24 Nonenzymatic Browning of Cookies, Crackers, and Cereals 559the extruded material and found a correlation be-
tween reflectance values and the total lysine content
of extruded wheat. The reflectance of the raw flour
was very different, and comparison could not be
made to determine the effect of extrusion.
Hunter “L” values determined for wheat flours,
commercial flaked-toasted, extruded-toasted, and
extruded-puffed breakfast cereals were found to be
positively correlated with available lysine (McAuley
et al. 1987).
During industrial baking of cookies, the effect of
time on color development and other parameters
(volume, structure, weight, crispness) was studied
by Piazza and Masi (1997). The development of
crispness increased with time and was found to be
related to the other physical processes that occur
during baking.
Bernussi et al. (1998) studied the effects of mi-
crowave baking on the moisture gradient and overall
quality of cookies, and they observed that color did
not differ significantly from that of the control sam-
ples (cookies baked using the traditional process).
Broyart et al. (1998) carried out a study on the
kinetics of color formation during the baking of
crackers in a static electrically heated oven. These
authors observed that the darkening step starts when
the product temperature reaches a critical value in
the range of 105–115°C. A kinetic model was devel-
oped in order to predict the lightness variation of the
cracker surface using the product temperature and
moisture content variations during baking. The evo-
lution of lightness appears to follow a first-order
kinetic influenced by these two parameters.
Color development has also been included, to-
gether with other parameters (temperature, water
loss, etc.), in a mathematical model that simulates
the functioning of a continuous industrial-scale bis-
cuit oven (Broyart and Trystram 2003).
Gallagher et al. (2003) observed different color
development in the production of a functional low-
fat, low-sugar biscuit depending upon the quantities
of sugar and protein present.
The manufacture of many breakfast cereals starts
with the cooking of whole cereal grains in a rotary
pressure cooker. During this operation, the grains
absorb heat and moisture and undergo chemical
(browning reactions) and physicochemical changes
as a consequence. The cooking stage is thought to
have a key influence on the properties, such as color,
flavor, and texture, of the final product. Horrobin et
al. (2003) studied the interior and surface color
development during wheat grain steaming and the
results obtained indicated a possible relationship
between color development and moisture uptake
during the cooking process.
In a study on the effects of oven humidity on
foods (bread, cakes, and cookies) baked in gas con-
vection ovens, Xue et al. (2004) observed that in-
creased oven humidity results in products with
lighter color and reduced firmness.
As mentioned above, the formation of Maillard
reaction products and intense color is responsible
for the organoleptic properties of this type of prod-
uct. Moreover, it is also important to consider that
the brown pigments formed could present some bio-
logical activities. Thus, Bressa et al. (1996) ob-
served a considerable antioxidant capacity in cook-
ies during the first 20–30 minutes of cooking (when
browning takes place). Whole grain breakfast cere-
als also have been proved to be an important dietary
source of antioxidants (Miller et al. 2000). Borreli et
al. (2003) studied the formation of colored com-
pounds in bread and biscuits, and they examined the
antioxidant activity and the potential cytotoxic ef-
fects of the formed products.FLUORESCENCE
During the advanced stages of the nonenzymatic
browning, compounds with fluorescence are also
produced. Recently, some analytical methods based
on fluorescence measurements have been used to
evaluate the extent of this reaction. For instance, the
FAST (fluorescence of advanced Maillard products
and soluble tryptophan) method proposed by
Birlouez-Aragon et al. (1998) is based on the deter-
mination of maximal fluorescence emission at an
excitation wavelength of 330–350 nm, which corre-
sponds to molecular structures formed between re-
ducing sugars and the lysine residues of proteins.
This fluorescence is dependent on heat treatment
and is related to protein nutritional loss. Thus, this
method, firstly validated on milk samples, has been
used in other foods modified by the Maillard reac-
tion, such as breakfast cereals. Birlouez-Aragon et
al. (2001) studied the correlation between the FAST
index, lysine loss, and hydroxymethylfurfural for-
mation during the manufacture of breakfast cereals
by extrusion and in commercial samples. The FAST
index was in good agreement with hydroxymethyl-
furfural formation. These authors also found that the
relationship between the FAST index and lysine loss