82 Part I: Principles
limited, despite their presence at increased concen-
trations (Ames 1990). Numerous studies have de-
monstrated a browning rate maximum at awvalues
from 0.5 to 0.8 in dried and intermediate-moisture
foods (Warmbier et al. 1976, Tsai et al. 1991, Buera
and Karel 1995).
Due to the complex composition of foods, it is
unlikely that the Maillard reaction involves only sin-
gle compounds (mono- or disaccharides and amino
acids). For this reason, several studies on factors
(pH, T, aw) that influence the Maillard reaction
development have been carried out using more com-
plex model systems: heated starch-glucose-lysine
systems (Bates et al. 1998), milk-resembling model
systems (lactose or glucose-caseinate systems)
(Morales and van Boekel 1998), and a lactose-
casein model system (Malec et al. 2002). Brands
and van Boekel (2001) studied the Maillard reaction
using heated monosaccharide (glucose, galactose,
fructose, and tagatose)-casein model systems to
quantify and identify the main reaction products and
to establish the reaction pathways.
Studies on mechanisms of degradation, via the
Maillard reaction, of oligosaccharides in a model
system with glycine were performed by Hollnagel
and Kroh (2000, 2002). The reactivity of di- and tri-
saccharides under quasi water-free conditions de-
creased in comparison with that of glucose due to
the increasing degree of polymerization.
Study of the Maillard Reaction in Foods
During food processing, the Maillard reaction pro-
duces desirable and undesirable effects. Processes
such as baking, frying, and roasting are based on the
Maillard reaction for flavor, aroma, and color forma-
tion (Lignert 1990). Maillard browning may be de-
sirable during manufacture of meat, coffee, tea,
chocolate, nuts, potato chips, crackers, and beer and
in toasting and baking bread (Weenen 1998, Bur-
dulu and Karadeniz 2003). In other processes such
as pasteurization, sterilization, drying, and storage,
the Maillard reaction often causes detrimental nutri-
tional (lysine damage) and organoleptic changes
(Lingnert 1990). Available lysine determination has
been used to assess Maillard reaction extension in
different types of foods: breads, breakfast cereals,
pasta, infant formula (dried and sterilized), and so
on (Erbersdobler and Hupe 1991); dried milks (El
and Kavas 1997); heated milks (Ferrer et al. 2003);
and infant cereals (Ramírez-Jimenez et al. 2004).
Sensory changes in foods due to the Maillard
reaction have been studied in a wide range of foods
including honey (Gonzales et al. 1999), apple juice
concentrate (Burdulu and Karadeniz 2003), and
white chocolate (Vercet 2003).
Other types of undesirable effects produced in
processed foods by Maillard reaction may include
the formation of mutagenic and cancerogenic com-
pounds (Lingnert 1990, Chevalier et al. 2001).
Frying or grilling of meat and fish may generate low
(ppb) levels of mutagenic/carcinogenic heterocyclic
amines via Maillard reaction. The formation of these
compounds depends on cooking temperature and
time, cooking technique and equipment, heat, mass
transport, and/or chemical parameters. Recently,
Tareke et al. (2002) reported their findings on the
carcinogen acrylamide in a range of cooked foods.
Moderate levels of acrylamide (5–50 g/kg) were
measured in heated protein-rich foods, and higher
levels (150–4000 g/kg) were measured in carbohy-
drate-rich foods such a potato, beet root, certain
heated commercial potato products, and crisp bread.
Ahn et al. (2002) tested different types of commer-
cial foods and some foods heated under home cook-
ing conditions, and they observed that acrylamide
was absent in raw or boiled foods, but it was present
at significant levels in fried, grilled, baked, and
toasted foods. Although the mechanism of acry-
lamide formation in heated foods is not yet clear,
several authors have put forth the hypothesis that the
reaction of asparagine (Fig. 4.5), a major amino acid
of potatoes and cereals (Mottram et al. 2002, Weis-
shaar and Gutsche 2002), or methionine (Stadler et
al. 2002) with reducing sugars (glucose, fructose)
via Maillard reaction could be the pathway. In 2003,
a lot of research was conducted to study the mecha-
nism of acrylamide formation, to develop sensible
analytical methods, and to quantify acrylamide in
different types of foods (Becalski et al. 2003, Jung et
al. 2003, Roach et al. 2003, Yasuhara et al. 2003).
Beneficial properties of Maillard products have
been also described. Resultant products of the reac-
tion of different amino acid and sugar model sys-
tems presented different properties: antimutagenic
(Yen and Tsai 1993), antimicrobial (Chevalier et al.
2001), and antioxidative (Manzocco et al. 2001,
Wagner et al. 2002). In foods, antioxidant effects of