4 Browning Reactions 83Maillard reaction products have been found in hon-
ey (Antoni et al. 2000) and in tomato purees (Anese
et al. 2002).
Control of the Maillard Reaction in Foods
For a food technologist, one of the most important
objectives must be to limit nutritional damage of
food during processing. In this sense, many studies
have been performed find useful heat-induced mark-
ers derived from the Maillard reaction, and most of
them have been proposed to control and check the
heat treatments and/or storage of foods. There are
many indicators of different stages of the Maillard
reaction, but this review cites one of the most recent
indicators proposed to control the early stages of the
Maillard reaction during food processing: the 2-
furoylmethyl amino acids as an indirect measure of
Amadori compound formation.
Determination of the level of Amadori com-
pounds provides a very sensitive indicator for early
detection (before detrimental changes occur) of
quality changes caused by the Maillard reaction as
well as a retrospective assessment of the heat treat-
ment or storage conditions to which a product has
been subjected (Olano and Martínez-Castro 1996,
del Castillo et al. 1999).
Evaluating for Amadori compounds can be car-
ried out through furosine [-N-(2-furoylmethyl)-
L-lysine] measurement. This amino acid is formed
by acid hydrolysis of the Amadori compound -N-
(1-deoxy-D-fructosyl)-L-lysine. It is considered a
useful indicator of the damage in processed foods
or foods stored for long periods: milks (Resmini et
al. 1990, Villamiel et al. 1999), eggs (Hidalgo et al.
1995), cheese (Villamiel et al. 2000), honey (Vil-
lamiel et al. 2001), infant formulas (Guerra-
Hernandez et al. 2002), jams and fruit-based infant
foods (Rada-Mendoza et al. 2002), fresh filled pasta
(Zardetto et al. 2003), prebaked breads (Ruiz et al.,
2004), and cookies, crackers, and breakfast cereals
(Rada-Mendoza et al. 2004).
In the case of foods containing free amino acids,
free Amadori compounds can be present, and acid
hydrolysis gives rise to the formation of the corre-
sponding 2-furoylmethyl derivatives. For the first
time, 2-furoylmethyl derivatives of different amino
acids (arginine, asparagine, proline, alanine, glutam-
ic acid, and -amino butyric acid) have been detect-
ed and have been used as indicators of the early
stages of Maillard reaction in stored dehydrated
orange juices (del Castillo et al. 1999). These com-
pounds were proposed as indicators to evaluate
quality changes either during processing or during
subsequent storage. Later, most of these compounds
were also detected in different foods: commercial
orange juices (del Castillo et al. 2000), processed
tomato products (Sanz et al. 2000), dehydrated fruits
(Sanz et al. 2001), and commercial honey samples
(Sanz et al. 2003).CARAMELIZATIONDuring nonenzymatic browning of foods, various
degradation products are formed via caramelization
of carbohydrates, without amine participation (Aj-
andouz and Puigserver 1999, Ajandouz et al. 2001).
Caramelization occurs when surfaces are heated
strongly (e.g., during baking and roasting), during
the processing of foods with high sugar content
(e.g., jams and certain fruit juices) or in wine pro-
duction (Kroh 1994). Caramelization is desirable to
obtain caramel-like flavor and/or development of
brown color in certain types of foods. Caramel fla-
voring and coloring, produced from sugar with dif-
ferent catalysts, is one of the most widely used addi-
tives in the food industry. However, caramelization
is not always a desirable reaction due to the possible
formation of mutagenic compounds (Tomasik et al.
1989) and the excessive changes in sensory attrib-
utes that could affect the quality of certain foods.
Caramelization is catalyzed under acidic or alka-
line conditions (Namiki 1988), and many of the
products formed are similar to those resulting from
the Maillard reaction.
Caramelization of reducing carbohydrates starts
with the opening of the hemiacetal ring followed by
enolization, which proceeds via acid- and base-cat-
alyzed mechanisms, leading to the formation of iso-
meric carbohydrates (Fig. 4.8). The interconversion
of sugars through their enediols increases with
increasing pH and is called the Lobry de Bruyn-
Alberda van Ekenstein transformation (Kroh 1994).
In acid media, low amounts of isomeric carbohy-
drates are formed; however, dehydration is favored,
leading to furaldehyde compounds: 5-(hydroxyme-
thyl)-2-furaldehyde (HMF) from hexoses (Fig. 4.9)
and 2-furaldehyde from pentoses. With unbuffered