 8 h, subsequently declining slowly. They can therefore be 3-methyl-1-butanol, and phenylethyl alcohol have been con- considered as precursors of other compounds such as furfural, sidered to be fermentation products, responsible for the sweet which increased after this time. It is important to mention that notes of most alcoholic beverages (20), but their presence in cyclotene (Figure 3) has been reported previously from the
agave exudates suggests that fermentation is not the only interaction between fructose or glucose with glutamine, threo- Maillard Compounds from Inulin of Agave tequilana J. Agric. Food Chem., Vol. 50, No. 4, 2002 Table 1. Maillard and Other Important Compounds Found in Exudates of A. tequilana Weber Var. azul at Four Different Times during the Cooking
Processa
alcohols
organic acids
aldehydes
amino acids and derivatives
sulfur compounds
furanones
terpenes
nitrogen compounds
a Concentration of compounds in ppm. b Kovats index based on short and long fatty acids; tR, retention time.
nine, or serine (4, 22-24). Meanwhile, butyrolactone is an methyl-4(H)-pyran-4-one from fructose-alanine interaction important fructose degradation product (2), and its constant concentration could indicate continued fructose degradation to Finally, the third group comprised compounds that increased butyrolactone and thereafter to other compounds.
throughout whole process. Furfural, maltol, and 5-(hydroxy- Maltol, 2,3-dihydroxy-3,5-dihydro-6-methyl-4(H)-pyran-4- methyl)furfural increased throughout the whole cooking time, one, and 2,3-dihydro-2-methyl-4(H)-pyran-4-one were among and the latter compound was the most abundant (not shown in the most abundant compounds, reaching concentrations >60 Figure 4), with a concentration of >4000 ppm. Its high
ppm. According to some reports (4, 16, 17, 24, 25), 2,3- concentration is reasonable and expected because it forms from dihydroxy-3,5-dihydro-6-methyl-4(H)-pyran-4-one could be dehydration and degradation of carbohydrates as well as from formed by the interaction between fructose or glucose with amino acids such as alanine, phenylalanine, serine, leucine, The Maillard reaction has been extensively investigated threonine, glycine, glutamine, or lysinie and 2,3-dihydro-2- fundamentally in model systems. However, its complexity in J. Agric. Food Chem., Vol. 50, No. 4, 2002 Figure 3. Time course of the formation of some representative minor Maillard compounds found in exudates obtained during cooking of agave pines.
3-Hydroxy-2-butanone and 1,2-butanediol might be precursors of other compounds.
Figure 4. Profile changes of some major Maillard compounds generated during cooking of agave pines.
food systems due to the presence of many different reducing be formed from the thermal processing of wheat, rye, barley, sugars and amino groups and multiple conditions can produce and chicory (27). All of these crops have in common fructans a wide variation of Maillard compounds. Also, a single as reserve carbohydrates, similar to agave. Furfural might compound might be generated by more than one pathway. The therefore be formed by the Heyns pathway.
great abundance of fructose with respect to glucose in agave Due to the larger amount of carbohydrates with respect to pines favors the Heyns rearrangement, and specific compounds amino acids or proteins in agave, caramelization processes might might be used as markers to identify this type of rearrangement.
also take place, generating R-dicarbonyl intermediates via retro- Although fructose and glucose are able to generate the same aldolization, which are precursors of oxygen heterocyclic type of compounds through isomerization, it is possible to compounds (15). However, the contribution of caramelization distinguish between Heyns and Amadori rearrangements by might be insignificant, and the presence of sulfur, amino measuring isotopic fractionation. Furfural has been shown to heterocyclic molecules, and products of Strecker degradation Maillard Compounds from Inulin of Agave tequilana J. Agric. Food Chem., Vol. 50, No. 4, 2002 is indicative of the Maillard reaction being the main process (2) Shaw, P. E.; Tatum, J. H.; Berry, R. E. Base-catalyzed fructose during the cooking of agave pines. It is well-known that Maillard degradation and its relation to non-enzymic browning. J. Agric. reaction products develop flavor and influence sensory char- Food Chem. 1968, 16, 979-982.
acteristics of food systems. During tequila elaboration Maillard (3) Ames, J. M.; Bailey, R. G.; Mann, J. Analysis of furanone, products are generated mainly during agave cooking, having pyranone, and new heterocyclic colored compounds from sugar-
glycine model Maillard systems. J. Agric. Food Chem. 1999,
an impact on the flavor characteristic of this beverage. Furans and pyrans impart sweet notes; benzaldehyde in the exudates (4) Chen, J.; Ho, C.-T. Comparison of volatile generation in serine/ adds green, floral, and flower notes with a threshold of 4 ppb; threonine/glutamine-ribose/glucose/fructose model systems. J. and phenylacetaldehyde has a flowery odor (19). Vanillin has Agric. Food Chem. 1999, 47, 643-647.
a sweet, creamy, and vanilla odor, and -damascenone is known (5) Lo´pez, M. G. Tequila aroma. In FlaVor Chemistry of Ethnic for its woody, sweet, fruity, and floral descriptors. Many of these Foods; Shaidi, F., Ho, C.-T., Eds.; Plenum: New York, 1999; compounds have received much attention as biologically active constituents in foods for their antioxidative properties (28).
(6) Ceden˜o, M. Tequila production. Crit. ReV. Biotechnol. 1995, 15,
Many volatiles generated during the cooking stage are (7) Lo´pez, M. G.; Dufour, J. P. Tequila. Charm analysis of blanco, transformed to other compounds in the subsequent processes reposado, and an˜ejo tequilas. In Gas Chromatography-Olfac- (fermentation, resting, and/or aging). However, some of them tometry. The State of the Art; Leland, J. V., Schieberle, P., persist in the final product, influencing the overall tequila flavor.
Buettner, A., Acree, T. E., Eds.; American Chemical Society: 3-Methyl-1-butanol and phenylethyl alcohol come from the Maillard reaction; however, their concentrations are higher in (8) Shu, C. K. Flavor components generated from inulin. J. Agric. the product due to the fermentation process. Fatty acids do not Food Chem. 1998, 46, 1964-1965.
show a constant level because acetic, propanoic, octanoic, and (9) Lo´pez, M. G.; Mancilla-Margalli, N. A. Maillard compounds dodecanoic acids are present in higher concentrations in the from the thermal processing of AgaVe tequilana Weber var. azul.
product, whereas others such as hexanoic and tetradecanoic acids In Frontiers of FlaVor Science; Schieberle, P., Engel, K.-H., Eds.; are most abundant in the exudates. On the other hand, furanoic Deutsche Forschungsanstalt fu¨r Lebensmittelchemie: Germany, compounds were lost during tequila production because their (10) Dubois, M.; Gilles, K. A.; Hamilton, J. K.; Rebers, P. A.; Smith, concentrations are notably lower than in exudates, except for F. Colorimetric method for determination of sugars and related 2-acetylfuran. The same pattern was observed for linalyl substances. Anal. Chem. 1956, 28, 350-356.
(11) Somogyi, M. Notes on sugar determination. J. Biol. Chem. 1952,
Benn and Peppard (18) reported that 3-methyl-1-butanol, linalool, phenylethyl alcohol, decanoic acid, vanillin, and (12) Somani, B. L.; Khanade, J.; Sinha, R. A modified anthrone- -damascenone are the most powerful odorants in tequila. These sulfuric acid method for the determination of fructose in the compounds are mainly generated during the cooking process, presence of certain proteins. Anal. Biochem. 1987, 167, 327-
but some of them increased in subsequent steps. On the other hand, Lo´pez (5) reported other Maillard compounds not present (13) Apriyantono, A.; Ames, J. M. Xylose-lysine model systems: the effect of pH on the volatile reaction products. J. Sci. Food Agric. in the exudates studied here. Among these, 2-acetyl-5-methyl- 1993, 61, 477-484.
furan, 3-furfuryl alcohol, and 3,4,5-trimethylpyrazole are sig- (14) Brands, C. M. J.; Alink, G. M.; van Boekel, M. A. J. S.; Jongen, nificant. Maillard compounds usually vary according to the type W. M. F. Mutagenicity of heated sugar-casein systems: effect and concentration of reactant and also the reaction conditions of the Maillard reaction. J. Agric. Food Chem. 2000, 48, 2271-
(17, 29). Therefore, the differences in Maillard compounds can be due to cooking parameters used in each distillery, in addition (15) Hollnagel, A.; Kroh, L. W. Degradation of oligosaccharides in to the quality and age of raw material, in this case A. tequilana nonenzymatic browning by formation of R-dicarbonyl com- pounds via a “peeling off” mechanism. J. Agric. Food Chem. Inulin hydrolysis throughout the whole cooking process of 2000, 48, 6219-6226.
A. tequilana Weber var. azul can be monitored by measuring (16) Oberparleiter, S.; Ziegleder, G. Amadori-verbindungen als aro- mavorstufen in kakao. Nahrung 1997, 41, 142-145.
Brix, which reflects reducing sugars production. On the other (17) Negroni, M.; D’Agostina, A.; Arnoldi, A. Autoxidation in xylose/ hand, the role of fructose during the Maillard reaction can be lysine model systems. J. Agric. Food Chem. 2000, 48, 479-
followed by measuring the presence of many heterocyclic compounds containing oxygen, sulfur, and nitrogen. Addition- (18) Benn, S. M.; Peppard, T. L. Characterization of tequila flavor ally, the abundance of 5-(hydroxymethyl)furfural, furfural, and by instrumental and sensory analysis. J. Agric. Food Chem. 1996,
methyl-2-furoate provides information on the original concentra- tion of carbohydrates compared to amino-bearing substances (19) Hofmann, T.; Munch, P.; Schieberle, P. Quantitative model at the beginning of the process. Besides Maillard molecules, studies on the formation of aroma-active aldehydes and acids the cooking treatment also generated thermal breakdown by Strecker-type reactions. J. Agric. Food Chem. 2000, 48, 434-
products. Maillard compounds formed during cooking of agave pines are largely dependent on cooking parameters; therefore, (20) Garnero, J. Heterocyclic aroma compounds precursors. In The Chemistry of Heterocyclic FlaVouring and Aroma Compounds; the differences in the flavor characteristics between tequilas can Vernin, G., Ed.; Ellis Horwood: Horwood, U.K., 1982; pp 17- be changed, directed, and/or controlled not only throughout the resting (reposado) and/or aging (an˜ejo) process but also during (21) Liza´rraga-Guerra, R.; Helmut, G.; Lo´pez, M. G. Identification of the most potent odorants in huitlacoche (Ustilago maydis)and austern pilzen (Pleurotus sp.) by aroma extract dilution LITERATURE CITED
analysis and static head-space samples. J. Agric. Food Chem.
1997, 45, 1329-1332.
(1) Bedinghaus, A. J.; Ockerman, H. W. Antioxidative Maillard (22) Chen, Y.; Xing, J.; Chin, C. K.; Ho, C. T. Effect of urea on reaction products from reducing sugars and free amino acids in volatile generation from Maillard reaction of cysteine and ribose.
cooked ground pork patties. J. Food Sci. 1995, 60, 992-995.
J. Agric. Food Chem. 2000, 48, 3512-3516.
J. Agric. Food Chem., Vol. 50, No. 4, 2002 (23) Tressl, R.; Kersten, E. Formation of 4-aminobutyric acid specific using the color activity concept. J. Agric. Food Chem. 2000,
Maillard products from [1-13C]-D-glucose, [1-13C]-D-arabinose, and [1-13C]-D-fructose. J. Agric. Food Chem. 1993, 41, 2278-
(28) Fuster, M. D.; Mitchell, A. E.; Ochi, H.; Shibamoto, T.
Antioxidative activities of heterocyclic compounds in brewed (24) Nishibori, S.; Bernhard, R. A. Formation of 2,3-dihydro-3,5- coffee. J. Agric. Food Chem. 2000, 48, 5600-5603.
dihydroxy-6-methyl-4(H)-pyran-4-one from fructose and -ala- (29) Wijewickreme, A. N.; Zrejpcio, Z.; Kitts, D. D. Hydroxyl nine under conditions used for baking. J. Agric. Food Chem. scavening activity of glucose, fructose, and ribose-lysine model 1994, 42, 1080-1084.
Maillard products. J. Agric. Food Chem. 1999, 64, 457-461.
(25) Chen, J.; Ho, C.-T. Volatile compounds generated in serine- monosaccharide model systems. J. Agric. Food Chem. 1998, 46,
1518-1522.
Received for review August 2, 2001. Revised manuscript received
(26) Shimamura, T.; Ukeda, H.; Sawamura, M. Reduction of tetra- October 26, 2001. Accepted October 29, 2001. We thank Conacyt for
zolium salt XTT by aminoreductone formed during the Maillard financial support. Part of this work has been presented during the 9th
reaction of lactose. J. Agric. Food Chem. 2000, 48, 6227-6229.
Weurman Flavour Research Symposium in Freising, Germany (1999).
(27) Frank, O.; Hofmann, T. Characterization of key chromophores formed by nonenzymatic browning of hexoses and L-alanine by

Source: http://www.agave.or.kr/info/thesis/maillard.pdf