558 Part V: Fruits, Vegetables, and Cereals
Since considerable amounts of furosine have been
detected in dried milk (Corzo et al. 1994), part of the
furosine found in cereal products containing dried
milk might already be present in dried milk ingredi-
ents. Besides furosine, Rada-Mendoza et al. (2004)
found the 2-furoylmethyl derivative corresponding
to GABA in samples of crackers and breakfast cere-
als; however, it was absent in most cookie samples.
The presence of this compound in breakfast cereals
and crackers may be attributed to the considerable
amount of free GABA present in the rice and corn
used in their manufacture. The presence of a sub-
stantial amount of free GABA in cornflakes has been
previously reported (Marchenko et al. 1973). The
variable amounts of dried milk used in the manufac-
ture of cereal-based products and the different levels
of free GABA in unprocessed cereals appears to
be a major drawback for the use of furosine and 2-
furoylmethyl-GABA as suitable indicators for differ-
entiating among commercial cereal-based products.
However, in the cereal industry, where exact ingredi-
ent composition is known, measurement of the 2-
furoylmethyl-GABA and furosine formed might be
used as indicators to monitor processing conditions
during the manufacture of cereal products.
HYDROXYMETHYLFURFURAL
Hydroxymethylfurfural is formed by the degradation
of hexoses and is also an intermediate product in the
Maillard reaction (Hodge 1953, Kroh 1994). Hy-
droxymethylfurfural is a classic indicator of brown-
ing in several foods such as milk (van Boekel and
Zia-Ur-Rehman 1987, Morales et al. 1997), juices
(Lee and Nagy 1988), and honey (Jeuring and Kup-
pers 1980, Sanz et al. 2003).
In the case of cereal-based foods hydroxymethyl-
furfural has been also used as chemical indicator.
Thus, this compound has been detected in dried
pasta (Acquistucci and Bassotti 1992, Resmini et al.
1993), baby cereals (Guerra-Hernández et al. 1992,
Fernández-Artigas et al. 1999b), and bread
(Ramírez-Jiménez et al. 2000, Cárdenas-Ruiz et al.
2004). In a study on the effect of various sugars on
the quality of baked cookies, furfural (in cookies
elaborated with pentoses) and hydroxymethylfurfur-
al (in cookies elaborated with hexoses) were detect-
ed (Nishibori and Kawakishi 1992). Hydroxymeth-
ylfurfural has also been found in model systems of
cookies baked at 150°C for 10 minutes (Nishibori
and Kawakishi 1995, Nishibori et al. 1998).
García-Villanova et al. (1993) proposed the de-
termination of hydroxymethylfurfural to control the
heating procedure in breakfast cereals as well as
in other cereal derivatives. Birlouez-Aragon et al.
(2001) detected hydroxymethylfurfural in commer-
cial samples of breakfast cereals (cornflakes), in sam-
ples (before and after processing) using traditional
cooking and roasting, and in a model system of wheat,
oats, and rice with two levels of sugars subjected
to extrusion. Hydroxymethylfurfural was formed
during the manufacture of cornflakes; however, only
traces were detected in the raw material. Hydroxy-
methylfurfural formation during extrusion increased
proportionally as sugar concentration increased.
Among all analyzed samples, the highest content of
hydroxymethylfurfural was found in commercial
samples.COLOR
Color is an important characteristic of cereal-based
foods and, together with texture and aroma, con-
tributes to consumer preference. Color is another
indication of the extent of Maillard reaction and
caramelization. The kinetic parameters of these re-
actions are extremely complex for cereal products.
As a consequence, the coloring reaction is always
studied globally, without taking into account indi-
vidual reaction mechanisms (Chevallier et al. 2002).
Color depends both on the physicochemical charac-
teristics of the raw dough (water content, pH, reduc-
ing sugars, and amino acid content) and on the oper-
ating conditions during processing (Zanoni et al.
1995).
Browning pigment (melanoidins) formation oc-
curs at the advanced stages of browning reactions,
and although is undesirable in milk, fruit juices, and
tomatoes, among other foods (De Man, 1980), it is
desirable during the manufacture of cookies, crack-
ers, and breakfast cereals. Color development has
been studied in cereal-based foods such as baby
cereals (Fernández-Artigas et al. 1999b), bread
(Ramírez-Jiménez et al. 2001), cookies (Kane et al.
2003), and gluten-free biscuits (Schober et al. 2003).
The formation of melanoidins and other products
of the Maillard reaction darkens a food, but a darker
color is not always attributed to the presence of
these compounds, since the initial composition of
the mixture can also afford color. In a study on the
protein nutritional value of extrusion-cooked wheat
flours, Bjorck et al. (1984) determined the color of