Studies on N-terminal glycation of peptides in hypoallergenic infant formulas: Quantification of α-N-(2-furoylmethyl) amino acids

Article abstract of DOI:10.1021/jf061821b

To obtain information about the extent of the early Maillard reaction between the N-termini of peptides and lactose, α-N-(2-furoylmethyl) amino acids (FMAAs) were quantified together with ε-A/-(2-furoylmethyl)lysine (furosine) in acid hydrolyzates of hypoallergenic infant formulas, conventional infant formulas, and human milk samples using RP-HPLC with UV-detection. FMAAs are formed during acid hydrolysis of peptide-bound N-terminal Amadori products (APs), and furosine is formed from the Amadori products of peptide-bound lysine. Unambiguous identification was achieved by means of LC/MS and UV-spectroscopy using independently prepared reference material. The extent of acid-induced conversion of APs to FMAAs was studied by RP-HPLC with chemiluminescent nitrogen detection (CLND). Depending on the corresponding a-A/-lactulosyl amino acid, between 6.0% and 18.1% of FMAAs were formed during hydrolysis for 23 h at 110 °C in 8 N HCl. From espi;-N-lactulosyllysine, 50% furosine is formed under these conditions. Whereas furosine was detectable in all assayed samples, five different FMAAs, α-FM-Lys, α-FM-Ala, α-FM-Val, α-FM-lle, and α-FM-Leu, were exclusively detected in acid hydrolyzates of hypoallergenic infant formulas in amounts ranging from 35 to 396 μmol/100 g protein. Taking the conversion factors into account, modification of N-terminal amino acids in peptides by reducing carbohydrates was between 0.3% and 8.4%. This has to be considered within the discussion concerning the nutritional quality of peptide-containing foods.

Full text of DOI:10.1021/jf061821b

J. Agric. Food Chem. 2007, 55, 723−727 723
Studies on N-Terminal Glycation of Peptides in Hypoallergenic
Infant Formulas: Quantification of
Amino Acids
r-N-(2-Furoylmethyl)
ILKA PENNDORF, DANIELA BIEDERMANN, SARAH V. MAURER,
AND THOMAS HENLE*
Institute of Food Chemistry, Technische Universit a¨ t Dresden, Bergstrasse 66,
D-01062 Dresden, Germany
To obtain information about the extent of the early Maillard reaction between the N-termini of peptides
and lactose, R-N-(2-furoylmethyl) amino acids (FMAAs) were quantified together with ꢀ-N-(2-
furoylmethyl)lysine (furosine) in acid hydrolyzates of hypoallergenic infant formulas, conventional infant
formulas, and human milk samples using RP-HPLC with UV-detection. FMAAs are formed during
acid hydrolysis of peptide-bound N-terminal Amadori products (APs), and furosine is formed from
the Amadori products of peptide-bound lysine. Unambiguous identification was achieved by means
of LC/MS and UV-spectroscopy using independently prepared reference material. The extent of acid-
induced conversion of APs to FMAAs was studied by RP-HPLC with chemiluminescent nitrogen
detection (CLND). Depending on the corresponding R-N-lactulosyl amino acid, between 6.0% and
18.1% of FMAAs were formed during hydrolysis for 23 h at 110 °C in 8 N HCl. From ꢀ-N-
lactulosyllysine, 50% furosine is formed under these conditions. Whereas furosine was detectable in
all assayed samples, five different FMAAs, R-FM-Lys, R-FM-Ala, R-FM-Val, R-FM-Ile, and R-FM-
Leu, were exclusively detected in acid hydrolyzates of hypoallergenic infant formulas in amounts
ranging from 35 to 396 µmol/100 g protein. Taking the conversion factors into account, modification
of N-terminal amino acids in peptides by reducing carbohydrates was between 0.3% and 8.4%. This
has to be considered within the discussion concerning the nutritional quality of peptide-containing
foods.
KEYWORDS: r-N-(2-Furoylmethyl) amino acids; furosine; hypoallergenic infant formula; N-terminal
glycation; peptides; Amadori product; Maillard reaction
INTRODUCTION
11) (Figure 1). The extent of glycation at the ꢀ-amino group of
peptide-bound lysine can be monitored by ꢀ-N-(2-furoylmethyl)-
lysine (furosine), which is formed in constant amounts together
with lysine and pyridosine during acid hydrolysis from APs such
as N-ꢀ-lactulosyllysine or N-ꢀ-fructosyllysine (2-4). Furosine
is a widely used marker for the evaluation of the early Maillard
reaction in a great variety of foods (5-7) and biological samples
(8). Numerous studies have focused on the side-chains of
peptide-bound lysine and arginine residues as main targets for
a derivatization by carbohydrates or their degradation products
(1). As compared to this, glycation reactions occurring at
N-terminal amino acids of peptides or proteins have not received
particular attention up to now, although in certain peptide-
containing foods, R-amino groups of N-terminal amino acids
may be quantitatively much more important than ꢀ-amino groups
of peptide-bound lysine. Furthermore, N-terminal glycation in
vivo is well known. Quantification of glycated hemoglobin
The Maillard reaction, also referred to as nonenzymatic
browning or glycation, is responsible for the formation of desired
flavors and colors but also for undesired derivatization of
essential amino acids, thus leading to a decrease in the nutritional
value of heated or stored foods (1). In the early stage of the
Maillard reaction, reducing carbohydrates such as glucose or
lactose react with amino groups from amino acids, peptides, or
proteins to amino ketoses, the so-called Amadori products (APs).
APs of the essential amino acid lysine are biologically not
available during digestion (2). The analysis of Amadori products,
therefore, is of importance to assess the impact of heating or
storage on the nutritional quality of foods. The major problem
in quantification of APs by amino acid analysis is the fact that
these amino acid derivatives are degraded during acid hydrolysis
to several reaction products, among which UV-active N-(2-
furoylmethyl) amino acids are of particular importance (3, 10,
(
HbA1C), in which the N-terminal valine of the R-chain is
*
Author to whom correspondence should be addressed [telephone
+49-351-463-34647; fax ++49-351-463-34138; e-mail thomas.henle@
chemie.tu-dresden.de].
modified by glucose, is used as a tool to monitor long-term
glycation in diabetic patients (1, 9).
+
1
0.1021/jf061821b CCC: $37.00
© 2007 American Chemical Society
Published on Web 01/12/2007

724 J. Agric. Food Chem., Vol. 55, No. 3, 2007
Penndorf et al.
B for 10 min, 0% to 10% solvent B in 5 min, 10% to 20% solvent B
in 30 min, 20% to 80% solvent B in 5 min, 80% solvent B for 5 min,
80% to 0% solvent B in 5 min, 0% solvent B for 10 min. The detection
wavelength was 280 nm.
For analysis of FM-Val and furosine, the HPLC system was as above,
but a RP-8 column “furosine dedicated” (Alltech, Unterhaching,
Germany) was used. A linear binary gradient was applied with water
containing 0.4% acetic acid (solvent A) and water containing 0.4%
acetic acid and 0.27% KCL (solvent B). The gradient was as follows:
0
% solvent B for 13.5 min, 0% to 50% solvent B in 7 min, 50% solvent
B for 1.5 min, 50% to 0% solvent B in 1 min, 0% solvent B for 9 min
3). The injection volume was 50 µL, the flow was 1.1 mL/min, and
(
the temperature was set at 34 °C.
For quantification of FMAAs, an external standard of furosine
(Neosystems, Strasbourg, France) was used.
LC-ESI-TOF-MS for Identification of FMAAs. An Agilent 1100
series HPLC system (Agilent Technologies, Palo Alto, USA) consisting
of a high-pressure gradient pump system, column oven, automatic
injector, and diode array detector was coupled to a PerSeptive
Biosystems Mariner time-of-flight mass spectrometer (TOF-MS)
equipped with an electrospray ionization source (ESI) working in the
positive mode (Applied Biosystems, Stafford, USA). RP-HPLC was
performed as described above for the quantification of FM-Val, FM-
Leu, and FM-Ile. MS conditions were as follows: quadrupole RF
voltage 799.80, nozzle temperature 140.01 °C, reflector potential
1
549.99, detector voltage 2299.99, first mass 100, last mass 700.
Preparation and Analysis of Reference Samples. 2 mmol of each
amino acid and peptide (ꢀ-N-acetyllysine, R-N-acetyllysine, alanine,
valine, leucine, isoleucine, isoleucinylglycin, and isoleucinylglycyl-
glycin, respectively; all from Merck, Darmstadt, Germany; peptides
from Bachem, Bubendorf, Switzerland) and 4 mmol of lactose
monohydrate were dissolved in a mixture of 11 mL of methanol and 9
mL of DMSO and were heated at 90 °C for up to 8 h under reflux.
Solvents were removed under vacuum. The dried residues were
dissolved in 20 mL of distilled water. After membrane filtration (0.45
µm), these solutions were used as reference samples containing the
original amino acid plus the corresponding Amadori products (“lactu-
losyl amino acid”, AP-solution). To obtain samples containing the
corresponding FMAAs, 700 µL of each AP-solution was hydrolyzed
with 1380 µL of 12 N HCL in screw-cap test tubes for 23 h at 110 °C.
The complete hydrolyzates were centrifugated (10 000 rpm, 20 min),
and the supernatant was dried under vacuum. The dry residues were
dissolved in 500 µL of 0.2 N hydrochloric acid. After membrane
filtration, these solutions were used as reference samples containing
FMAAs (FMAA solution). 10 µL of each AP- or FMAA-solution,
respectively, was analyzed using RP-HPLC with chemiluminescent
nitrogen detector (CLND). For this, an Agilent 1100 series HPLC
system (Agilent Technologies, Palo Alto, USA) consisting of a high-
pressure gradient pump system, column oven, automatic injector, and
UV-detector was used in combination with a nitrogen-sensitive detector
Antek 8060 (Baumel, Houston, Texas). A RP-18 column (Eurospher
Figure 1. Structures of determined FMAAs (A−F).
In the present study, we address the question whether early
Maillard reactions occurring at the N-termini of peptides are of
importance in foods such as hypoallergenic formulas, which
contain a multiplicity of peptides from hydrolyzed whey proteins
or casein. Selected N-(2-furoylmethyl) amino acids, which are
formed from Amadori products of N-terminal amino acids
during acid hydrolysis (Figure 1), were analyzed by RP-HPLC
with UV-detection in comparison to reference samples prepared
from amino acids and lactose.
EXPERIMENTAL PROCEDURES
Preparation of Samples for Chromatographic Analysis. Seven
samples of hypoallergenic infant formulas (peptide-containing) and four
samples of conventional infant formulas (intact protein-containing) were
obtained from local retail stores. Four human milk samples were
obtained from healthy volunteers. Of the infant formulas, 100 mg was
hydrolyzed with 1.2 mL of 7.95 N hydrochloric acid in screw-cap test
tubes at 110 °C for 23 h. Of the human milk samples, 2.0 mL was
hydrolyzed with 3.9 mL of 37% hydrochloric acid under the same
conditions. After cooling to room temperature, hydrolyzates were
centrifugated (10 000 rpm, 15 min), and the supernatant was dried under
vacuum. The dry residues were dissolved in 500 µL of 0.2 N
hydrochloric acid. After membrane filtration (0.2 µm), 50 µL was
subjected to LC-ESI-TOF-MS or into the RP-HPLC with UV- or
CLND-detection, respectively.
1
00-C18 column, 5 µm, 3 mm × 250 mm, Knauer, Berlin, Germany)
was used at a flow rate of 0.2 mL/min. Gradient elution was performed,
using water (solvent A) and methanol (solvent B), each containing 2%
of formic acid. The following gradients were applied for analyzing the
AP-solutions: alanine (0% to 10% solvent B in 25 min, 30 °C), R-N-
acetyllysine and ꢀ-N-acetyllysine (0% to 10% solvent B in 25 min,
5
0 °C), valine (0% to 15% solvent B in 25 min, 50 °C), leucine and
isoleucine (0% to 20% solvent B in 25 min, 50 °C). The following
gradients were applied for analyzing the FMAA-solutions: FM-Ala
RP-HPLC with UV-Detection for Quantification of FMAAs in
Acid Hydrolysates. For analysis of FM-Val, FM-Leu, and FM-Ile, an
HPLC system consisting of a pump K1001, a gradient mixing system,
a detector K-2501, a column oven, and an automatic injector Marathon
(0% to 10% solvent B in 25 min, 50 °C), R-FM-Lys/furosine (5% to
2
0% solvent B in 30 min, 50 °C), FM-Val (5% to 40% solvent B in 30
(
all from Knauer, Berlin, Germany) was used. The column was a
min, 50 °C), FM-Leu and FM-Ile (5% to 50% solvent B in 30 min,
50 °C). A solution of caffeine (1 mg/mL; Fluka, Buchs, Switzerland)
was used for external calibration. The concentrations of APs and
corresponding FMAAs in the sample solutions were calculated using
the theoretical nitrogen content of the corresponding compound. The
identity of FMAAs and amino acids was verified by LC-ESI-TOF-MS
(system described above).
Eurospher 100-C18 column (5 µm, 4.6 mm × 250 mm, Knauer, Berlin,
Germany) protected by a guard column (8 × 5 mm) containing the
same material. The injection volume was 50 µL, the flow rate was
0
.7 mL/min, and the temperature was set at 25 °C. A gradient was
applied with water (solvent A) and methanol (solvent B), each
containing 2% formic acid. The gradient was as follows: 0% solvent

N-Terminal Glycation of Peptides in Hypoallergenic Infant Formulas
J. Agric. Food Chem., Vol. 55, No. 3, 2007 725
Table 1. FMAAs (Means of Triplicates) in Seven Hypoallergenic (HA)
Infant Formulas, Measured after Acid Hydrolysis (7.95 N HCL, 110
°C,
23 h), As Compared to Amount of Amino Acid in Whey Protein (16)
and Calculated Range of Modification of Amino Acids Due to
Formation of APs
range of FMAAs in
HA infant formulas
amount of AAs in
whey protein
[mmol/100 g]
resultant range of
modification of AAs
[%]
FMAAs
[µ
mol/100 g protein]
ꢀ
-FM-Lys
1411 2410
−
65.7 (Lys)
4.3−7.3
(furosine)
R
-FM-Lys
35
119
−
−
167
310
214
232
396
65.7 (Lys)
61.7 (Ala)
64.0 (Val)
53.4 (Ile)
90.0 (Leu)
0.3−
3.2−
1.7−
2.8−
2.8−
1.4
8.4
5.3
6.2
6.7
FM-Ala
FM-Val
FM-Ile
69
−
105
163
−
−
FM-Leu
in hydrolyzates of hypoallergenic infant formulas and 1081 to
458 µmol/100 g or 275 to 371 mg/100 g protein in conventional
1
infant formulas, respectively (Table 1). Minor amounts of
furosine up to 18 µmol/100 g or 5 mg/100 g protein have been
determined in hydrolyzed samples of human milk. In a recently
published study, clearly smaller amounts of FM-Ala (14 mg/
1
3
00 g protein) have been quantified together with furosine (85-
06 mg/100 g protein) and R-FM-Lys (18-24 mg/100 g protein)
by Garcia-Banos et al. (12) in hydrolyzates of intact protein-
containing powdered enteral formulas, indicating that a sub-
stantial amount of N-terminal amino acids is modified by
reducing carbohydrates during Maillard reactions mainly in
peptide-containing hypoallergenic infant formulas. To the best
of our knowledge, this is the first report on glycated N-terminally
modified peptides in foods. FMAAs resulting from free amino
acids have been quantified by Sanz et al. (10, 11) and del
Castillo et al. (13), using the routine method for furosine analysis
established by Resmini et al. (5). These authors have reported
on the quantification of FM-Ala, R-FM-Lys, FM-Arg, and γ-N-
(2-furoylmethyl)aminobutyric acid together with furosine in
hydrolyzates of processed foods containing mainly polar free
amino acids. In hypoallergenic infant formulas, containing a
multiplicity of peptides, the main source for the formation of
Amadori products are more hydrophobic N-terminally peptide-
bound amino acids. For the determination of the more hydro-
phobic N-(2-furoylmethyl) amino acid derivatives, the hydro-
lyzed samples were analyzed using RP-HPLC on a RP-18
column with UV-detection. The FMAAs resulting from N-
lactulosylvaline (FM-Val, m/z 226.16), N-lactulosylleucine (FM-
Leu, m/z 240.18), and N-lactulosylisoleucine (FM-Ile, m/z
240.18) during acid hydrolysis were identified exclusively in
hypoallergenic formula samples (Figure 3a) by comparing
retention time, UV spectra (typical maximum at 278 nm), and
mass spectra as measured by ESI-TOF-MS with the correspond-
ing reference substances obtained after incubation of the said
amino acids with lactose and subsequent hydrolysis (Figure 3b).
For quantification of FM-Val, FM-Ile, and FM-Leu, an external
standard of furosine (elution time 8.2 min, chromatogram not
shown) was used. Values of FM-Leu as major derivative ranged
from 163 to 396 µmol/100 g or 39 mg to 95 mg/100 g protein
in the hydrolyzates of the hypoallergenic infant formulas (Table
1). The corresponding values for FM-Ile and FM-Val as further
derivatives of essential amino acids were between 105-232
µmol/100 g or 25-56 mg/100 g protein and 69-214 µmol/100
g or 16-48 mg/100 g protein, respectively (Table 1). Taking
the detection limit of 0.03 µmol/L into account, none of the
R-FMAAs was detectable in the conventional infant formula
or in the human milk samples. The phenomenon that mainly
hydrophobic amino acids were derivatized in the hypoallergenic
Figure 2. RP-HPLC with UV-detection using an RP-8 column (see
Experimental Procedures). (a) Acid hydrolysates of a hypoallergenic infant
formula (black) and a pre-infant formula (dotted). (b) Reference samples
for FMAAs obtained after acid hydrolysis of heated mixtures of lactose
with
R-N-acetyllysine, ꢀ-N-acetyllysine, or alanine, respectively.
RESULTS AND DISCUSSION
Our strategy to obtain information about the extent of
N-terminal glycation occurring at the N-termini of peptides in
hypoallergenic infant formula was based on the conversion of
Amadori products to N-(2-furoylmethyl)amino acids (FMAAs)
during acid hydrolysis, which could be analyzed and quantified
via RP-HPLC with UV-detection using different columns and
gradient systems. When using an RP-8 column and elution
conditions established for the routine analysis of furosine (5),
in addition to furosine, two new peaks eluting with retention
times of 10.5 and 24.0 min, respectively, could be detected
exclusively in acid hydrolyzates of hypoallergenic formulas
(Figure 2a). Peaks showing identical retention times were
detectable in the acid hydrolyzates (FMAA-solutions) of incuba-
tion mixtures containing lactose and alanine or ꢀ-N-acetyllysine,
respectively (Figure 2b). The two unknown peaks in the
hydrolyzates of the milk formulas were unambiguously identi-
fied as FM-Ala (m/z 198.13) and R-FM-Lys (m/z 255.18) by
comparing retention time, UV spectra (typical maximum at 278
nm) as measured via diode array detection, and mass spectra
as measured by ESI-TOF-MS with the reference samples. For
quantification of FM-Ala and R-FM-Lys, an external standard
of furosine was used according to Sanz et al., who successfully
applied furosine as a standard substance for the determination
of FMAAs in processed tomato products (10) and dehydrated
fruits (11). The amount of FM-Ala in acid hydrolyzed hy-
poallergenic formulas ranged from 119 to 310 µmol/100 g or
2
1
4 to 61 mg/100 g protein and that of R-FM-Lys from 35 to
67 µmol/100 g or 9 to 42 mg/100 g protein, respectively. Thus,
the extent of derivatization at the R-amino group of lysine
residues was significantly lower as compared to modification
at the ꢀ-amino group as indicated by a furosine content ranging
from 1411 to 2410 µmol/100 g or 359 to 613 mg/100 g protein

726 J. Agric. Food Chem., Vol. 55, No. 3, 2007
Penndorf et al.
Figure 3. RP-HPLC with UV-detection on an RP-18 column (see
Experimental Procedures). (a) Acid hydrolysates of a hypoallergenic infant
formula (black) and a pre-infant formula (dotted). (b) Reference samples
for FMAAs obtained after acid hydrolysis of heated mixtures of lactose
with valine, isoleucine, or leucine, respectively.
Figure 4. RP-HPLC with N-sensitive detection. (a) Heated mixture of
lactose with leucine. (b) Heated mixture of lactose with leucine after
hydrolysis with 7.95 N HCl. Note that elution conditions are different in
(a) and (b) (see Experimental Procedures for details).
Table 2. Yields of FMAAs Standard Deviation (6-fold Determination)
Formed during Acid Hydrolysis from APs As Measured via CLND, and
Conversion Factors Calculated Therefrom
±
samples may be due to the fact that the whey proteins used as
starting material were predominantly hydrolyzed in the hydro-
phobic regions of the proteins to avoid the formation of bitter
peptides. Therefore, it can be expected that mainly peptides
containing isoleucine, valine, and leucine as N-terminal amino
acids are present in the hydrolyzed whey protein of the
hypoallergenic infant formulas.
To assess the degree of derivatization due to formation of
Amadori products at the N-termini of peptides, it is important
to know to which extent APs are converted to FMAAs during
acid hydrolysis. For studying this, the synthesis of pure APs
and pure FMAAs is usually necessary (3). In our work, we used
a new approach by comparing absolute nitrogen contents
measured via RP-HPLC with chemiluminescent nitrogen detec-
tor (CLND) for an AP before hydrolysis and subsequently for
the corresponding FMAA present after hydrolysis. The com-
bination of HPLC with CLND is known as a specific and
selective chromatography method for analyzing underivatized
amino acids even in complex matrices or in peptide hydrolyzates
yield of
FMAAs [%]
conversion
factors
AP of
R
-N-acetyl-lysine
-N-acetyl-lysine
49.9
18.1
6.0
6.3
6.6
±
±
±
±
±
±
0.6
0.6
0.3
0.5
0.1
0.6
2.0
5.5
16.7
15.9
15.2
14.3
ꢀ
alanine
valine
isoleucine
leucine
7.0
acetyllysine and only 6-7% of the Amadori products of valine,
isoleucine, leucine, and alanine, respectively, are converted to
the corresponding R-N-(2-furoylmethyl)amino acids, indicating
significantly lower formation of R-FMAAs from corresponding
APs as compared to the formation of furosine from N-ꢀ-
lactulosyllysine in strong acid solutions, probably due to
pronounced instability of the R-N-glycated amino acids under
these conditions. Additional hydrolysis experiments using
peptide-bound APs formed from the dipeptides IleLeu or
IleGlyGly, respectively, during incubation with lactose gave
similar results for FM-Ile formation during acid hydrolysis.
Taking these conversion factors into account, it was possible
to calculate the amount of N-terminal Amadori products present
in the samples before hydrolysis from the amount of FM-AAs.
Therefrom, the extent of amino acid derivatization was estimated
by comparing the amount of APs with the total amount of the
corresponding amino acid, taking the average amino acid content
in bovine whey protein into consideration (Table 1). Deriva-
tization of N-terminal amino acids was between 1.7% and 8.4%.
These data obtained for the essential amino acids alanine, valine,
isoleucine, and leucine are comparable to values for lysine
measured in conventional infant formulas, demonstrating that
N-terminal glycation in peptide-containing foods and resulting
(14, 15). After the identity of FMAAs and amino acids in the
sample solutions was verified by LC-ESI-TOF-MS, the con-
centrations of APs and corresponding FMAAs were calculated
using the theoretical nitrogen content of the corresponding
compound based on an external calibration with a caffeine
standard solution (Figure 4). By comparing molar amount of
AP before hydrolysis with the amount of the corresponding
FMAA after hydrolysis, the conversion factors shown in Table
2
could be calculated. Using this approach, we found that 50%
of N-ꢀ-lactulosyllysine, which represents the AP of R-N-
acetyllysine, is converted to furosine during hydrolysis with 7.95
N HCl at 110 °C for 23 h. This value is in perfect agreement
with data obtained by Krause et al. (3), who had found 46%
yield of furosine for N-ꢀ-fructosyllysine and 50% for N-ꢀ-
lactulosyllysine after hydrolysis of synthetically prepared APs.
Compared to this, only 18% of the Amadori product of ꢀ-N-

N-Terminal Glycation of Peptides in Hypoallergenic Infant Formulas
J. Agric. Food Chem., Vol. 55, No. 3, 2007 727
derivatization of essential amino acids must be taken into
account as quality parameters to assess the extent of the early
stage of the Maillard reaction in heated or stored foods. Special
attention should be focused on hypoallergenic infant formulas,
which represent the sole intake for infants in the first 3 months.
For this food items, possible nutritional implications resulting
from N-terminal derivatization of essential amino acids in
addition to lysine should be investigated.
In conclusion, it was shown that the extent of early Maillard
reactions occurring at the N-termini of peptides is of quantitative
importance in foods such as hypoallergenic formulas, which
contain a multiplicity of peptides from hydrolyzed whey proteins
or casein. The quantification of FMAAs and the calculation of
APs therefrom may be a valuable tool to monitor the impact of
early Maillard reactions on the nutritional quality.
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(
(
(
(
10) Sanz, M. L.; del Castillo, M. D.; Corzo, N.; Olano, A. Presence
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ABBREVIATIONS USED
AP, Amadori product; FMAA, N-(2-furoylmethyl)amino acid;
CLND, chemiluminescent nitrogen detection.
ACKNOWLEDGMENT
We thank Dr. U. Schwarzenbolz for his help during the
LC-ESI-TOF-MS measurements.
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