Food Biochemistry and Food Processing

24 Nonenzymatic Browning of Cookies, Crackers, and Cereals 557

the results obtained by these authors seem to indi-
cate that the decrease of lysine availability is higher
for cereals with greater available lysine content in
total proteins.
Another important consideration is to avoid the
presence of reducing sugars during extrusion. Ly-
sine loss and browning are more intense when
reducing carbohydrates such as glucose, fructose,
and lactose (added as skim milk) are added to the
food mix at levels above 2–5% (Cheftel et al. 1981).
Singh et al. (2000) and Awasthi and Yadav (2000)
also found higher lysine loss and browning in tradi-
tionally elaborated biscuits when whey or skim milk
was added to the initial mixture.
Horvatic ́ and Eres (2002) performed an investiga-
tion of the changes in available lysine content during
industrial production of dietetic biscuits. They found
that dough preparation did not significantly affect
the available lysine content. However, after baking,
a significant loss (27–47%) of available lysine was
observed in the studied biscuits. The loss of avail-
able lysine was found to be significantly correlated
with technological parameters, mainly baking tem-
perature and time conditions.
The influence of storage on the lysine loss in
protein-enriched biscuits was studied by Noguchi et
al. (1982). Lysine loss was observed to increase
when samples were stored at room temperature for
long periods of time. By measurement of lysine,
Hozova et al. (1997) estimated the nutritional quali-
ty of amaranth biscuits and crackers stored during 4
months under laboratory conditions (20°C and 62%
relative humidity). Although a slight decrease in the

level of lysine was detected, this was not significant.

However, these authors suggested that lysine degra-

dation can continue with prolonged storage, and it is

necessary to consider this fact in relation to con-

sumers and the extension of storage time.

FUROSINE

The determination of furosine (
-N-2-furoylmethyl-

lysine), generated from the acid hydrolysis of Ama-

dori compounds formed during the early stages of

the Maillard reaction (Erbersdobler and Hupe

1991), has been used for the assessment of lysine

loss in malt (Molnár-Perl et al. 1986), pasta (Res-

mini and Pellegrino 1991, García-Baños et al.

2004), baby cereals (Guerra-Hernández and Corzo

1996, Guerra-Hernández et al. 1999), baby biscuits

(Carratú et al. 1993), and bread (Ramírez-Jiménez et

al. 2001, Cárdenas-Ruiz 2004). Other 2-furoylmethyl

derivatives such as that corresponding to GABA (-

aminobutyric acid), have been, among others, sug-

gested as indicators of the extent of the Maillard

reaction in vegetable products (Del Castillo et al.

2000; Sanz et al. 2000, 2001).

In commercial cookies, crackers, and breakfast

cereals the initial steps of the Maillard reaction also

have been evaluated by furosine determination

(Rada-Mendoza et al. 2004). Furosine was detected

in all analyzed samples, but showed a wide varia-

tion. Figure 24.1 illustrates, as an example, the

HPLC (high performance liquid chromatography)

chromatogram of the 2-furoylmethyl-amino acids

after acid hydrolysis of a breakfast cereal sample.

Figure 24.1.HPLC chromatogram of the 2-furoylmethyl-GABA (1) and furosine (2) in an acid hydrolyzate of a break-
fast cereal sample. (Taken from Rada-Mendoza et al. 2004 with permission from Elsevier.)